Submitted to: Annual Southern Conservation Tillage Conference for Sustainable Agriculture
Publication Type: Proceedings
Publication Acceptance Date: 7/10/2009
Publication Date: 7/20/2009
Citation: Endale, D.M., He, Z., Schomberg, H.H., Jenkins, M., Honeycutt, C.W. 2009. Total soil phosphorus zinc and copper concentrations as affected by long-term tillage and fertilization choices in a Cecil soil. Annual Southern Conservation Tillage Conference for Sustainable Agriculture. Interpretive Summary: Adoption of conservation tillage and use of animal waste as an alternative fertilizer source is increasing. The environmental consequences of the combination of these farm management choices needs to be thoroughly evaluated. Repeated long-term use of poultry litter (PL), an inexpensive alternative fertilizer source, can, for example, lead to elevated levels of nutrients in soils. Due to lack of incorporation, fertilizer application in no-till systems can also elevate nutrients in surface soils. Scientists from the USDA-ARS in Watkinsville, GA, and Orono, ME, monitored changes in total soil phosphorus (P), zinc (Zn) and copper (Cu) concentrations in a Cecil soil after 2, 5, 10 and 11 yrs of PL application under two tillage treatments (conventional tillage and no-till) and two fertilizer sources (conventional fertilizer and PL) in a cotton and corn production experiment each lasting 5 years. Application of 5 years of PL at an annual rate of 2 tons per acre based on crop Nitrogen requirement in a cotton-rye cover cropping system did not increase total soil P, Zn or Cu. While this is encouraging, the effect on longer term application of PL has not been established. A similar crop nitrogen requirement-based application of PL for corn (four years at 5 and one year at 10 tons per acre) however lead to substantial increases within the 0-6 in. soil depth, potentially increasing environmental risks from these nutrients. Corn has more than 2.5 times the nitrogen requirement of cotton. The results support the need for P-based application of PL in vulnerable soils and calls for continued longer term research to determine critical threshold values under combinations of different tillage and fertilization sources across regions. Producers, extension agents, local, state and federal agencies involved in enhancing sustainable agricultural practices through adoption of conservation tillage and poultry litter use would find these results useful.
Technical Abstract: Adoption of conservation tillage and use of animal waste as an alternative fertilizer source is increasing. The environmental consequences of the conbination of these farm management choices needs to be thoroughly evaluated. Poultry litter (PL) for example, while being an inexpensive and effective source of plant nutrients, could result in the buildup of phosphorus and heavy metals in soils when over applied. Changes in total soil P, Zn and Cu in a Cecil soil (fine, kaolinitic, thermic Typic Kanhapludults) were assessed after 2, 5, 10 and 11 yrs of PL application under two tillage treatments, conventional tillage (CT) and no-till (NT) and two fertilizer sources, conventional fertilizer (CF) and PL in a cotton (Gossypium hirsutum L.) and corn (Zea mays L.) production experiment at the USDA-ARS, J. Phil Campbell, Sr. Natural Resource Conservation Center in Watkinsville, Georgia. At the end of 5 years of the cotton phase, under an annual PL application rate of 2 tons/acre-1, concentrations of total soil P, Zn, and Cu did not increase. In Yr 10 (end of the corn phase), soil P, Zn and Cu concentrations increased approximately 1.5 to 3 times to 846, 50 and 42 lb/acre-1, respectively in the 0- to 6-in depth in NT, and 1116, 64, 54/lb acre-1, respectively, in PL treatments. Total P and Cu also increased in the 6- to 12-in depth with concentrations being approximately 1/2 times those in the in the 0-6 in depth. The increase was due to a 2 to 4 times greater input of P, Zn and Cu from PL fertilizer to meet the corn N requirement. The PL effect continued one year after the last PL application. In Yr 11, total P, Zn and Cu concentrations were much greater in the 0- to 1-in depth for NT and in the 0- to 1- and 1- to 2-in depths for PL. Changes with depth exhibited both linear and non-linear patterns based on treatment effects. The relationship between extractable and total P and Zn changed at a threshold value beyond which extractable P and Zn increased at more than double the initial rate. These results highlight the need to reevaluate the practice of PL application based on crop N requirement.