Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: Changes in Extractable Phosphorus in Amended Soils During a Growing Season

Authors
item SCHWARTZ, ROBERT
item Bell, Jourdan

Submitted to: Proceedings Great Plains Soil Fertility Conference
Publication Type: Proceedings
Publication Acceptance Date: March 1, 2006
Publication Date: March 1, 2006
Citation: Schwartz, R.C., Bell, J.M. 2006. Changes in extractable phosphorus in amended soils during a growing season. In: Proceedings Great Plains Soil Fertility Conference, March 7-8, 2006, Denver, Colorado. p. 257-263.

Interpretive Summary: Soils are most often the resource used in the final assimilation of many agricultural waste products. Manure and synthetic fertilizer vary in their contributions to soluble and extractable forms of P when applied to soils. Knowledge of these source and soil-dependent effects is required for planning fertilizer applications so that soil test P remains below threshold levels. Our objective was to evaluate changes in Mehlich 3 soil test P and water extractable P in soils amended with cattle manure and monoammonium phosphate (MAP) throughout a sorghum growing season. Soil test P and water extractable P increased immediately after fertilizer applications and began to decline 15 weeks after sorghum planting. At a soil test P level of 161 mg kg-1, water extractable–P averaged 39% greater for MAP amended as compared to manure amended plots. This fertilizer source dependency would limit the use of the Mehlich 3 extractant in making satisfactory P loss vulnerability assessments.

Technical Abstract: Recent studies indicate that soil extractable P and P in runoff are greatest immediately after fertilizer and manure applications. Our objective was to evaluate changes in Mehlich 3– and water– extractable P in soils amended with cattle (Bos taurus) manure and monoammonium phosphate (MAP) throughout a single growing season. Cattle manure and MAP were applied at a rate of 184 and 300 kg P ha-1, respectively, on a Pullman clay loam (Fine, mixed, superactive, thermic Torrertic Paleustoll). Unfertilized checks were included for P extractability comparisons. Grain sorghum (Sorghum bicolor (L.) Moench) was planted after fertilizer applications and received supplemental irrigation (180 mm). Soil samples (0-150 mm) were collected prior to fertilizer applications and periodically throughout the growing season. Changes in Mehlich 3– and water– extractable P with time exhibited a rapid initial increase after fertilizer applications followed by seasonal fluctuations and a decline 15 weeks after planting. Because of higher P applications rates, MAP –amended plots exhibited greater Mehlich 3 and water P extractabilities as compared to manure amended plots. However, at an average Mehlich 3–extractable P level of 161 mg kg-1, water extractable–P averaged 39% greater (P<0.05) for MAP amended as compared to manure amended plots. This fertilizer source dependency would limit the use of the Mehlich 3 extractant in making satisfactory P loss vulnerability assessments.

Last Modified: 9/29/2014
Footer Content Back to Top of Page