April's Ag Advice by April Borders With all of the water that we have had in our fields lately and with the fact that water has been standing in these fields for extended periods of time, it is very likely that nitrogen fertilizer has been lost due to denitrification. Denitrification is the process by which nitrogen converts back to a gas and escapes into the atmosphere.
According to SDSU Extension Soils Specialist Jim Gerwing, if corn survives in such waterlogged areas, it may be in need of nitrogen by the time the soil dries enough to let farmers address the problem.
Nitrogen deficiency can be spotted on early corn plants at the six to eight leaf stage, as the corn will appear pale colored, sometimes severely, but will not have striping on the leaves. Often some of the lowest leaves will turn brown.
Striping � especially if stripes run across the entire leaf � often indicates sulfur deficiency. Gerwing cautions that if a sulfur deficiency is not severe, the striping may not be pronounced and may look like nitrogen deficiency. Sulfur deficiency appears to be most pronounced on sandy, course-textured soils that are low in organic matter. It is also much more pronounced in no-till systems, since these soils stay colder and the release of sulfur from organic material is slower.
Zinc deficiency is also showing up in some corn. Zinc deficiency also causes striping, but only on parts of the leaf, not the whole leaf, and the plants don't get as yellow.
Producers can soil sample to determine whether a deficiency of nitrogen or sulfur is showing up, but you need to sample to at least two feet deep. To correct nitrogen deficiency, producers can side-dress with ammonia, or broadcast urea nitrogen over the top of the plants.
If the corn is over a foot tall or so, broadcasting fertilizer over the top sometimes causes some visible injury because the fertilizer gets down in the whorl. According to Gerwing, it usually doesn't cause any serious damage, but it can look pretty tough. Liquid 28-percent UAN (urea ammonium nitrate) can also be knifed in or applied to the soil surface between the rows.
Producers can also apply sulfur if you recognize a sulfur deficiency. You will need to use a sulfate form of sulfur. One option is ammonium sulfate, which is 21-0-0-24 as a grade. According to Jim Gerwing, about 100 pounds per acre of the material, which will supply 24 or 25 pounds of sulfur, should do the trick. The product can be broadcast over the soil surface and rainfall will move it right into the soil.
Because ammonium sulfate fertilizer is 21 percent nitrogen, it also gives crops an added shot of nitrogen. Fields with light, coarse-textured soils that have had heavy rain fall may need to use more nitrogen but a soil test should be done first to find out if nitrogen is deficient.
We are also seeing some deficiencies in our alfalfa fields. Sometimes we neglect to fertilize alfalfa because we think that it is capable of producing its own fertilizer. That is true when it comes to nitrogen but not phosphorus and potassium.
Alfalfa is by far the largest remover of phosphorus and potassium over any other crop that we have. It removes around 12 or 13 pounds of phosphorous per ton of hay, and 50 pounds of potassium for every ton of hay removed.
Potassium deficiency symptoms are small white spots on the leaves, often in a pattern around the edge of the leaf. There are no specific symptoms of phosphorus deficiency except that the plants are smaller and less vigorous. Again, you should do a soil test to determine whether there really is a deficiency before taking any action.
"When it comes to rates of phosphorus and potassium on alfalfa, really the soil test should rule," said Gerwing. An excellent time to apply the fertilizer would be immediately after producers have taken their first cutting of hay.
Be sure to be checking your fields for deficiencies and making corrections as needed. For more information on nutrient deficiencies, call the Clay County Extension Office at 677-7111.