Switching from conventional tillage to no-tillage: Soil N availability, N uptake,15N fertilizer recovery, and grain yield of durum wheat

This 2-year study, performed in a typical Mediterranean environment on three soil types (two Inceptisols and one Vertisol), aimed to improve understanding of the factors that play a major role in determining crop response when soil management shifts from conventional tillage (CT) to no-tillage (NT). The effects of NT on the soil nitrogen (N) availability, N uptake,15N fertilizer recovery, and grain yield of durum wheat were evaluated in comparison to CT under five different N fertilization rates (0, 40, 80, 120, and 160 kg N ha−1). Compared to CT, NT negatively affected grain yield in one of the two years but only in the two Inceptisols. On average, a considerable grain yield advantage of CT over NT (approximately +0.6 Mg ha−1of grain) was observed with no N fertilization. This benefit decreased progressively when N fertilizer rate increased to the point that at 120 kg ha−1of N applied differences between CT and NT were negligible. The differences between the two tillage systems in both grain yield and N uptake were attributable more to differences in the native soil mineral N (that materialized already during the vegetative phase of the crop cycle) than to differences between CT plants and NT plants in efficiency in taking up N from fertilizer. The differences between CT and NT for many of the traits observed in durum wheat plants increased with decreasing soil fertility and in particular with decreasing soil total N. In conclusion, the shift from CT to NT, which should be accompanied in any case by an increase in the N fertilization rate to take into account the reduction in soil N available for the crop, was less problematic in the Vertisol, which is more fertile and better structured than the two Inceptisols.