Effects of biochar on rice yield and nitrogen use efficiency in theNingxia Yellow River irrigation region

【Objectives】Nitrogen is a main nutrient required for crop growth and development. With the increased intensity of agricultural production in the Ningxia Yellow River irrigation region, nitrogen consumption has increased continuously, resulting in increasingly prominent problems such as soil compaction and low nitrogen utilization rates. In light of potential feasibility of biochar in improvement of soil and nitrogen utilization rate, effects of different biochar levels on rice yield and nitrogen utilization rates were investigated in field tests to provide a reference for biochar application in this region.【Methods】Representative intensive rice fields in Ningxia irrigated areaa were used in this study. The rice variety Ningjing No. 43 was used as the test material, and a split-plot experiment was performed. Two nitrogen application rates, conventional(N300, N300 kg/hm2)and no nitrogen application(N0), were employed, and four biochar levels, high(C3, 9000 kg/hm2), moderate(C2, 6750 kg/hm2), low(C1, 4500 kg/hm2)and no biochar(C0), were applied. The tests aimed to confirm impacts of biochar application on physical and chemical properties of anthropogenic-alluvial soil, rice yield, and nitrogen use efficiency. 【Results】1)The biochar application has no significant effect on the moisture contents of anthropogenic-alluvial soil after one rice planting season. The moisture contents of various soil layers under the same treatment are not significantly different. Soil pH values are also not changed significantly. 2)When the nitrogen fertilizer is applied, the C3 treatment significantly improves the total nitrogen, total phosphorus, and available potassium contents in anthropogenic-alluvial soil, and has no effect on the available phosphorus content, compared with the C0 treatment.The soil total nitrogen, total phosphorus, available potassium and available phosphorus in the C2 treatment are not significantly different from those in the C3 treatment, while the soil total nitrogen and available potassium of these two groups are significantly higher than the same variables in the C1 group. When fertilization is not performed, only the C3 and C2 treatments significantly increase the available potassium, and the other treatments have no effect on soil nutrient contents.3)The combined application of biochar(4500-9000 kg/hm2)and nitrogen fertilizer significantly increases the grain yield of rice, which is increased with the increase of biochar use amount, and the increased grain yields range from 15.26% to 44.89%. The grain yield of rice is significantly and positively correlated with the biochar application(r = 0.962). The plant height and grain number are also increased with the biochar application. Furthermore, the total nitrogen uptake in the aboveground parts of rice is increased with the biochar application, the C3 treatment increases the nitrogen uptake by 66.27 kg/hm2 over that of the C0 treatment, and significant differences are observed between the various treatment groups. When the nitrogen fertilizer is not used, the biochar addition(4500-9000 kg/hm2)has no significant effect on the grain yield of rice and the yield components of rice. The C1 and C2 treatments, but not the C3 treatment, significantly increase the total nitrogen uptakes in the aboveground parts of rice, and no significant differences are observed between the various carbon application groups. 4)Under the combined application of biochar and nitrogen fertilizer,both the agronomic efficiency and nitrogen use efficiency are increased with the biochar application.Compared to C0 treatment,the nitrogen agronomic efficiency increased by 10.87 kg/kg and nitrogen use efficiency by 22.09 percentage points in C3 treatment.【Conclusions】The combined application of biochar and nitrogen fertilizer can increase the rice yield in the Ningxia Yellow River irrigation region. In this experiment, the application of 9000 kg/hm2 biochar(C3)achieves the highest yield increase(44.89%). The plant height and grain number are also increased with the biochar application. The agronomic efficiency and nitrogen use efficiency are also increased with the biochar consumption.However, the biochar addition without the nitrogen application has no significant effect on the yield and yield components of rice.