THE EFFECT OF SHORT-ROTATION SESBANIA-SESBAN PLANTED FALLOWS ON MAIZE YIELD

Two provenances of Sesbania sesban var. nubica (Kakamega and Chipata) were planted in fallows for 1, 2 and 3 years at 0.5 m X 0.5 m, 0.7 m x 0.7 m and 1.0 m x 1.0 m spacing. Maize crop (MM604) was grown after fallow period at 0, 37, 74 and 1 12 kg N ha-1 to evaluate the effects of nitrogen (N) and fallow on grain yield. There were no significant differences between the two provenances of S. sesban. Wood biomass after 1, 2 and 3 years fallow at close spacing was 8.3, 17.6 and 21.4 t ha-1 for the Kakamega provenance and 10.8, 14.5 and 21.2 t ha-1 for the Chipata provenance. Litter fall in both provenances ranged from 0.6 t ha-1 in June to 0.01 t ha-1 in November. Stand mortality increased with plant density and fallow years: 27% in the first year and about 90% by the end of the third year. Weed biomass ranged from 6.8 t ha-1 to 6.0 t ha-1 at close and wide spacing respectively. Maize grain yield without N was 2.27, 5.59 and 6.02 t ha-1 after 1, 2 and 3 years fallow respectively compared with the control plots with 1.6, 1.2, 1.8 t ha-1 after 1, 2 and 3 years of continuous cropping. Even with addition of 112 kg N ha-1, yield in the control plots declined from 6.09 to 4.88 and 4.28 t ha-1 after 1, 2 and 3 years of continuous cropping. In the planted fallows at 112 kg N ha-1, maize yield increased from 6.75 to 7.16 and 7.57 t ha-1 following 1, 2 and 3 years fallow. It is concluded that short fallow rotations of 1-3 years using S. sesban have a potential in increasing maize yield even without fertilizers. Thus, increasing the fallow period decreases the effectiveness of inorganic fertilizers but increases grain yield for low fertilizer input.