Relationships between soil albedos and soil and air temperatures.

Relationships are derived between near-interface soil and air temperatures and the albedos and temperatures of the interface under low evaporation conditions. Simple theoretical approximations of these relationships are established for nearly identical soil conditions with different albedos. A demonstration experiment is discussed which proves that this theory is valid at the surface of plastic-covered dry soil. Field temperatures for bare and black plastic-covered relatively dry soil in Kenya at 7.5 cm depth are also in good agreement with the theory. (Abstract retrieved from CAB Abstracts by CABI’s permission

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

Effect of Cropping Systems and Nitrogen on Maize and Soybean Yields in Western Kenya

Low fertility in highly weathered and degraded soils largely accounts for poor and unsustainable crop yields in most African countries. Studies further reveal negative nutrient balances in major soil elements such as nitrogen (N) (> 46 kg ha-1 ) and phosphorus (P) (>3 kg ha-1 ) in most countries in sub-Saharan Africa (SSA), with average mining of the former in some parts of western Kenya estimated at up to 112 kg N ha-1 . Productivity of maize and soybean in Kenya, particularly in the western region is generally low, even with application of N, P and potassium (K) fertilizers. The high cost of inorganic fertilizers and decreasing soil productivity demands a reassessment of their use, vis-a-vis, other alternative soil nutrient replenishing technologies. An on-farm experiment was laid down in Bungoma-South, Vihiga, and Teso-North Sub Counties of Bungoma, Vihiga and Busia Counties, respectively of western Kenya to assess the effect of selected cropping systems, N fertilizer and manure on maize and soybean yields. The experiment followed a split-plot design with two factors (cropping systems as the main factor and fertilizer interventions as the sub factor) arranged in a randomized complete block design (RCBD) with three replications. The cropping systems consisted of conventional- that is of maize & soybean intercrop of alternate single rows of each crop, MBILI- planted with maize & soybean intercrop of alternate double rows of each crop- and maize and soybean monocrops. The fertilizer interventions comprised of calcium ammonium nitrate (CAN) and farmyard manure (FYM), both applied at two rates of 30 kg N ha-1 and 75 kg N ha-1 , and without fertilizer (absolute control). The experiment was conducted during two subsequent cropping seasons; short rains between August and December 2011 and long rains occurring between March and August 2012. Results showed that maize yields were significantly larger in both the monocropping (mean yield: 2.0 t ha-1 ) and MBILI systems (mean yield: 1.8 t ha-1 ) compared to conventional farming (mean yield: 1.3 t ha-1 ). For soybeans, significantly larger yields were recorded in the monocropping system (1 t ha-1 ) compared to the MBILI (0.8 t ha-1 ) and conventional (0.6 t ha-1 ) systems. Cropping without fertilizer application resulted to low yields at an average of 1.0 and 0.7 t ha-1 for maize and soybean, respectively. Application of CAN at 30 kg ha-1 resulted to an average maize yield of 2.5, 1.4 and 0.7 t ha-1 in Bungoma-South, Vihiga and Teso-North Sub Counties, respectively. At least maize yields increased when FYM was applied at 30 kg ha-1 by 8 and 14% in Bungoma-South, and Vihiga Sub Counties, respectively, above the yield obtained when CAN was applied at 30 kg ha-1 . Application of FYM at 30 kg ha-1 resulted to similar maize yield as those observed when CAN was applied at the same rate in Teso-North sub county. For Soybean crop, application of either CAN or FYM at 30 kg ha-1 gave very low yields in the entire Sub Counties and in both seasons. Only in Vihiga Sub County where an average of 1.1 t ha-1 was obtained while the other two Sub counties had much less yields. On average, application of either CAN or FYM at 75 kg ha-1 increased maize yields by 29% above those observed when the two fertilizers were applied at 30kg ha-1 . The same trend was observed with soybeans whose yields increased at an average of 26% when either CAN or FYM was applied 75 kg ha-1 . The mean Land Equivalent Ratio (LER) values were greater than 1.0 for the intercropping systems and 1.0 for the monocropping system indicating a yield advantage in intercropping over monocropping

Use of Wheat Straw, Soybean Trash and Nitrogen Fertiliser for Maize Production in the Kenyan Highlands

Making best use of available crop residues is an important component of integrated nutrient management. A field study was conducted over two seasons (1997 and 1998) in Kenya that examined use of wheat straw, soybean trash and nitrogen fertiliser as nutrient inputs for maize (Zea mays L.) production. The organic inputs were applied at the rate of 2 t ha-1 per season and urea was added at rates of 0, 20, 40, 80 and 100 kg N ha-1 in an incomplete factorial treatment structure that also included a complete control (no inputs) and 80 kg N ha-1 as urea without organic inputs. Maize grain yield ranged between 751 and 6836 kg ha-1 with lowest yields observed in the treatment receiving wheat straw alone and higher yields associated with soybean residue incorporation and during the second, wetter growing season. The 1998 crop benefited from more favourable rainfall, providing grain yield increase of 141% above control treatment as a result of combining 2 t ha-1 soybean trash and 100 kg N ha-1 urea. The generally high yields from soybean trash are explained in terms of its higher quality, faster decomposition and nutrient release compared to the lower quality wheat straw. A positive effect in increases of soil pH, C, N and P status as a result of cumulative use of crop residues was observed. Larger yields were obtained when organic and inorganic inputs were applied to soils, particularly when soil moistue was adequate and the organic inputs higher in mineralisable nutrients. Early indications of additional longer-term benefits through soil quality improvement were also measured. These findings suggest that better use may be made of crop residues than the burning following harvest as is currently practiced by many farmers in this area of western Kenya.La bonne utilisation de r\ue9sidus des cultures disponibles est une composante importante de la gestion int\ue9gr\ue9e des \ue9l\ue9ments nutritifs. Une \ue9tude en champs a \ue9t\ue9 conduite pendant deux saisons (1997 et 1998) au Kenya pour examiner l\u2019utilisation de la paille de bl\ue9, les fanes de soja et l\u2019engrais azot\ue9 comme intrants pour la production du ma\uefs (Zea mays L.). Les intrants organiques \ue9taient appliqu\ue9s \ue0 un taux de 2 t ha-1 par saison et l\u2019ur\ue9e \ue9tait ajout\ue9e \ue0 des taux de 0, 20, 40, 80 et 100 kg N ha -1 dans une structure de traitement factoriel incomplet qui comprenait aussi un contr\uf4le complet (pas d\u2019intrant) et 80 kg N comme ur\ue9e sans intrant organique. Le rendement en grains du ma\uefs variait entre 751 et 6856 kg ha-1, le plus faible rendement \ue9tait observ\ue9 dans le traitement ayant re\ue7u la paille de bl\ue9 seule et les plus haut rendements \ue9taient associ\ue9s avec l\u2019incorporation des r\ue9sidus de soja durant la seconde saison pluvieuse. La culture de la saison 1998 a b\ue9n\ue9ficie des pluies favorables aboutissant \ue0 une augmentation de rendement en grains de 141% plus que le traitement t\ue9moin r\ue9sultant de la combinaison de 2 t ha-1 de fanes de soja et de 100 kg N ha-1 d\u2019ur\ue9e. Les rendements g\ue9n\ue9rallement \ue9lev\ue9s obtenus \ue0 partir des fanes de soja sont expliqu\ue9s en termes de qualit\ue9, de d\ue9composition plus rapide et de lib\ue9ration des \ue9l\ue9ments nutritifs en comparaison de la pauvre qualit\ue9 de la paille de bl\ue9. Un effet positif dans l\u2019augmentation du pH du sol, de l\u2019\ue9tat du C, N et P r\ue9sultant de l\u2019utilisation cumulative des r\ue9sidus des cultures a \ue9t\ue9 observ\ue9. Des rendements \ue9lev\ue9s \ue9taient obtenus quand les intrants organiques, et inorganiques \ue9taient appliqu\ue9s aux sols, en particulier quant l\u2019humidit\ue9 du sol \ue9tait ad\ue9quate et les intrants organiques \ue9lev\ue9s en \ue9l\ue9ments min\ue9ralisables. Des indications pr\ue9coces des b\ue9n\ue9fices additionels \ue0 long-terme via l\u2019am\ue9lioration de la qualit\ue9 du sol ont \ue9t\ue9 aussi m\ue9sur\ue9es. Ces r\ue9sultats sugg\ue8rent que la meilleure utilisation peut etre faite des r\ue9sidus de cultures plus que le br\ue9lage apr\ue8s recolte comme il est pr\ue9sentement pratiqu\ue9 par la majorit\ue9 des agriculteurs dans cette r\ue9gion ouest du Kenya