Yield‐Based Management Zones and Grid Sampling Strategies: Describing Soil Test and Nutrient Variability

tial variability of soil fertility parameters. The grid cell method represents an area in which multiple cores are Alternatives such as yield-based management zones may solve collected and thoroughly mixed together to form a comproblems associated with grid soil sampling while effectively describing soil test and nutrient variability. The main objective was to delin- posite sample. The grid center method represents apoint, eate yield-based management zones using multiyear yield data and typically the center of a grid cell, in which multiple cores compare them with whole-field average and grid soil-sampling meth- are collected near the point to form a composite sample ods to determine the most effective strategy for describing soil test (Kuhar,1997;BrouderandMorgan,2000). Astudycomand nutrient variability. Research was conducted in four continuous paring these two grid sampling methods found that the no-till fields that had varied cropping histories and yield monitor data grid center method paired with an interpolation techforatleast3yrfrom1996through2000.Fouryield-basedmanagement nique such as kriging or inverse distance weighting exzone methods, (i) mean normalized yield map (MNY), (ii) coefficient plained more soil test P and K variability than the grid of variation map (CVM), (iii) MNY CVM, and (iv) yield region map cell method (Wollenhaupt et al., 1994). (YRM),wereevaluated. Threegridsoil-samplingstrategies,(i) gridcell, Besides determining which grid sampling method to (ii) grid center, and (iii) grid center with kriging at two sampling distances (68 and 98 m), were also tested. Grid cell sampling consistently use, there are other problems a grower must resolve becapturedmoresoiltestandnutrientvariabilitythanthegridcenterand fore grid soil sampling can be implemented on-farm. grid center with kriging methods. Of the yield-based management zone The first problem is how to determine the proper grid strategies, YRM was the most effective and in all four fields explained size to use in a given field. A study by Wollenhaupt more soil test and nutrient variability compared with the whole-field et al. (1994) in Wisconsin found that grid sampling on average approach. Yield region map also performed better than or a 98-m grid described up to 69% of soil test P and up similar to the 98-m grid center and 98-m grid center with kriging strate- to 97% of soil test K variability in two fields. They gies. When the field had low soil test values, YRM was also nearly further reported that by decreasing the grid size, larger as effective in capturing nutrient recommendation variability as the percentages of the variability in soil test P and K could 98-m grid cell method. However, compared with all other strategies, be captured. Franzen and Peck (1995) showed that to the 68-m grid cell method was the most effective way to describe soil test and nutrient variability. correctly capture the spatial variability in pH, P, and K of an Illinois field, soil samples needed to be taken on a 68-m grid. These studies demonstrate that no single grid size is applicable for all fields and that as the vari