LAUSR

Applying straw to agricultural production to improve soil productivity and crop yields is significant. However, the straw-only application is possibly not a practical choice for achieving environmental protection and high yield. This study evaluated the applicability of straw combined with biochar to the paddy field. Two-year pot experiments were conducted to examine the effect of straw combined with different proportions (0, 5, 20, 40 t ha-1) of biochar on soil nitrogen retention, phosphorous availability, rice yield, and physiological parameters. Five treatments were included: control (CK), 7 t ha-1 straw + 0 t ha-1 biochar (ST), 7 t ha-1 straw + 5 t ha-1 biochar (SC1), 7 t ha-1 straw + 20 t ha-1 biochar (SC2), 7 t ha-1 straw + 40 t ha-1 biochar (SC3). The results indicated that the biochar had an encouraging effect on paddy fields with straw returning: (1) SC3 treatment significantly increased ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) content in soils compared to ST, increasing by 30.19% and 42.72%, while SC2 treatment increased by 25.84% and 30.40%, respectively; (2) Regarding soil phosphorus availability, ST treatment showed a negative effect, while proper biochar application rate (20 t ha-1) effectively increased Olsen-P content (18.24%); (3) No significant difference among these treatments was observed in the photosynthetic characteristics. Notably, 20 t ha-1 biochar application (SC2) effectively enhanced rice components (stem, ear) dry biomass, improved rice yield (10.14%), and Harvest index (HI: 4.99%). Hence, the appropriate rate (20 t ha-1) of biochar combined with straw (7 t ha-1) returning is a promising strategy for increasing nitrogen retention and phosphorous availability, alleviating N and P losses and promoting rice growth and yield. These findings are expected to provide a new perspective in that straw-returning with biochar achieves high efficiency, ecological, and sustainable development of agriculture.