Soil Sampling for Fertilizer Recommendations in Conservation Tillage with Paratill Subsoiling

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Shallow sampling depths are recommended for collecting soil samples for lime and fertilizer recommendations when using conservation tillage. Some subsoiling implements used to disrupt the compacted horizon in some southeastern USA coastal plain soils can also disturb the surface soil. Our objective was to compare sampling depths for lime, P, and K recommendations in a conservation tillage system that includes paratill subsoiling. One-half of a 14-acre field was managed with conventional tillage. The other half was managed with conservation tillage which consisted of using a six-shanked paratill followed by planting. Soil samples from 0 to 3 inches and 0 to 6 inches were collected for four years on each side of the field around points in a 50-ft × 50-ft grid. The field was in a corn (Zea mays L.)-cotton (Gossypium hirsutem L.) rotation. Soil P and K concentrations differed for sampling depths in most years for both tillage systems. Generally, these differences were small but fertilizer P and K recommendation rates for the two sampling depths were the same more often for conventional tillage than for conservation tillage. After a lime application in 2002, pH of the soil 0 to 3-inch depth in the conservation tillage half of the field was 5.89 in 2003, 6.07 in 2004, and 6.29 in 2005 while the pH of the soil collected from the 0 to 6-inch depth was about 6.1 each year. When using the 0 to 6-inch sampling depth in fields managed with this conservation tillage system, it appears a separate sample for soil pH from a shallower depth may be beneficial in the years subsequent to a lime application.