Submitted to: Advances in Environmental Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2002
Publication Date: 1/1/2003
Citation: POTE, D.H., LORY, J.A., ZHANG, H. 2003. DOES INITIAL SOIL P LEVEL AFFECT WATER-EXTRACTABLE SOIL P RESPONSE TO APPLIED P? ADVANCES IN ENVIRONMENTAL RESEARCH. 7(2):503-509.
Interpretive Summary: In recent years, excessive growth of algae in many lakes, streams, and coastal waters has caused water-quality problems ranging from bad tastes and odors to toxic effects in fish, livestock, and people. Phosphorus (P) is an essential nutrient that algae obtain from the water, so the best way to control algae growth is often by decreasing P concentrations in runoff water. Previous studies have shown that heavy manure applications produce high P accumulation in agricultural soils and those high-P soils increase P concentrations in runoff. However these results have not shown that average P concentrations in watershed runoff will decrease if the manure is simply applied to lower-P soils instead of high-P soils within the same watershed. This research found that manure applications caused a greater increase in soil P when applied to high-P soil, so applying the manure only to lower-P soils should decrease P levels in watershed runoff. However, this research also indicated that such a strategy may not be beneficial at soil P levels above those tested in this experiment. Results of this research provide information for better management of manure applications to help control algae growth and improve the quality of water resources, so they are of interest to other scientists, extension agents, agricultural producers, and watershed managers.
Technical Abstract: Accelerated eutrophication of surface water is often caused by increased P concentrations in runoff. Previous studies indicate that high-P soils have increased P concentrations in field runoff, but have not provided sufficient evidence that overall water quality of a watershed will improve if manure applications are simply transferred from high-P soils to lower-P soils within the same watershed. If manure applications cause the same increase in soil P regardless of initial soil P level and the relationship between soil P and runoff P concentrations is linear, then such a strategy may only shift P loading from one part of the watershed to another. However, we hypothesized that added P causes a greater increase in soil P when applied to soil that is initially higher in soil P. To test this, P was applied (154 mg kg-1) as either poultry litter or inorganic phosphate to Captina soil from four sites where water- extractable soil P initially ranged from 8 to 69 mg kg-1. Soil moisture was returned to field capacity biweekly. After six-month and one-year equilibration times, each soil was analyzed again for water-extractable P, and soil P increases were correlated to initial soil P levels. All results supported our hypothesis, regardless of P source or equilibration time, but were best described by quadratic equations. Such curves suggest the hypothesis may not hold true for soils where water- extractable P levels are already above the range tested in this experiment.