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In the spring of 2014 we initiated what was to be the first year of a three year project evaluating starter fertilizers for soybean production in the southern Great Plains. The first and second year was and is being funded by the Oklahoma Soybean Board.
Year one was a bit experimental in that with so many products on the market we needed some initial work to help focus the direction for years two and three. I also added a treatment which I knew would have significant negative impact, for extension reasons. Keep in mind two locations in a single year does not make an experiment nor provide enough information to draw a definite conclusion. It is however enough to learn some lessons from and for us to plan for our 2015 trials.
The 2014 trial consisted of 12 treatments, Figure 1 and Figure 2. In these treatments I wanted to see the impact of a standard practice, see if a specific nutrient may be more so beneficial, and evaluate a few popular products. The spring of 2014 started out dry so at one of our two locations we pre-watered. This was done by hauling water to the Lake Carl Blackwell (LCB) 1000 gallons at a time and pumping through sprinklers. The other site, Perkins, we delayed planting until we had moisture.
The two locations were also selected due to differences in soil fertility. The LCB site is has good soil fertility, with exception of phosphorus (P), and the Perkins site pH was an issue. I would have expected a benefit from adding P at both of these locations. Figure 4 shows the soil test results.
At LCB as expected some of the treatments (Thio-Sul) reduced stand, some unexpectedly reduced stand (Fe) and others had less impact on stand (APP 5.0) than expected. The growth at LCB was tremendous, the 30 in rows covered over very quickly and the majority of the treatments hit me waist high by early August (I am 6’0”). Many of the treatments showed greater growth than check. But when it comes down to it, grain pays and green does not. Statistically there were no treatments that out preformed the un-treated check, however the K-Leaf and 9-18-9 did make 3 and 2 bpa more than the check respectively. What I am hypothesizing at this site is that the added nutrients, especially those with high P levels, significantly increased vegetative grown and these big plants were delayed into going reproductive and they started setting pods later in much hotter weather. While riding in the combine I could see that the plots with compact plants with clearly defined rows out yielded those were the vines had crossed over and we harvested through more of a solid mat of mature plants. A hot August is not uncommon and I am curious on whether this trend repeats itself. If it does this may direct us into research evaluating ways to force/promote the reproductive stage to start in these big plants. Even if we can force flowering to start earlier, it’s unknown whether yields will increase or not.
The same trends in treatments reducing stand can be seen at Perkins, however the impact was less extreme. Perkins being planted later due to waiting on moisture forced a later flowering date and I believe reduced overall yields. But the addition of P at this low pH site definitely made a difference. While again no treatments were statistically greater than the un-treated check the 2.5 gpa APP, DAP broadcast, APP/H2O, and Pro-Germ/H20 treatments increased yield by 5.6, 4.2, 3.8 and 1.7 bpa respectively.
Take home from year one was that at LCB the addition of a starter fertilizer had little benefit and if done wrong could cost you yield while at the low pH site of Perkins an addition 2.5 gallons of APP did get a 5 bpa bump, but do to variability in the trial the increase was not statistically significant. This year we will drop some of the treatments and incorporate a few new treatments. Based on the current weather we look to potentially being able to start with better soil moisture at planting. Again do not take this work and significantly adjust any plans you have for your 2015 soybean crop. This is however some interesting findings that I wanted to share and make everyone aware of. Finally thank you to the Oklahoma Soybean Board for providing funding for this work. www.oksoy.org/