Here is a useful article dealing with the yellow n deficient areas of fields. I have checked a few and wondered what amount was lost. Appearing to he all. Thought John did a great job of detailing what is going on. Del Voight – Penn State Extension.
by John E. Sawyer, associate professor, Department of Agronomy
Estimating N lossResearch conducted in Illinois (reported in the 1993 Integrated Crop Management Conference proceedings, pp. 75-89, and in Torbert et al., 1993, “Short-term excess water impact on corn yield and nitrogen recovery,” Journal of Production Agriculture 6:337-344) indicated approximately 4 to 5 percent loss of nitrate-N by denitrification per day that soils were saturated. An all-nitrate fertilizer was applied when corn was in the V1 to V3 growth stage. Soils were brought to field capacity moisture content and then an excess 4 inches of water (above ambient rainfall) was applied evenly over a 3-day period, which maintained saturated soils for 3 to 4 days on the heavier textured soils, or an excess of 6 inches of water was applied over an 8-day period (with saturated soils for an additional 3 to 4 days). The excess water application resulted in loss of 60 to 70 pounds N/acre on silt loam and clay loam soils, due to denitrification loss. On a sandy soil, virtually all nitrate was moved out of the root zone by leaching. On the heavier textured soils, addition of 50 pounds N/acre after the excess water was applied was sufficient to increase corn yields to approximately the same level where no excess moisture was applied. This was not the case on the sandy soil because more N was lost through leaching. When 8 inches of precipitation plus irrigation was received in May and June on the sandy soil, yield was reduced by 20 percent. Using the late spring soil nitrate testA procedure to measure additional N need is to use the late spring soil nitrate test. However, it is too late to sample with this test (1-foot soil samples should be collected when corn plants are 6 to 12 inches in height). If samples were collected at the appropriate time, then the following information can assist with interpretation of results. See ISU Extension publication PM 1714, Nitrogen Fertilizer Recommendations for Corn in Iowa, for full interpretation and use of this test. Assessing the corn cropBefore a decision is made to apply supplemental N, you should consider the potential productivity remaining after soils have dried. Has the stand been damaged, will the plants recover, is the area planted late or replanted, and is the yield potential reduced because of conditions other than N loss? It is possible that the combination of N remaining in the soil, plus N mineralized during the rest of the growing season, can supply adequate N. If corn at approximately the V6 to V8 stage is showing N-deficiency symptoms (due to N losses and not just due to waterlogged soils restricting root activity and growth), but otherwise has a good stand and appears to be growing well, then application of additional N should be beneficial. How to apply needed NWhen conventional application equipment can be moved through the field (the soils are dry enough and the corn is short enough), then injection of anhydrous ammonia or UAN solutions would top the list of best options. Next would come dribble UAN between corn rows, then broadcast urea. Broadcast UAN solution should be avoided because it can burn corn foliage, especially with large corn. If injection or conventional broadcast application is not possible (as is likely the situation due to the large corn in most of Iowa at this time), then UAN could be applied with high-clearance equipment with drop nozzles that direct the solution onto the ground, or urea could be aerially applied. How late can I apply N?It is best to get the N on as early as possible. However, yield responses that return income greater than the costs for application and fertilizer materials have been observed for N applied up to and slightly beyond the tassel stage. The magnitude of yield increase is dependent upon the severity of N deficiency and the ability of the crop to recover and respond to applied N (the growth and yield potential left after water damage and early season N deficiency). Any surface application is dependent upon rainfall to move applied N into the root zone, otherwise it cannot benefit the corn crop. |