# Response of Mung Bean Varieties (Vigna radiata L.) to Application Rates and Methods of Blended NPS Fertilizer at Humbo

Authors: Fekadu Mekonen Mota; Dereje Shanka Balla; Mesfin Bibiso Doda
Journal: International Journal of Agronomy
 (2021)

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## Abstract

Mung bean is among the important dry-land legumes in the country and in the study area. However, the productivity of the crop is constrained by biotic and abiotic factors, mainly poor soil fertility, lack of adaptable varieties, and peer agronomic practices. Field trial was initiated at Humbo District with the objective of investigating the rate of NPS-blended fertilizer and application methods on overall performance of mung bean (Vigna radiata L.) varieties. The treatments comprised factorial combination of four rates of NPS (0, 50, 100, and 150 kg ha−1), two types of application methods (broadcasting and drilling), and two mung bean varieties (Shewa Robit and N-26) laid out in RCBD with three replications. Analysis of variance revealed that NPS rates and varieties significantly affected phenology and yield components. Application methods affected yield and thousand-seed weight. Two-way interaction of NPS rates with varieties significantly influenced plant height and pod plant−1. Three-way interactions also significantly influenced aboveground dry biomass and grain yield. The greatest dry biomass (4273.7 kg ha−1) and grain yield (1539.2 kg ha−1) were produced by N-26 variety with fertilizer composed of NPS at 150 kg ha−1 using the drill application method. Partial budget analysis also revealed that the highest (ETB 46,934.4 ha−1) net benefit was obtained at 100 kg NPS ha−1 with variety N-26 from the drilled method. Hence, growing N-26 with 100 kg NPS ha−1 applied using the drilling method of fertilizer application was found as the most suitable treatment combination to improve the income of farmers and increase productivity of mung bean.


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## Body

## 1. Introduction

Mung bean (Vigna radiata L.) is amongst the important pulses cultivated in different agro ecological zones of the world [1]. It is known for its high vitamin A and protein, which can supply a balanced diet when taken in mixture with cereal, which contains low level of protein [2]. It is a short maturity and drought resistance crop, which conferees its adaptation to adverse environmental conditions and successfully grows in rain-fed areas [3]. Furthermore, it is adaptable for the semiarid and arid areas due to its short growing cycle [4], which may be related to attainment of the required degree days to reach maturity in a short period of time due to high temperature condition.Mung bean is locally called “Masho” in Amharic. It is a pulse crop that is recently introduced and cultivated in a limited area in low scale [5]. Mung bean is an important pulse crop for smallholders that have recently gained attention and announced as the sixth export commodity by Ethiopian Commodity Exchange [6]. In Ethiopia, mung bean is produced at about 41,633.2 ha with total production of 514,227.41 t and the average productivity of 1.23 t ha−1 [7]. Similarly, the current regional production is estimated at 122.14 ha with total production of 1150.63 t and the average productivity of mung bean is 0.94 t ha−1 [7]. There was huge gap between its potential and regional average productivity of 0.94 t ha−1 and national average productivity of 1.23 t ha−1, yet the yield gap is not narrowed. To this end, in Ethiopia, the confirmed yield potential reaches 1.5 tons under research field and 0.5 to 1.0 t ha−1 under farmer field with research recommended practices [8]. The low yields are ascribed to the lack of improved seeds, susceptible to disease, inadequate agricultural practices, and less awareness to farmers regarding production of the crop [9].Different authors reported low productivity of mung bean in Ethiopia compared to the production reported in other countries around the globe, which might be attributed to low soil fertility, which is also attributed to the limited use of inorganic fertilizer [9]. Both macronutrients and micronutrients increase nitrogen (N) fixation and the growth of mung bean plant. Like other legumes, it requires nutrients like N, phosphorus (P), and sulfur (S) for growth and development [10].Nitrogen containing fertilizers are essential for crops as source of proteins and play beneficial roles on crop performance, which contribute for maximizing production [11].Application of phosphorus with other micronutrients can increase the production [12]. Generally, P fertilizer is applied as a starter fertilizer before planting. Application of P can enhance root growth, improving flower formation and seed production [13]. The most commonly used fertilizers in Ethiopia were N and P, but they are not the only yield constraining elements. For instance, sulfur (S) is recently identified to be low in most soils [14]. Therefore, S is among the sixteen essential elements, which are important for many reactions and functions in all living cells and the fourth major nutrient, following NPK [15].In production of mung bean, inadequate use of fertilizer, absence of improved varieties, and application methods are among the important problems. The production of mung bean can be highly affected by nutrient management [16]. However, in Ethiopia, little has been done on the growth parameters of mung bean and on its production constraints in the past [17]. Responses to different varieties of mung bean to rates and application methods of fertilizer composed of NPS have not been examined adequately. Therefore, the purpose of this work is to generate information on influences of different rates and application methods of fertilizer composed of NPS for production of mung bean. Thus, this study was focused on the effects of fertilizer composed of NPS at different rates and application methods on production of mung bean varieties and identify economically optimum NPS fertilizer rate for mung bean production.


## 2. Materials and Methods

### 2.1. Description of the Study Area

The trial was executed at Abala Faracho kebele, Humbo district in Wolaita Zone, Southern Ethiopia. The site was located at 6°39ʹ59.99″N latitude and 37°49′59.99″E longitude at an altitude range of 1001 to 2000 masl. The area receives annual rainfall of 50–300 mm. The monthly mean maximum temperature (T) of the area is 32°C, while its minimum temperature is 15.5°C [18]. The soil type of experimental site is silty clay.


### 2.2. Experimental Materials

Blended NPS fertilizer used for this experiment was obtained from Wolaita Sodo University. Nutrients composition of 100 kg of NPS is 19 kg N, 38 kg P2O5, 0 kg K2O, 7 kg S, 0 kg Zn, 0 kg B (EthioSIS, 2016). Mung bean varieties, N-26 and Shewa Robit, were used, which were obtained from Melkassa Agricultural Research Center, and released in 2011. Their yield potential is 1.5 and 1.00 t ha−1 at research and farmer’s field, respectively. By now, they are widely adapted at different areas and produced by most producers for domestic consumption as well as for export.


### 2.3. Treatments and Experimental Design

Factorial combinations of mung bean varieties (Shewa Robit and N-26), four different levels of fertilizer composed of NPS (0, 50, 100, and 150 kg NPS ha−1), and two types of application method of fertilization Broadcast and drill (subsurface application at 5 cm soil depth) were used. Totally, 16 treatments were assigned randomly on experimental plots on N-26 and Shewa Robit mung bean varieties. Factorial randomized complete block design (RCBD) was used for laying out experiment with 3 replicates. Plot size was 2.1 m × 3 m with 6.3 m2 area having 7 rows. Plots and blocks were separated 1 and 1.5 m apart, respectively, and total experimental area was 15 m × 50.6 m (759 m2).


### 2.4. Experimental Procedures and Agronomic Managements

The field was ploughed three times by oxen, leveled, and prepared. Variety N-26 and Shewa Robit were sown on 10 May 2019, which was medium rainfall season. Two seeds per hole were planted in the row. Different rates of blended N, P, and S fertilizers were applied either by drill or broadcast method at sowing time for the respective treatment combination. In drill application method, NPS fertilizer was applied at 5 cm depth and covered with soil before sowing. Then, sowing was performed at 30 and 10 cm inter- and intrarow spacing respectively. Agronomic practices such as weeding, plant spacing, and disease management were kept uniform for all the experimental units.


### 2.5. Soil Sample Collection and Analysis

The studied soil samples were collected at 0–30 cm depth by zigzag method from different spots in the experimental field before planting by using soil auger. Then, the collected soil sample was air-dried, grounded to pass through a 2 mm sieve, thoroughly mixed, and made ready for physicochemical analysis.Laboratory analyses were done at Horticoop Ethiopia Laboratory at Debre-Zeit. Before planting, the collected soil sample was used for analyzing selected soil physicochemical properties [19]. Total % of N was analyzed by the Kjeldah method [20], and available P, S, B, and Zn were analyzed by the Mehlich III method [21], percent of organic carbon content was analyzed using method as described by Reeuwijk [22], and soil pH was determined using a pH meter (Belgium, C835), following standard laboratory procedure [23].


### 2.6. Crop Data Collection and Analysis

All phenological and yield component data were collected following standard procedure. Accordingly data were collected on days to 50% flowering and days to 90% flowering, height of the plant (cm), number of primary branches, and leaf area index (LAI), calculated as the ratio of total leaf area per five plants (cm2) per area of land occupied by the plants using standard procedure, number of pods per plant, number of seeds per pod, thousand-seed weight (g), grain yield, aboveground biomass (kg/ha), and harvest index. Leaf area was measured using leaf area meter from five plants in rows left for destructive sampling at maximum vegetative growth stage. Aboveground dry biomass yield was measured from five randomly selected plants from rows left for destructive sampling at physiological maturity and converted to hectare base. Grain yield was measured from the net plot area at harvest and adjusted to 10% moisture content. Harvest index (HI) was calculated as the ratio of grain yield to total aboveground dry biomass yield multiplied by 100.


### 2.7. Economic Analysis

Economic analysis was done using partial budget analysis according to the methods described by [24]. All varying costs were recorded and used for this analysis. Gross field benefits (GFB) ha−1 were determined by multiplying adjusted grain yield (kg ha−1) by market price at the time of harvest. Adjusted grain yield was calculated by reducing average grain yield by 10% to avoid overestimation of mung bean yield. Marginal rate of return (%) was calculated by taking the change in benefit to change in cost multiplied by 100. Total revenue (TR) is estimated as TR = adjusted yield (AY) × field price of the grain, and the gross field benefit for each treatment is calculated by multiplying the field price by the adjusted yield. Net revenue (NR) is computed as NR = TR − total variable cost (TVC). Value cost ratio (VCR) was estimated by dividing yield increase by cost of fertilizer used.


### 2.8. Data Analysis

The data collected was analyzed using SAS version 9.0 [25] and following the steps described by Gomez and Gomez [26]. Interpretations were made. Mean comparison was done for significant treatments using the LSD test at 5% probability level.


## 2.1. Description of the Study Area

The trial was executed at Abala Faracho kebele, Humbo district in Wolaita Zone, Southern Ethiopia. The site was located at 6°39ʹ59.99″N latitude and 37°49′59.99″E longitude at an altitude range of 1001 to 2000 masl. The area receives annual rainfall of 50–300 mm. The monthly mean maximum temperature (T) of the area is 32°C, while its minimum temperature is 15.5°C [18]. The soil type of experimental site is silty clay.


## 2.2. Experimental Materials

Blended NPS fertilizer used for this experiment was obtained from Wolaita Sodo University. Nutrients composition of 100 kg of NPS is 19 kg N, 38 kg P2O5, 0 kg K2O, 7 kg S, 0 kg Zn, 0 kg B (EthioSIS, 2016). Mung bean varieties, N-26 and Shewa Robit, were used, which were obtained from Melkassa Agricultural Research Center, and released in 2011. Their yield potential is 1.5 and 1.00 t ha−1 at research and farmer’s field, respectively. By now, they are widely adapted at different areas and produced by most producers for domestic consumption as well as for export.


## 2.3. Treatments and Experimental Design

Factorial combinations of mung bean varieties (Shewa Robit and N-26), four different levels of fertilizer composed of NPS (0, 50, 100, and 150 kg NPS ha−1), and two types of application method of fertilization Broadcast and drill (subsurface application at 5 cm soil depth) were used. Totally, 16 treatments were assigned randomly on experimental plots on N-26 and Shewa Robit mung bean varieties. Factorial randomized complete block design (RCBD) was used for laying out experiment with 3 replicates. Plot size was 2.1 m × 3 m with 6.3 m2 area having 7 rows. Plots and blocks were separated 1 and 1.5 m apart, respectively, and total experimental area was 15 m × 50.6 m (759 m2).


## 2.4. Experimental Procedures and Agronomic Managements

The field was ploughed three times by oxen, leveled, and prepared. Variety N-26 and Shewa Robit were sown on 10 May 2019, which was medium rainfall season. Two seeds per hole were planted in the row. Different rates of blended N, P, and S fertilizers were applied either by drill or broadcast method at sowing time for the respective treatment combination. In drill application method, NPS fertilizer was applied at 5 cm depth and covered with soil before sowing. Then, sowing was performed at 30 and 10 cm inter- and intrarow spacing respectively. Agronomic practices such as weeding, plant spacing, and disease management were kept uniform for all the experimental units.


## 2.5. Soil Sample Collection and Analysis

The studied soil samples were collected at 0–30 cm depth by zigzag method from different spots in the experimental field before planting by using soil auger. Then, the collected soil sample was air-dried, grounded to pass through a 2 mm sieve, thoroughly mixed, and made ready for physicochemical analysis.Laboratory analyses were done at Horticoop Ethiopia Laboratory at Debre-Zeit. Before planting, the collected soil sample was used for analyzing selected soil physicochemical properties [19]. Total % of N was analyzed by the Kjeldah method [20], and available P, S, B, and Zn were analyzed by the Mehlich III method [21], percent of organic carbon content was analyzed using method as described by Reeuwijk [22], and soil pH was determined using a pH meter (Belgium, C835), following standard laboratory procedure [23].


## 2.6. Crop Data Collection and Analysis

All phenological and yield component data were collected following standard procedure. Accordingly data were collected on days to 50% flowering and days to 90% flowering, height of the plant (cm), number of primary branches, and leaf area index (LAI), calculated as the ratio of total leaf area per five plants (cm2) per area of land occupied by the plants using standard procedure, number of pods per plant, number of seeds per pod, thousand-seed weight (g), grain yield, aboveground biomass (kg/ha), and harvest index. Leaf area was measured using leaf area meter from five plants in rows left for destructive sampling at maximum vegetative growth stage. Aboveground dry biomass yield was measured from five randomly selected plants from rows left for destructive sampling at physiological maturity and converted to hectare base. Grain yield was measured from the net plot area at harvest and adjusted to 10% moisture content. Harvest index (HI) was calculated as the ratio of grain yield to total aboveground dry biomass yield multiplied by 100.


## 2.7. Economic Analysis

Economic analysis was done using partial budget analysis according to the methods described by [24]. All varying costs were recorded and used for this analysis. Gross field benefits (GFB) ha−1 were determined by multiplying adjusted grain yield (kg ha−1) by market price at the time of harvest. Adjusted grain yield was calculated by reducing average grain yield by 10% to avoid overestimation of mung bean yield. Marginal rate of return (%) was calculated by taking the change in benefit to change in cost multiplied by 100. Total revenue (TR) is estimated as TR = adjusted yield (AY) × field price of the grain, and the gross field benefit for each treatment is calculated by multiplying the field price by the adjusted yield. Net revenue (NR) is computed as NR = TR − total variable cost (TVC). Value cost ratio (VCR) was estimated by dividing yield increase by cost of fertilizer used.


## 2.8. Data Analysis

The data collected was analyzed using SAS version 9.0 [25] and following the steps described by Gomez and Gomez [26]. Interpretations were made. Mean comparison was done for significant treatments using the LSD test at 5% probability level.


## 3. Results and Discussion

### 3.1. Physicochemical Properties of Soil

The studied soil is characterized by silty clay texture. The studied soil pH was analyzed to be 6.83, which is moderately acidic. The analysis for other soil chemical properties is shown in Table1.Table 1
Selected soil properties before planting.
Soil charactersValuesRatingReferenceSoil textureSand (%)20Clay (%)40Silt (%)40Textural classSilty claypH (water)6.83Moderate acidic[29]TotalN (%)0.13Moderate[29]Organic C (%)1.39Moderate[30]Available P (mg/kg)27.25Moderate[31]Available S (mg/kg)47.87Moderate[32]According to [27], the best production of mung bean requires sandy loam soil with good drainage at pH of 6.3–7.2. Neutral soil with pH of 6.7–7.3 and silty clay soil texture class might have less drainage problem for mung bean. According to the study of [28], the soil in the study site was deficient of N, P, and S. From composite soil sample of the studied site, total concentration organic carbon, N, P, and S, and their ratings were shown in Table 1.


### 3.2. Phenological Parameters

#### 3.2.1. Days to Flowering

Results revealed that days to flowering were significantly influenced due to two-way interaction between NPS rates and varieties. Increased blended NPS rate significantly decreased the amount of days to flowering of mung bean varieties. Accordingly, the maximum days to flowering (40) were recorded from interaction of 150 kg ha−1 blended NPS rate with variety Shewa Robit, whereas lowest days to flowering (33) were obtained from N-26 with no fertilizer applied (Table 2). The increased fertilizer rate has delayed flowering and maturity. Besides, application of S with NP fertilizer can enhance metabolic activity and nutrient utilization, which favors vegetative growth as reported by [33]. The study in [34] also reported increased vegetative growth with application of S (20 kg S ha−1). On the contrary, the study in [35] reported that nonsignificant interaction was found for application of P with common bean variety on days to flowering.Table 2
Interaction effects of NPS fertilizer rates with varieties on days to 50% flowering (DF), days to 90% physiological maturity (DM), plant height (PH), number of branches (NB), leaf area (LA), and leaf area indices (LAI).
VarietiesNPS rates (kg ha−1)DFDMpH (cm)NBLA (cm2 plant−1)LAIN-26033.00h61.16g61.76d6.2c256.28e0.85e5033.01g62.00f62.66cd6.3bc298.92cd0.99cd10035.00e63.33de64.1bcde6.93a376.12a1.25a15036.00d64.83e64.73bc6.98a371.22a1.23aShewa Robit036.16f66.06d59.00e6.1c220.26f0.73f5038.00c66.50c65.73ab6.6b293.72d0.97d10039.00b68.33b66.51ab6.3bc317.22bc1.05bc15040.00a71.66a67.75a6.5b325.00b1.08bLSD (0.05)0.331.532.570.418.720.06CV (%)3.752.033.414.465.175.17Means with the same letter(s) in a column are nonsignificant at (P≤0.05); CV = coefficient of variance, LSD = least significant difference, and NS = nonsignificant.


#### 3.2.2. Physiological Maturity

Delay in physiological maturity was observed with increase in blended NPS rate. The longer maturity date (71.66) was evidenced from interaction of 150 kg ha−1 blended NPS rate with Shewa Robit, whereas the lowest maturity date (61.16) was attained from N-26 with no fertilizer applied (Table 2). Accordingly, maturity date prolonged following the increase in the level of NPS, which might be related to role of N in the NPS that enhanced vegetative growth. According to [33], it is observed that N improved luxuriant vegetative growth, thereby delaying maturity in mung bean. In contrast, the study in [36] reported no significant effect of application of S (0–60 kg ha−1) on days to maturity on common bean.


### 3.3. Growth Parameters

#### 3.3.1. Plant Height

Plant height increased with increased fertilizer rate for both varieties. The highest (67.75 cm) height of the plant was found for variety Shewa Robit at rate of 150 kg NPS ha−1, whereas the minimum height (59.0 cm) was obtained from Shewa Robit with no fertilizer applied (Table 2). Thus, the highest in plant height is probably due to genetically different character of varieties and increased NPS fertilizer by enhancing of root development and crop growth. It could also due to favorable climatic conditions until physiological maturity especially timely rainfall throughout growing season. In addition, the P supplied from NPS fertilizer might have contributed for root proliferation contributing for improved nutrient uptake, thereby improving the increase in size and development of the plants. Consistent with this suggestion, the study in [37] indicated maximum (74.79) height of the plant of mung bean with application of 50–70 kg NP ha−1. The application of S enhances crop growth and increases nutrient uptake by the crop [38]. This study also corroborates the results of [39], who reported maximum plant height (99.72 cm) with maximum rate of NPS application (150 kg NPS ha−1) for common bean variety Nasir.


#### 3.3.2. Number of Primary Branches

Results indicated that branch number was notably affected by the two-way interaction of NPS rates and varieties. Significantly, the highest (6.98) branch number was recorded from interaction fertilizer composed of NPS at rate of 150 kg ha−1 with variety N-26, whereas the lowest branch number primary (6.1) was obtained from Shewa Robit with no fertilizer applied (Table 2). Thus, the highest mean was observed due to genetically different characteristics of varieties, and increased NPS fertilizer rate can enhance crop growth. The amounts of primary branches per plant were increased due to increased application of blended NPS fertilizer. This implies that higher vegetative growth was formed when there is higher availability of nutrients supplied from blended NPS fertilizer. Increased number of branch plant−1 was formed for the fact that vigorous growth by the plants is a result of better photosynthetic activities with adequate availability of nutrients at vegetative growth stages [33]. The study in [33] reported significantly higher (5.34) amount of branches plant−1 at maximum application of fertilizer (150 Kg NPS ha−1). Furthermore, Jawahar et al. observed significantly higher (5.91) number of branches plant−1 with the addition of 40 kg P2O5 ha−1 on mung bean production. The result was also consistent with the research finding of [40].


#### 3.3.3. Leaf Area

Leaf area was significantly affected by the two-way interaction between NPS rates and varieties. Accordingly, the maximum (376.12 cm2) leaf area was recorded from interaction of fertilizer composed of NPS at rate (100 kg ha−1) and variety N-26, whereas minimum leaf area (220.26 cm2) was obtained from variety Shewa Robit with no fertilizer applied (Table 2). Thus, the maximum mean leaf area was observed due to genetically different characteristics of varieties and increased NPS fertilizer rate, which can enhance leaf area. The highest leaf area plant−1 might also be attributed to the improved photosynthesis process following better supply of nutrients in balanced quantity to the plants at growing stages. This result is consistent with the findings of [41]. In contrast, the low leaf area was found from the treatment with application of 57 kg P ha−1 rather than that recorded at rate application of P 38 kg ha−1. In this result, also low leaf area was recorded from the treatment with addition of 150 kg ha−1 NPS rather than that recorded at rate application of blended 100 kg ha−1 NPS.


#### 3.3.4. Leaf Area Index

The two-way interaction between NPS rates and varieties was found to be significant (P≤0.05) on leaf area index. Significantly, the highest leaf area index (1.25) was recorded from interaction of fertilizer composed of NPS at rate (100 kg ha−1) with variety N-26, whereas the lowest leaf area index (0.73) was obtained from Shewa Robit with no fertilizer applied (Table 2). The greater in leaf area index resulted from improved availability of essential nutrients such as N, P, and S, which can boost physiological process, which in turn improves growth of leaf area [42]. Supporting this finding, the study in [43] recorded a significant increase in leaf area index of soybean following P application.


### 3.4. Yield and Yield Components

#### 3.4.1. Number of Pods per Plant

The number of pods per plant was highly influenced by the two-way interaction effect between NPS rates and varieties. The maximum (53.26) pods number was recorded for Shewa Robit at rate of 150 kg ha−1, whereas the lowest pod number (30.40) was also obtained from Shewa Robit when no fertilizer was applied (Table 3). Thus, the greater number of pods per plant with the addition of NPS fertilizer was due to immediate supply of fertilizer composed of NPS to the plants from inorganic fertilizer enhancing photosynthetic activities, thereby improving vegetative growth and development, which increased the production of pods upon translocation. This study is consistent with research findings of [33]. The study in [44] reported significant effect of NP fertilizers on pod production per plant of mung bean with the maximum number of pods in each plant (30.45) obtained at 52.5 kg N ha−1 and 26 kg P2O5 ha−1. This finding is consistent with the result of [45]. Similarly, the study in [35] reported a corresponding increase in pods number (2.31 to 10.62) when P rate increased from nil to 39.6 kg ha−1, which implies that the addition of P fertilizer could contribute to promoting the formation of nodes and pods in legumes. Further, research conducted by [46] indicated that pods number of common bean significantly increased with increased rate of P up to the highest rate of 92 kg P2O5 ha−1.Table 3
Interaction effects of varieties and blended NPS fertilizer rates on number of pods (PN) per plant, and number of seeds (SN) per pod, 1000-seed weight (g), and harvest index (%).
VarietiesNPS rate (kg ha−1)No. of pods per plant−1No. of seeds per pod−11000-seed weight (g)HI (%)N-26030.83d8.11c50.367c0.31cd5042.66c9.56b53.700b0.32b10049.53b11.86ab55.683a0.34a15050.96b11.96a55.800a0.34aShewa Robit030.40d6.53f41.283f0.30de5047.60c7.05e43.755e0.30e10052.78a7.6d46.948d0.31c15053.26a7.9cd46.938d0.32bLSD (0.05)3.910.490.668.13CV (%)7.264.361.152.14Numbers with the same letter(s) within a column are nonsignificant atP≤0.05; CV = coefficient of variance and LSD = least significant difference.


#### 3.4.2. Number of Seeds per Pod

The result revealed that seeds number per pod was also strongly influenced by the two-way interaction between NPS rates and varieties. There were significant increases in the number of seeds per pod with increase in blended NPS rate over control. Significantly, variety N-26 had higher pods number with increased NPS rate than variety Shewa Robit (Table3). Variety N-26 produced the highest (11.96) seeds number pod−1 at 150 kg ha−1, whereas the lowest (6.53) seeds number pod−1 was found for Shewa Robit at nil rate fertilizer (Table 3). The increase in the amount of seeds per pot with increased NPS rates is probably due to the higher vegetative growth and improved branching with increasing production of pod. The result was consistent with the research findings of [47] who reported significant interaction effect of NPS fertilizers rates and mung bean varieties on seed pod−1 of mung bean with the maximum amount of seeds pod−1 (8.84) obtained at 150 kg NPS ha−1 for variety N-26. In this study, the highest seeds number per pod−1 could probably be due to the combination of photosynthesis function of N, seed formation ability of P, and metabolic energy ability of S [48, 49]. This finding is also in line with the result of [50]. The finding of this result is also supported by [40]. However, the current study is not consistent with the result of [51], who reported nonsignificant effect of main effects of N and P as well as their interactions on the amount of seeds pod−1 of common bean.


#### 3.4.3. 1000-Seed Weight

1000-seed weight was significantly (P≤0.05) influenced by the two-way interaction between NPS rates. The maximum 1000-seed weight (55.8 g) was recorded from interaction of 150 kg NPS ha−1 application with variety N-26, followed by the maximum (55.68 g) obtained from interaction 100 kg NPS ha−1 with variety N-26, whereas the minimum 1000-seed weight (41.28 g) was found from Shewa Robit variety with no fertilizer applied (Table 3). Variety N-26 produced significantly maximum thousand-seed weight with increased NPS fertilizer rate than variety Shewa Robit. Such disparity in thousand-seed weight among the varieties may be attributed to genetically different characteristics of varieties and increase in NPS fertilizer rate over the control. This result is confirmed by the finding of [52], who determined that 1000-seed weight increased with P levels. This study is also in line with [53], who reported that the maximum (51.6 g) of mung bean was recorded at rate of 60 kg P ha−1 for 1000-seed weight, while lowest 1000-seed weight (46.96 gm) was found for control treatment.This is the fact that assimilated photosynthesis can be translocated from vegetative plant parts to the seed, thus considerably enhancing seed weight. The increase in 1000-grain weight showed that macronutrients along with micronutrients (i.e., S) are necessary for healthier and robust seeds in common bean [54]. Thus, the result is consistent with findings of [55]. The result is also supported by the findings of [44].


#### 3.4.4. Aboveground Dry Biomass

For the studied mung bean plant, aboveground dry biomass was also significantly (P≤0.05) influenced by the three-way interaction of NPS rates, varieties, and methods of application. For all varieties, aboveground dry biomass significantly increased with increase in blended NPS rate with drilling method of fertilizer application (Table 4). The maximum dry biomass (4273.7 kg ha−1) was obtained from interaction of 150 kg ha−1 blended NPS fertilizer with variety N-26 from the combination of drilled application followed by the same variety (4267.7 kg ha−1) at rate of 100 kg ha−1 blended NPS using drilling application method, while the minimum aboveground dry biomass (3038.1 kg ha−1) was obtained from Shewa Robit with no fertilizer application (Table 4).Table 4
Interaction effects of varieties, blended NPS fertilizer rates, and application methods on aboveground dry biomass (kg) and grain yield (g).
VarietiesNPS rates (kg ha−1)AGDM (kg ha−1)GY (kg ha−1)Appl. methodsAppl. methodsDrillingBroadcastingDrillingBroadcastingN-2603211.1g3185.3g1011.0h1000.1h503872.4e3871.0e1274.2e1244.2f1004267.7a4209.1abc1537.6a1459.9b1504273.7a4226.3ab1539.2a1468.4bShewa Robit03104.7gh3038.1h953.7i943.4i503463.3f3469.9f1066.8g1040.4g1004097.9cd4045.6d1315.4d1261.7ef1504155.1bcd4127.9bcd1367.6c1347.3cLSD (0.05)112.0927.71CV (%)1.771.36Numbers with the same letter in column are nonsignificant at 5% level of significance; LSD (0.05): least significant difference at 5% level; CV: coefficient of variation; AGDB: aboveground dry biomass, and GY: grain yield.The study in [33] reported the significantly highest aboveground biomass for mung bean variety N-26 at application of 100 kg ha−1 with 20 cm. The authors of [41, 56] also reported an increase in total dry matter per plant with N application for French bean and common bean, respectively. This result is consistent with the findings of [39], who reported a significant linear response of aboveground dry biomass to application of different levels of NPS in common bean. According to [57], there is the addition of P fertilizer with soil low in available P of acidic Nitisols, and an increase in the aboveground biomass of faba bean was found. The study in [35] also reported that P fertilization on soya bean did not significantly affect the aboveground dry biomass.


#### 3.4.5. Grain Yield

The analysis of variance revealed that grain yield was significantly (P≤0.05) influenced by the three-way interaction of NPS rates, varieties, and application method. The maximum grain yield (1539.2 kg ha−1) was found from interaction of 150 kg ha−1 blended NPS fertilizer rate with variety N-26 using drilled application method followed by maximum (1537.6 kg ha−1) grain yield recorded from the interaction of 100 kg ha−1 blended NPS fertilizer rate with the same variety and application method, but no statistical difference between them (Table 4), while, significantly, the lowest yield (943.4 kg ha−1) was observed from interaction of variety Shewa Robit with nil fertilizer applied (Table 5). This highest value was formed due to significant application of fertilizer composed of NPS. N at early growth stages promoted vegetative growth and created conditions conducive to high yield and played a critical role for chlorophyll formation and protein, directly increasing the plant protein content, thereby boosting yield [48]. In accord with the present finding, the authors of [33, 47] reported that grain yield of mung bean is significantly affected by two-way interaction effects of mung bean varieties and blended NPS rate.Table 5
Partial budget analysis of interaction effect of varieties and blended NPS rates with the application method on yield of mung bean during 2019 cropping season at Humbo.
TreatmentGAYAJAYGFPTVCNBMRR (%)MethodRatesVarietiesDr0Shewa Robit953.7858.3330041.55030041.55-50Shewa Robit1066.8960.1233604.280032804.2345100Shewa Robit1315.41183.8641435.1150039935.11019150Shewa Robit1367.61230.8443079.4220040879.4135Br0Shewa Robit943.4849.0629717.1029717.1-50Shewa Robit1040.4936.3632772.680031972.6282100Shewa Robit1261.71135.5339743.55150038243.55896150Shewa Robit1347.31212.5742439.95220040239.95285Dr0N-261011909.931846.5031846.5-50N-261274.21146.7840137.380039337.3936100N-261537.61383.8448434.4150046934.41085150N-261539.21385.2848484.8220046284.8DBr0N-261000.1900.0931503.15031503.15050N-261244.21119.7839192.380038392.3861100N-261459.91313.9145986.85150044486.85871150N-261468.41321.5646254.6220044054.6DDr = drilled application method, Br = broadcasting, GAY = gross average yield, AJAY = adjusted average yield (−10%), GFP = gross field price (mung bean price = 35 ETB kg−1, TVC = total variable cost, and NB = net benefit (ETB ha−1).Phosphorus enhanced cellular respiration in the production of the starch, protein, and fats plays a fundamental role in metabolism and energy producing reaction, building phospholipids, and nucleic acid and stimulates blooming and seed formation, which could increase yield [58].This result is consistent with that of [48], who described that the interaction effects of N and P levels on seed yield of mung bean were highly significant. The study in [59] who reported the application of P and S could maximize mung bean production. The study in [60] also reported highly significant effect of P fertilizer application rate on seed yield of mung bean and common bean. The study in [46] also reported that the application of P could maximize the yield of haricot bean. According to [13], P is considered to be important for stimulated root development and seed formation. Application method significantly influenced grain yield with increase in NPS rate (Table 4).Application method of drilling is suitable method than broadcasting. This could be due to avoiding easy evaporation of mobile nutrients such as N, S and can keep P fertilizer within the soil system for the adequate supply to crops. Disparity of broadcast results in nonuniform growth, wasting of fertilizer, and decreasing the usage coefficient of plant [61]. Drilling method for N-fertilizers in nutrient deficient soils may offer increased fertilizer absorption by the plant [62].


#### 3.4.6. Harvest Index

Harvest index was influenced significantly (P≤0.05) due to the two-way interaction of fertilizer rates composed of NPS and varieties. The maximum harvest index (0.34) was recorded from interaction effect of 150 kg ha−1 blended NPS fertilizer with variety N-26 followed by 100 kg NPS ha−1 with the same variety, but no statistical difference (Table 3). The minimum harvest index (0.30) was obtained from Shewa Robit with no fertilizer applied (Table 3). This study is consistent with the finding of [39, 47]. The study in [47] also reported that the maximum harvest index was obtained from N-26 variety at NPS rate of 150 kg ha−1, which was followed by the same variety N-26 (39.05%) at rate of 100 kg NPS ha−1. The study in [37] also reported an increase in harvest index of mung bean in response to addition of N and P.


### 3.5. Partial Budget Analysis

It is used to understand efficiency and economics of inputs and outputs of crop production. From this study, the mean yields of mung bean were estimated. The mean yields of mung bean were adjusted downward by 10% to reflect the difference between the experimental and farmers’ field yields [24].From the use of various interactions of fertilizers composed of NPS with varieties and with application methods, the total variable cost and net benefits were estimated. The total variable cost (TVC) was estimated during field experimental period that included the cost of fertilizers and cost of labor for fertilizers applications (Table5). Daily labor cost during experimental period was 100 ETB per person per day, and the field price of mung bean yield during harvesting period was 35 ETB kg−1. The total variable cost (TVC) was subtracted from gross field prices (GFP) to obtain net benefits (NB). After estimating net benefits, the treatments were arranged in increasing order of total variable costs to identify dominated and nondominated treatments. In this study, from sixteen treatments, three were dominated, and thirteen were nondominated (Table 5).Dominated treatments were absent from subsequent steps in the marginal analysis, whereas, for nondominated treatments, insignificant rate of returns was calculated. According to [24], the thirteen nondominated treatments gave more than 100% marginal rate of return (Table 5). Marginal rate of return (MRR) is a characteristic of the change from one treatment to another and since dominated treatments are not included, it will always be positive. So below 100% and/or negative MRR was considered as low and unacceptable to farmers, because such returns would not return capital and other related costs, and something would not be added to the cost of capital to repay the producers for the time and effort spent.The recommendation is not necessarily the treatment with the highest marginal rate of return compared to neither that of next lowest cost, or the treatment with the highest net benefit, nor the treatment with the highest yield. The identification of a recommendation requires a careful marginal analysis using an appropriate minimum rate of return [24]. In this study, the partial budget analysis indicated that the highest net benefit was obtained from variety N-26 supplied with fertilizer composed of NPS at rate of 100 kg ha−1 using drilling application 5 cm below seed, which gave highest net benefits of 46,934.4 ETB ha−1 (Table 5).


## 3.1. Physicochemical Properties of Soil

The studied soil is characterized by silty clay texture. The studied soil pH was analyzed to be 6.83, which is moderately acidic. The analysis for other soil chemical properties is shown in Table1.Table 1
Selected soil properties before planting.
Soil charactersValuesRatingReferenceSoil textureSand (%)20Clay (%)40Silt (%)40Textural classSilty claypH (water)6.83Moderate acidic[29]TotalN (%)0.13Moderate[29]Organic C (%)1.39Moderate[30]Available P (mg/kg)27.25Moderate[31]Available S (mg/kg)47.87Moderate[32]According to [27], the best production of mung bean requires sandy loam soil with good drainage at pH of 6.3–7.2. Neutral soil with pH of 6.7–7.3 and silty clay soil texture class might have less drainage problem for mung bean. According to the study of [28], the soil in the study site was deficient of N, P, and S. From composite soil sample of the studied site, total concentration organic carbon, N, P, and S, and their ratings were shown in Table 1.


## 3.2. Phenological Parameters

### 3.2.1. Days to Flowering

Results revealed that days to flowering were significantly influenced due to two-way interaction between NPS rates and varieties. Increased blended NPS rate significantly decreased the amount of days to flowering of mung bean varieties. Accordingly, the maximum days to flowering (40) were recorded from interaction of 150 kg ha−1 blended NPS rate with variety Shewa Robit, whereas lowest days to flowering (33) were obtained from N-26 with no fertilizer applied (Table 2). The increased fertilizer rate has delayed flowering and maturity. Besides, application of S with NP fertilizer can enhance metabolic activity and nutrient utilization, which favors vegetative growth as reported by [33]. The study in [34] also reported increased vegetative growth with application of S (20 kg S ha−1). On the contrary, the study in [35] reported that nonsignificant interaction was found for application of P with common bean variety on days to flowering.Table 2
Interaction effects of NPS fertilizer rates with varieties on days to 50% flowering (DF), days to 90% physiological maturity (DM), plant height (PH), number of branches (NB), leaf area (LA), and leaf area indices (LAI).
VarietiesNPS rates (kg ha−1)DFDMpH (cm)NBLA (cm2 plant−1)LAIN-26033.00h61.16g61.76d6.2c256.28e0.85e5033.01g62.00f62.66cd6.3bc298.92cd0.99cd10035.00e63.33de64.1bcde6.93a376.12a1.25a15036.00d64.83e64.73bc6.98a371.22a1.23aShewa Robit036.16f66.06d59.00e6.1c220.26f0.73f5038.00c66.50c65.73ab6.6b293.72d0.97d10039.00b68.33b66.51ab6.3bc317.22bc1.05bc15040.00a71.66a67.75a6.5b325.00b1.08bLSD (0.05)0.331.532.570.418.720.06CV (%)3.752.033.414.465.175.17Means with the same letter(s) in a column are nonsignificant at (P≤0.05); CV = coefficient of variance, LSD = least significant difference, and NS = nonsignificant.


### 3.2.2. Physiological Maturity

Delay in physiological maturity was observed with increase in blended NPS rate. The longer maturity date (71.66) was evidenced from interaction of 150 kg ha−1 blended NPS rate with Shewa Robit, whereas the lowest maturity date (61.16) was attained from N-26 with no fertilizer applied (Table 2). Accordingly, maturity date prolonged following the increase in the level of NPS, which might be related to role of N in the NPS that enhanced vegetative growth. According to [33], it is observed that N improved luxuriant vegetative growth, thereby delaying maturity in mung bean. In contrast, the study in [36] reported no significant effect of application of S (0–60 kg ha−1) on days to maturity on common bean.


## 3.2.1. Days to Flowering

Results revealed that days to flowering were significantly influenced due to two-way interaction between NPS rates and varieties. Increased blended NPS rate significantly decreased the amount of days to flowering of mung bean varieties. Accordingly, the maximum days to flowering (40) were recorded from interaction of 150 kg ha−1 blended NPS rate with variety Shewa Robit, whereas lowest days to flowering (33) were obtained from N-26 with no fertilizer applied (Table 2). The increased fertilizer rate has delayed flowering and maturity. Besides, application of S with NP fertilizer can enhance metabolic activity and nutrient utilization, which favors vegetative growth as reported by [33]. The study in [34] also reported increased vegetative growth with application of S (20 kg S ha−1). On the contrary, the study in [35] reported that nonsignificant interaction was found for application of P with common bean variety on days to flowering.Table 2
Interaction effects of NPS fertilizer rates with varieties on days to 50% flowering (DF), days to 90% physiological maturity (DM), plant height (PH), number of branches (NB), leaf area (LA), and leaf area indices (LAI).
VarietiesNPS rates (kg ha−1)DFDMpH (cm)NBLA (cm2 plant−1)LAIN-26033.00h61.16g61.76d6.2c256.28e0.85e5033.01g62.00f62.66cd6.3bc298.92cd0.99cd10035.00e63.33de64.1bcde6.93a376.12a1.25a15036.00d64.83e64.73bc6.98a371.22a1.23aShewa Robit036.16f66.06d59.00e6.1c220.26f0.73f5038.00c66.50c65.73ab6.6b293.72d0.97d10039.00b68.33b66.51ab6.3bc317.22bc1.05bc15040.00a71.66a67.75a6.5b325.00b1.08bLSD (0.05)0.331.532.570.418.720.06CV (%)3.752.033.414.465.175.17Means with the same letter(s) in a column are nonsignificant at (P≤0.05); CV = coefficient of variance, LSD = least significant difference, and NS = nonsignificant.


## 3.2.2. Physiological Maturity

Delay in physiological maturity was observed with increase in blended NPS rate. The longer maturity date (71.66) was evidenced from interaction of 150 kg ha−1 blended NPS rate with Shewa Robit, whereas the lowest maturity date (61.16) was attained from N-26 with no fertilizer applied (Table 2). Accordingly, maturity date prolonged following the increase in the level of NPS, which might be related to role of N in the NPS that enhanced vegetative growth. According to [33], it is observed that N improved luxuriant vegetative growth, thereby delaying maturity in mung bean. In contrast, the study in [36] reported no significant effect of application of S (0–60 kg ha−1) on days to maturity on common bean.


## 3.3. Growth Parameters

### 3.3.1. Plant Height

Plant height increased with increased fertilizer rate for both varieties. The highest (67.75 cm) height of the plant was found for variety Shewa Robit at rate of 150 kg NPS ha−1, whereas the minimum height (59.0 cm) was obtained from Shewa Robit with no fertilizer applied (Table 2). Thus, the highest in plant height is probably due to genetically different character of varieties and increased NPS fertilizer by enhancing of root development and crop growth. It could also due to favorable climatic conditions until physiological maturity especially timely rainfall throughout growing season. In addition, the P supplied from NPS fertilizer might have contributed for root proliferation contributing for improved nutrient uptake, thereby improving the increase in size and development of the plants. Consistent with this suggestion, the study in [37] indicated maximum (74.79) height of the plant of mung bean with application of 50–70 kg NP ha−1. The application of S enhances crop growth and increases nutrient uptake by the crop [38]. This study also corroborates the results of [39], who reported maximum plant height (99.72 cm) with maximum rate of NPS application (150 kg NPS ha−1) for common bean variety Nasir.


### 3.3.2. Number of Primary Branches

Results indicated that branch number was notably affected by the two-way interaction of NPS rates and varieties. Significantly, the highest (6.98) branch number was recorded from interaction fertilizer composed of NPS at rate of 150 kg ha−1 with variety N-26, whereas the lowest branch number primary (6.1) was obtained from Shewa Robit with no fertilizer applied (Table 2). Thus, the highest mean was observed due to genetically different characteristics of varieties, and increased NPS fertilizer rate can enhance crop growth. The amounts of primary branches per plant were increased due to increased application of blended NPS fertilizer. This implies that higher vegetative growth was formed when there is higher availability of nutrients supplied from blended NPS fertilizer. Increased number of branch plant−1 was formed for the fact that vigorous growth by the plants is a result of better photosynthetic activities with adequate availability of nutrients at vegetative growth stages [33]. The study in [33] reported significantly higher (5.34) amount of branches plant−1 at maximum application of fertilizer (150 Kg NPS ha−1). Furthermore, Jawahar et al. observed significantly higher (5.91) number of branches plant−1 with the addition of 40 kg P2O5 ha−1 on mung bean production. The result was also consistent with the research finding of [40].


### 3.3.3. Leaf Area

Leaf area was significantly affected by the two-way interaction between NPS rates and varieties. Accordingly, the maximum (376.12 cm2) leaf area was recorded from interaction of fertilizer composed of NPS at rate (100 kg ha−1) and variety N-26, whereas minimum leaf area (220.26 cm2) was obtained from variety Shewa Robit with no fertilizer applied (Table 2). Thus, the maximum mean leaf area was observed due to genetically different characteristics of varieties and increased NPS fertilizer rate, which can enhance leaf area. The highest leaf area plant−1 might also be attributed to the improved photosynthesis process following better supply of nutrients in balanced quantity to the plants at growing stages. This result is consistent with the findings of [41]. In contrast, the low leaf area was found from the treatment with application of 57 kg P ha−1 rather than that recorded at rate application of P 38 kg ha−1. In this result, also low leaf area was recorded from the treatment with addition of 150 kg ha−1 NPS rather than that recorded at rate application of blended 100 kg ha−1 NPS.


### 3.3.4. Leaf Area Index

The two-way interaction between NPS rates and varieties was found to be significant (P≤0.05) on leaf area index. Significantly, the highest leaf area index (1.25) was recorded from interaction of fertilizer composed of NPS at rate (100 kg ha−1) with variety N-26, whereas the lowest leaf area index (0.73) was obtained from Shewa Robit with no fertilizer applied (Table 2). The greater in leaf area index resulted from improved availability of essential nutrients such as N, P, and S, which can boost physiological process, which in turn improves growth of leaf area [42]. Supporting this finding, the study in [43] recorded a significant increase in leaf area index of soybean following P application.


## 3.3.1. Plant Height

Plant height increased with increased fertilizer rate for both varieties. The highest (67.75 cm) height of the plant was found for variety Shewa Robit at rate of 150 kg NPS ha−1, whereas the minimum height (59.0 cm) was obtained from Shewa Robit with no fertilizer applied (Table 2). Thus, the highest in plant height is probably due to genetically different character of varieties and increased NPS fertilizer by enhancing of root development and crop growth. It could also due to favorable climatic conditions until physiological maturity especially timely rainfall throughout growing season. In addition, the P supplied from NPS fertilizer might have contributed for root proliferation contributing for improved nutrient uptake, thereby improving the increase in size and development of the plants. Consistent with this suggestion, the study in [37] indicated maximum (74.79) height of the plant of mung bean with application of 50–70 kg NP ha−1. The application of S enhances crop growth and increases nutrient uptake by the crop [38]. This study also corroborates the results of [39], who reported maximum plant height (99.72 cm) with maximum rate of NPS application (150 kg NPS ha−1) for common bean variety Nasir.


## 3.3.2. Number of Primary Branches

Results indicated that branch number was notably affected by the two-way interaction of NPS rates and varieties. Significantly, the highest (6.98) branch number was recorded from interaction fertilizer composed of NPS at rate of 150 kg ha−1 with variety N-26, whereas the lowest branch number primary (6.1) was obtained from Shewa Robit with no fertilizer applied (Table 2). Thus, the highest mean was observed due to genetically different characteristics of varieties, and increased NPS fertilizer rate can enhance crop growth. The amounts of primary branches per plant were increased due to increased application of blended NPS fertilizer. This implies that higher vegetative growth was formed when there is higher availability of nutrients supplied from blended NPS fertilizer. Increased number of branch plant−1 was formed for the fact that vigorous growth by the plants is a result of better photosynthetic activities with adequate availability of nutrients at vegetative growth stages [33]. The study in [33] reported significantly higher (5.34) amount of branches plant−1 at maximum application of fertilizer (150 Kg NPS ha−1). Furthermore, Jawahar et al. observed significantly higher (5.91) number of branches plant−1 with the addition of 40 kg P2O5 ha−1 on mung bean production. The result was also consistent with the research finding of [40].


## 3.3.3. Leaf Area

Leaf area was significantly affected by the two-way interaction between NPS rates and varieties. Accordingly, the maximum (376.12 cm2) leaf area was recorded from interaction of fertilizer composed of NPS at rate (100 kg ha−1) and variety N-26, whereas minimum leaf area (220.26 cm2) was obtained from variety Shewa Robit with no fertilizer applied (Table 2). Thus, the maximum mean leaf area was observed due to genetically different characteristics of varieties and increased NPS fertilizer rate, which can enhance leaf area. The highest leaf area plant−1 might also be attributed to the improved photosynthesis process following better supply of nutrients in balanced quantity to the plants at growing stages. This result is consistent with the findings of [41]. In contrast, the low leaf area was found from the treatment with application of 57 kg P ha−1 rather than that recorded at rate application of P 38 kg ha−1. In this result, also low leaf area was recorded from the treatment with addition of 150 kg ha−1 NPS rather than that recorded at rate application of blended 100 kg ha−1 NPS.


## 3.3.4. Leaf Area Index

The two-way interaction between NPS rates and varieties was found to be significant (P≤0.05) on leaf area index. Significantly, the highest leaf area index (1.25) was recorded from interaction of fertilizer composed of NPS at rate (100 kg ha−1) with variety N-26, whereas the lowest leaf area index (0.73) was obtained from Shewa Robit with no fertilizer applied (Table 2). The greater in leaf area index resulted from improved availability of essential nutrients such as N, P, and S, which can boost physiological process, which in turn improves growth of leaf area [42]. Supporting this finding, the study in [43] recorded a significant increase in leaf area index of soybean following P application.


## 3.4. Yield and Yield Components

### 3.4.1. Number of Pods per Plant

The number of pods per plant was highly influenced by the two-way interaction effect between NPS rates and varieties. The maximum (53.26) pods number was recorded for Shewa Robit at rate of 150 kg ha−1, whereas the lowest pod number (30.40) was also obtained from Shewa Robit when no fertilizer was applied (Table 3). Thus, the greater number of pods per plant with the addition of NPS fertilizer was due to immediate supply of fertilizer composed of NPS to the plants from inorganic fertilizer enhancing photosynthetic activities, thereby improving vegetative growth and development, which increased the production of pods upon translocation. This study is consistent with research findings of [33]. The study in [44] reported significant effect of NP fertilizers on pod production per plant of mung bean with the maximum number of pods in each plant (30.45) obtained at 52.5 kg N ha−1 and 26 kg P2O5 ha−1. This finding is consistent with the result of [45]. Similarly, the study in [35] reported a corresponding increase in pods number (2.31 to 10.62) when P rate increased from nil to 39.6 kg ha−1, which implies that the addition of P fertilizer could contribute to promoting the formation of nodes and pods in legumes. Further, research conducted by [46] indicated that pods number of common bean significantly increased with increased rate of P up to the highest rate of 92 kg P2O5 ha−1.Table 3
Interaction effects of varieties and blended NPS fertilizer rates on number of pods (PN) per plant, and number of seeds (SN) per pod, 1000-seed weight (g), and harvest index (%).
VarietiesNPS rate (kg ha−1)No. of pods per plant−1No. of seeds per pod−11000-seed weight (g)HI (%)N-26030.83d8.11c50.367c0.31cd5042.66c9.56b53.700b0.32b10049.53b11.86ab55.683a0.34a15050.96b11.96a55.800a0.34aShewa Robit030.40d6.53f41.283f0.30de5047.60c7.05e43.755e0.30e10052.78a7.6d46.948d0.31c15053.26a7.9cd46.938d0.32bLSD (0.05)3.910.490.668.13CV (%)7.264.361.152.14Numbers with the same letter(s) within a column are nonsignificant atP≤0.05; CV = coefficient of variance and LSD = least significant difference.


### 3.4.2. Number of Seeds per Pod

The result revealed that seeds number per pod was also strongly influenced by the two-way interaction between NPS rates and varieties. There were significant increases in the number of seeds per pod with increase in blended NPS rate over control. Significantly, variety N-26 had higher pods number with increased NPS rate than variety Shewa Robit (Table3). Variety N-26 produced the highest (11.96) seeds number pod−1 at 150 kg ha−1, whereas the lowest (6.53) seeds number pod−1 was found for Shewa Robit at nil rate fertilizer (Table 3). The increase in the amount of seeds per pot with increased NPS rates is probably due to the higher vegetative growth and improved branching with increasing production of pod. The result was consistent with the research findings of [47] who reported significant interaction effect of NPS fertilizers rates and mung bean varieties on seed pod−1 of mung bean with the maximum amount of seeds pod−1 (8.84) obtained at 150 kg NPS ha−1 for variety N-26. In this study, the highest seeds number per pod−1 could probably be due to the combination of photosynthesis function of N, seed formation ability of P, and metabolic energy ability of S [48, 49]. This finding is also in line with the result of [50]. The finding of this result is also supported by [40]. However, the current study is not consistent with the result of [51], who reported nonsignificant effect of main effects of N and P as well as their interactions on the amount of seeds pod−1 of common bean.


### 3.4.3. 1000-Seed Weight

1000-seed weight was significantly (P≤0.05) influenced by the two-way interaction between NPS rates. The maximum 1000-seed weight (55.8 g) was recorded from interaction of 150 kg NPS ha−1 application with variety N-26, followed by the maximum (55.68 g) obtained from interaction 100 kg NPS ha−1 with variety N-26, whereas the minimum 1000-seed weight (41.28 g) was found from Shewa Robit variety with no fertilizer applied (Table 3). Variety N-26 produced significantly maximum thousand-seed weight with increased NPS fertilizer rate than variety Shewa Robit. Such disparity in thousand-seed weight among the varieties may be attributed to genetically different characteristics of varieties and increase in NPS fertilizer rate over the control. This result is confirmed by the finding of [52], who determined that 1000-seed weight increased with P levels. This study is also in line with [53], who reported that the maximum (51.6 g) of mung bean was recorded at rate of 60 kg P ha−1 for 1000-seed weight, while lowest 1000-seed weight (46.96 gm) was found for control treatment.This is the fact that assimilated photosynthesis can be translocated from vegetative plant parts to the seed, thus considerably enhancing seed weight. The increase in 1000-grain weight showed that macronutrients along with micronutrients (i.e., S) are necessary for healthier and robust seeds in common bean [54]. Thus, the result is consistent with findings of [55]. The result is also supported by the findings of [44].


### 3.4.4. Aboveground Dry Biomass

For the studied mung bean plant, aboveground dry biomass was also significantly (P≤0.05) influenced by the three-way interaction of NPS rates, varieties, and methods of application. For all varieties, aboveground dry biomass significantly increased with increase in blended NPS rate with drilling method of fertilizer application (Table 4). The maximum dry biomass (4273.7 kg ha−1) was obtained from interaction of 150 kg ha−1 blended NPS fertilizer with variety N-26 from the combination of drilled application followed by the same variety (4267.7 kg ha−1) at rate of 100 kg ha−1 blended NPS using drilling application method, while the minimum aboveground dry biomass (3038.1 kg ha−1) was obtained from Shewa Robit with no fertilizer application (Table 4).Table 4
Interaction effects of varieties, blended NPS fertilizer rates, and application methods on aboveground dry biomass (kg) and grain yield (g).
VarietiesNPS rates (kg ha−1)AGDM (kg ha−1)GY (kg ha−1)Appl. methodsAppl. methodsDrillingBroadcastingDrillingBroadcastingN-2603211.1g3185.3g1011.0h1000.1h503872.4e3871.0e1274.2e1244.2f1004267.7a4209.1abc1537.6a1459.9b1504273.7a4226.3ab1539.2a1468.4bShewa Robit03104.7gh3038.1h953.7i943.4i503463.3f3469.9f1066.8g1040.4g1004097.9cd4045.6d1315.4d1261.7ef1504155.1bcd4127.9bcd1367.6c1347.3cLSD (0.05)112.0927.71CV (%)1.771.36Numbers with the same letter in column are nonsignificant at 5% level of significance; LSD (0.05): least significant difference at 5% level; CV: coefficient of variation; AGDB: aboveground dry biomass, and GY: grain yield.The study in [33] reported the significantly highest aboveground biomass for mung bean variety N-26 at application of 100 kg ha−1 with 20 cm. The authors of [41, 56] also reported an increase in total dry matter per plant with N application for French bean and common bean, respectively. This result is consistent with the findings of [39], who reported a significant linear response of aboveground dry biomass to application of different levels of NPS in common bean. According to [57], there is the addition of P fertilizer with soil low in available P of acidic Nitisols, and an increase in the aboveground biomass of faba bean was found. The study in [35] also reported that P fertilization on soya bean did not significantly affect the aboveground dry biomass.


### 3.4.5. Grain Yield

The analysis of variance revealed that grain yield was significantly (P≤0.05) influenced by the three-way interaction of NPS rates, varieties, and application method. The maximum grain yield (1539.2 kg ha−1) was found from interaction of 150 kg ha−1 blended NPS fertilizer rate with variety N-26 using drilled application method followed by maximum (1537.6 kg ha−1) grain yield recorded from the interaction of 100 kg ha−1 blended NPS fertilizer rate with the same variety and application method, but no statistical difference between them (Table 4), while, significantly, the lowest yield (943.4 kg ha−1) was observed from interaction of variety Shewa Robit with nil fertilizer applied (Table 5). This highest value was formed due to significant application of fertilizer composed of NPS. N at early growth stages promoted vegetative growth and created conditions conducive to high yield and played a critical role for chlorophyll formation and protein, directly increasing the plant protein content, thereby boosting yield [48]. In accord with the present finding, the authors of [33, 47] reported that grain yield of mung bean is significantly affected by two-way interaction effects of mung bean varieties and blended NPS rate.Table 5
Partial budget analysis of interaction effect of varieties and blended NPS rates with the application method on yield of mung bean during 2019 cropping season at Humbo.
TreatmentGAYAJAYGFPTVCNBMRR (%)MethodRatesVarietiesDr0Shewa Robit953.7858.3330041.55030041.55-50Shewa Robit1066.8960.1233604.280032804.2345100Shewa Robit1315.41183.8641435.1150039935.11019150Shewa Robit1367.61230.8443079.4220040879.4135Br0Shewa Robit943.4849.0629717.1029717.1-50Shewa Robit1040.4936.3632772.680031972.6282100Shewa Robit1261.71135.5339743.55150038243.55896150Shewa Robit1347.31212.5742439.95220040239.95285Dr0N-261011909.931846.5031846.5-50N-261274.21146.7840137.380039337.3936100N-261537.61383.8448434.4150046934.41085150N-261539.21385.2848484.8220046284.8DBr0N-261000.1900.0931503.15031503.15050N-261244.21119.7839192.380038392.3861100N-261459.91313.9145986.85150044486.85871150N-261468.41321.5646254.6220044054.6DDr = drilled application method, Br = broadcasting, GAY = gross average yield, AJAY = adjusted average yield (−10%), GFP = gross field price (mung bean price = 35 ETB kg−1, TVC = total variable cost, and NB = net benefit (ETB ha−1).Phosphorus enhanced cellular respiration in the production of the starch, protein, and fats plays a fundamental role in metabolism and energy producing reaction, building phospholipids, and nucleic acid and stimulates blooming and seed formation, which could increase yield [58].This result is consistent with that of [48], who described that the interaction effects of N and P levels on seed yield of mung bean were highly significant. The study in [59] who reported the application of P and S could maximize mung bean production. The study in [60] also reported highly significant effect of P fertilizer application rate on seed yield of mung bean and common bean. The study in [46] also reported that the application of P could maximize the yield of haricot bean. According to [13], P is considered to be important for stimulated root development and seed formation. Application method significantly influenced grain yield with increase in NPS rate (Table 4).Application method of drilling is suitable method than broadcasting. This could be due to avoiding easy evaporation of mobile nutrients such as N, S and can keep P fertilizer within the soil system for the adequate supply to crops. Disparity of broadcast results in nonuniform growth, wasting of fertilizer, and decreasing the usage coefficient of plant [61]. Drilling method for N-fertilizers in nutrient deficient soils may offer increased fertilizer absorption by the plant [62].


### 3.4.6. Harvest Index

Harvest index was influenced significantly (P≤0.05) due to the two-way interaction of fertilizer rates composed of NPS and varieties. The maximum harvest index (0.34) was recorded from interaction effect of 150 kg ha−1 blended NPS fertilizer with variety N-26 followed by 100 kg NPS ha−1 with the same variety, but no statistical difference (Table 3). The minimum harvest index (0.30) was obtained from Shewa Robit with no fertilizer applied (Table 3). This study is consistent with the finding of [39, 47]. The study in [47] also reported that the maximum harvest index was obtained from N-26 variety at NPS rate of 150 kg ha−1, which was followed by the same variety N-26 (39.05%) at rate of 100 kg NPS ha−1. The study in [37] also reported an increase in harvest index of mung bean in response to addition of N and P.


## 3.4.1. Number of Pods per Plant

The number of pods per plant was highly influenced by the two-way interaction effect between NPS rates and varieties. The maximum (53.26) pods number was recorded for Shewa Robit at rate of 150 kg ha−1, whereas the lowest pod number (30.40) was also obtained from Shewa Robit when no fertilizer was applied (Table 3). Thus, the greater number of pods per plant with the addition of NPS fertilizer was due to immediate supply of fertilizer composed of NPS to the plants from inorganic fertilizer enhancing photosynthetic activities, thereby improving vegetative growth and development, which increased the production of pods upon translocation. This study is consistent with research findings of [33]. The study in [44] reported significant effect of NP fertilizers on pod production per plant of mung bean with the maximum number of pods in each plant (30.45) obtained at 52.5 kg N ha−1 and 26 kg P2O5 ha−1. This finding is consistent with the result of [45]. Similarly, the study in [35] reported a corresponding increase in pods number (2.31 to 10.62) when P rate increased from nil to 39.6 kg ha−1, which implies that the addition of P fertilizer could contribute to promoting the formation of nodes and pods in legumes. Further, research conducted by [46] indicated that pods number of common bean significantly increased with increased rate of P up to the highest rate of 92 kg P2O5 ha−1.Table 3
Interaction effects of varieties and blended NPS fertilizer rates on number of pods (PN) per plant, and number of seeds (SN) per pod, 1000-seed weight (g), and harvest index (%).
VarietiesNPS rate (kg ha−1)No. of pods per plant−1No. of seeds per pod−11000-seed weight (g)HI (%)N-26030.83d8.11c50.367c0.31cd5042.66c9.56b53.700b0.32b10049.53b11.86ab55.683a0.34a15050.96b11.96a55.800a0.34aShewa Robit030.40d6.53f41.283f0.30de5047.60c7.05e43.755e0.30e10052.78a7.6d46.948d0.31c15053.26a7.9cd46.938d0.32bLSD (0.05)3.910.490.668.13CV (%)7.264.361.152.14Numbers with the same letter(s) within a column are nonsignificant atP≤0.05; CV = coefficient of variance and LSD = least significant difference.


## 3.4.2. Number of Seeds per Pod

The result revealed that seeds number per pod was also strongly influenced by the two-way interaction between NPS rates and varieties. There were significant increases in the number of seeds per pod with increase in blended NPS rate over control. Significantly, variety N-26 had higher pods number with increased NPS rate than variety Shewa Robit (Table3). Variety N-26 produced the highest (11.96) seeds number pod−1 at 150 kg ha−1, whereas the lowest (6.53) seeds number pod−1 was found for Shewa Robit at nil rate fertilizer (Table 3). The increase in the amount of seeds per pot with increased NPS rates is probably due to the higher vegetative growth and improved branching with increasing production of pod. The result was consistent with the research findings of [47] who reported significant interaction effect of NPS fertilizers rates and mung bean varieties on seed pod−1 of mung bean with the maximum amount of seeds pod−1 (8.84) obtained at 150 kg NPS ha−1 for variety N-26. In this study, the highest seeds number per pod−1 could probably be due to the combination of photosynthesis function of N, seed formation ability of P, and metabolic energy ability of S [48, 49]. This finding is also in line with the result of [50]. The finding of this result is also supported by [40]. However, the current study is not consistent with the result of [51], who reported nonsignificant effect of main effects of N and P as well as their interactions on the amount of seeds pod−1 of common bean.


## 3.4.3. 1000-Seed Weight

1000-seed weight was significantly (P≤0.05) influenced by the two-way interaction between NPS rates. The maximum 1000-seed weight (55.8 g) was recorded from interaction of 150 kg NPS ha−1 application with variety N-26, followed by the maximum (55.68 g) obtained from interaction 100 kg NPS ha−1 with variety N-26, whereas the minimum 1000-seed weight (41.28 g) was found from Shewa Robit variety with no fertilizer applied (Table 3). Variety N-26 produced significantly maximum thousand-seed weight with increased NPS fertilizer rate than variety Shewa Robit. Such disparity in thousand-seed weight among the varieties may be attributed to genetically different characteristics of varieties and increase in NPS fertilizer rate over the control. This result is confirmed by the finding of [52], who determined that 1000-seed weight increased with P levels. This study is also in line with [53], who reported that the maximum (51.6 g) of mung bean was recorded at rate of 60 kg P ha−1 for 1000-seed weight, while lowest 1000-seed weight (46.96 gm) was found for control treatment.This is the fact that assimilated photosynthesis can be translocated from vegetative plant parts to the seed, thus considerably enhancing seed weight. The increase in 1000-grain weight showed that macronutrients along with micronutrients (i.e., S) are necessary for healthier and robust seeds in common bean [54]. Thus, the result is consistent with findings of [55]. The result is also supported by the findings of [44].


## 3.4.4. Aboveground Dry Biomass

For the studied mung bean plant, aboveground dry biomass was also significantly (P≤0.05) influenced by the three-way interaction of NPS rates, varieties, and methods of application. For all varieties, aboveground dry biomass significantly increased with increase in blended NPS rate with drilling method of fertilizer application (Table 4). The maximum dry biomass (4273.7 kg ha−1) was obtained from interaction of 150 kg ha−1 blended NPS fertilizer with variety N-26 from the combination of drilled application followed by the same variety (4267.7 kg ha−1) at rate of 100 kg ha−1 blended NPS using drilling application method, while the minimum aboveground dry biomass (3038.1 kg ha−1) was obtained from Shewa Robit with no fertilizer application (Table 4).Table 4
Interaction effects of varieties, blended NPS fertilizer rates, and application methods on aboveground dry biomass (kg) and grain yield (g).
VarietiesNPS rates (kg ha−1)AGDM (kg ha−1)GY (kg ha−1)Appl. methodsAppl. methodsDrillingBroadcastingDrillingBroadcastingN-2603211.1g3185.3g1011.0h1000.1h503872.4e3871.0e1274.2e1244.2f1004267.7a4209.1abc1537.6a1459.9b1504273.7a4226.3ab1539.2a1468.4bShewa Robit03104.7gh3038.1h953.7i943.4i503463.3f3469.9f1066.8g1040.4g1004097.9cd4045.6d1315.4d1261.7ef1504155.1bcd4127.9bcd1367.6c1347.3cLSD (0.05)112.0927.71CV (%)1.771.36Numbers with the same letter in column are nonsignificant at 5% level of significance; LSD (0.05): least significant difference at 5% level; CV: coefficient of variation; AGDB: aboveground dry biomass, and GY: grain yield.The study in [33] reported the significantly highest aboveground biomass for mung bean variety N-26 at application of 100 kg ha−1 with 20 cm. The authors of [41, 56] also reported an increase in total dry matter per plant with N application for French bean and common bean, respectively. This result is consistent with the findings of [39], who reported a significant linear response of aboveground dry biomass to application of different levels of NPS in common bean. According to [57], there is the addition of P fertilizer with soil low in available P of acidic Nitisols, and an increase in the aboveground biomass of faba bean was found. The study in [35] also reported that P fertilization on soya bean did not significantly affect the aboveground dry biomass.


## 3.4.5. Grain Yield

The analysis of variance revealed that grain yield was significantly (P≤0.05) influenced by the three-way interaction of NPS rates, varieties, and application method. The maximum grain yield (1539.2 kg ha−1) was found from interaction of 150 kg ha−1 blended NPS fertilizer rate with variety N-26 using drilled application method followed by maximum (1537.6 kg ha−1) grain yield recorded from the interaction of 100 kg ha−1 blended NPS fertilizer rate with the same variety and application method, but no statistical difference between them (Table 4), while, significantly, the lowest yield (943.4 kg ha−1) was observed from interaction of variety Shewa Robit with nil fertilizer applied (Table 5). This highest value was formed due to significant application of fertilizer composed of NPS. N at early growth stages promoted vegetative growth and created conditions conducive to high yield and played a critical role for chlorophyll formation and protein, directly increasing the plant protein content, thereby boosting yield [48]. In accord with the present finding, the authors of [33, 47] reported that grain yield of mung bean is significantly affected by two-way interaction effects of mung bean varieties and blended NPS rate.Table 5
Partial budget analysis of interaction effect of varieties and blended NPS rates with the application method on yield of mung bean during 2019 cropping season at Humbo.
TreatmentGAYAJAYGFPTVCNBMRR (%)MethodRatesVarietiesDr0Shewa Robit953.7858.3330041.55030041.55-50Shewa Robit1066.8960.1233604.280032804.2345100Shewa Robit1315.41183.8641435.1150039935.11019150Shewa Robit1367.61230.8443079.4220040879.4135Br0Shewa Robit943.4849.0629717.1029717.1-50Shewa Robit1040.4936.3632772.680031972.6282100Shewa Robit1261.71135.5339743.55150038243.55896150Shewa Robit1347.31212.5742439.95220040239.95285Dr0N-261011909.931846.5031846.5-50N-261274.21146.7840137.380039337.3936100N-261537.61383.8448434.4150046934.41085150N-261539.21385.2848484.8220046284.8DBr0N-261000.1900.0931503.15031503.15050N-261244.21119.7839192.380038392.3861100N-261459.91313.9145986.85150044486.85871150N-261468.41321.5646254.6220044054.6DDr = drilled application method, Br = broadcasting, GAY = gross average yield, AJAY = adjusted average yield (−10%), GFP = gross field price (mung bean price = 35 ETB kg−1, TVC = total variable cost, and NB = net benefit (ETB ha−1).Phosphorus enhanced cellular respiration in the production of the starch, protein, and fats plays a fundamental role in metabolism and energy producing reaction, building phospholipids, and nucleic acid and stimulates blooming and seed formation, which could increase yield [58].This result is consistent with that of [48], who described that the interaction effects of N and P levels on seed yield of mung bean were highly significant. The study in [59] who reported the application of P and S could maximize mung bean production. The study in [60] also reported highly significant effect of P fertilizer application rate on seed yield of mung bean and common bean. The study in [46] also reported that the application of P could maximize the yield of haricot bean. According to [13], P is considered to be important for stimulated root development and seed formation. Application method significantly influenced grain yield with increase in NPS rate (Table 4).Application method of drilling is suitable method than broadcasting. This could be due to avoiding easy evaporation of mobile nutrients such as N, S and can keep P fertilizer within the soil system for the adequate supply to crops. Disparity of broadcast results in nonuniform growth, wasting of fertilizer, and decreasing the usage coefficient of plant [61]. Drilling method for N-fertilizers in nutrient deficient soils may offer increased fertilizer absorption by the plant [62].


## 3.4.6. Harvest Index

Harvest index was influenced significantly (P≤0.05) due to the two-way interaction of fertilizer rates composed of NPS and varieties. The maximum harvest index (0.34) was recorded from interaction effect of 150 kg ha−1 blended NPS fertilizer with variety N-26 followed by 100 kg NPS ha−1 with the same variety, but no statistical difference (Table 3). The minimum harvest index (0.30) was obtained from Shewa Robit with no fertilizer applied (Table 3). This study is consistent with the finding of [39, 47]. The study in [47] also reported that the maximum harvest index was obtained from N-26 variety at NPS rate of 150 kg ha−1, which was followed by the same variety N-26 (39.05%) at rate of 100 kg NPS ha−1. The study in [37] also reported an increase in harvest index of mung bean in response to addition of N and P.


## 3.5. Partial Budget Analysis

It is used to understand efficiency and economics of inputs and outputs of crop production. From this study, the mean yields of mung bean were estimated. The mean yields of mung bean were adjusted downward by 10% to reflect the difference between the experimental and farmers’ field yields [24].From the use of various interactions of fertilizers composed of NPS with varieties and with application methods, the total variable cost and net benefits were estimated. The total variable cost (TVC) was estimated during field experimental period that included the cost of fertilizers and cost of labor for fertilizers applications (Table5). Daily labor cost during experimental period was 100 ETB per person per day, and the field price of mung bean yield during harvesting period was 35 ETB kg−1. The total variable cost (TVC) was subtracted from gross field prices (GFP) to obtain net benefits (NB). After estimating net benefits, the treatments were arranged in increasing order of total variable costs to identify dominated and nondominated treatments. In this study, from sixteen treatments, three were dominated, and thirteen were nondominated (Table 5).Dominated treatments were absent from subsequent steps in the marginal analysis, whereas, for nondominated treatments, insignificant rate of returns was calculated. According to [24], the thirteen nondominated treatments gave more than 100% marginal rate of return (Table 5). Marginal rate of return (MRR) is a characteristic of the change from one treatment to another and since dominated treatments are not included, it will always be positive. So below 100% and/or negative MRR was considered as low and unacceptable to farmers, because such returns would not return capital and other related costs, and something would not be added to the cost of capital to repay the producers for the time and effort spent.The recommendation is not necessarily the treatment with the highest marginal rate of return compared to neither that of next lowest cost, or the treatment with the highest net benefit, nor the treatment with the highest yield. The identification of a recommendation requires a careful marginal analysis using an appropriate minimum rate of return [24]. In this study, the partial budget analysis indicated that the highest net benefit was obtained from variety N-26 supplied with fertilizer composed of NPS at rate of 100 kg ha−1 using drilling application 5 cm below seed, which gave highest net benefits of 46,934.4 ETB ha−1 (Table 5).


## 4. Conclusion

The results of this study revealed that mung bean varieties responded differently to different rates of NPS fertilizer. Further, the economic return obtained from different varieties of mung bean at different rates of NPS varied. This suggests that we need to apply agronomic and economic optimum rates of NPS fertilizer for mung bean varieties differently in order to obtain the maximum grain yield and economic return. Thus, though it is for one year as far as there is enough rainfall particularly during planting and even if it is intermittent until grain filling, it can be recommended that, for better production of mung bean in Humbo districts of Wolaita Zone and in areas similar to the study area, producers shall better use variety N-26 supplied with blended NPS fertilizer at rate 100 kg ha−1 using drilling application 5 cm below the seed.



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*Source: 3786720-2021-11-18.xml*