Research In Acid Soils
Research No-1
Influence of Amendments Added to Acid Soils on Biochemical Properties, Nitrogen Uptake and Hybrid Maize Yields in Nakuru County, Kenya
Aim: The current study investigated effect of soil amendments; lime (L), manure (FYM) and minjingu phosphate rock (PR) added to soils on soil microbial biomass carbon and nitrogen (SMB-C and SMB-N), available soil nitrogen (N), crop N uptake and grain yields of two maize hybrids (H513 and H614). Study Design: Two experiments, one for each maize hybrid as test crop, were laid out in a randomized complete block design with a 23 factorial arrangement. The factors each at two levels were L (0 and 3 t ha-1), PR (0 and 60 kg P ha-1) and FYM (0 and 5 t ha-1) giving a total of eight treatments; L, RP, FYM, L+RP, L+FYM, RP+FYM, L+RP+FYM and control (nothing applied). Methods: Soil and plant samples for the determination of SMB-C and SMB-N, available soil N, and crop N uptake were collected at maize seedling, tasseling and physiological maturity. Place and Duration of the Study: The experiment was conducted in Molo district of Nakuru County, Kenya during the long rain seasons of 2009 and 2010. Results: SMB-C and N levels were higher in 2010 than 2009, with lower levels obtained at maize tasseling for both maize hybrids. Available soil N and crop N uptake were higher at maize seedling and declined towards maturity. Statistically significant (P<.05) increases in SMB-C and SMB-N and available soil N and uptake were obtained with the application of soil amendments over the control. In all treatments, H513 had lower N uptake than H614 at tasseling and maturity stages of maize growth and correspondingly higher available N in soil. Maize yields (t ha-1) were higher in 2010 than 2009 and in H614 than H513. The H614 yields were significantly higher (P<.05) in L+PR+FYM (3.9) and, L+PR+FYM (4.1) and L+PR (3.9) treatments in 2009 and 2010, respectively. For H513, yields were significantly higher in L+PR+FYM (2.1 and 2.4) and L+PR (1.9 and 2.1) treatments in 2009 and 2010, respectively. Conclusion: The L+PR+FYM treatment is a feasible acid soil amendment for its superiority in the measured soil and crop parameters. The H513 matured faster than H614 and because of this attribute, is a viable option in response to the diminishing rainfall amounts and unpredictable weather patterns experienced in the County.
Research No-2
Genetic Effects for Maize P Efficiency Traits in Acid and Non-acid Soils of Western Kenya
Soil acidity is a major constraint to maize (Zea mays L.) productivity in tropical soils due to toxic levels of aluminium (Al) and phosphorus (P) deficiency. The objectives of this study were to: (i) determine the genetic effects of certain traits associated with phosphorus efficiency in maize (ii) compare the genetic control of maize P efficiency traits in acid and non-acid soils. Six F1 single crosses derived from acid soil tolerant and susceptible lines were used in this study. The parental inbred lines, the F1’s, F2’s, BC1P1, BC1P2, from each of the six crosses were evaluated in two low P acid and two low P non-acid soils in Kenya. Mean genetic effect (m), additive genetic effects (a), dominant genetic effects (d) and epistatic digenic effects (aa, ad, dd) were computed for Shoot dry matter (SDM), Root Length density (RLD), P content (PC), P utilization efficiency (PUE) and P efficiency (PE). For most of the traits, greater variation was accounted for by dominance followed by epistatic and additive genetic effects in both acid and non-acid soils. Means for all the traits studied were significantly higher at high P conditions (36 kgP/ha) in non-acid soils compared to acid soils for all the generations. Both RLD and PE exhibited higher means under non-acid soils compared to acid soils under both P conditions. Mean heritabilities were generally higher in non-acid soils compared to acid soils. There was higher reduction in PE in acid soils (25-50%) compared to non-acid soils (15 to 30%). The magnitude of both additive and non-additive gene effects were always greater in non-acid compared to acid soils pointing to the effects of soil acidity on gene action. The inheritance of major PE traits did not differ in acid and non-acid soils even though soil acidity affected the magnitude of the gene effects.
Research No-3
Micro-Dosing of Inorganic Inputs on Maize Production on an Acid Soil in Kenya: An Agronomic and Economic Evaluation
Aims: The study determined the effect of micro-dosing of lime, P and N fertilizers on maize grain yield and economic benefits.
Study Design: The experiment was a 2 x 2 x 3 split-split plot laid out in randomized complete block design with N (0 and 37.5 kg N ha-1) in the main plot, P (0 and 13 kg P ha-1) in the sub-plot and lime (0, 0.77 and 1.55 tons lime ha-1) in sub-sub plot. 37.5 kg N and 13 kg P ha-1 are 50% of the recommended fertilizer rates for maize production in Kenya while 0.77 and 1.55 tons lime ha-1 are 25 and 50% of the actual requirement.
Place and Duration of Study: The study was carried on nutrient deficient acid soil on a small holder farmer (SHF) field in Busia County, Kenya during the years 2008 and 2009.
Methodology: Lime was applied once during the long rain in the year 2008 while P and N fertilizers each cropping season.
Results: Grain yield increased by 148 and 40% due to 50% of both the recommended N and P fertilizers, respectively and 5-17% due to 25-50% of the lime requirement. Majority (57-75%) of the production costs were due to inorganic inputs. Only combined application of 50% of both the recommended N and P fertilizers produced economically viable returns throughout the cropping period. Combination of 50 and 25% of the recommended P and lime, respectively and 50 and 25% of the recommended N and lime, respectively produced economically viable returns only during the second and third cropping seasons. A combination of 50% of both the recommended P and lime produced economically viable returns during the third cropping season only.
Conclusion: Small holder farmers producing crops on Kenya’s acid soils deficient in N and P such as in Busia County can realize economically viable returns by micro-dosing of N, P fertilizers and lime.
Research No-4
Lime-Aluminium- Phosphorus Interactions in Acid Soils of the Kenya Highlands
Liming and phosphorus (P) applications are common practices for improving crop production in acid soils of the tropics. Although considerable work has been done to establish liming rates for acid soils in many parts of the world, information on the role of the lime-Al-P interactions on P fertility management is minimal. A green house pot experiment was conducted at Waruhiu Farmers Training Centre, Githunguri to evaluate the lime-Al-P interactions in acid soils of the Kenya highlands. Extremely acidic (pH 4.48) and strongly acidic (pH 4.59) soils were used for the study. Four lime (CaO) rates and phosphorus (Ca (H2PO4)2 rates were used. The liming rates were: 0, 2.2, 5.2 and 7.4 tonnes ha-1 for extremely acidic soil and 0, 1.4, 3.2, and 4.5 tonnes ha-1 for the strongly acidic soil. Phosphorus applications rates were: 0, 0.15, 0.30 and 0.59 g P kg-1 soil for the extremely acidic soil and 0, 0.13, 0.26, and 0.51 g P kg-1 for the strongly acidic soils. The experiments were a 42 factorial laid in a randomized complete block design (RCBD) and replicated three times. Data collected included: soil chemical properties and P adsorption. The soils had high exchangeable Al (>2 cmol Al kg-1), Al saturation of (>20% Al) and low P. Lime-Al-P interaction significantly (P≤0.05) increased soil pH, extractable P, reduced exchangeable Al, Al saturation, P adsorption and standard phosphorus requirements (SPR). Use of 7.4 tonnes ha-1 lime in extremely acidic soils and 4.5 tonnes ha-1 lime in strongly acidic soils significantly reduced exchangeable Al and SPR by >70%. Lime positively correlated with soil pH, extractable P, and Langmuir maximal adsorption constant and negatively correlated with SPR and exchangeable Al. It was therefore concluded that lime and P positively interact to reduce Al and P adsorption rates in acid soils in the Kenya highlands.
Research No-5
Phosphorus Adsorption and Its Relation with Soil Properties in Acid Soils of Western Kenya
Low available phosphorus (P) is one of the major hindrances to crop production in acid soils of western Kenya. Although considerable work has been done to establish P levels in the region, there is paucity of information on which to base fertilizer recommendations due to potential crop production differences caused by different soil types and climate. Phosphorus adsorption capacity and its relationship with some soil properties were evaluated in acid soils from nine locations of western Kenya. Adsorption data was obtained by equilibrating the nine soil samples with 30ml of KH2PO4 in 0.01 M CaCl2, containing 0, 80, 150 and 300 µg ml-1 for 48 hours with shaking for 30 minutes at intervals of 8 hours. Langmuir, Freundlich and Tempkin adsorption models were fitted to the test results and relationship between P adsorption and soil properties determined by correlations. The result of this study showed that the soils were strongly to extremely acidic (pH 4.83 - 3.76), had high exchangeable Al3+ (>2 cmol Al kg-1), Al saturation of (> 20% Al) and calculated maximal phosphorous adsorption varied from 770.83 to 1795.83 mg kg-1 soil. Comparing the models, Freundlich linear model showed a better fit to the tested soils compared to Langmuir and Tempkin models. The regression coefficients (R2) for the fitted Freundlich P adsorption isotherms was highly significant ranging from (0.995- 1.000) for all tested soils. Analysis of relationship between adsorption maximum and soil attributes revealed that adsorption maximum positively correlated with clay content, exchangeable P, exchangeable acidity and Aluminium saturation and negatively correlation with organic matter and electrical conductivity. Due to differences in maximal P sorption capacities within the tested area, blanket P fertilizer recommendation may affect crop productivity in some sites. There is therefore need for further research to determine optimal Phosphorus requirements for soils in each research site.