Long-term effects of no tillage treatment on soil N availability, N uptake, and 15N-fertilizer recovery of durum wheat differ in relation to crop sequence

No tillage (NT) soil management has largely been promoted because of its potential to generate both economic and environmental benefits. However, it often leads to reductions in crop yield and quality, which in many cases have been attributed to the effects this technique has on the nitrogen (N) dynamics in the soil-plant system. This 2-year study, performed within a long-term experiment in which NT was continuously applied for over 15 years, aimed to verify whether and to what extent the use of NT affects soil N availability, recovery of 15N-labeled fertilizer, and N use efficiency (NUE) and its components (N uptake efficiency, NUpE; N utilization efficiency, NUtE). Durum wheat was the focal crop. NT was evaluated and compared with conventional tillage (CT) within three crop sequences: continuous wheat (WW), wheat-faba bean (WF), and wheat-berseem clover (WB). At the same time, the timing of N fertilization was varied (either distributing 100 kg N ha-1 all at once at crop emergence or applying 50% at crop emergence and 50% at the end of tillering, no N-fertilizer treatment was included as a control). The data indicated that, compared to CT, NT had a detrimental effect on wheat productivity in WW but improved yields in WF and WB. NT was associated with less N uptake by wheat, mainly attributable to a decrease in soil N availability, and to a lesser extent, to a decrease in the 15N-fertilizer recovery. This reduction in uptake was markedly more evident in WW than in WF or WB, and when all of the 15N-fertilizer was applied at crop emergence. The effects of tillage system on NUE varied by crop sequence: NT increased NUE (+18% on average compared to CT) in WF, but had the opposite effect in WW (-17% on average). These results suggest that the adoption of the NT technique by farmers must be accompanied by a reorganization of the components of crop management, such as crop rotation and the rate and timing of N fertilization.