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Fluid Journal : Fluid Journal 1999-2001
3 Fluid Journal Fall 2000 gal/A rate of 10-10-10. This may explain the yield decrease observed for this treatment at several sites. The fact that 8-0-8 has no P, and the 6-gal/A rate of 10-10-10 applies the same P and K as the 3-gal/A rate of 3-18-18 but also applies more N, did not help explain the responses. Ten trials. Figure 3 shows the mean grain yields for all 1996 sites, as well as for the responsive site. There were statistically significant treatment effects at only one site where a 3-gal/A rate of 10-10-10 and 4.5 gal/A rate of 8-0-8 increased yields (a 6-bu/A mean increase). This greater response to the low rate of 10-10-10 and 8-0-8 (which produced insignificant burning this year compared with the 3-18-18) was not observed in 1995. The high rate of 10-10-10 (6 gal/A) did not reduce or increase yield, but produced significant leaf damage. There was no leaf damage due to the application of 3-1 8-18. The lack of response to this fertilizer in 1996, compared to the others, cannot be explained. Response across all sites was not statistically significant although there was an average yield advantage of about 1 bu/A over all treatments. In search of answers The study of relationships between yield response and site variables such as variety, soil type, and others were of no help in explaining the occurrence of responses. The only apparent relationship observed, which cannot be statistically confirmed, was observed in 1994. This year, responses were higher and more frequent at ridge-till and no-till fields compared with fields managed with chisel or disk tillage. The average increase over all trials was 3 bu/A in ridge-till and 2 bu/A in no-till. There was no increase at fields managed with chisel or disk tillage. It is likely that foliar fertilization alleviated problems with early nutrient uptake, which sometimes occur even in high-testing soils managed with these systems. Data analysis in 1995 and 1996 showed that three groups of strongly correlated site variables explained 37 percent of the observed yield responses. One group included soil P and K, small plant P and K concentrations, and leaf K concentration. Another group included total plant weight, N uptake, and P uptake at the R2 to R3 stage. The third group included leaf P and rainfall during July. Study of these relationships suggests that yield responses were higher or more frequent when soil P and K availability, nutrient uptake, plant weight, and rainfall in the late spring or summer were low. Dr. Mallarino is associate professor and Dr. Ul-Haq is postdoctoral research associate in the Department of Agronomy, Iowa State University.
Fluid Journal 1996-1998
Fluid Journal 2002-2004