Nitrogen and Phosphorus Fertilization on a Long-Term No-Tillage Corn, Soybean, and Wheat Rotation


29 Apr 2016

2015 Annual Interpretive Summary

Continuous no-till corn–wheat-soybean crop rotations (three crops in two years) are common in the mid-Atlantic USA. Poultry litter (PL) can serve as a fertilizer source, however, N-based application rates of PL result in over-application of P relative to crop requirements. Addition of aluminum sulfate (alum) has shown to reduce water-soluble P in PL. A long-term study was established in VA in 2003 to determine impacts of PL fertilizer treatments on soil pH and Mehlich-1 extractable P (M1-P) over time and at depth in a no-till corn/wheat/soybean rotation. Experimental blocks were split and one side started in corn and the other side started in wheat/soybean in the first year of the rotation so that each crop would be present in every year of the study. Fertilizer treatments included a 0-P control, P applied via triple superphosphate based on soil test recommendations (TSP), and N-based applications of PL and PL amended with alum (PLA). Treatments were applied to the wheat and the corn crops in each year of the study.

Soil pH (0 to 5 cm) decreased in all treatments over time; however, trends showed PL and PLA had higher soil pH than the control and TSP treatments after 1 year. Soil pH at depth (averaged over treatments) indicated acidification of only the top 0 to 5 cm. Mehlich-1 P (0 to 5 cm) generally increased over time in PL and PLA, and was greater than no-fertilizer and TSP treatments (157, 141, 62, and 67 mg P/kg, respectively) in 2011 due to N-based manure applications. Concentrations of M1-P were also greater in PL and PLA than control and TSP treatments at the 5 to 15 cm depth, indicating P leaching. The 0-P control did not fall below 55 mg P/kg during the study indicating soils testing “Very High” in P may take 10+ years for additional P fertilizer to be beneficial for crop production.