SUNFLOWER AND SOIL RESPONSE TO SEVEN YEARS OF TILLAGE, RESIDUE MANAGEMENT AND NITROGEN FERTILIZER

A 7-years (2006-2012) field study was carried out at the research station of Baikola, Neka, Iran; the experiment included treatments varying in: (1) wheat straw management: plus residue (+R) and minus residue (-R); (2) tillage system: zero tillage (ZT) and conventional tillage (CT); and (3) Nitrogen rates: 0 (control), 80, 160 and 240 kg N ha(-1) (N1-N4). After 7 years of continuous practice, ZT+RN4 and ZTR+RN3 had the best soil quality and produced the highest sunflower yields of average 2010-2012 (5250 and 5150 kg ha(-1), respectively). Removing the residues, i.e. treatments ZT-RN1 (average 2010-2012: 2150 kg ha(-1)), gave the lowest yields and less favorable soil physical and chemical characteristics compared to the other practices. Organic C, total N, moisture, aggregates stability, mechanical resistance, pH and EC were the factors that defined the difference in soil quality between conventional tillage and zero tillage. The principal component combining the variables organic C, total N, aggregate stability and moisture content showed the highest correlations with final seed yield (R = 0.87 for sunflower). The findings suggest that ZT+R together with nitrogen fertilization would improve some soil properties, crop production and may also be better for the sustainability of high crop production.