Yield production efficiencies as affected by nutrient management strategies under different rice cropping systems

Context: Smart nutrient management strategies enhance rice yield while conserving resources. Nutrient Expert® (NE) was designed to offer fertilisation decision support for smallholders to improve productivity compared with farmers’ practice (FP) and commonly used soil testing-based management (ST). So far, NE-led yield increase in rice was analysed in terms of nutrient use efficiency. However, the crop physiological basis of the yield increase has not been investigated in detail, especially not in terms of the crucial parameter “radiation use efficiency (RUE)”. Methods: We analysed data from multi-location field experiments conducted in 2019 and 2020, varying in management of the cropping system and nutrient supply. Yield formation was dissected into components, consisting of the efficiency of intercepting incident radiation by the canopy (ε_i), the efficiency of converting intercepted radiation into biomass (ε_c, or RUE), and the efficiency of partitioning biomass to grains (ε_p, or harvest index). Results: Overall, season-long values of ε_i with suitable fertilisation were in the range of 0.7–0.8; ε_c ranged from 0.6 to 1.9 g MJ^–1, depending on soil nutrients, environmental conditions, and genotype. ε_p values were in the range of 0.5 – 0.6. Despite higher ε_i of FP due to the increase in N input, NE had a slight yield advantage, mainly attributed to the improved ε_c and ε_p. Across most rice cropping systems, correlations of yield were strongest with ε_c, followed by the correlation with ε_i, among the three efficiencies. Conclusions and implications: We identified ε_c as the major, and ε_i as the second important, physiological parameter underlying the yield increase by NE-based nutrient management. This differs from the results of crop improvement during the Green Revolution when ε_p primarily contributed to yield gain in major cereal crops.