Prospects of soil moisture conservation by fallowing in areas of medium agricultural potential in smallholder farming

Abstract

The medium agricultural potential areas are characterized by low and unreliable rainfall with a drought period of variable length between the rainy seasons. Rainfall is frequently inadequate resulting in crop failure in some years underlining the importance of soil moisture conservation as a means of ensuring a crop. These medium potential areas are located largely north and south of the equatorial belt. In Kenya the medium potential areas are found in Agroclimatic Zone IV and the drier parts of Agroclimatic Zone II, within the semi-humid and semi-arid environment. Research conducted on a Ferral Chromic Luvisol (at Katumani, Agroclimatic Zone IV) has shown benefits of a clean fallow on moisture conservation and increased yields. However, efficiency of moisture storage was low resulting in substantial water loss in the top 60 cm, below which soil moisture was at about 1 bar suction. On an Andosol (at Njoro, Agroclimatic Zone III) benefits of a clean fallow soon after wheat harvest proved beneficial by conserving soil moisture and increasing wheat yields of the next crop. The plots that were kept free of weeds soon after wheat harvest lost soil moisture to near or beyond wilting point in the top 40 cm of soil while the lower depths contained moisture at around field capacity ( 1 3 bar ). However, evaporation losses were substantial in the order of 290 mm for the six month fallow period, sufficient moisture to grow a crop. The plots that were left with weeds lost soil moisture in the entire rooting zone (135 cm) to near wilting point and much more at the surface soil layers. Despite the inefficiency of soil moisture storage the benefits of fallowing on yields are evident as moisture is the main determinant of yield in each season but the farmers have been reluctant to adopt the practice. The reasons for this may be economic. The amount of water lost through evaporation from the clean fallow is sufficient to produce a short-season, low water demanding crop. The crop should preferably be shallow rooted to exploit moisture in the top 40–60 cm that is lost even under clean fallow conditions. A thus cropped fallow would be an attractive alternative to a clean fallow, particularly to small scale farmers.