ISSUE 7 June 26, 2008
CROP YELLOWING, POST MORTEMS, AND CALLS TO ACTION
Following the last couple weeks of rainy weather, a number of wheat fields are showing yellow patterns. The time of wheat head emergence is a time of heavy requirement for nitrogen, and some fields are a little short in areas. Look for yellowing on lower leaves, with newer leaves emerging greener. For some fields, there is a general shortage due to application of surface urea and a long length of time before significant rain fell. I think the number of fields exhibiting this problem is few, due to the exceptionally dry status of surface soils during this period and the resulting low urease activity. For most fields, yellowing is either seen in depressions where water may have sat for many days, or in the coarser-textured hilltops/slopes where leaching occurred. If the percentage of acres showing these symptoms is large, a post-anthesis application of 30 lb N/a as 28% might increase protein content about 1/2%. 30 lb N as 28% will cost about $21/a plus application, so check to see if this might be profitable.
In corn, now that the weather has warmed, there are differences in greenness in most fields. I have seen problems with nitrogen availability, sulfur deficiency and zinc deficiency so far in my travels within the state. Nitrogen would be the result of poor selection of application method, or leaching in sandy soils, or denitrification in eastern counties due to water-logged/poorly drained soils. Look for yellowing on lower leaves, with the new leaves emerging greener. There is still plenty of time to side-dress traditionally, or dribble 28% between the rows (not over the whorl!!!) using a long hose or drop-nozzle.
Look for sulfur deficiency on coarse-textured hilltops and slopes with lower organic matter. Many areas have received large rains during a day or two, and any residual sulfate may be gone. Look for yellow upper leaves, with lower leaves remaining greener.
Many growers are not used to growing corn, and so may have taken zinc for granted. Look for stunted plants with yellow-striped upper leaves, usually on low organic matter hilltops and slopes. Foliar application of one quart/acre of zinc chelate will help to snap the corn out of its deficiency. DO NOT APPLY WITH HERBICIDE (See last weeks pest report). Apply in a separate application.
I have heard the first reports of failures to nodulate with granular inoculants this spring. One of the reports was poor calibration by the grower, which resulted in very spotty nodulation due to the low inoculant application rate and inability to deliver that low a rate through the air seeder. The second report is simply lack of nodulation by an experienced grower from a lot where another grower achieved successful nodulation. This report is a mystery. Given the high crop prices, and the need even for legumes for adequate nitrogen, now is the time to check and see if nodulation is taking place under peas, especially in fields far removed from the last time peas were in the rotation. Check soybeans when the plants have about 3 trifoliates. If there is no nodulation, application of supplemental N will be needed to carry the crop. I think the field that needs help will be rare, but better to find out now than August.
Finally, some crops, like the poorly nodulated peas, or the safflower field that was seeded without nitrogen, will need a rescue treatment of N. It is important to keep in mind the difference between "ideal" and "best-you-can-do". We recommend primary fertilizer management practices because these most consistently increase grower profit with the least crop injury. Anything else is more risky and often increases crop injury. Application of top-dressed N to a solid-seeded crop falls into the "increases crop injury" category. I would recommend either urea broadcast, or, more practically, stream-bar liquid N (28%). In sunflower, field pea, soybean, and safflower, expect some leaf injury. Occasionally, some fertilizer might nuke a major growing point, causing the plant to branch. This is probably more serious in sunflower than in the other crops, but it will happen. Applying the liquid stream-bar at a slight angle to the row may not decrease the overall plant injury, but will not result in low stretches of row being injured. It will also be important to apply the stream-bar liquid when the wind is low enough that the stream is intact and not dispersed. A windy day will disperse the liquid stream into a broadcast application, resulting in widespread and unwanted injury to the crop. Remember, that even with some leaf injury using stream-bars, the yield increase from the fertilizer will outweigh the injury if the nitrogen is needed.
Dr. Dave Franzen
NDSU Extension Soil Specialist