Blended controlled-release nitrogen fertilizer with straw returning improved soil nitrogen availability, soil microbial community, and root morphology of wheat

Microbial activities and nitrogen (N) availability in soil directly affect root morphology and consequently crop yield. These relationships are even more critical at the filling stage of wheat due to the grain formation. The objective of this study was to compare effects of blended controlled-release N fertilizer (CRFS) and conventional urea (BBFS) on soil microflora, soil N content, and root growth of wheat at the filling stage in a field with straw return for seven years. The method of 16 s rRNA and ITS high-throughput sequencing was used to probe soil microbial status, and the in-situ root scanner was used for in-situ observation and monitoring of wheat root morphology during two growing seasons. The results showed that CRFS increased the relative abundance of Penicillium and Aspergillus fungal genera and reduced the operational taxonomic unit of nitrifying bacteria of the genus Nitrospira compared to BBFS treatment. Nitrate, ammonium, total N, and organic matter in soils treated CRFS were 15.8 %, 10 %, 7.5 %, and 11.6 % higher than these in soils treated with BBFS, respectively, while the total root length, root surface area, and root volume from CRFS treatment were 57.6%, 48.8 %, and 54.1 % higher than these from BBFS, respectively. Above-ground growth of wheat showed that CRFS increased plant height by 5.8-12.6 %, net photosynthetic rate by 13.5-22.2 %, N content of stems and spikes by 10.0 % and 64.1 %, respectively compared to BBFS. Wheat yield and economic efficiency were increased by 9.9-46.8 %, 11.6-41.7 %, respectively with CRFS treatments than these with BBFS treatments. Wheat received reduced application rate (2/3) of CRFS had similar availability of N and plant growth as the full rate of BBFS. Therefore, using blended controlled-release N fertilizer is a practically and environmentally feasible approach for wheat production in the straw retuning wheat-corn rotation system.