Assessment of Field Sectoral Grain Yield Using Soil Moisture, NDVI and Nutrient Dynamics in Northern Kazakhstan

A comparison of five agronomic management sectoral variants was conducted on a spring wheat field (rainfed farming) in Northern Kazakhstan to evaluate grain yield stability and its relationship with soil and crop conditions. Four experimental plots (without replication) involved the combined use of the SoilPoint Soil Booster (SPB) preparation and mineral nitrogen application at rates of 0, 2, 6, or 10 kg N/ha, alongside reduced herbicide application rates. The control plot (located at the field edge) received 20 kg N/ha without SPB application. Analysis of yield data, crop characteristics, results from three soil survey cycles, moisture sensor readings (one per SPB plot), and satellite NDVI data revealed four key findings. First, the SPB-N2 variant demonstrated the best results in terms of both total plot yield and sample cut data: the yield was 3.47 t/ha compared to 2.57 t/ha in the control (an increase of +35.0%). Secondly, the SPB-N2 variant recorded the highest average soil profile moisture index (40.31%), whereas the SPB-N10 variant showed the lowest (35.84%) and experienced the most significant decline in this indicator over the observation period (a drop of 21.29 percentage points). Thirdly, the plot with the highest yield was characterized by the lowest nitrate nitrogen content (13.6 mg/kg) based on the initial survey and did not exhibit the maximum NDVI value (0.37). The SPB-N10 variant had the highest NDVI (0.40) but demonstrated the lowest yield among the SPB-treated plots (3.09 t/ha). Fourthly, a zone of reduced yield was identified that cut across the boundaries of different treatment variants, indicating spatial heterogeneity within the field. Seasonal changes in nutrient content followed a specific pattern: levels of nitrate nitrogen, K₂O, sulfur, Mg, and Mn decreased across all variants. Collectively, these results identify the SPB-N2 variant as the most consistently productive and demonstrate that rankings based on average greenness indices and nitrate content (from the first survey) do not align with rankings based on grain yield. The lack of replication in the experimental design and the use of point measurements for soil moisture make it impossible to definitively attribute the results to the impact of specific agronomic practices or to the plot's general water-retention capacity. This study is relevant to ensuring food security (Goal 2)—given that Kazakhstan is a key grain producer in Central Asia—and to the study of ecosystem sustainability (Goal 15).