J. R. Okalebo

Effect of combining organic residues with Minjingu phosphate rock on sorption and availability of phosphorus and maize production in acid soils of western Kenya

Experiments were conducted in both the greenhouse and the field on highly weathered (Orthic Ferralsol) soils to evaluate the effect of combining on-farm organic residues (chicken manure, farmyard manure, sugar bagasse) with Minjingu phosphate rock (MPR) on soil pH, extractable (available) and sorbed phosphorus (P), and to assess the cost benefit for maize production. The greenhouse study results indicated that, in the first eight weeks of incubation, soil pH increased linearly with increase in MPR rates and decreased thereafter. The available P also increased linearly. Chicken manure and sugar bagasse were most and least effective respectively in reducing P sorption, while there was a significant negative relationship between P adsorption maxima and extractable P. The field experiment data showed that the available P values increased significantly above the control in all the treatments where MPR and organic materials were applied separately or combined. Treatment effects on Langmuir sorption maxima (S max ) in the field were variable. An increase in S max with an increase in MPR rates was noted. However, there was a positive relationship between S max and available P ( r = 0.52 to 0.69), suggesting the diversity of factors affecting the complex nature of P dynamics under field conditions. MPR applied alone in the first season gave a significant residual positive effect on maize grain yield for two additional seasons. The economic analysis revealed that a single application of chicken manure (2 t ha −1 ) combined with MPR at 60 kg P ha −1 gave the highest incremental net benefit equivalent to US

Effect of organic and inorganic phosphorus sources on maize yields in an acid soil in western Kenya

657 ha −1 during the three maize cropping seasons.

EFFECTS OF COMBINING ORGANIC MATERIALS WITH INORGANIC PHOSPHORUS SOURCES ON MAIZE YIELD AND FINANCIAL BENEFITS IN WESTERN KENYA

Maize production in western Kenya is commonly limited by P deficiencies and aluminum phytotoxicity. Due to high costs of imported fertilizers and lime, focus is now shifting to solutions that utilize local resources. We tested the effect of three inorganic P sources i.e., triple superphosphate (TSP), Minjingu phosphate rock (MPR) and Busumbu phosphate rock (BPR), each applied in combination with two organic materials (OMs) i.e., farmyard manure (FYM) and Tithonia diversifolia green manure (tithonia), or with urea on soil chemical properties related to soil acidity, P availability and maize yields for three consecutive seasons in western Kenya. The OMs and inorganic P sources were applied to provide 20 and 40xa0kgxa0Pxa0ha−1 respectively in their combination. Where urea was used, the inorganic P sources were applied at 60xa0kgxa0Pxa0ha−1. Maize did not respond to application of TSP, MPR or BPR with urea in the first two seasons. However, after three seasons, maize significantly responded to application of MPR with urea. FYM was more effective than tithonia in increasing the labile inorganic P pools but it gave lower maize yields than tithonia which was more effective in reducing the exchangeable Al. It appears that the ability of an OM to lower the exchangeable Al is more important in increasing maize yields than its ability to increase P availability. The effectiveness of the inorganic P sources in increasing maize yields followed the order of their effectiveness in increasing available P, i.e., TSPxa0>xa0MPRxa0>xa0BPR, once Al phytotoxicity was reduced by application of tithonia but the difference between TSP and MPR was not significant. The extra maize yield obtained by the additional 40xa0kgxa0Pxa0ha−1 from the inorganic P sources was, however, in most cases not substantial enough to justify their use. Economic considerations may therefore favour the use of tithonia or FYM when applied alone at 20xa0kgxa0Pxa0ha−1 than when combined with any of the inorganic P sources used in this study at a total P rate of 60xa0kgxa0ha−1.

Coppicing improved fallows are profitable for maize production in striga infested soils of western Kenya

Due to escalating costs of imported fertilizers, there is renewed interest in the use of local nutrient resources in managing soil fertility in Kenya. We tested the effect of two organic materials, farmyard manure (FYM) and Tithonia diversifolia (tithonia), and an inorganic N fertilizer, urea, when applied alone or in combination with three inorganic P sources, triple superphosphate (TSP), Minjingu phosphate rock (MPR) and Busumbu phosphate rock (BPR), on maize yields and financial benefits. The study was conducted for three consecutive seasons, from March 2007 to August 2008 in western Kenya. FYM and tithonia were applied to supply 20 kg P ha −1 in treatments where they were used either alone or in combination with the inorganic P sources while 40 kg P ha −1 was from the inorganic P sources in the combination. Where urea was used, the inorganic P sources were applied at 60 kg P ha −1 . When applied in combination with urea, MPR was a better P source for maize than TSP or BPR. However, when applied in combination with FYM or tithonia, TSP was the best P source. Treatments including tithonia were more effective in increasing maize yields than those without it with a similar total P application rate. The agronomic effectiveness of tithonia did not, however, translate to economic attractiveness, mainly due to very high labour costs associated with its use. FYM when applied alone at 20 kg P ha −1 was the only treatment that exceeded a benefit:cost ratio of 2 and, therefore, the most likely, of the tested technologies to be adopted by farmers.

Comparison of effects of phosphorus sources on soil acidity, available phosphorus and maize yields at two sites in western Kenya

Strigahermonthica (striga) weed is a major threat to crop production in sub-Saharan Africa, and short duration improved fallow species have recently been found to reduce the effects of this weed because of their ability to replenish soil nitrogen. The objective of this study was to compare the efficacy and profitability of coppicing improved fallow species (Gliricidia sepium [gliricidia], Leucaena trichandra [leucaena] and Calliandra calothyrsus [calliandra]) and non-coppicing species (Sesbania sesban [sesbania], Mucuna pruriens [mucuna], and Tephrosia vogelii [tephrosia]), in controlling striga. Natural fallow and a sole maize crop were included as control treatments. The fallow treatments were split into two and either fertilized with N or unfertilized. The results showed that coppicing fallows produced higher biomass than non-coppicing fallows. For example, Callindra (coppicing fallow species) produced 19.5 and 41.4xa0Mgxa0ha−1 of leafy and woody biomass, respectively after four cumulative harvests as compared with Sesbania (non-coppicing species), which produced only 2.3 and 5.9xa0Mgxa0ha−1 leaf and woody biomass, respectively. Improved fallows reduced striga population in proportion to the amount of leafy biomass incorporated into the soil (rxa0=xa00.87). N application increased cumulative maize yield by between 15–28% in improved fallow systems and by as much as 51–83% in the control treatments. Added total costs of the coppicing fallows did not differ significantly from those of the non-coppicing fallows and control treatments. However, the added net benefits of the coppicing fallows were significantly higher (US

Occurrence and genetic diversity of phosphate-solubilizing bacteria in soils of differing chemical characteristics in Kenya

527 for +N and 428 for −N subplots; Pxa0<xa00.01) than those of the non-coppicing fallows (US

Do Commercial Biological and Chemical Products Increase Crop Yields and Economic Returns Under Smallholder Farmer Conditions

374 for +N and 278 for −N), and the least for the control treatments. The most profitable fallow system was Tephrosia with net added benefits of US

Screening of sesbania for tolerance to aluminum toxicity and symbiotic effectiveness with acid tolerant rhizobia strains in acid soil in Western Kenya.

453.5xa0ha−1 season−1 without N, and US

EFFECT OF PHOSPHATE FERTILIZER APPLICATION METHODS AND NITROGEN SOURCES ON MAIZE IN WESTERN KENYA: AN AGRONOMIC AND ECONOMIC EVALUATION

586.7xa0ha−1 season−1 with added N.

Evaluating and Upscaling Effectiveness of Fertilizer Materials to Replenish Soils of Western Kenya

The effects of farmyard manure (FYM), Tithonia diversifolia (tithonia) and urea when applied alone or in combination with Minjingu phosphate rock (MPR), Busumbu phosphate rock (BPR) or triple superphosphate (TSP) on soil acidity, P availability, maize yields and financial benefits were evaluated at Bukura and Kakamega in western Kenya. A reduction in exchangeable acidity and Al was observed in most tithonia- and FYM-treated soils, but not with inorganic P sources when applied in combination with urea. The effectiveness in increasing available soil P followed the order; TSP > MPR > BPR among inorganic P sources, and FYM > tithonia among organic materials at both sites. At Bukura, a site higher in both available P and Al saturation compared with Kakamega, maize did not respond to inorganic P sources applied in combination with urea. Maize, however, responded when inorganic P sources were applied in combination with FYM or tithonia at this site. At Kakamega, maize responded to TSP but not to MPR or BPR when applied with urea. Application of TSP in combination with tithonia gave the highest maize yields at both sites. Of the tested technologies, only FYM when applied alone at Bukura was economically attractive.