Accurate control of the production process of field crops, performed in the system of precision agriculture, means a spatially differentiated implementation of agrotechnical measures based on spectral measurements. The study of the optical properties of spring wheat crops under changing conditions of agricultural technology was carried out in a multifactorial microfield experiment at the Menkovsky branch of the Agrophysical Research Institute (Leningrad Region, Gatchinsky District). The experimental scheme included the study of the effect of sowing rates (5 and 6 million seeds per ha), doses of nitrogen fertilizers (0, 60 and 120 kg a.s. per ha) and weed infestation of experimental plots (natural background, application of herbicide). According to the research results, it was revealed that the optical properties of spring wheat crops are largely determined by the degree and type of weed infestation (8,5-48,1%), to a lesser extent – by the introduction of nitrogen fertilizers (2,7-21,6%). The influence of the sowing rate on the spectral characteristics of crop is insignificant (0,1-0,8%). Under the influence of herbicidal treatment and disposal of a significant part of the soil surface from weeds, a decrease in the NDVI index is noted (by 0,07-0,34); the introduction of nitrogen fertilizers influences the increase in the NDVI index (by 0,07-0,08 and 0,13-0,14 at N60 and N120, respectively), due to the growth of the aboveground mass of cultivated and weed plants. Against the background of herbicidal treatment, it is possible to correct the nutritional regime using nitrogen fertilizing and a sufficient forecast of the yield of spring wheat, based on the NDVI values for the stemming and earing phases, respectively. The obtained experimental data will become a framework for improving the theoretical and practical basis for using modern monitoring opportunities to substantiate ways to improve the efficiency of managing the state of soil-plant systems and the production process of grain crops in the North-West of the Russian Federation.
