Michigan State University Extension
Soils & Soil Management - Fertilizer - 06029707
07/10/97
Fertilizer Recommendations for Field Crops in Michigan Extension Bulletin E-550A, March 1992
D. R. Christenson, D. D. Warncke, M. L. Vitosh, L. W. Jacobs and J. G. Dahl, Department of Crop and Soil Sciences
Crop response to increasing levels of soil fertility or applied fertilizer is continuous-that is, yield increases do not occur in a stepwise manner, but increase gradually with increasing levels of available nutrients. The recommendations in the tables of this bulletin reflect this type of response to applied nutrients over a range of soil test values. Equations are used to calculate the recommendations and are given as footnotes to each table.
Nitrogen (N)-Nitrogen needs depend on the crop to be grown, yield goal and previous management practices. A reliable nitrogen soil test taken before planting is not currently adopted for general use in the Great Lakes States. However, progress has been made using a pre-sidedress test for adjusting nitrogen recommendations for corn. This test is taken to a depth of 1 foot and analyzed for mineral nitrogen. Credit given for this nitrogen is subtracted from the current nitrogen recommendation based on yield goal.
Bacteria living symbiotically in alfalfa and clover root nodules use atmospheric N in their growth and development. Some of this "fixed" N is available directly to the host plant and some is excreted into the soil where it is available for plant uptake. When the bacteria die and the nodules decompose, additional nitrogen becomes available. Because of this nitrogen fixation by the bacteria, leguminous crops do not usually need or respond to applied nitrogen fertilizer.
When alfalfa or clover is the previous crop, a nitrogen credit is given based on percent stand. The N credit (lb/acre) for alfalfa is given by the equation: 40 + (0.60 times percent stand), where 5 to 6 plants per square foot is a 100 percent stand. For clover the equation is: 30 + (0.30 times percent stand).
Credit for nitrogen supplied from animal manures needs to be subtracted from the nitrogen recommendations listed in this bulletin. See the section titled "Manure and Other Organic Materials" for more information.
Several sources of nitrogen fertilizer are suitable for crop production. The materials are usually equally effective and should be purchased on the basis of cost per pound of actual nitrogen, convenience of application and supply.
Efficiency of nitrogen fertilizer use can be improved and nitrate contamination of surface and groundwaters can be minimized by using recommended nitrogen rates and timely nitrogen application. Proper scheduling of irrigation water to minimize leaching also minimizes nitrogen losses and maximizes efficiency.
Fall application of nitrogen is not recommended on either organic or mineral soils. Similarly, do not broadcast nitrogen on frozen ground with greater than 3 percent slope. When applying anhydrous ammonia, be sure to completely trap the gas in the soil.
Most nitrogen carriers leave an acidic residue in the soil. It requires approximately 2 pounds of limestone to neutralize the acidifying effect of each pound of nitrogen derived from urea, ammonium nitrate, anhydrous ammonia or nitrogen solutions, and 5.5 pounds if ammonium sulfate is used.
ORGANIC SOILS. Even though there is a considerable amount of nitrogen converted to the nitrate form from the organic matter in organic soils, much of it is lost through denitrification. The net available nitrogen released ranges from 40 to 100 pounds per acre. On sandy mucks the amount released is less so increase recommendations given in (Vis. 16) by 30 to 40 pounds.
Phosphorus (P)-PHOSPHORUS needs are based on soil test, crop to be grown and yield goal. Small plants need more phosphorus than most other nutrients, making it important to have this phosphorus available for growth early in the growing season. Previous research conducted on soils testing less than 30 pounds of phosphorus has shown both an early season growth response and a yield response to banded phosphorus. However, more recent research on soils testing higher in phosphorus has not shown the yield response from banded phosphorus even though there may be an early season improvement in plant growth. There is little chance that banded phosphorus will increase crop yields of most field crops when grown on mineral soils testing above 60 pounds per acre.
More than half of the soils in Michigan used for field crop production test very high in available phosphorus. Research shows that some reduction in soil test levels can occur without reducing crop yields. Research shows that drawdown of soil test P is similar to buildup, taking 5 to 18 pounds of P2O5 removal to decrease the soil test 1 pound. Reducing the amount of phosphate fertilizer applied does not cause a sudden reduction in the soil test value of high testing soils.
ORGANIC SOILS: - When phosphorus is recommended for crops grown on organic soils, banding 25-40 pounds of phosphate per acre is suggested, particularly for early planted crops. However, when soil test levels are high, banded phosphorus is not suggested.
In newly developed fibrous peats, banded phosphorus applications are more effective because phosphorus remains fairly mobile. After being in production for five years, available phosphorus levels begin to increase and routine phosphorus management can be followed.
Potassium (K)-The terms potassium and potash are often confused. Potassium is the element and is expressed with the chemical symbol K. Potash is K2O and is the expression used for expressing percent contained in a fertilizer. For example, 0-0-60 is potassium chloride and contains 60% K2O (potash).
The availability of potassium in a soil is related to the types and amounts of clay minerals present. Depending on the soil texture, 2 to 6 pounds of K2O are required to increase the soil test by 1 pound K per acre. The present soil test used for potassium can adequately predict the availability of potassium for most Michigan soils. However, some soils fix potassium in forms that are not readily available to plants. Because routine soil testing does not determine the various types of clay minerals or the fixing ability of a soil, soils containing vermiculitic clays may require higher than recommended rates of potash (K2O) to build up the available soil potassium. Once such soils have a medium to high potassium soil test level, they continue to supply potassium for some time, even though crop removal may be considerable.
Small seedlings have less need for potassium than for phosphorus. However, once plants start to grow rapidly, they use larger amounts of potassium. Since there is not a large demand for potassium by seedlings, broadcast application of potassium is as effective as banded potassium. Where the soil test is below 100 pounds per acre, banding 50-75 pounds of K2O per acre to the side and below the seed may be beneficial.
Fall application Of potassium on loamy sand and sand soils is not recommended because potassium can leach into the subsoil and may not be available for crop growth. However, potassium fertilizer can be broadcast in the fall on the finer textured soils.
| Visual title - Visual size | Visual title - Visual size |
|---|
| Nitrogen recommendations for field crops grown on organic soils - 27K |
