Response of rainfed safflower to nitrogen fertilization under Mediterranean conditions

The deep root system of safflower (Carthamus tinctorius L) may be able to take up moisture and nutrients, especially nitrogen (N) that has been leached below the rooting zone of most other crops. The objective of the present study was to test the hypothesis that safflower would not respond to N fertilizer when grown after crops fertilized at economic levels. Field experiments were conducted for 5 years under Mediterranean rainfed conditions at a site with moderate soil mineral N levels in Lebanon's Bekaa Valley (513 mm long-term, annual precipitation). In the first series of experiments, there were four N application rates: 0, 40, 80 and 120 kg ha(-1), with three or six replicates. Seed and straw yield, leaf chlorophyll, shoot and seed N content and other agronomic characters were measured. In the second experiment, there were two N application rates: 0 and 40 kg ha(-1). No significant response to N application was detected, except for N concentration in the lower part of the shoot at maturity in 2001-2002; in that season, a total of 125 kg ha(-1) N was removed by the crop from the control which had no added N, suggesting that safflower is an efficient user of carryover N from prior cropping. Growing safflower after a fertilized crop may remove N from the lower part of the soil profile and thus reduce the possibility of this accumulated N eventually reaching the ground water. Cropping with safflower in rotation with other crops may have environmental benefits as well as saving on the costs of N fertilizers. The study supports the wider adoption of safflower in Mediterranean dryland cropping systems. (C) 2010 Elsevier B.V. All rights reserved.