Evaluation and mapping of soil erosion susceptibility: an example from Kenya

Abstract. The erosion susceptibility of the Erosion Research Farm at Kabete Campus was mapped using a qualitative parametric method. A grid soil survey of the 4 ha farm was combined with a map of slope gradients, slope segments being delineated by breaks in slope. Rainfall erosivity and soil erodibility were also measured. Areas with the greatest erosion susceptibility according to this method were those occupying convex slope positions and slopes of more than 30%. Field observations and soil loss measurements generally supported the erosion susceptibility rating map produced by this method. The soil and erosion susceptibility maps were useful for planning erosion control measures and for selecting suitable sites for runoff plot experiments.     

Effects of soil management practices and tillage systems on surface soil water conservation and crust formation on a sandy loam in semi-arid Kenya

The effect of different soil management practices on crust strength and thickness, soil water conservation and crop performance was investigated on a ferric lixisol in a semi-arid environment of eastern Kenya.

The study proved that manure and mulching with minimum tillage have a greater effect on the water balance of crusted soils and maize emergence. There was increase in steady infiltration rates, amount of soil water stored in the soil and better drainage. The physical effect of mulch was less important in the rehabilitation of crusted soils in the study site when it was incorporated into the soil. Manure and surface mulch with minimum tillage should therefore be taken into account in land management and water conservation in the semi-arid areas of Kenya. The response of crops to the improved water availability due to manure with minimum and with conventional tillage and surface mulch was very clear. These management practices should be recommended when considering the effectiveness of soil and water management techniques in the study area.     

Agronomic assessment of phosphorus efficacy for potato (Solanum tuberosum L) under legume intercrops

Abstract

Phosphorus (P) is an essential element and its efficient use is of global importance. This study evaluated the effect of growing potato under legume intercrops on P uptake and use efficiency indices: P harvest index (PHI), P uptake efficiency (PuPE), P partial factor productivity (PPFP) and P partial balance (PPB). The experiment was carried out for four consecutive seasons with treatments comprising potato cultivated under legume intercrops: none (T1), dolichos (Lablab purpureus L) (T2), peas (Pisum sativum L) (T3) and beans (Phaseolus vulgaris L) (T4). Across the seasons, the mean haulm P uptake for T2 (6.7?kg P ha^?1), T4 (5.5) and T3 (4.5) were 6%, 23% and 36% lower than that observed in T1 (7.1?kg P ha^?1), respectively. On the other hand, tuber P uptake was highest in T1 (21.8?kg P ha^?1) and T2 (21.3?kg P ha^?1) and were significantly higher than 13.2?kg P ha^?1 in T3 and 15.1?kg P ha^?1 in T4. This had a profound effect on PuPE, which was equally highest in T1 (0.26?kg total P uptake kg^?1 P supply) and T2 (0.25) and lowest in T3 (0.16) and T4 (0.18). Similarly, PPFP, PHI and PPB followed a similar trend, with highest values in T1 (57?kg tuber dry matter yield kg^?1 P supply, 76.4?kg tuber P uptake kg^?1 total plant’s P uptake and 0.20?kg tuber P uptake kg^?1 P supply, respectively). Among the tested legume intercrops, dolichos competed least for P with the main crop (potato) hence it can be integrated into potato-based cropping systems without compromising potato tuber yield.     

Evaluation of forage legumes for introduction into natural pastures of semi‐arid rangelands of Kenya

To address the potential of legumes to contribute to improved quality and quantity of natural pastures in the semi‐arid rangelands of Kenya, five legume species were introduced and evaluated in a small‐plot field experiment over three growing seasons. The investigated species were glycine (Neonotonia wightii), siratro (Macroptilium atropurpureum), dolichos (Lablab purpureus cv. Rongai), velvet bean (Mucuna pruriens) and shrubby stylo (Stylosanthes scabra cv. seca). Treatments included two cutting heights (ground level and 15 cm) and two cutting intervals (at 2 and 4 months). The mean dry matter (DM) yields of glycine and siratro were highest when the legumes were harvested at ground level at 2‐month intervals (10·31 and 7·81 t ha^?1 year^?1 respectively). Mean DM yield of stylo was highest when the legume was harvested at 15 cm after 4 months (3·52 t ha^?1 year^?1). These three legumes also produced high organic matter through litter fall, which contributed to soil fertility. Evidence from a supporting pot experiment showed effective nodulation and potential for N fixation. These legumes also possessed deep tap roots and withstood heavy defoliation. These three legumes were selected for further integration with grasses in natural pastures. The DM yields of dolichos and velvet bean when harvested at 15 cm after 2 or 4 months were low (2·48 and 1·91 t ha^?1 year^?1), and these species were considered inappropriate for further investigation.