Long term effects of tillage practices and N fertilization in rainfed Mediterranean cropping systems: durum wheat, sunflower and maize grain yield

Abstaract Long term investigations on the combined effects of tillage systems and other agronomic practices suchas mineral N fertilization under Mediterranean conditions on durum wheat are very scanty and findingsare often contradictory. Moreover, no studies are available on the long term effect of the adoption of con-servation tillage on grain yield of maize and sunflower grown in rotation with durum wheat under rainfedMediterranean conditions. This paper reports the results of a 20-years experiment on a durum wheat-sunflower (7 years) and durum wheat–maize (13 years) two-year rotation, whose main objective wasto quantify the long term effects of different tillage practices (CT = conventional tillage; MT = minimumtillage; NT = no tillage) combined with different nitrogen fertilizer rates (N0, N1, N2 corresponding to 0,45 and 90 kg N ha−1for sunflower, and 0, 90 and 180 kg N ha−1for wheat and maize) on grain yield, yieldcomponents and yield stability for the three crops. In addition, the influence of meteorological factorson the interannual variability of studied variables was also assessed. For durum wheat, NT did not allowsubstantial yield benefits leading to comparable yields with respect to CT in ten out of twenty years. Forboth sunflower and maize, NT under rainfed conditions was not a viable options, because of the unsuit-able (i.e., too wet) soil conditions of the clayish soil at sowing. Both spring crops performed well with MT.No significant N × tillage interaction was found for the three crops. As expected, the response of durumwheat and maize grain yield to N was remarkable, while sunflower grain yield was not significantlyinfluenced by N rate. Wheat yield was constrained by high temperatures in January during tillering anddrought in April during heading. The interannual yield variability of sunflower was mainly associatedto soil water deficit at flowering and air temperature during seed filling. Heavy rains during this latterphase strongly constrained sunflower grain yield. Maize grain yield was negatively affected by high tem-peratures in June and drought in July, this latter factor was particularly important in the fertilized maize.Considering both yield and yield stability, durum wheat and sunflower performed better under MT andN1 while maize performed better under both CT and MT and with N2 rates. The results of this long termstudy are suitable for supporting policies on sustainable Mediterranean rainfed cropping systems andalso for cropping system modelling