Effects of continuous rice straw compost application on rice yield and soil properties in the Mekong Delta

A field experiment was conducted to study the effects on yield and soil properties of the continuous application of rice straw compost to an alluvial soil in the Mekong Delta, Vietnam. Fourteen rice crops, two crops per year, were grown by direct seeding of the crop. There were seven treatments: F0C- (no fertilizer and compost), F0C+ (compost with no fertilizer), F20C+, F40C+, F60C+, F80C+ (20, 40, 60 and 80% of the fertilizer application rate with compost, respectively), F100C- (full strength fertilizer application as N:P2O5:K2O at 100:30:30 kg ha-1 in the dry season and 80:30:30 kg ha-1 in the wet season without compost). Compost prepared from the rice straw was applied at 6 Mg ha-1 (fresh weight) at the cultivation of each crop. The F0C+ treatment showed higher yield than the F0C- treatment by 0.68 Mg ha-1 on average in the wet season, but not in the dry season. The rice yield in F0C- declined at a rate of 0.163 Mg ha-1 year-1 in the wet season, but there was no decline in rice yield in F0C+. In treatments with compost, the yield reached its plateau at F40, suggesting that compost could replace part of the fertilizer. Although there were no significant differences in the total C concentrations in the soil among the treatments, even after 12 consecutive crops, soil penetration resistance appeared to be lower with compost than without compost. This long-term field trial showed that the continuous application of rice straw compost has some positive effects on rice yield as well as on soil physical properties.