Objectives Nitrogen (N) fertilization plays important roles in yield and efficiency of rice production. We studied the suitable N management for different planting areas, rice varieties, and cultivation methods, etc., for the efficient rice production in the Yangtze River Basin, China.
Methods Literatures were searched in CNKI and Web of Sciences, using key words with N application rate, sum of base and tillering N fertilizer (BTN rate), planting area, rice variety, cropping system, transplanting density, soil property, etc. There were total of 56 published papers meet the requirement of N, and a total of 956 sets of qualified data were screened out from the field experiments of the papers. Meta-analysis was used to quantitatively analyze the effects of N fertilizer management on N uptake, aboveground dry matter weight (ADMW), and yield of rice under different N application rates, basal+tiller fertilizer rates (sum of basal and tiller fertilizers), planting areas, varieties, planting modes, transplanting densities, and soil properties.
Results Both the N uptake and ADMW of rice would not stop increasing with the enhancement of N fertilizer rate until the total N rate and the basal+tiller fertilizer rate beyond 300 and 180 kg/hm2, when they were higher than 250 kg/hm2 and 120 kg/hm2, there was no significant yield increase. The grain yield increase caused by N fertilizer in the upper reaches of the Yangtze River Basin was 24.9%, significantly lower than those in the middle reaches (42.4%) and lower reaches (41.8%) of rice planting areas. Although there was no significant difference among rice varieties, hybrid rice varieties had an advantage in increasing N uptake and rice yield compared to japonica and indica rice, with an increase of 12.6%−15.2% and 3.5%−5.1%. N fertilizer significantly improved less N uptake, ADMW, and yield of single cropping rice compared to double cropping rice and paddy-rice rotation. For example, the yield of single cropping rice was increased by 29.1%, while the yield of double cropping rice and paddy-rice rotation were increased by 46.3% and 43.8%, respectively. When the transplanting density was controlled within 106/hm2, increasing the transplanting density could effectively improve the N uptake and ABDW of rice. Under high soil organic matter (>25 g/kg) and available P (>20 mg/kg), and low available N (<90 mg/kg) and potassium in soil (<80 mg/kg), rice yield responded the highest to N fertilizer, with rice yield increase ofv43.3%−48.5%, the total contribution rates of SOM, AP, AN, and AK to rice yield and nitrogen uptake reached 61.7% and 40.2%, respectively. N dry matter production efficiency, rice production efficiency, and harvest index all decreased when N rate exceeded 250 kg/hm2, while N absorption use efficiency, agronomic use efficiency, and partial productivity all decreased with increasing nitrogen application rate.
Conclusions Increasing the application of nitrogen fertilizer in the Yangtze River Basin can effectively improve rice yield. To decrease the risk of yield reduction and increase N use efficiency, the total N input should not exceed 250 kg/hm2, the sum of base and tillering N should controlled within 120 kg/hm2, and the gap with the total N input could be top dressed as ear fertilizer. In the upstream of the Yangtze River Basin, hybrid rice is preferred as the good variety advantages. Under single cropping system, the rice cultivars with long growth period should be chosen to reduce their dependence on N fertilizer. Double rice cropping or paddy-rice rotation system is beneficial for improving soil fertility and achieving the goals of reducing N, increasing yield and N use efficiency. In the double rice cropping or paddy-rice rotation system of the middle and lower reaches, reasonable increase of transplant density (< 106/hm2) can further improve rice yield and N use efficiency.