Responses of agronomic components of rapeseed (Brassica napus L.) as influenced by deficit irrigation, water salinity and planting method

Shortage and salinity of irrigation water are two major constraints that influence rapeseed production in arid and semi-arid regions of central and southern Iran. In this study, effects of deficit irrigation with different salinity levels and planting methods (in-furrow and on-ridge) as strategies for coping with water and salinity stresses on yield and yield quality of rapeseed were investigated in a two-year experiment. Irrigation treatments consisted of full irrigation (FI), 0.75 FI and 0.50 FI in first year and FI, 0.65 FI and 0.35 FI in second year and salinity levels of irrigation water were 0.6 (well water), 4.0, 7.0 and 10.0 dS m(-1) in first year and 0.6, 4.0, 8.0 and 12.0 dS m(-1) in second year. In 0.75 FI and 0.5 FI irrigation treatments, seed yield reduced by 15.0 and 25.9%, respectively and in 0.65 FI and 0.35 FI it decreased by 20.8 and 33.0% relative to FI, respectively. Planting in-furrow increased yield by 5.3 and 13.7%, respectively, in first and second year (with frost occurrence in dormant period in second year) relative to on-ridge planting. Deficit irrigation and salinity decreased dry matter, plant height, seed oil content, oil and protein yields and 1000-seed weight in both years. Results indicated that 11.0, 13.1 and 11.8% deficit irrigation (reduction in applied irrigation water compared to full irrigation) could be imposed without loss in seed yield, oil and protein yields of rapeseed, respectively. In-furrow planting increased water use efficiency compared with on-ridge planting by 7.0 and 13.2% for first and second year, respectively. Increase in salinity level at same conditions of deficit irrigation and planting method decreased water use efficiency. Therefore, deficit irrigation and in-furrow planting method strategies can be used to increase water use efficiency in water scarce conditions.