Stability of spatial variability of wheat and maize biomass in a small field managed under two contrasting tillage systems over 3 years

Abstract

Site-specific management of fields based on spatial variability should reduce the total input of chemicals and reduce their negative effects on the environment. The objective of this study was to determine whether spatial variability of crop biomass in a small field (0.25 ha) is stable over several years, and whether site-specific management can be applied to the field. We examined the pattern of spatial variability of above-ground biomass of wheat and maize for 3 years. The field was divided into two plots. One plot was minimum-tilled (MT) with a rotary tiller and the other was conventionally tilled (CT) with a moldboard plow and disc-harrows. Above-ground biomass was measured at harvest at 100 locations on a 2.5 m×5 m spacing in each plot. For the analysis of spatial variability patterns, the raw data were divided into trends (large-scale structure) and residuals (small-scale structure) by median polishing. Comparison among trends showed that the spatial variability pattern was stable only in conventionally tilled (CT) maize over the 3 years. This result suggests the possibility of site-specific management based on prior knowledge. Wheat and maize tended to show inverse spatial variability patterns in trends. The trends in wheat were considered to reflect the variability among rows, suggesting the opportunity for post-emergence, site-specific management along the direction of field management. The residual data, on the other hand, showed no significant correlation among sampling locations. Semivariograms based on the residual data showed that the range of spatial correlation of biomass was not clearly larger than 2.5 m, which was the distance between rows. Therefore, site-specific management based on the residual data is difficult because of the weak spatial dependence and the lack of temporal stability.