Paecilomyces variotii Extracts and Controlled-Release Urea Synergistically Increased Nitrogen Use Efficiency and Rice Yield

A novel biostimulant, Paecilomyces variotii extracts (ZNC), with the ability to promote N absorption in the plant at a very low level has been proved in the lab experiment, but its chemical composition and practical effect in the field remain unclear. In this work, we determined the molecular composition of ZNC. Then, a three-year field experiment was conducted to investigate the synergistic effects of controlled-release urea (CRU) without ZNC or with ZNC at three doses (87.5, 175, and 262.5 mL ha(-1)) on the yield, nitrogen use efficiency (NUE), and net returns of rice. Results indicated that ZNC contained more carbohydrates, amino acids, alkyl structures, and less aromatic structures with a molecular weight between 140 and 2507 Da. Rice yield was 6.9-21.0% higher with CRU than with conventional urea. Combining CRU with ZNC at a dose of 87.5 mL ha(-1) performed the best and significantly increased rice yields by 8.7-12.1%, NUE by 15.0-20.2%, and average net returns by 10.9-15.4% during three rice-growing seasons compared to the application of CRU only, which is attributed to the positively increasing panicles and N uptake of rice. With the increased dose of ZNC, the yield of rice showed a decreasing trend, but the yield was still higher/not significant than the CFF treatment without ZNC. Therefore, the planting patterns with the combination of CRU and biostimulant are an efficient way to increase the rice grain yield and net returns.