Abstract

Anis Sholihah, Sri Rahayu Utami, Sugeng Prijono and Eko Handayanto

A study was conducted to evaluate the N recovery of 15N labelled crop residues (rice straw=RS; soybean=SY) with 15N isotope dilution technique on growth of maize. The 15N labelled crop residue from the rice and soybean crops that were grown in glass-house under three 15N concentrations, that is, 0.625 mM N (N1), 2.5 mM N (N2) , and 10 mM N (N3) supplied as CO(15NH2)2, in 30 cm diameter plastic pots containing 5 kg of quartz sand. Eight weeks after planting the above-ground biomass was pruned and oven dried at 60°C for 48 h and analyzed for polyphenol, lignin, N, C, C/N and % 15N-abundance. The seven treatments (six types of crop residues and one treatment with no added residues) were arranged in a completely randomized block design with four replicates. The maize was plant pots containing 10 kg of soil and placed in a glass-house. The varying supply of 15N concentrations resulted in varying quality of crop residues. The amounts of mineral N in the soil supplied with crop residues were significantly greater than in the control at 2, 4 and 8 weeks. The amounts of mineral N in soils amended with residues of SY and RS with a 10 mM N supply were significantly (P<0.05) greater than those grown with 2.5 mM and 0.625 mM N supplies during the incubation time. The N recovery by maize shoot from residues with 10.0 mM N was greater (80.86% on average) than that from residues with 2.5 mM N (70.06% on average) and that from residues with 0.625 mM N (58.43% on average). On average, the %N recovery of crop residue N by maize estimated by the 15N method was 10.73% more than that estimated by the difference method.