Sesbania tree fallows on phosphorus-deficient sites: Maize yield and financial benefit

Rotation of Sesbania sesban (L.) Merr., a fast-growing N-2-fixing tree, wit h maize (Zea mays L,) has potential for increasing fertility of tropical so ils, where fertilizer use by resource-poor farmers is limited, At two sites in Kenya (Ochinga, with a Kandiudalfic Eutrudox soil, and Muange, with a K andic Paleustalf), we compared maize yields and financial returns for (i) s esbania grown for three or Pour seasons followed by three maize crops (sesb ania fallow), (ii) one maize crop followed by natural regrowth of vegetatio n for three seasons and then three maize crops (natural fallow), and (iii) maize monoculture for seven seasons. After the falloffs, plots were split w ith and without added P. Maize responded to P at both sites. Cumulative gra in yields for seven seasons of maize monoculture were 8.4 Mg ha(-1) at Ochi nga and 5.6 Mg ha(-1) at Muange, They were comparable to cumulative maize y ields for sesbania follow (Ochinga, 10.6 Mg ha(-1); Muange, 4.5 Mg ha(-1)) and natural fallow (Ochinga, 7.7 Mg ha(-1); Muange, 4.2 Mg ha(-1)), even th ough maize was grown for only three or four seasons in the fallow treatment s, Sesbania fallow was financially attractive at Ochinga (greater than or e qual to 500 nlm rain in each season) but not at Muange, where low rainfall (<300 mm in each postfallow season) limited maize yield. Phosphorus fertili zation of maize at Ochinga increased (P < 0.2) net benefit for sesbania fal low. Improved fallows have potential to supply nutrients to crops, but they are unlikely to eliminate the need for P fertilizers on P deficient soils.