IJERD – International Journal of Environmental and Rural Development (2020) 11-1

Research articleerd

Cover Crop Mixtures Effects on Soil Physical and ChemicalProperties in JapanTORU NAKAJIMA*
Faculty of Regional Environment Science, Tokyo University of Agriculture, Japan
Email: tn206473@nodai.ac.jp

RIKU NAKAMURA
Faculty of Regional Environment Science, Tokyo University of Agriculture, Japan

RYUJI KAWAMURA
Faculty of Engineering, Kasetsart University, Bangkok, Thailand

MACHITO MIHARA
Faculty of Regional Environment Science, Tokyo University of Agriculture, Japan
Received 6 December 2019

Accepted 23 May 2020(*Corresponding Author)

Abstract Agricultural management practices such as cover crop could restore soil physicaland chemical properties, and in turn positive effect of crop productivity. However, it can varywith soil type, climate, and type of cover crop species. In addition, different cover crops
provide different benefits to agricultural land. For instance, legumes (e.g. clover (Trifoliumrepers L.)) fix atmospheric nitrogen (N) for their own use. After terminating the legume cover
crop, it will release N into the soil as the residues decompose and provide available N to themain crops. Some of cover crop (e.g. phacelia (Hydrophylloideae)) are able to suppress weeds
or prevent insect damages by competition, shading, and allelopathy. Recently, researchersreported that cover crop mixture may provide greater diversity of benefits than monoculture
cover crop. Therefore, the objective of this study was to demonstrate soil physical andchemical properties assessment under cover crops (clover, phacelia, and their mixture)
vegetation.
Keywords cover crop, mixture, soil organic carbon, soil physical and chemical property

INTRODUCTION
Cover crops have numerous benefits for agriculture practices (Murrell et al., 2017). According to theSoil Science Society of America (SSSA), cover crops are defined as a “close-growing crop thatprovides soil protection, seeding protection, and soil improvement between periods of general crop
production, or between trees in orchards and vines in vineyard, and when plowed under andincorporated into the soil, cover crops could be referred to as a green manure crop” (SSSA, 2008).
In addition, cover crops have the potential to enhance ecosystem services such as 1) increasing food,feed, fiber, and fuel productivity 2) soil organic carbon and other nutrient and water cycling, and 3)
soil, water, and air quality/health improvement (Blanco-Canqui et al., 2015). Cover crop may bealternative for chemical fertilizer and pesticide. While actively growing, cover crops increase solar
energy harvest and carbon flux into the soil, providing food for soil microorganisms, while
simultaneously increasing evapotranspiration from the soil (Dabney et al., 2007). Moreover, covercrops have been proposed in the United State to increased soil organic carbon (SOC) stock of erodedand degraded soils and sequester SOC and according to the research, the result showed that covercrop management could increase SOC by 1.12 Mg-C ha-1 yr-1 with no-tillage agricultural practices(Olson et al., 2014).
Different cover crops provide different benefits to agricultural land. For instance, legumes (e.g.
clover (Trifolium repers L.)) fix atmospheric nitrogen (N) for their own use. After terminating thelegume cover crop, it will release N into the soil as the residues decompose and provide available NⒸ ISERD182

IJERD – International Journal of Environmental and Rural Development (2020) 11-1

to the main crops. Some of cover crop (e.g. phacelia (Hydrophylloideae)) are able to suppress weeds
or prevent insect damages by competition, shading, and allelopathy. Cover crop may be alternative
for chemical fertilizer and pesticide.
Recently, researchers reported that cover crop mixtures could provide greater diversity ofbenefits than monoculture cover crop (Murrell et al., 2017; Tribouillois et al., 2016). Cover crop
mixtures increase plant species diversity, in turn, potentially increasing ecosystem services that
directly or indirectly improve main crop productivity (Zhang et al., 2007; Clark et al., 1994; Murrell
et al., 2017). Yet the effects of cover crop mixtures on soil physical and chemical properties vary byclimate, soil type, management practices, and a species of cover crops. Thus, there is a need for site,soil, and cover crop species-specific research on cover crop mixtures.
OBJECTIVE
The objective of this study was to demonstrate soil physical and chemical properties assessment
under cover crops (clover, phacelia, and their mixture) vegetation.
METHODOLOGY
Experimental Design
The experiment was carried out at the field research plot, Tokyo University of Agriculture(35°38’29’’N, 139°37’56’’E, 40.3m elevation) during July to October in 2018 (Fig. 1). On average
this site received 1464 mm of precipitation annually and mean annual temperature was 15.0 ℃,
respectively. Treatments included four cover crop systems: clover (Trifolium repers L.), phacelia(Hydrophylloideae), their mixture (clover and phacelia), and control (without cover crop) using
Wagner pot (diameter = 256 mm, height = 297 mm, 1/2000a-scale). In this study, soils were takenfrom subsoil under arable land and were relatively the sterile soils. Soil are classified as Andosol andsilty loam (sand 69.1 %, silt 19.9 %, and clay 11.0 %) by IUSS (International Union of Soil Sciences)classification.
2nd July

4th September

25th September
2 weeks

2 months

Crop Growth

Harvest and Soil Sampling

Decomposition

3 weeks

Planting Jp. Mustard Spinach

Plowing into Soil

Planting Cover Crop

Cover Crop Growth

17th October

Soil Moisture Sensor

Fig. 1 Experimental schedule
Soil Analysis
Soil pH and electrical conductivity (EC) were determined using 1:1 soil to water ratio (Glendon andDani, 2002). Concentration of SOC and total nitrogen (TN) were measured following the dry
combustion method (960℃) using an automatic nitrogen-carbon analyzer (Sumika ChemicalAnalysis Service, Ltd., Tokyo, Japan). Briefly, the soil samples preparation was as follow; ovendried (below 60℃) samples were ground with a mortar and pestle to allow passage through a 250
μm sieve, and then roller ground to yield a fine and homogeneous sample. Soil hardness was measureusing yamanaka soil hardness tester (Daiki Rika Kogyo Co., Ltd, Tokyo, Japan). Saturated hydraulicconductivity (Ks) was measured with a mini disk infiltrometer (METER Group Inc., USA). TemporalⒸ ISERD183

IJERD – International Journal of Environmental and Rural Development (2020) 11-1

changes of water content were measured by TDR (time-domain reflectometer) (5TE, METER GroupInc., USA).
Statistical Analysis
Analysis of variance was conducted comparisons between clover, phacelia, mixture, and control. The
data were analyzed statistically using Tukey’s test in R-Studio (Studio 2012). Statistical significancewas computed at p ≤ 0.05, unless otherwise stated.
RESULTS AND DISCUSSION
Soil Physical and Chemical Properties
Data of soil physical and chemical properties of different cover crop treatments (clover, phacelia,and mixture, and control vegetations) are shown in Table 1. Cover crop vegetation did not
significantly affect pH. A similar trend in EC was observed at different cover crop treatments. Covercrop treatments significantly affect SH (p < 0.05). Cover crop with Mixture can alleviate soil
compaction by penetrating compact layers and acting similar to tillage tools or bio drill. BlancoCanqui et al (2015) stated that cover crop can alleviate compaction and reduce the susceptibility ofthe soil compaction. this benefit depends on the length of cover crop, and the amount andcharacteristics of the length and the size of roots. In addition, cover crop may improve soil
compatibility by improving soil aggregation and increasing SOC concentration. Cover crop
treatments significantly affected the Ks (p < 0.05). Ks under Control treatment was higher than othertreatments. Cover crop may have intact bio-channel (e.g. root) which increase the subsurface channel
network and may enhance the Ks. Cover crop mixture can positive impacts on Japanese mustard
spinach. However, weather conditions (e.g. precipitation and temperature) and soil type are also
important factors impacting vegetable yields response to cover crop management. The cover croptreatment especially Mixture improved the overall soil physical and chemical properties and Japanesemustard spinach in this study.
Table 1 Effects of cover crops on soil, pH, electrical conductivity (EC), soil hardness (SH),saturated hydraulic conductivity (Ks), and yield of Japanese mustard spinachpHECSHKs-mS cm-1mmcm s-1

Japanese mustard
spinachMg ha-1

Clover6.82a

0.129a19.5b2.36×10-3

13.6abPhacelia

6.83a

0.136a19.5b2.51×10-3

8.52bMixture

6.87a

0.131a20.8ab

3.69×10-3

15.6aControl

6.80a

0.125a26.5a

6.63×10-4

10.8ab*Means with different letters among before vs. after logging soil for each depth are not significantly different at p ≤ 0.05.

The data in Fig. 2 show the soil organic carbon and total nitrogen contents under clover, phacelia,
their mixture, and control treatments. The largest SOC concentration was observed in Mixture
treatment, while the lower SOC concentrations were observed in Control and Clover. Similarly, thegreatest TN concentration was obtained in Mixture treatment, while lower TN concentrations wereobtained Clover, Phacelia, and Control. In general, cover crop residues and root accumulate on thesoil surface layer. It leads to increase SOC concentration. Moreover, belowground biomass such as
root inputs may particularly be important to increase SOC concentration (Blanco-Canqui et al., 2015).
In turn, for the long-term strategy, cover crop mixture increases the SOC concentration, and it may
improve the vegetable production.

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IJERD – International Journal of Environmental and Rural Development (2020) 11-1

23.0

1.80

(a)

(b)
1.75

Total Nitrogen (g kg- 1)

Soil Organic Carbon (g kg- 1)

22.5

22.0

21.5

21.0

20.5

1.70

1.65

1.60

1.55

20.0

1.50

CloverPhacelia

MixtureContolClover

Phacelia

Treatment

MixtureContolTreatment

Fig. 2 Soil organic carbon (a) and total nitrogen (b) contents under clover, phacelia, theirmixture, and control treatments
Means with same letter within treatments do not differ significantly with p ≤ 0.05.
Error bars represent ± one standard deviation.

Figure 3 shows that temporal changes of water content under clover, phacelia, and their mixture
treatments. Phacelia and Mixture had higher the volumetric water content than Clover during theexperiment. In general, cover crop roots and surface residues improve soil macro-porosity which
increase water retention capacity (Blanco-Canqui et al., 2015). Cover crop also can improve soil
hydraulic properties such as water infiltration, water retention capacity, and saturated hydraulicconductivity through improved the soil structure, especially, soil aggregation.
Volumetric Water Content (m3 m-3)

0.30
CloverPhacelia
Mixture

0.25
0.20
0.15
0.10
0.05
0.00
051015202530

3540DayFig. 3 Temporal changes of water content under clover, phacelia,
and their mixture treatments
CONCLUSION
The hypothesis that that the cover crop mixtures could provide greater diversity of benefits than
monoculture cover crop and increase plant species diversity, in turn, potentially increasing ecosystemservices that directly or indirectly improve main crop productivity is proven. The data also support
following conclusions: 1) Cover crop with Mixture can alleviate soil compaction by penetratingⒸ ISERD185

IJERD – International Journal of Environmental and Rural Development (2020) 11-1

compact layers and acting similar to tillage tools or bio drill 2) Cover crop mixture can positive
impacts on Japanese mustard spinach 3) Cover crop also can improve soil hydraulic properties suchas water infiltration, water retention capacity, and saturated hydraulic conductivity through improved
the soil structure, especially, soil aggregation.
ACKNOWLEDGEMENTS
The authors greatly acknowledge Dr. Yoshiyuki Ohshima at Department of Agricultural Chemistry,
Tokyo University of Agriculture for his laboratory assistance and invaluable discussions.
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