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

Abstract

Rotation of Sesbania sesban (L.) Mere., a fast-growing N2-fixing tree, with maize (Zea mays L.) has potential for increasing fertility of tropical soils, where fertilizer use by resource-poor farmers is limited. At two sites in Kenya (Ochinga, with a Kandiudalfic Eutrudox soil, and Muange, with a Kandic Paleustalf), we compared maize yields and financial returns for (i) sesbania grown for three or four seasons followed by three maize crops (sesbania fallow), (ii) one maize crop followed by natural regrowth of vegetation for three seasons and then three maize crops (natural fallow), and (iii) maize monoculture for seven seasons. After the fallows, plots were split with and without added P. Maize responded to P at both sites. Cumulative grain yields for seven seasons of maize monoculture were 8.4 Mg ha-1 at Ochinga and 5.6 Mg ha-1 at Muange. They were comparable to cumulative maize yields for sesbania fallow (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 though maize was grown for only three or four seasons in the fallow treatments. Sesbania fallow was financially attractive at Ochinga (≥500 mm rain in each season) but not at Muange, where low rainfall (<300 mm in each postfallow season) limited maize yield. Phosphorus fertilization of maize at Ochinga increased (P < 0.2) net benefit for sesbania fallow. Improved fallows have potential to supply nutrients to crops, but they are unlikely to eliminate the need for P fertilizers on P-deficient soils.