N and P Placement and Timing of Dryland Winter Wheat Varieties

Nitrogen fertilizer is commonly applied to winter wheat in the High Plains to achieve moderate to high yields. Typically, anhydrous N is applied in the summer or early fall with a tillage operation. Some growers apply liquid N in the spring if winter and spring moisture are high to take advantage of higher yielding condition. Phosphate fertilizer is less frequently used on winter wheat than N fertilizer. There are two main methods of P fertilization for calcareous soils: banding with the seed (seedrow) and banding with a knife (chisel). Banding N and P together is referred to as dual placement. We studied these common methods and timing of N and P fertilization (chisel N in fall, surface banding liquid N in spring, dual placement of N and P in fall, chisel P in fall, seedrow P at planting, and no fertilizer) on three varieties of winter wheat in Southwestern Kansas to determine which treatment produces the highest yield and variable net income. We included a comparison of with and without carpramid (Amisorb), a polymer reported to increase nutrient adsorption (Murphy and Sanders, 1998; Thompson, 2000), to the high rate dual placement P and N. Wheat yield response to timing of N fertilization varies with moisture. Spring application of N was reported to increase wheat yields in higher moisture areas such as Illinois (Welch et al., 1966). In drier areas there tended to be little yield difference between fall and spring N applications, when using low or nonvolatile N fertilizers (Christensen and Meints, 1982; Kolberg et al., 1993). A three-year study conducted in Eastern Colorado reported yield and income advantage to spring-applied N compared to fall-applied N (Vaughan et al., 1990). Residual soil moisture and plant residue from the preceding crop also affected wheat yield response to N timing: wheat following grain sorghum produced the highest yields with a split N application (fall and late winter); whereas, when wheat followed soybean, preplant N produced higher yields than split N application (Kelley and Sweeney, 2000). Wheat fertilization recommendations state the advantages of fall-applied N (less expensive N source, applied with common tillage operation) and the advantages of spring-applied N (higher grain yield, increase in protein, timed to moisture conditions) (Sander, 1988; Davis et al., 1996). Banding P fertilizer is recommended compared to broadcasting and incorporating P (Sander, 1988). The two most frequently used P banding methods are applying P with the seed at planting (seed) and knife application. Sander and Eghball (1999) reported that both P banding methods worked similarly with optimum wheat planting date, but seed placement produced higher yields than knife when planting was delayed.