Recall that last month a summary of the Wisconsin "on farm" corn starter fertilizer study was presented. Some of that information is presented here again as background along with some surprising new insights that the data is revealing.
During 1995 and 1996, UW-Madison researchers in cooperation with crop consultants, county extension agents, and corn farmers from around the state have been involved in corn starter fertilizer study. These were trials were performed on farm fields that usually had soil tests for phosphorus and potassium in the high to excessively high categories (as many fields in the area do). Data was collected from 44 fields in 1995 and 31 fields in 1996. Grain yields were measured from replicated field strips where corn was planted with and without starter fertilizer. Over the two years, about 40 percent of 75 fields showed a positive economic response to starter fertilizer. The average overall yield increase was about 4 bushels per acre.
Looking over data from the 75 site fields spanning 1995-96, it was difficult to predict based on soil fertility level alone as to when economic returns could be realized from starter fertilizer. Remember, the majority of these fields had soil test levels in the high to excessively high categories. Two of the variables analyzed were planting date and hybrid relative maturity. Conventional thinking would be that the biggest benefits from starter fertilizer would come with early planting dates when soils are often cold and wet. However, the opposite situation seems to be the case on high fertility soils, especially when long season relative maturity hybrids are planted.
Dr. Larry Bundy and Todd Andraski, UW Extension Soil Scientists, have described this effect by using a term called PDRM (planting date as Julian days + relative maturity). For example, a 100 RM hybrid planted on May 15 (Julian days = 135th day of the year) would have a PDRM of 235 (100 + 135). For the 75 corn fields in the 1995-96 starter fertilizer studies, this relationship is summarized in Figure 1 as the percent of fields with economic returns (those with more than a 4.5 bushel per acre yield advantage) to starter fertilizer. Note that when the PDRM was below 220, starter response was only seen in about 13% of the fields. However, as PDRM increased beyond 245 the percent of fields realizing an economic response increased to 60%.
Based on these results, the Table 1 was developed for East -central Wisconsin corn growers as a guide to help determine expected odds of economic returns from starter fertilizer in high fertility situations and using no more than the recommended rate of 10-20-20 pounds per acre.
First, it is critical to know the fertility level of fields. Where soil fertility levels are in the optimum or below range, corn will always respond to recommended rates of starter fertilizer regardless of planting date or hybrid maturity. There has always been the question of starter fertilizer use on the excessively high testing soils for P and K. The Wisconsin recommendation has been to apply 10 lbs. of N, 20 lbs. of P2O5, and 20 lbs. of K2O as a minimum to capture the starter response. Certainly there is not a need to apply more than this on the excessively high testing soils and this is where many producers could realize some cost savings. Now we also know that the probability of starter fertilizer response is dependant on the combination of planting date and hybrid relative maturity with the highest increase of response probability coming with late plantings of high relative maturity hybrids.
For more information contact Mike Rankin|
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