Soil phosphorus availability in no-till versus conventional tillage following freezing and thawing cycles

Abstract

Projected global warming may result in colder soil temperatures and a greater number of soil freezing and thawing cycles (FTC) during the winter in cool temperate and high-latitude regions. We evaluated the effects of seasons and repeated FTC on soil P availability in the topsoil of no-till (NT) and conventional tillage (CT) systems. In order to determine P availability during fall 2007 and spring 2008, soil samples (0-15 cm) were collected in both seasons from a long-term corn-soybean rotation experiment in plots that received 0, 17.5 and 35 kg P ha-1 and 160 kg N ha-1 every 2 yr since 1992. In addition, soil cores (0-5 cm) were collected in fall 2007 in plots that received 35 kg P ha-1 and 160 kg N ha-1 every 2 yr and were enriched or not with 2 g of soybean residues. Under controlled conditions, the cores were subjected to various FTC treatments, with each cycle consisting of 5 d of freezing and 5 d of thawing. The water-extractable P (Pw) and Mehlich 3 extractable P (PM3) contents were higher in soil samples collected in the spring compared with those collected the previous fall. After one and three FTC, Pw values averaged 17.4 mg kg-1 in NT and 7.5 mg kg-1 in CT and were not influenced by the addition of soybean residues. At the end of the sixth FTC, the Pw content of soil cores collected in NT increased up to 25.9 mg kg-1 with the addition of residues but decreased in the absence of residues. The effects of freezing and thawing on soil cores with crop residues occurred at the end of the sixth FTC, where PM3 in the NT + residues treatment increased twofold, reaching 100 mg P kg-1. These results confirm that both Pw and PM3 in NT can be enhanced by increasing the number of FTC.Key words: Global warming, freeze/thaw cycles, water-soluble phosphorus, phosphorus management, no-till