EFFECTS OF TILLAGE, CROP-ROTATION AND NITROGEN-FERTILIZATION ON WHEAT-GRAIN QUALITY GROWN UNDER RAIN-FED MEDITERRANEAN CONDITIONS

The grain quality of wheat is influenced by the protein content, which in turn depends on environmental conditions and cropping practices. W e carried out a 3-year field study in a rainfed Mediterranean region o n the effects of tillage, crop rotation and nitrogen fertilization on the grain quality of hard red spring wheat (Triticum aestivum) in term s of protein content, test weight and alveogram indices. Tillage treat ments were no tillage (NT) and conventional tillage (CT). Crop rotatio ns were wheat-sunflower (Helianthus annus L.) (WS), wheat-chickpea (Ci cer arietinum L.) (WCP), wheat-fababean (Vicia faba L.) (WFB), wheat-f allow (WF) and continuous wheat (CW). Fertilizer nitrogen was used at three different rates: 50, 100 and 150 kg N ha(-1). A split-split plot design with four replicates was used. Grain protein content was found to be inversely proportional to rainfall during the growing season. T he tillage method was also found to affect grain protein content, test weight and some grain quality indices. Through its effect on moisture and nitrate in the soil. The crop rotations that included a legume (W CP and WFB) had marked effects on wheat quality. The increased grain p rotein content and resulted in improved rheological properties of the dough (viz. a higher alveogram index and a more balanced tenacity/exte nsibility ratio). However, no differences due to N dilution in the pla nt were observed in the wettest year studied, which was also the highe st yielding. Increasing the fertilizer N rate increased the grain prot ein content; this variable had the most marked influence on grain qual ity indices, though in the year that gave the highest yield the N dilu tion effect was observed. The many significant interactions among expe rimental variables reveal a close relationship among grain yield, prot ein content, grain quality and the wheat growth conditions. Specifical ly, the amount of rainfall and its distribution in the growing season strongly influenced N availability and uptake by the crop, as well as wheat-grain quality indices. (C) 1998 Elsevier Science B.V. All rights reserved.