Critical tissue concentration and chloride requirements for wheat

Previous research in the Pacific Northwest and Great Plains has provided evidence that wheat (Triticum aestivum L.) yields are often improved by Cl- fertilization. Published reports on critical tissue concentrations and Cl- requirements for wheat are few in number. Our objectives were to define a critical plant Cl- concentration !head emergence) for maximum yield, develop a Cl- fertilizer recommendation, and determine the effect of Cl- fertilizer on grain protein. Thirty-two field experiments (18 winter and 14 spring wheat) were conducted in Montana between 1988 and 1995. Experiments included comparisons with multiple cultivars and Cl- rates (0-90 kg ha(-1)). Relative yield vs. plant Cl- concentration relationships Here assessed from 219 cultivar x experiment episodes. Three zones of Cl- status were identified: (i) a deficiency zone, plant Cl- <1.0 g kg(-1), where significant (P < 0.10) field responses to applied Cl- occurred in 59 of 86 episodes (69%); (ii) an adequate Cl- status zone, plant Cl- greater than or equal to 4.0 g kg(-1), where yield responses occurred in only 2 of 44 episodes (<5%); and (iii) a critical range between these two zones, where responses were observed in 25 of 89 episodes (28%). Regression of plant Cl- concentration on soil (0-60 cm) plus fertilizer Cl- revealed that deficient, critical range, and adequate Cl- zones mere associated with <7.5, 7.5 to 32, and greater than or equal to 33 kg Cl- ha(-1), respectively. The proposed guideline for wheat is to add sufficient Cl- to reach the upper end of the critical range (4.0 g kg(-1) plant Cl-). This recommendation ensures adequate Cl- nutrition for maximum field and kernel weight, although at some sites a slight reduction in grain protein (0.5%) may result.