Fall fertility issues: Answers for your questions
What happened to all of the nitrogen you applied last fall and this spring to your 2012 corn with the intent of producing a bumper crop? The corn plants certainly did not use it, so where is it, and is it available for use by the 2013 crop? About every corn grower is asking that question, wanting to save money by not having to buy more nitrogen for the crop next year. Let’s tackle this hot topic with the help of University of Illinois fertility specialist Fabian Fernandez.
Subscribers to Corn Belt Update (inquire at Stu@farmgateblog.com for subscription information) learned in early September what to consider about nutrient resources that may be available after the poor 2012 crop. There are ways to assess the nutrient reserves that might be available, albeit with some difficulty:
- Knowing your P & K resources is difficult, says Illinois fertility specialist Fabian Fernandez. Uptake was hard for crops because of the lack of moisture, but measuring what remains is also hard. He says, “During the season, plants have extracted P & K out of the more easily available pools, but because of the lack of moisture, the soil has to a large extent been unable to replenish those pools from less available nutrient pools--what could be called "nutrient reserve pools." While some of the moisture we are beginning to receive will certainly help the replenishment process from the nutrient reserves in the soil, those processes take time. The longer you wait in the fall to collect samples, the more reliable K test values will be.
- Knowing how much N to apply is not easy either, says Fernandez. The indirect method is easiest, which he says is a function of calculating how much grain and biomass was produced and removed, and subtracting that from the amount of the last soil test. He says the direct method is more reliable, and that is determining the soil nitrate-N level. He says, “A composite of at least 12 cores should be collected, taken to a depth of two to three feet from representative portions of the field and at different positions with respect to the crop-row. Each foot of sampling depth should be kept as a separate sample for analysis.” But some of that will be lost over the winter, so he suggests sample and apply nitrogen in the spring.
Once you have obtained a soil analysis of the nitrogen present, you can proceed with building and managing your desired level. But what source of nitrogen will you choose?