Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: November 30, 2000
Publication Date: November 1, 2000
Interpretive Summary: Large manure applications or continuous applications where nutrient removal by crops are minimal, will eventually result in a soil saturated with P where P runoff or leaching could present an environmental problem. Besides landscape position and climate, the reactive surfaces of the soil will determine its potential to sorb and desorb P. We studied sorption and release of P in a beef and a pig manure on an acid and a calcareous soil b using, along with soil tests, P adsorption isotherms to determine maximum P adsorption and the P buffering capacity (PBC) which is the soil's affinity to sorb P. While soil tests give a quick indication of levels of P, it does not address the soil's potential to sorb more P which is readily obtained by the PBC. Land managers can use the PBC as a guide for further manure application or implementation of best management practices to reduce P levels.
Technical Abstract: The potential for P removal from surface-applied manure and its subsequent transport into surface or ground water are dependent on a number of factors broadly defined under 1) P loss potential due to site and transport characteristics, and 2) P loss potential due to management and source characteristics. The first factor assesses P transported off the field with hrunoff, leaching, and drainage water, and the second, quantity, availability, and forms of P at the site and the likelihood that this soil P (manure, and other sources) can present an environmental hazzard. This report focuses on the P source (manure) and soil chemical characteristic as measured by fertility indices and sorption and release of P in semiarid soils. Beef and hog manures were subjected to various P availability extractants singly and in combination with soils of varying reactive clay surfaces. The data showed that over 2/3 of the manure-P is inorganic, and that the bulk of this P could be extracted by the Olsen or Bray-1 procedures. When added to soils, P incorporation with wetting and drying cycles resulted in greater sorption of P than broadcast and immediate extraction. Soils with CaCO3 also sorbed more P than non-calcareous soils. Where disposal is required, application of manure not to exceed 90% of the soil P saturation value (P buffering capacity ò 10) on deep calcareous soils followed by incorporation on relatively level ground should minimize soil P removal from the site.