Factors of intra-field phytomass variability in steppe agricultural landscapes of Kazakhstan

Abstract

The yield of grain crops and its predictability largely depends on the intra-field heterogeneity of landscape conditions. We used the example of steppe agricultural landscapes in the Akmola region to solve the following objectives: 1) to evaluate the informative value of NDVI for assessing yield depending on hydrothermal conditions; 2) to determine the effect of intra-field patchiness on NDVI values and yield; 3) to determine the dependence of intra-field variation of phytomass on the tract and facies structure and hydrothermal conditions. We used data on wheat and barley yields and intra-field NDVI variability in 80 field plots in 2009‒2013, data on the tract and facies structure, and hydrothermal parameters. We studied the relationships between spatial and temporal variability of phytomass, landscape and hydrothermal factors by means of correlation and variance analysis. It was established that NDVI was only partially informative for direct assessment of grain yield. The index values for July dates better reflect the yield than in June and August. The hypothesis that NDVI patchiness in the field area depends on the cultivated crop was not confirmed. The yield in fields with complex facies structure is usually lower than in homogeneous fields. In dry years, the intrafield variation of phytomass is less pronounced than in wet years. The proximity to the hill is a significant factor that increases the spatial variability of phytomass due to the additional introduction of moisture and sediment along the rills. High facies patchiness either reduces yield or increases its temporal variability and reduces predictability.