C and N mineralization of cowpea crop residue and its effect on yield of lowland rice

English. Incubation and pot experiments have been conducted in the laboratory and in the greenhouse of Soil and Plant Nutrition Group, Center for the Application of Isotopes and Radiation. The aim of the first experiment was to study the effect of different growing stages and rates of cowpea crop residue applied as green manure on the C and N mineralization during a certain time of incubation. The purpose of the second experiment was to study the effect of the results gained from the first experiment on lowland rice yield. Plant material of cowpea crop from three different growing stages i.e. at first harvest, full blooming, and one month after planting was applied to the soil at 4 levels, namely 0, 0.2, 0.5, and 1.0 percent for the incubation experiment was carried out by CO2 trapping method in a system made by the joints of 4 erlenmeyers. At the pot experiment Atomita IV, 2a lowland rice variety was used. Parameters observed in the incubation experiment were C released as CO2 which is determined by percentage of 14C trapped by the system and ammonium-N and nitrate-N content in the soil during 30 days of incubation. While for the pot experiment, parameters observed were yield of rice plant and total-N and -C in the green manure remained in the soil after one growing season of rice. The incubation experiment resulted in showing that the average of C and N mineralization of cowpea crop residue after 30 days of incubation was the lowest when cowpea crop residue was applied to soil as green manure at the first harvest of its growing stage. Contrary, results obtained from the pot experiment showed that at this application the highest yield and N uptake in the rice plant was obtained.

Indonesian. Telah dilakukan dua percobaan, yaitu percobaan inkubasi di laboratorium dan percobaan pot di rumah kaca Kelompok Tanah dan Nutrisi Tanaman. Percobaan pertama bertujuan untuk mempelajari pengaruh fase pertumbuhan tanaman dan takaran sisa panen kacang tunggak yang diaplikasikan sebagai pupuk hijau terhadap mineralisasi C dan N selama waktu inkubasi tertentu. Percobaan kedua bertujuan untuk mempelajari pengaruh pupuk hijau dari berbagai fase pertumbuhan tanaman dan takaran terhadap produksi tanaman padi sawah. Bahan tanaman kacang tunggak dari tiga fase pertumbuhan tanaman, yaitu saat panen pertama, saat berbunga penuh, dan saat umur 1 bulan, masing-masing diaplikasikan ke tanah dengan empat takaran, yaitu 0, 0,2 persen, 0,5 persen, dan 1,0 persen untuk percobaan inkubasi dan 0, 2,50, 6,25, dan 12,50 g/pot untuk percobaan pot