Fodder quality of safflower across an irrigation gradient and with varied nitrogen rates

Abstract

The main aim was to investigate the effects of irrigation head and N fertilization on the nutritional quality of safflower (Carthamus tinctorius L.) grown for forage. A pot experiment (Exp. I) and two field experiments (Exp. II and III) were performed. Experiment I included nine treatments, comprising three N concentrations (10, 50, and 100 mg L-1) in the irrigating water and three irrigation rates (21.8, 32.6, and 52.21/pot) in 10-L pots, 12 pots m-2 with a planting density of 60 plants m-2. In the field experiments one line of sprinklers was used, creating water-head gradients perpendicular to the line (from nil up to 345 and 185 mm in Exp. II and III, respectively), with N rates in the range of 0 to 300 kg ha-1. The dry matter (DM) content of the shoot in Exp. II and III declined steeply from 331 to 134 g kg and from 368 to 291 mg g-1, respectively, as the irrigation head increased from nil to the highest value. As the N rate increased, the concentrations of N-NO3- in the leaves increased up to 520 mg g-1- much lower than the designated toxic threshold for ruminants. Increasing the water head in the field experiments decreased the nutritional value of safflower, as indicated by falls in the contents of: neutral detergent fiber (NDF) (48.4-59.8% and 45.2-49.0% in Exp. II and III, respectively) and water-soluble carbohydrates (WSC) (7.65-3.21% and 8.50-8.12% in Exp. II and III, respectively), and decreased in vitro DM digestibility (64.7-52.1% and 69.3-64.5% in Exp. II and III, respectively). Safflower can be regarded as a high-quality forage crop for semiarid and arid regions with limited water resources. Copyright © 2008 by the American Society of Agronomy. All rights reserved.