Precision Farming Profitability Reference C Soil Sampling and

Precision Farming Profitability Reference C: Soil Sampling and Analysis By Sylvie Brouder, Mark Morgan

Figure 1. Strategies for collecting soil samples. Area composite sampling: soil test values represent an area. Precision Farming Profitability, p. 76

Figure 2. Strategies for collecting soil samples. Multiple core grid point sampling: Soil test values represent a point. Precision Farming Profitability, p. 76

Figure 3. Strategies for drawing input maps. With area sampling the application map will have uniform rates for each separately sampled area or zone. Rates may vary between neighboring areas or zones. . Precision Farming Profitability, p. 76

182 166 140 92 North (m) Soil Test K (ppm) 1 125 100 85 62 135 259 382 506 East (m) Figure 4. Strategies for drawing input maps. With point sampling, statistical programs are used to estimate the soil test levels in areas where cores were not collected. Application maps that vary rates within a grid unit can then be drawn. Alternatively, this contoured soil test map can be used to develop maps that apply the most appropriate uniform rate to a given grid unit. Precision Farming Profitability, p. 76 629

Figure 5. Moldboard plowing used to thoroughly mix the soil in the plow layer. Current tillage practices including chiseling allow nutrients to become highly concentrated in the surface soil. The result is that cores must be collected to a consistent depth or soil testing results will be inconsistent as shown in Table 1. Precision Farming Profitability, p. 77

Table 1. The effect of the depth of the core on the soil test values from fields that were moldboard plowed or chiseled. Soil Test P (Bray 1, ppm) Core Depth Precision Farming Profitability, p. 77 Plow Chisel Soil Test K (ppm) Plow Chisel

Whole Field Area = ~150 acres Figure 6. Initially sampled on a 2. 5 acre grid (area composite sample), similar adjacent grid units have been combined for resampling. The number of samples has been reduced from 56 to 33. Re-sampling “grid size” now ranges from 2. 5 to 15 acres Precision Farming Profitability, p. 79

Table 2. Acceptable commercial testing laboratory performance in Indiana for common soil tests. Precision Farming Profitability, p. 79