On June 8, the Institute of Agricultural Resources and Regional Planning (IARRP) of the Chinese Academy of Agricultural Sciences (CAAS) organized experts to evaluate "the effect of fertilizer saving, quality improvement and synergy of winter green manure in south paddy fields".

The expert group of the appraisal meeting was composed of Professor Hu Feng from Nanjing Agricultural University, Professor Zhang Qiang from Shanxi Agricultural University, Professor Chai Qiang from Gansu Agricultural University, and researchers Tian Youguo and Du Sen from the National Agricultural Technology Extension Service Center.

Since 2008, with the support of the project of "Integrated Research and Demonstration of Green Manure Crop Production and Utilization Technology" (2008-2010, 2011-2015) and the China Agriculture Research System - Green Manure (2017-present), as well as IARRP and the relevant provinces (autonomous regions) in the south rice region, a total of more than ten scientific research and teaching units have jointly carried out large-scale experimental research on the green manure-rice production system.

The expert group believes that over the years, the project team has organized and carried out 38 joint positioning experiments in 14 experimental sites in eight provinces (districts) in the south rice area on issues such as the replacement of chemical fertilizers with green manure and the combined utilization effect of green manure and rice straw, accumulating a large amount of precious experimental data.

Through the research, the comprehensive effects of using winter green manure in rice fields in south China have been clarified. They include high and stable yields, fertilizer saving and land raising, and improvements in quality and efficiency, and provide important support for the use of green manure in China to reduce the volume of chemical fertilizers and increase efficiency in rice fields.

The main outcomes of the research are:

1. Clarification of the effects of use of winter green manure in south paddy fields, such as high and stable yields and efficient resource utilization.

Planting and incorporating winter green manure can achieve stable yield while saving nitrogen and replacing potassium by 40% in successive rice crops, and the utilization rate of nitrogen fertilizer and potassium fertilizer can be increased by 15.8 and 10.8 percentage points respectively. Averaged over many years, the rice yield of winter fallow-conventional application of chemical fertilizers (conventional control) was 6939 kg/hm2. After utilizing green manure, chemical fertilizer was moderately replaced, which can increase rice yield. Winter green manure compared with conventional nitrogen fertilizer and 20% reduction of nitrogen fertilizer led to yield increases of 5.7% and 3.8%, respectively, compared with the conventional control, and the corresponding nitrogen fertilizer use efficiency was increased by 7.8 and 12.6 percentage points. Winter green manure compared with conventional nitrogen and potassium fertilizer and 20% reduction of nitrogen and potassium fertilizer led to yield increases of 7.0% and 4.0%, respectively, compared with the conventional control, and the corresponding potassium fertilizer use efficiency increased by 22.1 and 20.5 percentage points.

2. Discovery of a technical path for winter green manure combined with chemical fertilizer to significantly improve the nutritional quality of rice

Under the combined application of winter green manure and chemical fertilizer, the content of total amino acids and essential amino acids in rice increased by 30.9% and 48.7%, respectively, compared with the conventional control.

3. Quantification of the effect of winter green manure on soil fertility improvement in paddy fields

The organic carbon and total nitrogen of paddy fields under the combined application of winter green manure and chemical fertilizer increased by 0.221 and 0.027 g/kg per year, respectively, compared with the conventional control. After use of green manure, compared with conventional nitrogen and potassium fertilizer and 20% reduction of nitrogen and potassium fertilizer, the content of soil-available potassium increased by 9.9 and 7.6 mg/kg compared with the conventional control.