IJERD – International Journal of Environmental and Rural Development (2018) 9-1

Research article
erd

Effects of Gypsum and Rice Husk Biochar on Surface
Discharge and Nutrient Loss from Farmlands in Budalangi,
Kenya
BENARD ONYANGO ODHIAMBO
Graduate School of Agriculture, Tokyo University of Agriculture, Japan
Email: benaxodhis@yahoo.com

MACHITO MIHARA*
Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, Japan
Email: m-mihara@nodai.ac.jp
Received 31 December 2017

Accepted 10 May 2018(*Corresponding Author)

Abstract Loose soils from recent cultivation, especially before the crops well cover thesurface are highly vulnerable to erosion. The effects of gypsum and rice husk biochar on
runoff, loss of soil and nutrients from farmlands in most parts of Kenya are rarely
documented. This study aims to discuss effects of surface application of gypsum and ricehusk biochar on discharge of sediments and nutrient loss from farmlands in Budalangi,
Kenya. Gypsum and rice husk biochar were incorporated into the soil and erosion
experiments conducted in the laboratory. Two soil types, loam and silt loam were used inthis experiment involving four treatments: control (C), gypsum (G), rice husk biochar(RHB) and a combination of rice husk biochar and gypsum (G+RHB). The effects of G
application at a rate of 5 t ha-1 and RHB on runoff volumes, sediment yield and level ofnutrient losses were evaluated. The results showed that treatment of G induced a significant
reduction in runoff and sediment yield followed by RHB+G and RHB. By plotting the dataobtained, it was observed that average runoff decreased by 52.7%, whereas sediment yielddecreased by 88% in G treatment. RHB+G treatment showed a reduction in average runoffof 42.3%, whereas sediment yield by 75%. RHB treatment showed 30.7% average
reduction in runoff with 71% in sediment yield for loam soil. Similar trends were observed
for silt loam soil. Addition of G increased levels of magnesium in both loam and silt loam
soils to about five times the initial levels. Total nitrogen loss was minimized by between
15% and 27%, with total phosphorous loss minimized by 50% to 70% between the different
treatments. Based on these findings, it can be suggested that amending soil with G and RHB
can be effective in controlling soil and nutrient loss from farmlands.
Keywords gypsum, rice husk biochar, soil loss, nutrient loss, farmlands

INTRODUCTION
Land degradation is a threat to both low and high agricultural potential areas in Kenya. Loose soils
especially from recent cultivation before the crops well cover the surface is highly vulnerable toerosion, thus there is need to protect soil during this stage as soil surface is in bare condition(Carroll et al., 2000).
Nutrient loss from farmlands especially small-scale farms has been mainly through crop
harvest and soil erosion due to use of insufficient quantities of both organic and inorganic fertilizer
to replenish soil fertility. According to Smaling et al., (1993), the average annual nutrient depletion
rates of -22 kg of N, -2.5 kg of P and -15 kg of K estimates per hectare of cultivated land have beenreported in sub-Saharan Africa. For example in Kenya, depletion rates of -112 kg N ha-1, -2.5 kg P
ha-1 and -70 kg K ha-1 were reported on small-scale farmers’ fields in western Kisii highlands.
Complementary to conventional strategies like mulching and changing slope gradients, soil
and water conservation can be achieved by amending the soil properties responsible forⒸ ISERD

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deterioration of the stability of soil structure. An option given for improving soil structural stability
is surface application of soil amendments such as gypsiferous materials and anionic polymers(Cochrane et al., 2005). Gypsum minimizes dispersion of clay particles hence boosting soil
permeability and subsequently stabilizing soil aggregates. It has been widely used especially inreclamation of sodic soils since it is calcium-rich and dissolves at high pH (Horneck et al., 2007).
The Ca2+ ions in gypsum (CaSO4.2H2O) replace the exchangeable Na+ ions on soil surface. This
property together with its electrolyte concentration makes it effective to be used as a soil
amendment especially for reclamation of sodic soils (Korcak, 2001). Its relative solubility in water
makes it applicable in agricultural fields. In cultivated arid and semi-arid lands (ASALs),
application of gypsum and its contribution to soil solution ionic concentration is necessary as it
limits instability in soil structure which would otherwise lead to surface sealing andcommencement of runoff with subsequent erosion (Ellen et al., 2006). On the other hand, overapplication of gypsum would lead to its accumulation on the soil surface, hence need of scraping
and this would otherwise require a lot of labor to break it up.
Biochar is a product of slow thermo-chemical pyrolysis of biomass materials. Organic
materials such as crop residues, sewage sludge and livestock excreta can be converted to biochar
and used as soil amendments (Jien and Wang, 2013). Biochar is essential due to its richness incarbon content thus it is useful in amending soil and boosting soil organic matter content. The
objective of this study is to discuss the effectiveness of gypsum and rice husk biochar inminimizing the discharge of sediments and nutrient loss from farmlands in Budalangi, Kenya.
METHODOLOGY
Soil and Rice Husk Biochar Collection and Preparation
Soil was sampled from the surface at a depth of about 0-25 cm in the study area located withincoordinates N 0° 7′ 0″ to N 0° 9′ 0″ and E 34° 1′ 30″ to E 34° 3′ 30″. This area forms part of thelower catchment of river Nzoia watershed. The soils were classified as loam and silt loam based on
the IUSS (International Union of Soil Scientists) taxonomy from the results of soil particle size
distribution analyses conducted in the laboratory. Some of the common crops grown in this area
include maize (Zea mays), beans (Phaseolus vulgaris) and groundnuts (Arachis hypogaea).
The biochar used in this study was produced from rice husks at a pyrolysis temperature ofabout 450 oC. This was done at the Institute of Environmental Rehabilitation and Conservation,
Japan. After pyrolysis, the rice husk biochar used was then ground to pass through a 2 mm sieve.
This was to ensure that all the biochar used in the experiment had similar particle size.
Experimental Design
Runoff experiment was conducted in the laboratory of Land and Water Use Engineering, Tokyo
University of Agriculture, Japan using erosion plots measuring 0.91 m long by 0.03 m wide by
0.025 m deep and water supplied by a Marriott bottle to attain constant flow rate of 0.83 cm3s-1 atconstant pressure, for a concentrated surface flow scenario. The experiments involved four
treatments; control, C, gypsum, G, (5 t ha-1, an optimum rate from former studies); rice husk
biochar, RHB, (5 t ha-1) and combination of gypsum and rice husk biochar, G+RHB, (1:1 w/w) in
three replications. G and RHB amendments were broadcasted on the soil surface and subsequently
mixed for each treatment. For G+RHB treatment, soil samples were mixed with amendments at
gypsum/rice husk biochar mix ratio of 1:1 w/w for both loam and silt loam textured soil. The soils
were compacted in the erosion plots based on the dry densities of 1.25 gcm-3 and 1.39 gcm-3 forloam and silt loam soils respectively. Erosion plots were then pre-wetted for 24 h at 0% inclination
prior to commencement of the experiments. This pre-wetting was to attain field capacity.

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RESULTS AND DISCUSSION
Soil and Rice Husk Biochar Properties
Table 1 shows some of the basic properties of soil and rice husk biochar used in this study. The
soils were acidic (pH 6.4 and 6.2) with low electrical conductivity (0.17 mScm-1 and 0.2 mScm-1).
Table 1 Physical and chemical properties of soil (0-25 cm) and rice husk biochar used
Particle-size distribution
Sand
Silt
Clay
P (*10-5)
pH
EC
Ca
%
cms-1
mScm-1
LS
38.2
45.7
16.1
28.3
6.4
0.17
2.7
SLS
23.4
53.2
23.4
9.3
6.2
0.2
2.4
RHB
8.1
0.1
6.0
LS=Loam soil; SLS= Silt loam soil; RHB= Rice husk biochar; P=Permeability
Item

Na
0.4
1.3
0.3

Mg
mgkg-1
0.2
0.2
0.4

TN

TP

855
579
915

736
421
355

Surface Runoff
The amounts of surface runoff generated under different treatments compared to control are asshown in Table 2. From the results, there was a trend of an increase in cumulative amount of
surface runoff produced with time in each treatment with a decrease between the treatments whencompared to control.
Table 2 Surface runoff under different treatments
Treatment
Discharge (Lm-2)
Percentage reduction from control
G14.73d
52.7
RHB
21.58b
30.7
Loam
G+RHB
17.95c42.3
Control
31.12a*G
22.97d
27.2
RHB
17.91b
43.2
Silt loam
G+RHB
21.43c32.1
Control
31.54a*G=Gypsum; RHB= Rice husk biochar; G+RHB= Gypsum + rice husk biochar*Values followed by the same letter within the column are not significantly different at p=0.05 confidence level.
Soil texture

G treatment showed a significant reduction in surface runoff of 52.7% in loam soil and 27.2%
in silty loam soil, whereas, RHB treatment showed a reduction of 30.7% in loam soil and 43.2% insilty loam soil. In the case G+RHB treatment, the surface runoff was reduced by 42.3% and 32.1%
in loam and silty loam soils respectively.
Infiltration
Table 3 Infiltration under different treatments
Specific infiltration (Lm-2)
Percentage change from control
G37.99d98.3
RHB
32.60c
70.1
Loam
G+RHB
33.55b75.1
Control
19.16a*G
35.09b
59.4
RHB
30.88b
40.3
Silt loam
G+RHB
33.15b50.6
Control
22.01a*G=Gypsum; RHB= Rice husk biochar; G+RHB= Gypsum + rice husk biochar*Values followed by the same letter within the column are not significantly different at p=0.05 confidence level.
Soil texture

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Surface application of G followed by its incorporation into the soil increased specific infiltration
amount by almost double. On addition of RHB, specific infiltration amount was increased by about
70%. Concurrent application of G+RHB increased specific infiltration amount by 75.1% in loamsoil. For silt loam soil, an increase of 59.4%, 40.3% and 50.6% were observed on treatment with G,
RHB and a concurrent application of G+RHB, respectively. Gypsum at the surface dissolves during
pre-wetting and releases electrolytes into the soil solution. This leads to reduction in soil dispersion
and surface seal formation encouraging infiltration.
Addition of biochar significantly increased infiltration amount probably due to increased soil
bulk density. Increase in bulk density results in an increase in total porosity (Abrol et al., 2016).
Soil Loss
Specific load generated from the experimental plots under different treatments are as shown in
Table 4. With a constant discharge of water at a rate of 0.83 cm3s-1, specific load generated was
0.94, 0.109, 0.273 and 0.24 t ha-1 for control, G, RHB and G+RHB, respectively on loam soil. On
silt loam soil, 1.708, 0.095, 0.208 and 0.143 t ha-1 specific load was yielded for control, G, RHB
and G+RHB, respectively. On average, reductions in specific load generated per treatmentcompared to control was found to be 88%, 71% and 75% for G, RHB and G+RHB treatments,
respectively on loam soil and 94%, 88% and 92% for G, RHB and G+RHB treatments, respectively
on silt loam soil.
When data was subjected to mean separation analysis using 1-way analysis of variance(ANOVA) statistical test at 95% level of confidence (p=0.05), there were significant differences in
reduction of specific loads generated under all the treatments when compared to control in both soil
textures. The results showed a steady increase in specific soil loss in the first 5 minutes followed bya slow decrease with time. The increase in specific soil loss in the first 5 minutes for control
treatment could be attributed to the high occurrence of fine particles in the surface runoff. The fineparticles are as result of breakdown of aggregates from pre-wetting before the experimentcommenced. Also, the subsequent decrease can be attributed to the development of deposited layerthat was formed by deposition which is size-selective.
Table 4 Specific load of surface runoff under different treatments
Specific load (*10-3 t ha-1)
Percentage reduction from control
G
109.07c88
RHB
273.27b
71
Loam
G+RHB
240.41b75
Control
940.03a*G
95.47b
94
Silt loam
RHB
208.28b88
G+RHB
143.28b92
Control
1708.82a*
G=Gypsum; RHB= Rice husk biochar; G+RHB= Gypsum + rice husk biochar*Values followed by the same letter within the column are not significantly different at p=0.05 confidence level.
Soil texture

Treatment

During the experiments, it was observed that on the soil surface of control plot, there wasformation of rills which began as very small channels on the soil surface and widened anddeepened as the experiment progressed. Sediment transfer was mainly dominated by these rillflows. Conversely, on addition of amendments, there was minimal rills formation throughout theexperiments. Since rill formation is generally associated with higher sediment concentration in
runoff, this could be one of the explanations for the high sediment concentration in control plot
compared to treated plots.
On addition of G, there was a significant reduction in soil loss probably because the soil
surface was well aggregated which minimized breakdown of these aggregates by runoff.
Application of gypsum is able to maintain surface roughness of the soil as well as increaseelectrolyte concentration in both runoff and the infiltrating water. According to Shainberg et al.,
1989, an increase in electrolyte concentration prevents aggregate dispersion; bigger particles areⒸ ISERD

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less eroded. RHB treatment showed a reduction in amount of soil loss compared to control. This
could be as a result of redistribution of relative proportions of soil aggregate sizes. Also, it can be
attributed to an increase in roughness of soil surface due to accumulation of relatively large
particles of RHB as surface runoff occurs. The surface roughness may have interfered with thelateral movement of detached soil particles in the runoff as the accumulated particles of RHB acted
as traps, with finer soil particles accumulating behind them.
The reduction in cumulative soil loss as a result of application of soil amendments could be
attributed also to a decrease in shearing action by flowing water or in a reduced soil erodibility as aresult of aggregate stability (Peterson et al., 2002). Under no treatment, soil aggregates may
disintegrate quickly in water leading to an accumulation of these dispersed particle in the surface
runoff and thus resulting in a higher concentration of particles in the surface runoff as in control
plots.
Concentration of Cation in Surface Runoff
The transfer of chemicals to surface runoff is mainly through three processes: (1) adsorption anddesorption of chemically reactive components by soil constituents, (2) transportation of the
dissolved portions of these reactive chemicals to soil surface by convection and diffusion, and/or(3) through chemical dissolution into runoff and through release by return flow. Zhang et al.,(1997) observed chemical loss under free drainage conditions; an indication that there is possibilityof loss of chemicals from farmlands as was observed in this study.

Fig. 1 SAR under different treatments for loam and silt loam soils
Nutrient Loss
The concentration of soil nutrients (nitrogen and phosphorous) in surface runoff was determined byabsorption photo-spectroscopy procedure and results showed in Table 5. The average
concentrations of total nitrogen in surface runoff from plots treated with G were found to be 0.59
mgL-1 for loam soil and 1.67 mgL-1 for silt loam soil plots. TN concentration of treatment with
RHB was 0.69 mgL-1 and 1.57 mgL-1 for loam and silt loam soils, respectively. These were higher
compared to the respective plots treated with a combination of G+RHB. The results also indicated a
reduction in total phosphorous in surface runoff on application of the amendments compared tocontrol.
A study by Pamela et al., (2010) on selected Kenyan acid soils indicated low levels of
essential plant nutrients especially phosphorous and exchangeable bases with high levels of
exchangeable aluminium. The study noted that for increased and sustainable crop production, thereis need for soil management practices that will increase nutrient availability and enhance uptake ofthe nutrients. Helen et al., (2005) measured equilibrium phosphorous concentration (EPCO) of
riverbed materials to check whether the materials are acting as source or/and sink of soluble
reactive phosphorous under low flows and during periods of high eutrophication risks. This wasdone especially by estimating differences in SRP (soluble reactive phosphorous) flux transfers, anⒸ ISERD

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indication that the catchment area could be one of the sources of phosphorous in the riverbed
materials.
Table 5 Total nitrogen and total phosphorous concentration in surface runoff under
different treatments
Total nitrogen (mgL-1)
Total phosphorous (mgL-1)
G
0.59
0.066
RHB
0.69
0.100
Loam
G+RHB
0.61
0.063
Control
0.81
0.210
G
1.67
0.170
RHB
1.57
0.273
Silt loam
G+RHB
1.70
0.130
Control
1.79
0.360
G=Gypsum; RHB= Rice husk biochar; G+RHB= Gypsum + rice husk biochar
Soil texture

Treatment

Pesticide residues of long half-life such as dichlorodiphenyltrichloroethane (DDT) andhexachlorocyclohexane (HCH) and their isomers have been estimated and found to be available in
the tissues of the sampled vegetables from riverbed agriculture (Hans et al., 1999). This is a
probable indication that farm inputs such as pesticides and other soil nutrients could be finding
their way into water systems from farmlands within water catchment areas.
CONCLUSION
The application of gypsum at 5 t ha-1 was found to be more effective in reducing surface runoff,
sediment transfer and loss of nutrients such as N and P from farmlands. It was closely followed by
the concurrent application of a combination of gypsum and rice husk biochar and then applicationof rice husk biochar alone. Rice husk biochar helps in improving soil stability as it cannot
decompose due to its complete carbonization hence, its structure do not collapse for a long periodof time. It also improves soil moisture retention capacity. Since rice husk biochar is basicallycarbon, its burying into the soil assists in carbon sequestration thus, important in reducing carbon
concentration in the atmosphere.
All soil amendments used in this study were effective in maintaining a good and wellaggregated soil surface that resulted in a minimized detachment of soil particles and probably asurface that was resistant to surface sealing (seal formation) as infiltration was also improved on
application of these soil amendments. Due to increased infiltration, there could be an increase insoil moisture hence, important for establishment of vegetation cover. Therefore, it was concluded
that surface application of soil amendments on farmlands especially before vegetation isestablished during which the soil surface is bare and vulnerable to erosion, may be effective on
minimizing erosion and subsequent transfer of sediments and nutrient losses from farmlands prior
to establishment of vegetation cover.
Considering the cost of gypsum especially on large scale, application of rice husk biochar isrecommended for the study area.
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