Response Of Winter Oilseed Rape Growth To Water And Nitrogen Supply And Its UAV Multispectral Remote Sensing Monitoring Study

There is a shortage of agricultural water in Northwest China,and the application of fertilizer in this area is unreasonable and the utilization efficiency of fertilizer is low,which causes problems such as waste of resources and environmental pollution.In response to the above problems,a two-year field experiment was carried out,five nitrogen levels(N0:0kg/ha,N1:120 kg/ha,N2:200 kg/ha,N3:280 kg/ha,N4:360 kg/ha)and three irrigation levels(I0:no supplementary irrigation,I1:supplementary irrigation during overwintering stage,I2:supplementary irrigation during overwintering stage and budding stage)were set up.The physiological growth indicators,water and nutrient indicators and final grain quality and yield of winter oilseed rape were measured,meanwhile,the multi-spectral image was obtained at the same time with the field experiment.The study proposed a water-nitrogen application management scheme suitable for winter oilseed rape cultivation in the region,and realized small area remote sensing monitoring of crops growth.The main conclusions are as follows:(1)The effects of different water-nitrogen application combinations on physiological and growth indexes of winter oilseed rape were investigated.The physiological and growth indexes showed a trend of increasing first and then decreasing with the advancement of the growth period,reaching the maximum at the flowering stage,and then decreasing.Different nitrogen and irrigation levels had significant effects on the physiological growth indicators.Under the same irrigation levels,the physiological and growth indexes increased first and then decreased with the increase of nitrogen application,which reached the maximum at N2 or N3,and there was no significant difference between the two levels.Under the same nitrogen levels,the physiological growth indexes of winter oilseed rape reached the maximum under I2.(2)The patterns of water consumption,water and nitrogen utilization efficiency and nitrogen accumulation distribution in different organs of winter rapeseed under different water and nitrogen application levels were clarified.Under the same irrigation level,WUE and PUE reached the maximum under the N3,and there was no significant difference between the N2 and N3.Under the same nitrogen level,the water consumption of winter oilseed rape under I2 was higher than that of I1 and I0,but the WUE and PUE of the two years reached the maximum under I2.Nitrogen application rate had a significant effect on nitrogen accumulation and nitrogen use efficiency.The nitrogen accumulation,nitrogen agronomic efficiency and nitrogen physiological efficiency of winter oilseed rape reached the maximum at N2 or N3 levels,and there was no significant difference between N2 and N3 levels.(3)A comprehensive optimal water-nitrogen application management strategy for winter oilseed rape in the region that is conducive to high-quality,high-yield,high-efficiency and environmental protection was proposed.The seed yield of winter oilseed rape in both years reached the maximum under I2N3,which were 2460.40 kg/hm~2(2020-2021)and 2668.98 kg/hm~2(2021-2022),but both were not significantly different from I2N2 treatment.Based on entropy right TOPSIS method,the main quality and yield indexes of winter oilseed rape were evaluated.And the results showed that I2N2 processing score is the highest,which indicated that the combination of I2 irrigation level and N2 nitrogen application level is suitable for the water-nitrogen application of winter oilseed rape in Northwest China.(4)Estimation models of winter oilseed rape growth indicators based on multi-spectral data of canopy was established.The estimation accuracy of winter oilseed rape growth indicators based on PSO-SVM and GA-SVM was better than SVM and RF,and the estimation efficiency of PSO-SVM was higher than that of GA-SVM.The comprehensive comparison of estimation results showed that PSO-SVM was better for estimating growth indexes of winter oilseed rape at different growth stages.The estimation model was the best for the estimation of crop leaf area index,followed by aboveground biomass.Meanwhile,the estimation results showed that for the nutritional growth stage the estimation was better than that for the reproductive growth stage,in which the R~2of aboveground biomass,leaf area index and leaf water content validation set of winter rape based on PSO-SVM were 0.946,0.931 and 0.883,RMSE were 41.346 kg/ha,0.125 cm~2/cm~2and 0.077,and RPD were 3.921,3.795,and 2.334,respectively.