Influence of Rice Straw Biochar Application on Soil Nutrient Dynamics and Rice Productivity Under Different Irrigation Regimes

This study aimed to investigate the effects of biochar on soil nutrient dynamics and rice productivity under different irrigation regimes. A pot experiment of rice straw biochar application (0, CK; 2%, C1; 4%, C2; 6%, C3) combined with three types of irrigation regimes (continuous flooding, CF; intermittent irrigation, II; saturated moisture, SM) was conducted. The N content of the biochar increased by 25.27–32.26% after application, while the C (12.09–19.06%), P (25.58–32.56%), and K (89.74–91.67%) contents in the biochar decreased. The total N content in the biochar-amended soil peaked at the heading stage of the first year. Compared with CK, the total N increased by 14.47–34.87%, 17.20–49.04%, and 28.85–42.31% under CF, II, and SM, respectively. The available P content in the biochar-amended soil was highest at the jointing stage under CF conditions, whereas it was highest at the heading stage under SM. In addition, the maximum increase in available P was 19.34, 14.32, and 16.10 mg kg−1 under CF, II, and SM, respectively. The increase in available K content induced by biochar was the most significant and reached a maximum (13.1, 11.5, and 10.5 fold under CF, II, and SM, respectively) at the jointing stage. Biochar had the better potential for yield enhancement (10.78–35.32%) under II, mainly by increasing the effective panicles (0–6.6%) and spikelets per panicle (17.57–24.91%) and dry matter productivity (8.66–27.65%). The increase in P and K in the soil may have directly originated from the biochar, while N was not. Continuous flooding promoted the release of P and K from the biochar, whereas biochar plus intermittent irrigation benefitted rice production.