EFFECTS OF SOIL AMENDMENTS ON PHYSICAL PROPERTIES AND MAIZE GRAIN YIELD IN POORLY RESPONSIVE SOILS OF WESTERN KENYA

Abstract

Poor soil responsiveness to fertilizer application is an emerging problem whose cause is yet to be well understood. This was the basis for a study in Western Kenya to unravel the underlying physical characteristics of these soils that influence the performance of fertilizer use on maize grain yield. The study was conducted on eight on-farm fields equally distributed in Busia-North and Bungoma-Southwest counties during the long rain (LR) and short rain (SR) seasons of 2015. A RCBD was adapted with three fertilizer treatments as amendment strategies: an absolute control, a combination of organic and inorganic fertilizers and a pure inorganic fertilizer. The latter two fertilizer treatments aimed at providing balanced nutrition consisting of primary macro (N, P and K), secondary macro- (Ca) and micro- (Zn and Cu) nutrients. The influence of the amendments on water infiltration, penetration resistance (at three depths; 10, 20 and 30 cm) and maize grain yield was assessed twice during the study period. A study on inherent physical characteristics (texture, stable aggregates and water content) at the onset revealed a restriction for crop roots in the soil subsurface layers. In each region, two of the four fields had adequate rooting depth (> 20 cm) while the two had inadequate (< 20 cm) for maize growth. Texture across all the fields was predominantly sand of classes: sandy loam, loamy sand and sandy. Stable aggregates relied on silt due to low C and clay contents. Infiltration rates of the shallow fields (9.25 cm hr-1) were lower than that of the deep fields (12.98 cm hr-1); while addition of organic amendments increased water movement significantly. Penetration resistance increased with depth. Upper soil layer had < 0.5 MPa readings while at 30 cm depth, > 3 MPa as the critical threshold limiting rooting of crops. Compaction was prominent in shallow fields compared to those with adequate rooting depth. The overall yield was low (< 1 t ha-1) where amendments were not applied and significantly increased with nutrients application (> 3 t ha-1). Higher grain yield was observed in LR (3.46 t ha-1) compared to SR (2.13 t ha-1). Combination of organic and inorganic fertilizers improved water infiltration and reduced compaction as organic matter aids in overall soil permeability. However, shallow fields faced further physical constraint where addition of organic materials was insignificant. Designation of proper nutrient amendments and practices such as deep tillage is required to alleviate challenges in PRS.