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Precipitation has been plentiful this spring and early summer, which is great for farm fields, gardens and flowers.

However, we had been lacking warm weather and growth until the last week of June/early July. This lack of heat may have affected some early planted crops and limited the ability to access areas to plant.

As of June 17, we had the coolest season on record and the seventh wettest season at the UW Agricultural Research Station in Marshfield.

Highest crop yields will be obtained only where environmental conditions are favorable at all stages of the crop growth. Area farmers need warm temperatures and occasional rain showers this summer to achieve the optimum yields for their crops.

Fertilization

Retired UW-Madison professor L.G. Bundy reported, “Profitable corn production requires an adequate soil fertility program. Insufficient nutrients lower yields; excess nutrients will lower profit margins and many damage the environment through nutrient runoff and leaching. Corn must receive adequate amounts of nutrients to fully realize yield benefits from other management practices such as early planting dates, section of adapted hybrids, and effective weed and insect control.”

Corn uses substantial amounts of nitrogen, phosphate, potash and relatively small amounts of secondary nutrients and micronutrients. The nutrients taken up by the plant must be supplied either from soil reserves or by adding nutrients. A deficiency of any of these nutrients can reduce yields.

The best way to determine the level of nutrients available in the soil and the kinds and amount of supplemental fertilizer needed is through soil testing and using calibrated fertilizer recommendations based on the soil sampling results.

Soil sampling procedures and information on fertilizer recommendations based on soil test results can be found on the UW Soils Lab website — https://uwlab.soils.wisc.edu/.

Farmers may be also concerned about nitrogen loss in their crops due to delayed planting and ponding water in fields. Corn yields are more often limited by inadequate supplies of nitrogen than by deficiencies of other essential nutrients.

This is because corn has a high nitrogen requirement and losses of applied nitrogen can occur during the growing season by leaching, denitrification, or other processes. Thus, it is important for farmers to accurately determine corn nitrogen requirements and to use effective management practices to minimize losses of applied nitrogen.

Corn requires annual additions of nitrogen from commercial fertilizer, manure or previous legume crops because the amount of soil-supplied nitrogen is usually less than the total crop requirement.

The nitrogen requirements differ from sandy soils (sand and loamy sands) depending on whether or not they are irrigated.

The lower recommendations for non-irrigated sandy soils reflect the lower corn yield potential in an environment where moisture is often inadequate.

For medium and fine-textured soils, nitrogen recommendations are based on soil yield potential and organic matter content. The yield potential ranking for each soil series is based on soil characteristics such as drainage, depth of root zone, and water holding capacity. Soils with very high or high yield potentials receive higher nitrogen recommendations than those with a medium or low yield potential ranking. Yield goals are not a factor in making nitrogen recommendations. Yields are more variable than optimum nitrogen rates because corn recovers nitrogen more efficiently in favorable growing conditions and less efficiently in poor growing conditions.

Timing of application

The nitrogen application rate decision in the most important management factor affecting the profitability of nitrogen use in corn production and the risk of nitrate loss to groundwater.

The key initial step in arriving at the nitrogen rate decision is to use the appropriate recommendations for the soil and to credit the amounts of nitrogen provided from non-fertilizer sources. Soil nitrate tests can often help to identify optimum nitrogen rates for corn on a site-specific basis. In addition to the rate applied, other nitrogen management options can also influence fertilizer effectiveness. These options include the nitrogen fertilizer source used and the method and timing of nitrogen application.

Two soil nitrogen tests are available. The pre-plant soil nitrate test assesses the nitrogen requirements by measuring the residual soil profile nitrate before planting the corn. The pre-side dress soil nitrate test estimates nitrogen availability mainly from organic nitrogen sources and predicts the amount needed for a side dress or in-season nitrogen application.

Benefits from side dress applications are likely to be greatest on sandy soils and fine-textured, poorly drained soils where the risk of nitrogen loss through leaching or denitrification are high. Delaying nitrogen application for 4-6 weeks after planting will avoid early season nitrogen losses and provide available fertilizer nitrogen to the crop when it is needed.

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For more information on Corn Fertilization, please reference UW-Madison Division of Extension publication A3340 at https://learningstore.extension.wisc.edu or contact the Extension Dunn County office at 715-232-1636.

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