IJERD – International Journal of Environmental and Rural Development (2016) 7-1

Research articleerd

Potential of a New Slow-release Urea Fertilizer under On-farmConditions in a Semi-arid Environment
INSA KÜHLING*
University of Applied Sciences Osnabrück, Osnabrück, Germany
Email: i.kuehling@hs-osnabrueck.de

DMITRY REDOZUBOVState Agrarian University of the Northern Transurals, Tyumen, Russian Federation

CHRISTIAN JEISMANNSouth Westphalia University of Applied Sciences, Soest, Germany

IGOR KOMISSAROVState Agrarian University of the Northern Transurals, Tyumen, Russian Federation

DIETER TRAUTZ
University of Applied Sciences Osnabrück, Osnabrück, Germany
Received 6 January 2016

Accepted 11 April 2016(*Corresponding Author)

Abstract Nitrogen (N) fertilizers play an important role to increase grain yield and grain quality
in crop production systems. In Western Siberia, predominantly used N-fertilizers for cereal
production are urea and ammonium-nitrate (‘Selitra’). Due to semi-arid climate, only one
fertilizer application is common, simultaneously with sowing and directly into the seed furrow.
A new kind of slow-release fertilizer is a modified urea with silicate coating and urease
inhibitor and was developed at the State Agrarian University of the Northern Transurals(Russian Federation). In a field trial, the comparative performance of the novel fertilizer type
was tested with spring wheat near the city of Ishim in Tyumen region (Western Siberia) on 3.4
ha under on-farm conditions. 4 levels of the slow-release urea (25/50/75/100%) were compared
to 100% of conventional urea, 100% of Selitra and an unfertilized control in randomized
complete block design with 4 replications. Results showed significant differences in soil nitrateavailability but no differences in ammonium release. Differences between N-levels dispersed
during heading, afterwards only plots with Selitra fertilization showed significant higher nitratevalues. Leaf chlorophyll content as indicator for plant Nitrogen supply showed significant
differences from beginning stem elongation on. The harvested grain yield showed no significant
differences between the compared fertilizer types at the 100% N-level. Even if the grain yieldwith reduced dose of slow-release fertilizer was on the same level, it was not significantly
higher than the unfertilized control. From the results of this field trial there seems to be no
beneficial advantage of the tested slow-release fertilizer so far.
Keywords slow-release fertilizer, silicate coating, urease inhibitor, Nitrogen use efficiency,spring wheat, Western Siberia

INTRODUCTION
Nitrogen (N) fertilizers play an important role to increase wheat productivity and grain protein content.
In Western Siberia predominantly ammonium-nitrate (‘Selitra’) and urea are used for N-fertilization.

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Due to the dry sub-humid climate (Selezneva, 1973), only one N-application is common,simultaneously during sowing.
Also from an economic point of view, N-fertilizers play a key role in grain production processes
and due to high inputs of energy, they mainly affect the total economic balance (Lubkowski, 2014).
Urea is the most used Nitrogen fertilizer around the world agriculture, because of the high Nitrogencontent by 46.6% (Trenkel, 1997; Zheng et al., 2009). When urea is applied to a soil, it is almost
immediately hydrolysed into ammonium carbonate, which breaks down to carbon dioxide (CO2) andammonia (NH3), producing high soil pH and ammonia loss (Eriksen and Kjeldby, 1987; Fenn andKissel, 1973). The remainder of the ammonium in the soil can be converted to nitrates by the soil
bacteria. Therefore, reducing water solubility of urea granules by physical or chemical inhibitors isvery important and can improve the Nitrogen use efficiency (NUE) by preventing or slowing downthese processes.
Such types modified fertilizers are described as ‘enhanced efficiency fertilizers’ which are able toreduce the risk of nutrient losses to the environment, retain nutrients in a less leachable forms, reducesolubility and maintain nutrients in the root zone by physical barriers (coating) (Trenkel, 2010).
Furthermore, three different subtypes are characterised: (1) Stabilised fertilizers have a chemical
inhibitor to slow down the hydrolysis of urea with further transformation to NH4+ and inhibitors to stop
the oxidation of ammonium (NH4+) to nitrate (NO3–); (2) Slow-release fertilizers are less-soluble and N
is initially not plant available but needs to be converted into plant available N forms; (3) Controlledrelease fertilizers are quick soluble fertilizers with a coating of hardly soluble material with apredictable rate of Nitrogen release when used at the manufacturer specified temperature (Trenkel,1997; 2010).
Prognoses for the development of the fertilizer industry development predict an increase until
2020 to 1.9 – 2.2 million tons of slow- and controlled-release fertilizer products. One of the drawbacks,
particularly for the currently most widespread polymer-coating, is the remaining amount of uselesspolymer that is left in the soil after nutrient consumption (Trenkel, 2010). A perspective alternative although not yet used on a technological scale - is to produce slow-release fertilizers by using Calcium
Silicate (CaSiO3) as a mineral coating material, which can easily be decomposed by silicate bacteria toenvironmental friendly inorganic elements. The new type of such a slow-release urea fertilizer wasdeveloped at the State Agrarian University of the Northern Transurals (Russian Federation). A
combination of a physical barrier by CaSiO3-coating and a chemical urease inhibitor was chosen todelay the release of plant available Nitrogen.
The objective of this study was to compare the performance of the novel slow-release urea
fertilizer against common practice and to evaluate the potential for improving of the Nitrogen use
efficiency under practical conditions.
METHODOLOGY
Study Area
We installed a 3.4 ha field trial with spring wheat in Ishim (Tyumen province, Russia, Fig. 1) in RCBD
with 4 replications to compare 4 levels of coated urea ‘CU’ (100/75/50/25%) against 100% ofconventional uncoated urea ‘UU’, 100% of Selitra ‘S’ and a unfertilized control ‘C’. 100% equals 70kg/ha N (Table 1). The fertilizer was applied directly into the seed furrow. The seed rate was constantover all variants by 240 kg ha-1 for 600 plants per m . The plots were sown with the regional variety‘Ikarus‘ on May 19th, harvest took place on September 28th, weed regulation was done only once asusual for the region.

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IJERD – International Journal of Environmental and Rural Development (2016) 7-1

Fig. 1 Location and mean annual agro-climatic conditions of the study area
Souces: CGIAR-CSI (2009), GADM (2012), WorldClim (2013)

Table 1 Investigated variants with amounts of fertilizer and Nitrogen appliedvariantControl
S100
UU100
CU100
CU75CU50CU25

fertilizer type

N level [%]noSelitra
uncoated urea
coated urea
coated urea
coated urea
coated urea

0
100
100
100
75
5025

applied fertilizer[kg ha-1]
0203
150
153
115
7738

applied Nitrogen[kg ha-1]
0.0
70.0
70.0
70.0
52.2
35.0
17.5

Fertilizer Production
The fertilizer was produced on the laboratory scale by ’Биотех‘ at the State Agrarian University of theNorthern Transurals. Liquid Na2SiO3 was poured over usual urea in the first step. Secondly, liquidCaCl2 was added which induced the drying process. Finally, urease inhibitor was applied on thecoating. The coating material was between 1% and 3 % of the total mass of the fertilizer granules.
Analyses and Statistics
Soil Nmin (NO3 + NH4) analysis for 0-30 cm was done reflectometric (Merck) and for determination ofleaf chlorophyll content a SPAD-502 (Minolta) was used at the youngest fully developed leaf.
Comparisons among means were carried out in R using the package agricolae (LSD-Test, p<0.05) (RCore Team, 2013). Between values with the same letter, there is no significant difference.
RESULTS AND DISCUSSION
Soil NitrogenⒸ ISERD46

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The results of soil analysis showed significant differences in nitrate content but no significant
differences in ammonium content (Fig. 2). Homogeneous preconditions were given by a constant levelof both Nmin fractions before fertilization. During leaf development, the variants Nitrogen availability
differentiated, but only between the fertilizer types and not among the CU variants. Later in thegrowing season, only the S100 plots showed significant higher NO3 content in the soil.

Fig. 2 Soil Nmin components NO3-N and NH4-N in 0-30 cm before sowing/fertilization and at
3 development stages
Boxes show lower and upper quartiles, black line depicts the median, whiskers between min and max.

Even if there were no significant differences between soil ammonium contents, due to thedifferences in nitrate levels, a closer look on the proportions was necessary. Table 2 shows significant
differences in the ammonium share, starting during leaf development, where values in unfertilized
control plots were highest. This trend of low NH4 proportion in conjunction with high nitrate content
continued until the last measurement.
Table 2 NH4-N proportion of total Nmin (0-30 cm) at 3 sampling dates for all variants
development stage
before sowing/fertilization
leaf development
stem elongation
heading

Control
28% a
32% a
27% a
35% ab

S10027% a
10% b
11% c
23% b

UU100
21% a
12% b15% bc
27% ab

CU100
23% a15% b13% c
28% ab

CU7527% a
14% b16% abc
33% ab

CU5026% a17% b26% ab
37% ab

CU2526% a
19% b27% a
43% a

Leaf Nitrogen
The SPAD-meter readings of the leaf-chlorophyll content are known to be a good indicator for leaf
Nitrogen content (Uddling et al., 2007; Markwell et al., 1995). The results showed a plausible response
according to the N-level since beginning stem elongation (Fig. 3). Reduced N levels resulted after
heading in significant lower leaf chlorophyll contents.

Fig. 3 SPAD-meter readings at 4 development stages
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IJERD – International Journal of Environmental and Rural Development (2016) 7-1

Yield Results and N Balance
The harvest results confirmed the observed soil and plant parameters, as there were no significant
differences between the 100% variants of the three fertilizer types for all yield parameters (Table 3).
The only significant differences occurred between unfertilized control and 75-100% fertilized plots forgrain yield and the number of grains per ear.
Table 3 Selected yield parametersCgrain yield [dt ha-1]
26.7 cprotein content [%]9.3 a1000 kernel weight [g] 38.3 abc
ears per m
356.4 agrains per ear
19.9 cS100
39.9 a8.7 a40.4 a393.3 a25.2 aUU100
40.2 a10.8 a39.7 ab398.2 a25.3 aCU100
39.6 a9.1 a39.7 ab406.2 a24.6 aCU75
35.1 ab10.2 a38.1 bc
361.3 a25.4 aCU50
33.5 abc
9.7 a
37.2 c378.2 a23.7 abCU25
30.4 bc
10.6 a39.1 abc
357.3 a21.7 bc

All fertilizer types at 100% N-level resulted in comparable grain yields, among protein contents
there were no differences at all (Fig. 4).

Fig. 4 Harvest results for grain yield (left) and protein content (right)
Error bars show 1 standard error of the mean

The last step was to balance the Nitrogen inputs and outputs for all variants and to calculate the N
use efficiency (NUE=N uptake/fertilizer N). Table 4 shows a slight advantage for UU100 with an
optimal NUE of 1.0, but also S100 and CU100 were on a good level. Higher NUE above 1.0 leads tounsustainable soil mining and should be avoided.
Table 4 Nitrogen balance and Nitrogen use efficiency (NUE)

CS100
UU100
CU100
CU75
CU50
CU25

protein yield[dt ha-1]
2.5
3.5
4.3
3.6
3.6
3.1
3.2

N uptake[kg ha-1]
39.9
55.7
69.2
57.5
56.9
49.9
51.4

fertilizer N[kg ha-1]
0.0
70.0
70.0
70.0
52.5
35.0
17.5

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soil N[kg ha-1]
32.9
35.2
33.5
32.1
33.3
32.3
33.5

balance

NUE

-6.9
49.5
34.3
44.5
28.9
17.4
-0.4

0.8
1.0
0.8
1.1
1.4
2.9

IJERD – International Journal of Environmental and Rural Development (2016) 7-1CONCLUSION
The expected possibility to harvest the same with reduced fertilization by an enhanced fertilizer type
did not fulfil since the grain yield was not significant higher than the unfertilized control for reduced
variants. Therefore, we could not derive beneficial effects of the novel slow-release fertilizer from theresults of this field trial. More field site years as well as further research on the laboratory scale tounderstand the short-term behaviour of the coated urea are needed.
ACKNOWLEDGEMENTS
This work was conducted as part of project SASCHA (Sustainable land management and adaption
strategies under climate change for the Western Siberian grain belt). We are grateful for funding by theGerman ministry of education and research (BMBF) within their sustainable land management funding
framework (funding reference 01LL0906D).
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