The Effects of residual N of several soybean varieties on corn and decomposition of soybean in the soil

إنجليزي. Experiment were conducted in Desa Sidobinangun, Kecamatan Seputih Banyak, Kabupaten Lampung Tengah in wet season of 1994/95. A randomized complete block design was used in this experiment with four replications. In the first season 8 varieties and lines of soybean were planted. After harvest, the plant stover was chopped up and incorporated to the soil. In the second season, corn was planted with adding 3 treatments (0, 45 and 90 kg N fertilizer/ha). In the same locations, stover of 8 varieties and lines of soybean was packed in the small bags and burried in the soil. Observation was done every 2 weeks to analyze the decomposition of soybean stover. Results of the experiments indicated that different varieties and lines affect significantly soybean growth and grain yield. In contrast, residual of different varieties of soybean stover did not affect the growth yield of corn which was planted after soybean. The highest yield of corn was obtained from treatment of 90 kg N/ha. This means that N fertilizer was still needed to get high yield of corn which was planted after soybean. Nitrogen resulted from N fixation was enough for maintaining N nutrient in the soil, not adding N in the soil. The rate of decomposition of soybean stover (leaf was not included because at harvest the leaf was already dropped) was not different among varieties and lines. At 8 weeks after stover burried in the soil about 50 percent of soybean stover decreased slowly with time

الأندونيسية. Penelitian dilaksanakan di Desa Sidobinangun, Kecamatan Seputih Banyak, Kabupaten Lampung Tengah pada musim hujan 1994/95. Rancangan yang digunakan adalah rancangan acak kelompok dengan 4 ulangan. Pada musim pertama 8 varietas dan galur ditanam. Setelah panen, brangkasan dibenamkan kembali ke dalam tanah dan lahan ditanami jagung. Perlakuan ditambah dengan perlakuan pemupukan N (0, 45 dan 90 kg N/ha). Pada lokasi yang sama, brangkasan dari 8 varietas dan galur dimasukkan ke dalam kantong dan dibenamkan ke dalam tanah. Pengamatan dilakukan tiap 2 minggu untuk analisis dokumentasi tanaman kedelai. Hasil penelitian menunjukkan, bahwa perbedaan varietas dan galur mempengaruhi pertumbuhan dan hasil secara nyata. Sebaliknya, brangkasan dari berbagai varietas kedelai tidak mempengaruhi pertumbuhan dan hasil jagung yang ditanam setelah kedelai. Hasil jagung tertinggi didapat dari perlakuan pupuk N 90 kg/ha. Ini berarti pupuk N masih diperlukan untuk mendapatkan hasil jagung yang tinggi. Nitrogen hasil dari fiksasi N hanya untuk mempertahankan kandungan N dalam tanah bukan untuk menambah hara. Laju dekomposisi brangkasan kedelai (daun tidak termasuk karena pada saat panen daun sudah rontok) tidak berbeda diantara varietas dan galur. Pada 8 minggu setelah dibenamkan, brangkasan kedelai sudah terdekomposisi sekitar 50 persen