Effects of Tillage on Phosphorus Release Potential in a Spanish Vertisol
- Concepción Saavedra,
- Juan Velasco,
- Purificación Pajuelo,
- Francisco Perea and
- Antonio Delgado *
No-till (NT) practices usually increase the P content in soil surfaces. The main purpose of this work was to study the long-term effects of the soil tillage system on the P release potential in the surface layer of a Vertisol from southwest Spain and to correlate it with changes in P content and forms. The three tillage treatments investigated were: (i) conventional tillage (CT) with a moldboard plow and field cultivator; (ii) minimum tillage (MT) with a field cultivator; and (iii) NT, which involved direct sowing into crop residue from the previous year. After 21 yr, NT resulted in enhanced organic matter, Olsen P, organic P, and total P contents relative to CT and MT in the top 5 cm of soil. The ratio of labile inorganic P fractions to P related to sparingly soluble pedogenic Ca phosphates in the surface soil layer was much greater under NT (0.8) than under CT (0.57) or MT (0.55). This was ascribed to a decreased precipitation of sparingly soluble Ca phosphate because of the enrichment in organic matter under NT, and accounted in part for the higher portion of inorganic P related to labile fractions in NT (0.19 vs. 0.09 in CT and 0.10 in MT). The increased P release potential of surface soil as estimated by using P sinks indicated that an increased dissolved P concentration in runoff and a greater amount of potentially releasable P per unit mass of surface soil lost through erosive processes can be expected with NT than with MT or CT.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
Copyright © 2007. Soil Science Society of America