To provide dependable fertilizer recommendations each field should be tested at least once every third year. The soil supplies 13 nutrient elements that are required by corn for proper growth. Most of these elements are not required in fertilizer because their levels in Ontario soils are sufficient to meet crop requirements. Most corn growers need to consider only nitrogen, phosphorous and potassium when planning their fertilizer program, although deficiencies of zinc or magnesium are sometimes encountered. A lack of nitrogen results in stunted yellow plants, reduced yields, delayed maturity and increased lodging.
Excessive nitrogen can result in reduced yields, and increased lodging.
Extreme levels can result in nitrate accumulation in the stalk which may lead to production of silo gas. Therefore, it is important that nitrogen application rates be appropriate for the yield expected. Because of the complexity of the nitrogen cycle in soil, no reliable test has been found to measure the ability of soil to supply nitrogen in Ontario. Recommendations for nitrogen are based on a standard application rate with adjustments for soil texture, manure usage, crop rotation, time of application and expected yield. Several forms of nitrogen fertilizer are available for use in corn.