The concept is simpler than the procedure to get samples or the interpretation of results. If you know how much nitrogen is left in the stalk as the plant begins to dry down just before harvest, you should get a clue on how well the plant utilized nitrogen applied for the season.
The first step is taking samples. We followed Danny Greene of Greene Crop Consulting, Inc., as he took stalk samples recently. He was in a field where he was taking what they call 'guided samples.' According to Greene the positions to take the samples were based on examining aerial maps flown over the field late in the season. Four spots were picked in this field. Each was precisely marked with GPS coordinates. Greene uses a hand-held computer from Ag Leader designed for scouting and soil sampling with built-in GPS to find the four points.
Once at the right spot he uses a sampling device made for this purpose. It has an 8-inch stand so that the sample will be cut 8 inches above ground level. It cuts about an 8-inch section of stalk. When he samples, he cuts sections from 12 stalks at each location. To make sure he's not just following some effect that might have affected one row, he takes four samples from each of three rows at the location. The samples are returned to the office to air dry, and will later be sent to Brookside labs for analysis.
"We're trying to learn and we're also sharing what we find with farmers," Greene says. "We also have some plots where different rates of N were applied, and we are sampling those areas as well. The first step is to get representative samples from the fields. The second step is to dry the samples and send them to the lab. When we get the results, we'll be ready for the third step – interpreting why we saw what we saw."
It may not be too late to get stalk samples, especially in later-maturing fields. Consult your agronomist or fertilizer dealer to see if he or she believes you could benefit from having this type of information.