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 − ). Relative yield vs. plant Cl − concentration relationships were assessed from 219 cultivar × 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) yield responses to applied Cl − occurred in 59 of 86 episodes (69%); (ii) an adequate Cl − status zone, plant Cl − ≥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 were associated with <7.5, 7.5 to 32, and ≥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 yield and kernel weight, although at some sites a slight reduction in grain protein (0.5%) may result.