Nitrogen contribution of cowpea green manure and residue to upland rice

Abstract

Cowpea, Vigna unguiculata (L.) Walp., is well adapted to acid upland soil and can be grown for seed, green manure, and fodder production. A 2-yr field experiment was conducted on an Aeric Tropaqualf in the Philippines to determine the effect of cowpea management practice on the response of a subsequent upland rice crop to applied urea. Cowpea was grown to flowering and incorporated as a green manure or grown to maturity with either grain and pods removed or all aboveground vegetation removed before sowing rice. Cowpea green manure accumulated on average 68kgN ha -t, and aboveground residue after harvest of dry pods contained on average 46 kg N ha -1. Compared with a pre-rice fallow, cowpea green manure and residue increased grain yield of upland rice by 0.7 Mg ha-I when no urea was applied to rice. Green manure and residue substituted for 66 and 70 kg urea-N haon upland rice, respectively. In the absence of urea, green manure and residue increased total aboveground N in mature rice by 12 and 14 kg N ha ~, respectively. These increases corresponded to plant recoveries of 13% for applied green manure N and 24% for applied residue N. At 15 d after sowing rice (DAS), 33% of the added green manure N and 16% of the added residue N was recovered as soil (nitrate + ammonium)-N. At 30 DAS, the corresponding recoveries were 20 and 37% for green manure N and residue N, respectively. Cowpea cropping with removal of all aboveground cowpea vegetation slightly increased (p < 0.05) soil (nitrate + ammonium)-N at 15 DAS as compared with the pre-rice fallow, but it did not increase rice yield. Cowpea residue remaining after harvest of dry pods can be an effective N source for a subsequent upland rice crop.

Mineralization of labeled N from cowpea [Vigna unguiculata (L.) Walp.] plant parts at two growth stages in sandy soil

“…This indicated that the contribution of N to the following crop from decomposing cowpea roots will be approximately one fifth of the whole cowpea plant used as green manure. In a field study, when above ground material was removed, cowpea roots increased soil mineral N content but not the yield of the following upland rice crop (John et al, 1992). When cowpea tops were used as green manure, however, rice yield was increased.…”

Does incorporation of cowpea-maize residue mixes influence nitrous oxide emission and mineral nitrogen release in a tropical luvisol?

“…Grain legumes are considered appropriate resources for soil fertility replenishment on smallholder farms due to their capacity to fix atmospheric N 2 in addition to direct food provision (Snapp and Silim 2002;Ojiem 2006). Cowpea (Vigna unguiculata), which is an acid tolerant and drought tolerant tropical legume (John et al 1992) has an efficient atmospheric N 2 fixing capacity, high biomass N accumulation (Franzluebbers et al 1994) and is highly compatible with maize (Zea mays) in intercropping systems commonly practised by smallholder farmers throughout the tropics (Sakala et al 2000). As a result, cowpea has a great potential for soil fertility management in tropical agricultural systems.…”

Cowpea [Vigna unguiculata (L.) Walp.] Yield Variance and Supported Character

“…Certain organs such as leaves and seeds can be used as food. The forage and residues substitute 66 kg urea-N / ha and 70 kg urea-N / ha within urea substitution, and 12 kg urea-N / ha and 14 kg urea-N / ha without urea [1]. Fresh weight and production of mint plant essential oil increased by 23.4% and 25.2% by application of cowpea forage.…”