Duration of sesbania fallow effect for nitrogen requirement of maize in planted fallow-maize rotation in western Kenya

The duration of the residual effect of sesbania (Sesbania sesban) fallow on subsequent crops willdetermine the interval at which sesbania must be grown to replenish N in a planted fallow±croprotation cycle. An experiment was conducted from 1995 to 1998 (seven cropping seasons) ontwo farms in western Kenya, an area subject to a bimodal annual rainfall pattern. The aim wasto compare the effect of a single-season sesbania fallow with continuous annual cropping withand without phosphorus fertilizer, on a P-deÆcient soil. Phosphorus was applied at a rate of 500kg ha71in a single application to meet the phosphorus needs of subsequent crops for the nextÆve to ten years. Sesbania was established simultaneously with maize by direct seeding in theÆrst rainy season of 1995 and allowed to grow as a pure fallow through the second rainy season.Following the harvest of this fallow crop, sole maize in the Ærst post-fallow season and maize-bean intercrops in the subsequent four seasons were grown with and without nitrogen at a rateof 100 kg ha71. Added phosphorus on average increased maize yields by 3.7 times over thecontrol, indicating that phosphorus fertilizer is essential for good yields. The amount ofphosphorus recycled by sesbania fallow was inadequate to meet the crop needs in P-deÆcientsoils. While continuously cropped maize in the presence of phosphorus responded to nitrogen inall seasons, the crop following sesbania responded only from the third season. In the Ærst post-fallow season, sesbania increased maize grain yields over continuous maize by 1.4 t ha71withphosphorus fertilizer and by 1.3 t ha71without phosphorus fertilizer. The residual effect ofsesbania with phosphorus fertilizer lasted for two seasons, while without phosphorus it lasted foronly one. In these Kenyan highlands, farmers who can afford fertilizer should buy phosphorusfertilizer and rely for nitrogen on planted fallow with species such as sesbania grown for oneseason every two years. For farmers who cannot afford fertilizer, one-season fallow every yearmay be more attractive because of labour savings and the Ærewood produced by sesbania.

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DOI:

https://doi.org/10.1017/S0014479702000273

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