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United States Department of Agriculture

Agricultural Research Service

Title: Evaluation of Some Phosphorus Index Criteria in Cultivated Agriculture in Clay Soils

Authors
item Torbert, Henry
item Harmel, Daren
item Potter, Kenneth
item Dozier, M. - TEXAS A&M UNIVERSITY

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 7, 2004
Publication Date: February 1, 2005
Citation: Torbert III, H.A., Harmel, R.D., Potter, K.N., Dozier, M. 2005. Evaluation of some phosphorus index criteria in cultivated agriculture in clay soils. Journal of Soil and Water Conservation. 60(1):21-29.

Interpretive Summary: There are growing concerns regarding the fate of nutrients from land application of animal waste. In recent years, P indices have been developed in most states to provide information regarding nutrient loss potentials from animal waste application. However, in many cases, these P indices have not been fully tested, especially in cultivated agriculture. A rainfall simulator was used to examine the impact of manure rate (4), manure incorporation, and soil slope (2) on runoff losses of P and N on heavy clay soils under cultivated agriculture. The four application rates were also applied to a grass pasture. Increased losses of dissolved N and P were observed with increasing litter application rate, but a large reduction in these losses were observed when litter was incorporated. However, increased soil slope did not impact the level of runoff losses of N and P. This indicates that for clay soils, care should be taken to not over ascribe changes in slope to the P index. The results from this study indicate that incorporation of the litter when applied to a field may have a large impact on reducing the amount of P and N lost in runoff.

Technical Abstract: There are growing concerns regarding the fate of nutrients from land application of animal waste. In recent years, P indices have been developed to provide information regarding nutrient loss potentials from animal waste application methods and topography. However, in many cases, these P indices have not been fully tested, especially in cultivated agriculture. Three factors commonly utilized in soil P indices for manure management are manure rate, manure incorporation, and soil slope. Rainfall simulations were conducted to examine the impact of these three factors on runoff losses of P on heavy clay soils under cultivated agriculture. Four manure litter application rates (0, 4.5, 9.0, and 13.5 Mg ha-1) were applied on two different soil slopes (5% and 9%) on a Heiden clay (fine, montmorillonitic, thermic Udic Chromusterts). The litter was surface applied to a corn (Zea mays L.) production area, with or without incorporation. The four application rates were also applied to a permanent Bermuda grass (Cynodon dactylon (L.) Pers.) pasture on a 5% slope. A rainfall simulator was used to generate water runoff for 30 minutes from 1.5 X 2.0 m plots. Runoff samples were analyzed for runoff volume, sediment, sediment N and P, soluble NH4-N, NO3-N and PO4-P. The results were analyzed using regression analysis techniques based on application rates. The soluble NO3-N concentration was not affected by either litter incorporation or soil slope in the cultivated sites, but was greatly increased with increasing litter application in the pasture sites. Increased losses of dissolved NH4-N and PO4-P were observed with increasing litter application rate, with a significant reduction in losses observed when litter was incorporated. However, increased soil slope did not significantly impact the level of runoff losses of NH4-N and PO4-P.

Last Modified: 8/27/2014
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