Combining inorganic fertilizers (NPK) with organic materials has become a common practice for sustainable agricultural production in low productivity rice fields.
The effect of annual application of inorganic fertilizer in combination with organic fertilizer and NPK on rice seed yield and soil chemistry was investigated in a 4-year field trial. Six treatments, including control (no fertilizer), NPK alone, NPK plus 1.5 Mg ha-1 mushroom compost (NPK + MC), NPK plus 3.6 Mg ha-1 green manure (NPK + GM), NPK plus cow dung 4.7 Mg ha-1 (NPK + CM) and NPK plus rice straw 3.0 Mg ha-1 (NPK + RS)-were applied in this study.
The results showed that rice yield was 11.4% and 9.3% higher in 2014 under NPK + CM and NPK + RS treatments, respectively, compared to NPK treatment alone. No significant difference in rice yield was observed between plots treated with NPK and NPK + MC or NPK + GM. Application of CM on the soil surface resulted in a significant increase in soil pH (0.16-0.29 units), cation exchange capacity (CEC) (17.4-21.9%), and a decrease in exchangeable acidity and Al3+ concentration at 0-20 cm soil depth, compared to NPK treatment alone. However, no significant differences in soil pH or alkaline cation concentrations were observed in the 0-10 cm soil layer after NPK alone or NPK plus the other three organic amendments. In addition, application of NPK + CM at 4.7 Mg ha-1 y-1 showed the highest available P concentrations at 0-10 cm depth.