Analysis of Spatial Soil, Crop and Yield Data in a Winter Wheat Field

Abstract

In 2001 and 2002, soil and crop parameters were measured on a winter wheat field in Sauveniere, as part of a precision farming research project. One of the objectives was to study the processing of precision farming data for correct use in precision management. Different methods to study the relation between soil and crop were tested: correlation analysis, principal component analysis of soil parameters and clustering of soil and yield parameters. Crop and soil data were interpolated to a 6m grid and a 10 m grid to check the effect of grid size on the correlations between field data. Correlations were very similar for the 2 datasets, with slightly higher values for the 10 grid data (difference of 0 to 0.02 in correlation values). Grain and straw yield in 2001 were correlated to soluble phosphate, texture parameters, soil electrical conductivity, and potassium (coefficient of determination R² values up to 0.30 for grain yield). Crop optical measurements in May 2001 had lower correlation to soil parameters than yield (coefficient of determination R²= 0 to 0.18). Correlations were higher in March 2002, with coefficient of determination values up to 0.66 for optical mesurements. Correlation of grain yield to soil was very low in 2002, in part because of the incidence of eye spot disease. Principal component analysis of soil parameters resulted in three principal components describing the overall soil texture variation over the field, soil organic matter and soil nitrogen in early spring and acidity and phosphate variability. Correlations between yield and crop measurements and soil principal components were as expected from the correlation analysis. Clustering soil parameters resulted in soil zones that did not coincide with crop variability. Clustering yield and soil electrical conductivity did lead to zones that could be used to set up management zones. The average soil properties of these zones could be used to find parameters linked to yield variability and as a start to determine causes of variability in crop growth and yield, using a broader knowledgde on the soil-plant interaction. The grid size influenced the results of the analysis and should be further investigated, to determine the best methods for processing precision farming data. The soil data collected from the top 30 cm layer and the soil electrical conductivity only explain a limited part of variability in crop growth and yield. This means that either the top 30 cm was not representative of growth conditions or that other, non-measured soil parameters were important for crop growth. Root depth, water availability and soil compaction were probably important for the crop growth in 2001.