Different techniques to identify management zones impact nitrogen and phosphorus sampling variability

The efficiency of the management zone approach to improve fertilizer recommendations relies on accurately locating zone boundaries. The objective of this study was to determine the impact of different techniques of identifying management zones on soil NO3--N and Olsen-P (sodium bicarbonate extractable-P) sampling variability. Soil samples were collected on a 60 by 60 m or denser grid, in three fields (65, 53, and 40 ha). These samples were analyzed for NO3 -N and Olsen-P. Soil nutrient data was used to simulate the effect of different techniques to identify P and N management zone boundaries. Approaches evaluated for locating management zone sampling boundaries included: (i) sampling areas impacted by old homesteads or animals separately from the rest of the field, (ii) sampling different grid cells. (iii) use of geographic information systems (GIS) or cluster analysis to identify zones based on apparent electrical conductivity (EC) elevation, aspect, and distance (connectedness); and (iv) sampling each soil series separately. An F statistic was used to determine if the sampling approach reduced nutrient sampling variability. Results suggested that: (i) old homesteads or areas impacted by animals should be sampled separately from the rest of the field; (ii) grid-cell sampling was more consistent in reducing within zone soil-test variability than the other techniques tested; and (iii) zones that are not continuous should be sampled and managed separately.