Influence of Cropping System and Residue Management on Selected Soil Chemical Properties

Declining soil fertility in sub-Saharan Africa caused by continuous cropping without nutrient inputs has resulted in declining crop yield. The study was aimed to determine the effects of crop rotation and crop residue management on soil pH, organic carbon, nitrogen and available soil P. A split plot experimental design was set up with crop management system (maize monocropping and maize – bean rotation) as main plots and crop residue (maize stover) as sub plots, in three consecutive cropping seasons. At planting, all plots received 60 kg of P2O5/ha and 60 kg of K2O/ha. Results for the three cropping seasons indicated slight decrease in soil acidity, (5.42±.11), increase in soil organic carbon (2.39±.40) and soil total nitrogen from the initial value of 0.15% to 0.22±.03 due to legume rotation. Available soil P improved from 2.99 to 8.65±1.63 cmol kg-1showing significant differences (P≤0.05) under rotation system plus addition of crop residue. Rotation of maize and legumes with crop residue addition is recommended for farmers, which will benefit them in improving soil fertility

Maize Response to Micro Dose Inorganic Inputs on an Acid Smallholder Farm in Kenyan Lower Midland

The study determined nitrogen, phosphorus fertilizers and lime micro doses effects on soil chemistry and maize performance on an acid soil smallholder farm. Treatments were micro doses (50% of recommendations) of N (0 and 37.5 kg N ha-1), P (0 and 13 kg P ha-1) fertilizers and lime (0 and 2.26 tons lime ha-1). Nitrogen, Pfertilizersand lime significantly (p<0.05) increased soil N, P and pH. Agronomic N-fertilizer use efficiency were 29 and 35 kg ha-1 kg-1 N-fertilizer due to 37.5 kg N and 37.5 kg N+2.26 tons lime ha-1, respectively. Grain agronomic P-fertilizer use efficiency was 24 and 30 kg ha-1 kg-1 P-fertilizer due to 13 kg P and 13 kg P+2.26 tons lime ha-1 , respectively. N-fertilizer recovery were 47 and 50% due to 37.5 kg N and 37.5 kg N+2.26 tons lime ha-1,respectively and P-fertilizer recovery efficiency were 14 and 16% due to 13 kg P and 13 kg P+2.26 tons lime ha-1,respectively. Grain yield increments were 72, 27 and 12% due to 37.5 kg N, 13 kg P and 2.26 tons lime ha-1, respectively. Therefore, N-, P-fertilizers and lime micro doses can improve maize grain yield on acid nutrient deficient smallholder farms

Response of Maize to Organic and Inorganic Sources of Nutrients in Acid Soils of Kenya

aize yield in Kericho County, Kenya is limited by infertile acidic soils. The effect of inorganic sources of nutrients and amendments; triple superphosphate (TSP), calcium ammonium nitrate (CAN) and lime, were compared to a range of organic nutrient sources; Farmyard manure (FYM) of low and high quality, dried cow dung, goat manure, tithonia applied as green manure or dried, in a greenhouse and field experiment. Two soils collected from two farmers’ fields in Sigowet and Litein locations (Hereafter referred to as Sigowet and Litein) were used in the greenhouse where maize was grown for six weeks and its biomass yield determined. The treatments that showed promise were used in a subsequent field experiment where maize was grown to maturity and grain yield determined. In the greenhouse, maize responded to application of all the sources of nutrients and amendments, except lime when applied without TSP, on Sigowet’s soil. On Litein’s soil, maize did not respond to application of lime alone or with TSP, TSP and dried tithonia. High quality FYM gave the highest increase (136%) in dry matter yields on Litein’s soil. In the field experiment, goat manure gave the highest grain yield. Maize failed to significantly respond to either CAN or TSP when applied alone but the application of the two in combination (TSP + CAN) effected a significant response indicating that both N and P were deficient in this soil. All the manures, except low quality FYM, gave yields that were higher or comparable to the standard recommended fertilizer practice (TSP + CAN) and could be economically attractive substitutes as they are locally available. There was a poor correlation between dry matter biomass yield in the greenhouse and grain yield in the field. Extrapolation of greenhouse findings to different fields should therefore be treated with caution

Response of Leucaena leucocephala (Lam.) De Wit (Leucaena) Provenances to Aluminium in Potted Soil Experiment

Aims: To determine the level of acid or aluminium tolerance provenances in Leucaena (Leucaena leucocephala) a favourite agroforestry tree in Kenya. Study Design: The set up was a 2-factor (provenance-aluminium) experiment in a completely randomized design with three (3) replications and data were subjected to multivariate analysis of variance. Place and Duration of Study: Potted acid soil experiments were carried out at the Maseno ICRAF/KEFRI centre and Chepkoilel campus farm, Moi University, between June 2009 and July 2010. Methodology: Potted acid soil experiments were carried out at the Maseno ICRAF/KEFRI centre (pH 4.8) and Chepkoilel campus farm, Moi University (pH 5.0) to assess the effect of varying aluminium concentrations on growth of three local leucaena provenances: K156 (Gede), K136 (Kibwezi) and KIT2724 (Kitale). Aluminium was applied at 0, 100, 200 and 300 M. The number of leaves per seedling, seedling height, root length, root collar diameter and dry weight were recorded at 60 and 120 days after planting. Results: Generally Aluminium at 100 M significantly (p0.05) enhanced growth of the seedlings at both sites. However, aluminium at 200 M reduced seedling growth. Conclusion: The Leucaena provenance K156 could be used in acid soils because it is tolerant. However, more local provenances should be screened for acid tolerance

Comparison of soil phosphorous extraction by Olsen and double acid methods in acid soils of Western Kenya

hosphorous is an essential nutrient in plants required for root establishment. In the soil, it is applied as DAP, TSP or phosphate rocks. In acid soils, aluminium and iron are dominant and tend to “fix” phosphorous, making it unavailable for plant uptake. Phosphorous deficiencies are monitored through soil chemical analysis. There are many methods for the extraction of available forms; however the choice is dependent on several factors among them soil pH. Forty soil samples were collected from three different acid soils in Western Kenya. The samples were air dried, sieved under 2.0 mm sieve and stored in sample bags for subsequent analysis. Phosphorous extraction of was carried out using a basic extractant (Olsen bicarbonate method) and acid extractant (double acid method). The extracts were measured colorimetricaly by the ascorbic acid method at 880 nm wavelength. The methods were compared in terms of extracting efficiency, correlations and soil critical levels. The soils had a pH range of between 4.5 – 6.1; phosphorous, 1.66 – 55.37 mg P/ kg by Olsen method and 3.01 – 158.17 mg P /kg by double acid method. The methods were linearly correlated (r = 0.95), however, double acid extracted more phosphorous than Olsen by a factor of 2.67

Effect of organic and inorganic phosphorus sources on maize yields in an acid soil 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 40 kg P ha-1 respectively in their combination. Where urea was used, the inorganic P sources were applied at 60 kg P ha-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 inincreasing 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., TSP[MPR [BPR, 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 40 kg P ha-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 20 kg P ha-1 than when combined with any of the inorganic P sources used in this study at a total P rate of 60 kg ha-1

Phosphorus Sorption and Lime Requirements of Maize Growing Acid Soils of Kenya

In Kenya, maize (Zea mays L.) is mainly grown on acid soils in high rainfall areas. These soils are known for low available phosphorus (P), partly due to its sorption by aluminium (Al) and iron oxides. The study determined soil P sorption, lime requirements and the effects of lime on soil pH, Al levels and available P on the main maize growing acids soils in the highlands east and west of Rift Valley (RV), Kenya. Burnt lime containing 21% calcium oxide was used. The soils were strongly to extremely acid (pH 4.85-4.07), had high exchangeable Al3+ (> 2 cmol Al kg-1) and Al saturation (> 20% Al), which most maize germplasm grown in Kenya are sensitive to. The base cations, cation exchange capacity and available P (< 10 mg P kg-1 bicarbonate extractable P) were low, except at one site in the highlands east of RV indicative with history of high fertilizer applications. Highlands east of RV soils had higher P sorption (343-402 mg P kg-1) than the west (107-258 mg P kg-1), probably because of their high Al3+ ions and also the energies of bonding between the soil colloids and phosphate ions. Highlands east of RV also had higher lime requirements (11.4-21.9 tons lime ha-1) than the west (5.3-9.8 tons lime ha-1). Due to differences in soil acidity, Al levels and P sorption capacities within and between highlands east and west of RV, blanket P fertilizer and lime recommendations may not serve all soils equally well. Keywords: acid soils, phosphorus sorption, lime requirement

Micro-Dosing of Lime, Phosphorus and Nitrogen Fertilizers Effect on Maize Performance on an Acid Soil in Kenya

High cost of inorganic fertilizers and lime has precluded their use by smallholder farmers to remedy the problem of soil acidity and infertility in Kenya. To address the problem, we tested a precision technique referred to as micro-dosing, which involves application of small, affordable quantities of inorganic inputs on an acid soil in Busia County, Kenya. Experimental treatments were N-fertilizer (0 and 37.5 kg N ha-1), P-fertilizer (0 and 13 kg P ha-1) and lime (0, 0.77 and 1.55 tons lime ha-1). 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. Soil chemical changes, maize grain yield and nutrient recovery were determined. Lime and P-fertilizer significantly affected only the top-soil pH, Ca, Mg and available P, while the effects of N-fertilizer were evident on both top- and sub-soil N likely due to its faster mobility than P and lime. Grain P-fertilizer recovery efficiencies were 14 and 16-27% due to 13 kg P and 13 kg P + 0.77-1.55 tons lime ha-1, respectively. N-fertilizer recovery efficiencies were 37 and 42-45% due to 37.5 kg N and 37.5 kg N + 0.77-1.55 tons lime ha-1, respectively. Fertilizers applied to supply 37.5 kg N, 13 kg P and 0.77-1.55 tons lime ha-1 increased grain yield above the control by 134, 39 and 12-22%, respectively, therefore micro-dosing of these inputs can increase maize production on Kenyan acid soils

Enhancing Maize Grain Yield in Acid Soils of Western Kenya Using Aluminium Tolerant Germplasm

Abstract: Maize (Zea mays L.) is one of the world’s most important cereals and is a staple food for many people in developing countries. However, in acid soils (pH < 5.5), its productivity is limited by aluminium (Al) toxicity, besides other factors. The objectives of this study were to: develop Al tolerant maize inbred lines for a maize breeding program in Kenya, develop single cross hybrids (SCHs) from some of the tolerant inbred lines and determine Al tolerance levels of the SCHs. One hundred and seventy five inbreds and 49 SCHs were developed and screened in nutrient culture containing 0 or 222 μM using Relative Net Root Growth (RNRG), hematoxylin staining (HS) and under Al saturated field conditions (44%-45.6%) at Sega and Chepkoilel. Seedling root growth was inhibited in 95% of the inbreds. F1 hybrids obtained from inbreds varying in Al tolerance, exhibited tolerance equal to or greater than that of the more tolerant parent indicating a positive transgressive inheritance to Al toxicity. Fifty eight percent of the F1 SCHs were heterotic for tolerance to Al toxicity. Al tolerance estimated by RNRG was well correlated to that of HS (r2 = 0.88, P < 0.005) but minimally correlated with the field estimates (r2 = 0.24-0.35), implying that RNRG can predict field selection under Al toxic soils by between 24% and 35%. Plant breeders should therefore employ both approaches in selecting cultivars under Al stress. This study has developed and identified Al tolerant inbreds and SCHs for use in the acid soils of Kenya and similar regions

Effects of lime, phosphorus and rhizobia on Sesbania sesban performance in a Western Kenyan acid soil

Aluminium (Al) toxicity, phosphorus (P) deficiency and low rhizobia populations limit Sesbania (Sesbania sesban) performance in tropical acid soils. The study determined the i) indigenous rhizobia populations that nodulate sesbania and ii) effects of lime (0 and 4 t/ha), P-fertilizer (0 and 60 kg/ha) and acid tolerant rhizobia (0 and inoculation) on soil and selected sesbania accessions performance in Western Kenya acid soil. Study site had acid soil, low available P, nitrogen (N) and rhizobia populations that nodulate Sesbania (146 cells/g soil). Lime increased soil pH, while both lime and P-fertilizer increased available P. Aluminium toxicity tolerant and P-efficient accessions (SSBSA004, SSUG3, SSUG4 and SSUG5) had faster growth, higher nodulation, shoot P, and shoot N and response to treatments than the sensitive one (SSBSA203). After 7 months of growth, SSUG3 had highest shoot length (306 cm) and dry matter (5.64 tons/ha), hence, most suitable for building poles and fuel wood. SSUG5 accumulated the highest shoot N (222 kg N/ha) and was therefore, most suitable soil N replenishment. Thus, in acid P deficient and low rhizobial population soils of Western Kenya, the use of lime, P-fertilizer, rhizobia inoculation and Al toxicity tolerant Sesbania are important for Sesbania establishment and growth. Key words: Rhizobia, Sesbania, soil acidity, aluminum toxicity, lime, phosphorus