Influence of Line-Planted Trees and Phosphorus Application on Water Use of Maize in Sub-Humid Western Kenya

ABSTRACT

Planting of trees in rows is common on farms in western Kenya where phosphorus deficiency is also a major constraint to maize production. The influence of soil P status and simultaneous agroforestry systems on water use have, however, not been reported for the region. Effects of line-planted Grevillea robusta (upperstorey trees), Calliandra calothyrsus and Senna spectabilis (both managed as hedges) and P application on water use efficiency were investigated in maize. The experiment was laid out as a splitplot with tree species forming main plots while 250 kg P/ha and no P applications formed subplots. Seasonal evapotranspiration was greater under Grevillea by 40.8 mm (5.2%) in the Long Rains and by 49.3 mm (10.2%) in the Short Rains. Application of P significantly increased seasonal evapotranspiration (ET) by 1.7% in Long Rains and 2.4% in the Short Rains. Maize water use efficiency was higher with P (6.9 kg/ha/mm in Long Rains and 9.5 kg/ha/mm in the Short Rains) than without P (0.8 kg/ha/mm in the Long Rains and 2.1 kg/ha/mm in Short Rains). The results revealed enormous potential for increasing maize WUE in these soils by overcoming P deficiency. Combining Grevillea trees with P enhanced use of seasonally available water.