Spatiotemporal Analysis of Rice Yield Variability in California

Agricultural producers and researchers have been aware of spatial and temporal yield variability for a long time (Mercer and Hall 1911, Lark and Stafford 1997, Lowenberg-DeBoer et al. 1997). Most farmers recognize that spatial variability in yield exists when they harvest. However, this knowledge is generally of an informal, anecdotal nature, which must be made more precise if it is to be used effectively in precision agriculture. Currently, we know little about the spatial structure neither of these yields patterns, nor of the consistency of these patterns from year to year (Jaynes and Colvin 1997). The consistency of the spatial and temporal structure of crop yield across the field needs to be investigated before implementing any management strategy. The stability of the spatial structure over time will indicate whether the same physical and ecological processes are controlling yield from year to year. Lack of temporal stability of the spatial structure may indicate that the factors controlling yield are dynamic. In this project we describe yield spatial and temporal structure of a rice field in California. Three general questions are addressed: First, how much spatial variability in yield is present in both systems and how is this variability structured? Second, how stable are the patterns of variability through time? Third, what are the underlying factors causing these patterns? This paper describes initial results of this research effort. Yield spatial structure is assumed to consist of a large-scale deterministic structure or trend and a small-scale stochastic structure (Cressie 1993). Quantification of these structures allows us to determine if there is significant spatial yield variability in California and how this variability is structured.