Díaz-Zorita et al. (2004) reported that wheat yield increased significantly in the soils from the sandy pampas region of Argentina with chloride fertilization. These authors also reported that, averaged over the 10 locations, the grain yield response to Cl-fertilization was 253 kg ha-1, and it was mostly explained by a greater number of grains per square meter. Several studies conducted in the Great Plains and the Pacific Northwest regions of the United States suggest that Cl-fertilization applied in the form of KCl improved the grain yield of wheat and other crops (Engel et al., 1997). Schumacher and Fixen (1989) also reported that many well-drained soils in the upper Midwest of the United States are low in this essential plant nutrient. For spring wheat, chloride fertilizer added to low chloride testing soil (<17 mg kg-1 soil or <34 kg ha-1 in the top 60 cm soil profile) results in a positive yield gain 70% of the time (Fixen et al., 1986a). A peculiar leaf spot complex that results in tissue necrosis and yield losses has been present in wheat fields of the Pacific Northwest and Great Plains for decades (Chester, 1944; Smiley et al., 1993a, 1993b; Engel et al., 2001). This nonpathogenic leaf spot complex results from inadequate Cl-nutrition (Engel

et al., 1994, 1997). Data in Table 14.1 show the influence of Cl fertilization on leaf spot severity and grain yield of durum wheat.