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Title: Stratification of phosphorus forms from long-term conservation tillage and poultry litter application

item CADE-MENUN, BARBARA - Agri Food - Canada
item He, Zhongqi
item ZHANG, HAILIN - Oklahoma State University
item Endale, Dinku
item Schomberg, Harry
item LIU, COREY - Stanford University

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2015
Publication Date: 3/13/2015
Citation: Cade-Menun, B.J., He, Z., Zhang, H., Endale, D.M., Schomberg, H.H., Liu, C.W. 2015. Stratification of phosphorus forms from long-term conservation tillage and poultry litter application. Soil Science Society of America Journal. 79:504-516.

Interpretive Summary: Cecil and related soils occupy over half of the 16.7 million hectare Southern Piedmont in the southeastern USA. Row crop (such as cotton and corn) agriculture with a long history of tillage has exacerbated erosion in the region. To reduce erosion from tillage, conservation tillage practices such as no-till have been introduced in the Southern Piedmont. Poultry litter is abundant in the Southern Piedmont region, as more than half of the broiler poultry produced in the USA come from there. In light of concerns about the forms of P accumulating in Cecil soils from long-term poultry litter application, and the potential for these P forms to become stratified with long-term zero tillage, this study characterized the P forms in the different layers of Cecil soils from a long-term tillage study. The distribution of cations in these extracts and in the final residue was also determined to further understand the factors controlling the distribution of P forms in these soils. Data showed stratification of P in tilled soils fertilized with poultry litter, but not in tilled soils receiving chemical fertilizer, suggesting that poultry litter is more difficult to mix into the soil with tillage than chemical fertilizer. Thus, methods must be developed to reduce nutrient stratification, either by occasional tillage under zero-till or injecting P fertilizers into subsoil under zero-till.

Technical Abstract: Phosphorus (P) stratification leaves high P concentrations at the soil surface, which are vulnerable to loss in runoff. Understanding P forms at the soil surface may help control P loss, but little information is available on how P forms stratify in soil. We used 31P-nuclear magnetic resonance spectroscopy (31P-NMR) and chemical analysis to characterize P forms and the elements controlling P cycling in Cecil soil that became P stratified after 11 years of cropping management conducted under combinations of tillage (conventional and no-till, CT and NT) and inorganic(CF) and poultry litter (PL) fertilization. Samples from three soil depths (0–2.5, 2.5–5 and 5–15 cm) were sequentially extracted in NaOH-EDTA (NE) and HCl prior to 31P-NMR. The NE recovered 63-83% of total P in a range of P forms; HCl recovered 2-16% of total P, mainly orthophosphate. Phosphorus forms and concentrations were evenly distributed through soil only in the CT treatment with CF. Stratification of orthophosphate and phytate occurred in NT samples fertilized with PL and CT, with the highest concentrations in the top 2.5 cm. Increased orthophosphate and phytate concentrations were detected at the soil surface for CT/PL samples, indicating PL is not as well mixed by tillage as CF. These results show that P fertilizers should be placed below the soil surface under no-till, to reduce potential P loss in surface runoff.