Rapid decay of dolichos [Lablab purpureus (L.) Sweet] residue leads to loss of nitrogen benefit to succeeding maize (Zea mays L.)

Abstract

The traditional natural fallows are no longer practicable in sub-Saharan Africa and technologies to replace them are being popularised through management of short fallow systems. Dolichos [Lablab purpureus (L.) Sweet] is among the legumes used to improve such fallows and its residues are incorporated to improve yield of succeeding cereal. Two field studies were conducted to determine dolichos residue mineralisation schedule and response of maize to timing of the residue incorporation, to establish if the current residue incorporation practice maximises nutrient benefit to succeeding cereal. Dolichos residue was applied at 2 t/ha in litterbags, buried in the field at 15-cm depth and retrieved after 1, 2, 4, 8 and 16 weeks, and the remaining debris analysed for loss of weight, N, P and K. A parallel split-plot experiment was set up to determine response of maize to time of residue incorporation, with or without fertiliser nitrogen supplementation. The main plot treatments were nitrogen fertiliser applied at 0, 30 and 60 kg/ha at sixth fully opened leaf in maize. The subplot treatments were residue management regimes, which included four residue incorporation times of 2, 4, 6, and 8 weeks before sowing maize, residue removal off the field, residue mulched on surface and traditional weedy fallow. Results show rapid loss of N, with 50% being released within the first 2–4 weeks after burying. Residue incorporated at 2 and 4 weeks before sowing improved maize yield, while residue removal off-field reduced yield comparably with the traditional weedy fallow. However, there were no statistical differences among the timing of the dolichos residue incorporation. These results reflect poor synchrony of mineralised N and uptake by succeeding maize as currently practiced and suggest residue incorporation closer to sowing maize to benefit the cereal.

Lablab purpureus—A Crop Lost for Africa?

“…Despite this decline, however, lablab appears to persist as a garden crop (rather than a field crop) in eastern and southern Africa; and recent market surveys from eastern Africa suggest that there is a high demand (and subsequently a good price) for lablab in Kenya (Ngailo et al 2003). There is almost no ongoing lablab research in Africa, except for programs focusing on improving soil properties by using green-manure/forage crops, such as in maize-based systems of Kenya (Mureithi et al 2003; Cheruiyot et al 2007; Lelei et al 2009), Malawi (Sakala et al 2004) and Nigeria (e.g., Ibewiro et al 2000; Amodu et al 2004; Gbaraneh et al 2004; Rahman and Ogungbile 2006), or sorghum- and millet-based systems in the semi-arid tropics of Mali (Kouyaté et al 2000). Almost all of these African initiatives have included and continue to include one popular late-maturing forage cultivar, cv.…”