Soil carbon and nitrogen regulation using organic and inorganic fertilizers for leaf physiological activity, grain yield and nutritional quality improvements in rice

Organic fertilizers are widely used in agriculture production and change the soil carbon (C) and nitrogen (N) contents, thus improving crop production. The increased amount of soil C and N exhibit a greater potential to improve the leaf physiological activity, yields and grain quality of rice by improving soil fertility indices. To understand the relationship between soil C and N contents with leaf physiological activity and grain quality; organic fertilizers (i.e., cattle manure (CM) and poultry manure (PM)) coupled with chemical fertilizer (CF) was applied at the different proportion. The recommended rate of N 150 (kg ha −1 ) was provided from manure and CF using six treatments, i.e., T 1 — CF 0 ; T 2 —100% CF; T 3 —60% CM + 40% CF; T 4 —30% CM + 70%CF; T 5 —60% PM + 40% CF, and T 6 —30% PM + 70% CF. Results showed that soil organic C (SOC), total N (TN), leaf net photosynthetic rate ( Pn ), SPAD values, grain yield and grain quality attributes were significantly increased with combined organic and inorganic fertilizer application. Averaged over the years, T 6 treatment significantly improved SOC, TN, Pn , starch content (SC), amylose content (AC), and grain yield by 16%, 12%, 9%, 7%, 12%, and 24%, respectively, compared to CF-only. However, no significant differences among T 4 and T 6 were observed for studied parameters. In addition, the linear regression exhibited that SOC (R 2 = 0.70** & R 2 =0.50*) and TN (R 2 = 0.62* & R 2 =0.58*) were positively correlated with grain SC and AC, respectively. Likewise, Pn (R 2 = 0.51* & R 2 =0.62*) were also positively associated with SC and AC, respectively. The correlation analysis showed that improving SOC and TN played a key role in enhancing leaf physiological activity and grain nutritional quality. Thus, the combination of organic and inorganic fertilizers at a 30:70 ratio is a promising option for the improvement of soil fertility and grain yield of rice as well as grain nutritional traits.