Yield and nitrogen uptake of rice and soil nitrogen supply capacity under fertilizer reduction in a rice-rice-Chinese milk vetch rotation system, northern Jiangxi Province, China

Objectives Chinese milk vetch (CMV) and rice rotation is an efficient practice to take use of fallow paddy field during winter season, and maintain the productivity of paddy field. We studied the potential of fertilizer reduction on rice yield and N efficiency and the soil N supply capacity under the rice-rice-CMV rotation system.

Methods The field experiment under rice-rice-CMV rotation was established in Gao’an, Jiangxi Province in 2016. The treatments included no fertilizer control (CK), conventional fertilizer rate without returning CMV (F100), and returning CMV combined with conventional chemical fertilizer rate of 100%, 80%, 60%, and 40% (GF100, GF80, GF60 and GF40) for early rice, and the following late rice was applied with conventional fertilizer rate in all the treatment plots. Plant (including grains) and soil samples were collected at the tillering, jointing, booting, and maturity stages of early rice and at maturity stage of late rice to measure the aboveground biomass, yield, and nitrogen content of rice. The N uptake and utilization efficiency of rice aboveground were calculated, and the N supply capacity and available phosphorus and potassium content of soil were measured.

Results Compared with F100 treatment, GF80 significantly increased early rice yield by 707.8 kg/hm², or by 10.12% on average of six years, and did not impact the late rice yield; GF40 and GF60 didn’t significantly affect the early and late rice yield. GF40, GF60 and GF80 treatments didn’t significantly affect grain biomass at maturity stage of early rice while significantly increased grain biomass by 7.76%, 8.62%, and 9.48% of late rice at maturity stage, respectively. GF40, GF60 and GF80 treatments significantly increased N use efficiency of early and late rice by 21.37%−57.16%. Simultaneously, GF40 treatment increased N agronomic efficiency (NAE) of early rice by 99.77%, and GF40, GF60 and GF80 treatments increased NAE of late rice by 20.61%, 22.88% and 17.17%, respectively. Furthermore, GF40, GF60 and GF80 treatments increased N partial factor productivity of early rice by 140.28%, 55.33%, and 23.09%. GF40 and GF60 treatments decreased grain nitrogen uptake by 21.16% and 11.43%, while GF80 treatment did not cause grain N decrease of early rice. GF40, GF60, and GF80 treatments significantly increased grain N uptake of late rice by 18.21%, 29.23% and 26.19%, respectively. GF40, GF60, and GF80 treatments significantly increased potential and total soil nitrogen supply capacity by 21.38%−316.31% and 18.50%−250.61% at the tillering stage, jointing stage, and booting stage of the early rice and maturity stage of late rice.

Conclusions Under rice-rice-Chinese milk vetch rotation system, reducing chemical fertilizer 20%–60% only in early rice could significantly increase soil nitrogen supply capacity during the early and late rice growth period, and significantly improve the N use efficiency, N agronomic efficiency and partial productivity, and sustained rice yield. Reducing chemical fertilizer 20% for early rice could significantly increase grain yield, maintained nitrogen uptake of early rice, and enhanced grain nitrogen uptake of late rice.