ISSUE 7 June 18, 1998
As of the second week of June, there were few green corn fields in North Dakota. Yellow corn could mean several factors, including low N levels, but in most cases the yellow color is probably due to the cool weather during the last three weeks. Corn is a warm weather crop and despite corn breeders advances in shorter day length corn varieties adapted to our growing season, the research has not overcome a corn plants preference for 80 degree days and warm evenings. Until the crop experiences several days of 80+ degree temperatures in a row, the corn will continue to appear yellow and growth will be slow. Corn growers should not be lulled to sleep over the slow growth now, because when temperatures do reach more acceptable levels, the plants will shoot up rapidly, putting pressure on growers to finish spray and sidedress N applications quickly. By working in between the raindrops during this cool period, the work load will be decreased during future rapid growth.
In certain parts of the state, heavy rains early this spring and later on in the early growing season saturated some soils and in some cases resulted in corn acres being replanted. Soil tests from these areas indicate that N was lost, probably due to denitrification (loss of N to unusable gas forms by low oxygen requiring soil bacteria). Loss of 50% of soil nitrate-N within 24 hours of flooding is possible in warm soils. Flooded areas should be sampled to 2 feet in depth and supplemental N added as recommended by the soil test results.
Side-dress N application can be made with urea, ammonia or liquid N solutions. Urea should be applied with a cultivator, or some other means that will not allow the granules to enter the whorl. Urea in the whorl can cause burning of the leaves. Similarly, liquid N solutions should be side-dressed, preferably into the soil at least an inch, with 2-3 inches being better able to cover the trench. Ammonia is the form of N most often used. Application should be deep enough to allow for proper application trench coverage. Failure to cover the trench adequately could allow vapors to be lost, decreasing the application efficiency, but also resulting in burned leaves. N application rates are not restricted as long as the application is between the rows and not close to the plants. I have observed up to 300 lb N/acre in a side-dress application with no ill effects to corn.
If the season gets away from a producer and corn becomes too tall to side-dress, dribbling N using a liquid N solution has been successful. Using a high-clearance sprayer, the unit is set up with drop nozzles and a straight-stream orifice selected for proper pressure and volume required. With 28% N, 10 gallon is roughly 30 lb N. This type of application is most successful if significant rainfall occurs within 48 hours of application.
New soybean growers are being introduced to iron chlorosis this week. If soybeans came up green, and then turned yellow in areas of the field when the first trifoliate leaf emerged, and the leaves are yellow mostly in-between veins, this is iron chlorosis. Iron chlorosis can be the result of both manganese and iron deficiency, but most of our problems appear to be related to iron availability.
Based on recent research at NDSU supported by Pioneer Hi-Bred Int., the factors most responsible for iron chlorosis in the region appear to be a combination of high levels of free lime (carbonates) and high levels of soluble salts compared to normal corn-belt levels. These factors evidently interfere with the normal means of iron availability to and/or uptake into soybeans. There are certainly differences between varieties in tolerance to iron chlorosis, but as yet, no real resistance.
Some work has suggested that seed treatments or foliar sprays of certain iron products, especially Iron EDDHA chelate may sometimes be effective, however, results have been inconsistent. Minnesota work with foliar products fifteen years ago points out that foliar treatments are most inconsistent when soluble salt levels were high (our area). Another problem with foliar treatments is that many of the iron chlorosis problems are so small spatially with green areas that the entire field needs to be sprayed, which decreases the economics of the application. A recent greenhouse study at NDSU also suggests that application of iron could bring out manganese deficiencies, which would also decrease application efficiency.
Another contribution to soybean yellowing and chlorosis is the problem with early season N availability. A recent greenhouse study at NDSU in which different levels of lime and gypsum were mixed into soil from non-chlorotic areas the previous year showed that nodule numbers were reduced with added lime and gypsum. Even plants not obviously showing interveinal chlorosis were more yellow with high levels of lime and salt due probably to poor nodulation and N availability. Soybean producers should soil test for N before planting and apply up to 50 lb N/acre if soil test levels are below 50 lb/acre nitrate-N.
The greatest tool to use against iron chlorosis is variety selection. Producers should pay attention to local plots particularly when they are in an area affected by chlorosis. Some seedsmen may seed show-plots into areas not historically affected by chlorosis, but producers should seek out areas affected so that better seed decisions can be made.
COPPER PROBABLY NOT A CURE-ALL
One danger in announcing a new deficiency sighting is that some people see a leaf and visualize a forest. At least one consultant in North Dakota is promoting copper for suppression of scab in wheat. There is no evidence that application of copper has any affect on scab. That possibility is something that will be studied in plots this summer, but there is no compelling evidence that copper has any role in promoting scab-less wheat. Our present observations are for growth and greenness differences on a sandy-loam textured hilltop with less than 2% organic matter and a DTPA copper test of 0.3 ppm on water-worked glacial till derived soils-period.
Dr. Dave Franzen
NDSU Extension Soil Specialist