Active Crop Canopy Sensor-based Precision Nitrogen Management Of Winter Wheat(Triticum Aestivum L.)and Rice(Dryza Sativa L.)

Over-application of nitrogen (N) fertilizers as well as improper timing are among the major problems for winter wheat and rice management in China, and have resulted in very low N use efficiencies (NUE) and high risk of environmental contamination. However, effective N nutritional status diagnosis methods and N fertilizer recommendation algorithms are lacking in practical production. In this study, we systematically evaluated the potential of Crop Circle ACS-470sensor with the configuration of NIR, red edge and green bands for estimating winter wheat and rice N status at critical growth stages, and developed this sensor-based precision N management strategy by conducting several site-years of field experiments. In addition, four years of fixed field experiments were conducted four years to evaluate different N management strategies for intensive winter wheat-summer maize double cropping system in North China Plain (NCP). The main results were concluded as follows:(1) Three years of winter wheat field experiments were conducted to evaluate the performance of Crop Circle ACS-470and GreenSeeker for estimating N status. The results indicated that Crop Circle CIRE and MSR_RE indices performed better for estimating biomass when biomass was above6000kg ha-1and Crop Circle CIG and MSR_G performed better for estimating plant N uptake when it was above130kg ha-1, as compared with GreenSeeker sensor. The Crop Circle ACS-470sensor had better performance for estimating plant N concentration and NNI than GreenSeeker. Across site-years, growth stages and varieties, the GRDVI performed consistently well for estimating NNI, with R2being0.78.(2) The Crop Circle CIG and the INSEY calculated with GRDVI could be used to estimate early-season plant N uptake and grain yield potential at Feekes growth stages4-7, with R2being0.87and0.61, respectively. The Crop Circle sensor-based N fertilizer recommendation algorithm was developed for winter wheat in NCP. Nine on-farm evaluation experiments indicated that this Crop Circle sensor-based precision N management strategy achieved similar grain yield as farmer’s practice, but significantly increased partial factor productivity of N fertilizer by59-74%.(3) The results of calibration experiments and on-farm validation experiments indicated that MCARI1had consistent correlations with rice aboveground biomass (R2=0.79) and plant N uptake (R2=0.83) across growth stages. It could overcome the saturation effect of GreenSeeker NDVI. Four red edge-based indices, RESAVI, MRESAVI, REDVI and RERDVI, performed equally well for estimating NNI across growth stages (R2=0.76). For rice plant N concentration, the highest R2was0.33, and none of the indices performed satisfactorily with validation using farmers’ field data.(4) The Crop Circle ACS-470sensor had better performance than GreenSeeker sensor for estimating rice yield potential and responsiveness to additional topdressing N application at stem elongation, booting, or heading stage. Based on these results, the Crop Circle sensor-based precision N management strategy was developed for rice according to the N fertilization optimization algorithm in Northeast China. (5) Four years of fixed field experiments were conducted to evaluate different N management strategies for the intensive winter wheat-summer maize double cropping system in NCR The N fertilizer rate determined with soil Nmin-based in-season root zoon N management (IRNM-soil Nmin), GreenSeeker-based precision N management (PNM-GS), green window-based in-season N management strategy (INM-GW) and regional optimum N management (RONM) were significantly reduced45%,62%,46%and40%compared to the farmer’s N practice (FNP), respectively, without significant change in grain yield. As a result, the IRNM-soil Nmin, PNM-GS, INM-GW and RONM increased N use efficiency, reduced N surplus, apparent N losses and GHG emission. In conclusion, the PNM-GS is the better strategy for winter wheat-summer maize double cropping system in NCP for improved NUE and reduced environmental contamination compared with other N management strategy in this study.