Tuesday, November 14, 2006

Impacts of Organic Fertilizer Management on Soil Quality and Crop Productivity of Rice-Wheat Systems.

A. Tirol-Padre, CSWS, International Rice Research Institute, DAPO Box 7777, Manila, Philippines, Jagdish Ladha, IRRI, India Office, CG Block, IRRI-India Office 1st Fl. CG Block, NASC Complex DPS Marg, New Dehli, 110012, INDIA, A.P. Regmi, National Wheat Research Program, Regional Agriculture Research Station, Padsari, Bhairahawa, Rupandehi, Nepal, A.L. Bhandari, Agronomy Dept, Punjab Agricultural Univ, Ludhiana, India, and K. Inubushi, Chiba Univ, Faculty of Horticulture, Matsudo, Japan.

The impacts of continuous applications of an organic source (farmyard manure, FYM; green manure, GM; and wheat straw, WS) in combination with inorganic fertilizers (NPK) on soil quality and productivity of rice-wheat systems were investigated in two long-term experiments  in Ludhiana, India, after 20 years, and in Bhairahawa, Nepal, after 15 years, by measuring changes in the total and decomposable soil C and N pools, and soil microbiological parameters relative to unfertilized and inorganically fertilized controls. In Ludhiana, total C, hot-water-extractable C (HWEC), and total N were significantly higher than the unfertilized control only in the FYM+NPK treatment. Rice grain yield was significantly correlated with HWEC and total N but not with total C. In Bhairahawa, the FYM+NP and GM+NP treatments increased total C and N but not HWEC relative to the control. A decline in HWEC was observed over the years with no significant year x treatment interaction. Rice grain yield had a significant correlation with HWEC and total C and N in Bhairahawa. The FYM amendment increased available P, cation-exchange capacity (CEC), potential mineralizable N (PMN), and dehydrogenase activity compared with the control at one or both sites, but microbial biomass C, basal soil respiration, flush of CO2 after rewetting of dried soil, and qCO2, were not different among all treatments. Increase in carbon as a fraction of the applied organic fertilizers was 11-23% from FYM, 4-21% from GM, and 3% from WS, while increase in N was 37-39% from FYM, 19-41% from GM, and 24% from WS based on the increase in total C and N relative to an inorganically fertilized control. This study demonstrates that current practice of inorganic fertilization alone can not maintain soil quality needed to sustain current levels of crop productivity. There is a need to further develop feasible organic-supplemented fertilization strategies.