2. Nutrient Management for the Best ROI
(start at 43:44 to listen about new technology)
About a year ago, we started working with some new technology; Nutrisense Sensors. This is technology from Europe that can measure nitrate and potassium; now we have the ability to monitor those along with our soil moisture content. This past year, there were three sites in North America with these sensors: here (on corn), California (on trees) and Washington State (on fruit crops). We installed this two miles north of here. We put one sensor at 8 inches, so we are looking at the root zone, and another at 30 inches. We also used suction lysimeters. These are tubes that have a mesh sponge on one end. Each week we would put a vacuum on the PVC tube and shut the valve for a day. The moisture in the soil would come into the tube and we would suction it out with a syringe. This allows us to measure the nutrient content of the water in the soil pore and compare it to readings that we were getting of the sensor. One thing to keep in mind: the sensor is measure the soil pore water plus the nutrients attached to the soil colloid. The water we collected contains the soluble portion, so they are measure two different pools of nutrients. In addition, we would take corn leaves, run them through a garlic press and measure the SAP (potassium, nitrate, calcium and sodium) in the tissue at the same spot at the same time. One thing we found with the SAP measurements, if you measure in the morning, then have a hot sunny day, and measure in the afternoon, these values could change 40%. If you want to create a benchmark, you have to check these at the same time of day, with similar conditions to really understand what is happening.
With all these reference points, we were able to graph all this data and learn.
This graph is from June 13th to August 8th. This is in heavy clay soil with CECs of 25-30. Our belief system has always been that we don’t leach nitrate, because of how heavy our soils are. What we learned this year challenged that thinking. The green line is the nitrate level at 24 inches. In June, there were some rain events, and as you can see, the nitrate value was continually climbing.
Meanwhile, you can see on this chart the 24 inch potassium in dark red is continually dropping. This chart is later in the season, July 29-August 11, so we are in the grain fill. We did some applications of in season potassium, but we know that in these soils, potassium is one of our limiting factors; this wasn’t a surprise to see potassium levels drop. What did surprise us was that the nitrate increased while the potassium was dropping. If you go back to the nutrient interaction graphic, you will see that too much nitrate blocks potassium.
Another event in November gives us more data to make us question if nitrate is leaching down into the soil. This is another rain event after the growing season and harvest. The nitrate at 24 inches is the dark green; as you can see, the level rises quite sharply. That is nitrate that we paid $1 per pound for last year; those are dollars getting pushed down into the soil profile that we can’t get back. One thing we are going to reevaluate this year is our nitrogen management. We need to watch what we are doing with in season nitrogen; not only are we being inefficient, but it isn’t getting into the plant like it should be.
Here is a nutrient uptake chart from a presentation from the National No-till Conference. This shows the nutrients required weekly to grow 400 bushel corn. To get to v6, we only need ten pounds. This is when most of us are applying 50-100% of our nitrogen, and expecting it to be available later in the year. This data is just challenging our thinking on how we are applying different nutrients and when; we encourage you to look at your practices and what you can do to match these uptakes.
Another piece to the nitrate issue, especially for those in Nebraska, is nitrate and groundwater. The University of Nebraska has been monitoring the vadose zone (the ground between where crops are grown, and the aquifer); they have found high levels of nitrate in the vadose zone (https://nebraskavadose.unl.edu/). Most of the places we work in Nebraska have a sandy loam soil. We know nitrogen moves easier in sand; what would that sensor look like in Nebraska, if we have nitrates leaching through our heavier clay soil? Our goal is to have 50 of those sensors in Nebraska this year, to help farmers understand how to do better with nitrogen management.