Soil nitrogen supply and nitrogen uptake for local rice grown in unfertilized acid sulfate soil in South Kalimantan

• Published in: Tropics Vol. 15; no. 4; pp. 349 - 354
• Main Authors: PURNOMO, Erry, HASEGAWA, Toshihiro, HASHIDOKO, Yasuyuki, OSAKI, Mitsuru
• Format: Journal Article
• Language: English
• Published: JAPAN SOCIETY OF TROPICAL ECOLOGY 01.01.2006
• Subjects: multiple transplating; Nitrogen mineralisation; Siam Unus variety
• ISSN: 0917-415X; 1882-5729
• DOI: 10.3759/tropics.15.349

Most of acid sulfate soil areas in South Kalimantan are recommended for growing rice. Due to unfavourable soil conditions such as low pH and unpredictable water level, farmers grow local rice varieties. The farmers use a multiple transplanting system not only to multiply the seedling population but also to cope with the conditions. In addition, most farmers do not apply fertilizer after the last transplanting, but the yield level is not low. Nutrient (particularly nitrogen, N) availability and utilization by the rice crop are the key for this, but N balance in the local multiple transplanting system has been poorly understood. We therefore studied the balance between soil N supply from the mineralization and crop N uptake in the local transplanting system in South Kalimantan. The experiment took place in Tambaksirang Baru (03°26’31”S, 114°35’29”E), Gambut District South Kalimantan. Two farmers, paddocks separated by a village road were chosen for the study. The N mineralisation measurements were carried out on a monthly basis after the planting. At each sampling date, above and belowground parts of rice plants were collected for biomass and N content determination. At the end of the growing season, we observed that the biomass, N uptake and release from the soil were 9.5 and 7.1 Mg DM ha-1; 36.0 and 27.8 kg N ha-1; and 13.37 and 8.32 kg N ha-1 for plot 1 and 2 respectively. The higher N in the crop than that supplied by soil indicates that there are other sources of N for local rice grown in acid sulfate soil.