Combined return of rice straw and organic fertilizer to yellow-mud paddy soil to improve the rice productivity and substitute chemical fertilizers

Crop straw and livestock manure, the main components of organic fertilizer resources, play important roles in the improvement of soil fertility and reduction of chemical fertilizer. To provide a basis for improving the soil fertility, crop yield and benefits of rice in a southern hilly area, various amounts of combined rice straw and organic fertilizer were returned to yellow-mud paddy soils under uniform total N input conditions and the effects on the rice production capacity, chemical fertilizer substitution, and plant nutrient uptake were studied. The field experiment was conducted in a yellow-mud paddy field in Minqin County, Fujian Province over four consecutive years. The experiment involved six treatments with uniform total N input but varying percentages of replacing N from a mix of rice straw and organic fertilizer (RO); that was, 0 (RO0, CK), 20% (RO20), 40% (RO40), 60% (RO60), 80% (RO80), and 100% (RO100) of N input. The dry amounts of rice straw applied in treatments of RO20, RO40, RO60, RO80, and RO100 were 750 kg∙hm⁻², 1500 kg∙hm⁻², 2250 kg∙hm⁻², 3000 kg∙hm⁻², and 3750 kg∙hm⁻², respectively; and the shortage of N was supplied by organic ferilizer. The variations in rice yield, nutrient uptake, and soil fertility factors were analyzed. As a result, the 4-year average yield of rice grains of RO20, RO40, RO60, and RO80 treatments significantly increased by 8.4%–13.9% relative to the yield of CK (P<0.05). However, the increasement of yield tended to decline with the increased application rates of organic materials, as the rice yield of RO100 was comparable to that of CK. Among the yield components, the effective spike significantincreased by RO treatments. The benefits of rice of RO20 and RO40 treatments were 2204 ¥∙hm⁻² and 527 ¥∙hm⁻² higher than that of CK, respectively. The uptake of N, P and K by rice plants under various RO treatments significantly increased by 8.5%−14.9%, 8.5%−14.8% and 8.6%−16.9%, respectively, compared with CK, except for RO100 treatment. The recovery rate change of N in all RO treatments increased by 6.5−11.4 percentage points, with the differences between RO20 and RO80 or RO100 were statistically significant (P<0.05). Although the contents of Ca, Mg and Zn in rice grains increased, the content of Fe decreased following the return of organic materials. The RO treatments increased soil pH and the contents of organic matter, total N, available P, available K, microbial biomass C, microbial biomass N and urease activity; but decreased the soil bulk density. In conclusion, the combined return of rice straw and organic fertilizer to yellow-mud paddy soil for 4 consecutive years improved rice productivity and fertilizer uptake. In this study, the combination of organic materials can completely replace the chemical fertilizers. Based on the rice yield, reduction of chemical fertilizer use, and improvement of farmer earnings and soil fertility, RO20 treatment was considered as the best fertilization regime, followed by RO40 treatment.