Conservation tillage induced changes in organic carbon, total nitrogen and available phosphorus in a semi-arid alkaline subtropical soil

A multi-year experiment was conducted to compare the effects of conservation tillage (no-till and ridge-till) with conventional plow tillage on organic C, N, and resin-extractable P in an alkaline semi-arid subtropical soil (Hidalgo sandy clay loam, a fine-loamy, mixed, hyperthermic Typic Calciustoll) at Weslaco, TX (26890N 978570W). Tillage comparisons were established on irrigated plots in 1992 as a randomized block design with four replications. Soil samples were collected for analyses 1 month before cotton planting of the eighth year of annual cotton (planted in March) followed by corn (planted in August). No-till resulted in significantly ðp < 0:01Þ greater soil organic C in the top 4 cm of soil, where the organic C concentration was 58% greater than in the top 4 cm of the plow-till treatment. In the 4–8 cm depth, organic C was 15% greater than the plowtill control. The differences were relatively modest, but consistent with organic C gains observed in hot climates where conservation tillage has been adopted. Higher concentrations of total soil N occurred in the same treatments, however a significant ðp < 0:01Þ reduction in N was detected below 12 cm in the ridge-till treatment. The relatively low amount of readily oxidizable C (ROC) in all tillage treatments suggests that much of the soil organic C gained is humic in nature which would be expected to improve C sequestration in this soil. Against the background of improved soil organic C and N, bicarbonate extractable P was greater in the top 8 cm of soil. Some of the improvement, however, appeared to come from a redistribution or ‘‘mining’’ of P at lower soil depths. The results indicate that stratification and redistribution of nutrients were consistent with known effects of tillage modification and that slow improvements in soil fertility are being realized. Published by Elsevier Science B.V.