Obviously, it’s been a cool, cloudy and wet spring. So much so that corn planting, as of last week, stands at only 88%, 11% behind the five-year average of 99%. Only 44% of the soybean crop has been planted, way behind the 99% we experienced last year at this time. The stark weather contrast between this year and last has not only limited farmers’ ability to get into their fields, but also may have consequences in regards to soil fertility.
During drought conditions, it is normal for a ‘bank’ of nitrogen to be stored in the soil as there isn’t sufficient moisture to move it in the soil, so it stays put. Soil samples taken by Iowa State last fall indicated that it may be possible to have upwards of 100 lbs N/A carryover to this season, which is roughly double what may normally carry over from year to year. However, with all of the moisture that has fallen this spring, a significant amount of that nitrogen may have already leached out of the soil.
My suspicion is that the same thing may be happening with sulfate as well. Observations that I’ve made as I drove past corn fields last week generally show a yellowish, chlorotic plant that is starved for nutrition, at the V3-V6 stages on average.
The Iowa Soybean association is recommending farmers do a late-spring, pre-sidedress soil nitrate analysis in early June when the plants are 6-12 inches tall. The benefit of this test is that it predicts the amount of nitrogen available before the corn plant begins taking up more nutrients as it matures. ISA is recommending that if the test shows less than 21ppm nitrate, there is a high probability that the cost of an additional nitrogen application would be covered by the increase in yield you will see from that application. It’s completely up to the individual, but it may also be worthwhile to consider a sulfate source to sidedress along with additional nitrogen.
There are other compounding factors when soil is waterlogged for prolonged periods. Not only does the saturated soil predispose corn and other plants to disease pressure, it depletes the soil of oxygen, which has many negative impacts on plants. One of which tends to be exacerbated when it happens early in the season is restriction of root growth and development. Fortunately, we are not dealing with temperature extremes along with the saturated soil which would make the situation even worse. Things look to warm up this week; hopefully the soil will start to dry out a bit so we can all get back to our regularly scheduled growing season!