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Fluid Journal : Winter 2016
allows for treatment randomization and replication, such as typical small plot studies. However, each research location had 16 replications, whereas traditional small plot studies have 4 replications. The advantage of this design over multiple traditional small plots was it allowed for comparisons across the landscape within the same experimental unit while it maintained independence between samples. Sample independence is an issue when statistically analyzing traditional strip trials where a single treatment is applied to a strip the length of the experiment. This design also allowed differences in soil type and soil test P, pH, and other soil attributes to be tested as main effects in the statistical model. Individual replications were pooled together based on soil attributes prior to statistical analysis. Figure 1. Inherent variability in soil test phosphorus (Olsen P) at St. Charles in 2014. Figure 2. Inherent variability in soil test phosphorus (Olsen P) at Waseca in 2014. Winter 2016 The Fluid Journal Locations. Research locations (Gaylord and Stewart in 2012; New Richland, Willmar, and Janesville in 2013; and Waseca, New Richland, and St. Charles in 2014) were established in the spring. Six locations were in south- central Minnesota, one (Willmar) was in west-central Minnesota, and one (St. Charles) in southeast Minnesota. Soil samples. Prior to fertilizer application, one composite soil sample (0-6 inch depth) was taken from two neighboring plots or an area about 20 feet wide by 45 feet long. A total of 4 samples were taken from each of the 16 replications at each location. Each sample was analyzed for soil test P (both Bray P1 and Olsen), pH, CaC03 and exchangeable K. One composite (6-12 inches) soil sample for soil test P (both Bray P1 and Olsen) was taken from each of the 16 replications to characterize the subsoil at each site. Treatments. Fertilizer treatments (eight) were a factorial combination of broadcast and starter applied P fertilizer at multiple rates. Two rates (0 and 120 Ib P205/A) of triple super phosphate were broadcast-applied pre-plant and incorporated with tillage. Then four rates [0, 2.5, 5 and 7.5 gallA (0, 9.9, 19.7, and 29.6 Ib P205/A)] of APP were applied in-furrow at planting. Broadcast P rates were the main plots and starter rates were sub-plots in a split plot arrangement of randomized complete block design. Other essential crop nutrients [nitrogen (N), potassium (K), sulfur (S), and zinc (Zn)] were applied prior to spring tillage at rates to optimize corn production. The majority of these experimental sites were corn following soybeans; therefore the authors feel the effect of N in the starter treatments would be minimal. Conditions. Extraordinarily cool and wet conditions occurred during the spring of 2013 and 2014, which delayed field operations and planting at some locations. Corn was planted on May 15 at New Richland, June 2 at Willmar, and June 2 at Janesville in 2013. Harvesting. At the V5 growth stage of corn, eight whole corn plants were harvested from each plot, dried at 1500 F, weighed to determine dry matter yield, ground, and analyzed for total P. Stand counts and NDVI readings were also taken at V5. Yield. Corn grain yields were 16