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Fluid Journal : Fluid Journal 2005-2007
Winter 2006 Fluid Journal 2 response to APP simply due to nitrogen (N) or the combination of N and P? Or, did the PA bands result in reduced P availability as the season progressed? Thus, the study treatments were changed in 2003 and 2004 to better answer the question of whether or not banded APP enhances P uptake and increases yield. 2004 results Minidoka. Results from this location showed no significant difference for any harvest parameters measured. The yields were very poor in this field due to severe weed pressure, water availability, and a possible herbicide carryover effect. Although there were large differences in total yield, there were no apparent trends and the differences were likely due to massive spatial variability across plots (Figure 1). Rockford. The results from this field showed significant differences in beet root nitrate concentrations, with only the 3-inch APP treatment showing an increase over the broadcast UAN check. No significant differences were observed with electrical conductivity, a measure of yield quality. Fertilizer addition to sugarbeets is often accompanied by increases in various salts within the root (magnesium, sodium, potassium, iron, nitrate, etc.), which is an important quality factor during the sugar extraction process. The salts tend to bind with the sugar compounds, effectively reducing sugar extraction efficiency. The sugar companies measure the electrical conductivity and the nitrate concentrations in order to offer financial incentives for growers to reduce these problematic interactions. Sugar percentage declined with fertilizer application, particularly with both sources of fertilizer at the 3-inch depth (Figure 2). Again this is not surprising, as fertilizer application often results in a reduction of sugar percentage in sugarbeets. Total yield and the net total sugar production proved to have significant differences as well. All three depths for the APP and the top two depths for the UAN showed significant increases in total yield in relation to the check. A similar trend existed with sugar percentage for net sugar yield. The surface band applied UAN and the APP applied 6 inches below the soil surface were the only treatments significantly greater than the broadcast UAN check (Figure 3). The results are similar to those from the previous year, in which there was no response at one trial location and the APP performed best at the other. However, the surface UAN band treatment did not increase sugar yield in the previous year at either location, as it did at the Rockford location in 2004. Depth counts The inclusion of the UAN treatments in these studies effectively separates the N contribution of the starter. Although the results from the various trials over the past three years are slightly different, it is interesting to note that the APP band 6 six inches below the soil surface performed better than all other treatments for three of the five locations. In both nonresponsive locations, the yields were relatively low. These results suggest that response to starter P is most effective under high- yielding environments. During the first 6 to 9 weeks, sugarbeet roots are oriented dominantly downward, as compared to a diagonal orientation for most other plant species. The early architecture of sugarbeet roots results in more subsoil exploration and less of the surface soil. Subsurface P concentrations tend to be low, especially in alkaline, calcareous soils common in the western states, even if the surface soil is high in P. This combination of sugarbeet roots not effectively exploring the surface soil and low subsoil P levels results in a potential problem for P availability early in the season. Deep banding APP seems to correct this problem. Dr. Ellsworth is a soil fertility specialist at Twin Falls and Dr. Hopkins is a cropping systems soil scientist at Idaho Falls in the College of Agriculture and Life Sciences, University of Idaho. Figure 3. Sugarbeet N and P placement effect on sugar yield for the Rockford location, 2004.
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