How important is the timing of nitrogen application on corn? Should producers consider micronutrients in their soil fertility program? These are just a couple of the questions that were discussed at the 2nd Annual Girad Agronomy Night held on Jan. 22.
Dorivar Ruiz Diaz, soil nutrition specialist with K-State Research and Extension, and Peter Scharf, nutrient management specialist with the University of Missouri Extension were the keynote speakers of the event. Ruiz Diaz focused on soil phosphorus and micronutrients. Scharf presented on nitrogen sensing technology in corn and its impacts.
Scharf began with how his research started. After some time, he noticed that within a small plot, the variability in nitrogen level was great. Applying this logic on a larger scale, he began measuring the nitrogen levels across a whole field and found it to be the same. In fact, some spots of the field would require only 0-80 pounds of nitrogen to optimize profit while other areas might require 200-250 pounds of nitrogen. The common practice would be applying 150 pounds N across the whole field, which would greatly over and under nourish spots within the field.
Scharf determined that a way to measure this variability would greatly increase profitability. Although there are a few methods of measuring plant nitrogen needs, the most feasible and usable for most producers is a nitrogen sensor mounted on a ground vehicle. Scharf estimated that the sensors are most valuable in years with wet springs when nitrogen loss can be great. He showed one example where 180 pounds of N was applied prior to planting while another plot had only 110 pounds applied when the corn was knee high. The knee-high plot out-yielded the pre-plant by 44 bushels per acre with 70 pounds less nitrogen.
Scharf went on to say that he has observed years where the nitrogen for the corn crop could have been applied as late as the 7-foot-tall stage and still be effective. However, this may not work for every producer. In an ideal situation, some starter nitrogen should be applied prior to planting. At somewhere near the knee-high stage, using a sensor to determine how much nitrogen is needed to maximize profit would be ideal. However, the nitrogen sensors are nowhere near perfect at this point. Like most technology, the sensors develop a very accurate reading, but the issue is what to do with the reading. It is recommended that producers try several of the available algorithms to find the preferred one.
For every bushel of corn produced, 0.33 pounds of phosphate (P2O5) is removed. For reference sake, the rate would be 0.5 bushel of wheat and 0.8 per bushel of soybeans. Thus, in years like 2014 where our yield was very good, higher amounts of phosphorus were removed. This fact has encouraged many producers to consider variable rate technology. High yielding areas of a field yield more and therefore remove more. To maintain the productivity (and profitability) of those areas, applying varying rates may be a valid option.
Another takeaway point of Dorivar’s presentation was the importance of a balanced soil nutrition plant. In a study completed in 2012, the yield of three treatments was measured. Those treatments were: nitrogen only, nitrogen plus 40 pounds of phosphate, and nitrogen plus 40 pounds of phosphate and 40 pounds of potash. Although there was not much difference between the latter two, both yielded much higher (approximately 25 to 30 percent) than the treatment that was just nitrogen only.
Dorivar also pointed out that the way the soil is tested can greatly affect the results of that test. This is most evident in fields under no-till conditions. In a given area of soil, if a sample was taken at a 8-inch depth, the soil test phosphate would be 19 ppm. However, if that was broken down and taken every 2 inches, the concentrations would be 106 ppm at 0-2 inches, 6 ppm at 2-4 inches, 7 ppm at 4-6 inches, and 5 ppm at 6-8 inches. Obviously, if only the surface was sampled, an accurate picture of the soil phosphate would not be possible.
Dorivar wrapped up his portion of the event by talking about secondary and micronutrients. Although the research studies he has conducted fail to give an easy answer concerning these nutrients, one item that did stand out was the fact that they could provide a yield boost, particularly in traditionally low yield environments. He speculated that in traditionally high yielding fields, the soil itself could be providing those nutrients, while a poorer soil may not be.