Submitted to: Crop Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2007
Publication Date: 2/18/2008
Citation: Bauer, P.J., Frederick, J.R., Busscher, W.J., Novak, J.M., Fortnum, B.A. 2008. Soil sampling for fertilizer recommendations in conservation tillage with paratill subsoiling. Crop Management doi:10.1094/CM-2008-0218-01-RS. Interpretive Summary: Soil sampling is critical for correct fertilizer application recommendations. We conducted this research to determine if changes in sampling depth were needed when farmers use a paratill subsoiler to reduce soil compaction in a conservation tillage system. We found that for phosphorus and potassium, either of two sampling depths (0 – 3-inches or 0 – 6-inches) could be used with relative confidence. When using the 0 – 6-inch depth for recommendations for these two nutrients, it appears a separate sample for soil pH from a shallower depth may be beneficial in the years subsequent to a lime application for lime recommendations. This information will be used by growers, extension agents, and crop consultants in managing fertilizer and lime applications on fields managed with conservation tillage.
Technical Abstract: 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 soil horizon in the southeastern USA coastal plain 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 – 3-inches and 0 – 6-inches were collected for four years on each side of the field around points in a 50-ft X 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. After a lime application in 2002, pH of the soil 0 – 3-inch depth was approximately 5.9 units in 2003, 6.1 units in 2004, and 6.3 units in 2005 while the pH of the soil collected from the 0 – 6-inch depth was 6.1 units each year. The results suggest that either sampling depth can be used with relative confidence for conservation tillage systems that include paratill subsoiling for P and K recommendations. When using the 0 – 6-inch depth, it appears a separate sample for soil pH from a shallower depth may be beneficial in the years subsequent to a lime application.