Meeting the soil’s lime requirement is the first essential step in an efficient and successful fertility program. For fields where corn is grown in rotation with legume crops, maintain the pH between 6.5 and 7.0. The performance efficiency of the triazine herbicides and the availability of most plant nutrients are greatest within this pH range; pH for continuous corn fields should be maintained between 6.2 and 7.0.
Apply lime whenever it is required. During the last year of corn in a rotation, and before small grains or legume forage crops are planted, are critical times to meet lime requirements and minimize corn herbicide residue problems on the succeeding small grains. In addition, replace atrazine and/or simazine with shorter residue herbicides in this last year of corn.
Reduced tillage systems can contribute to the development of an acidic soil surface, often referred to as an “acid roof,” because of surface applications of nitrogen fertilizers and manure and the decay of organic materials in this layer. Therefore, the pH of the 1- to 2-inch surface of minimum and no-tillage corn fields should be measured each year. Collect several soil cores, each 1 to 2 inches deep, thoroughly mix them in a clean bucket, and remove a sample for pH measurement. A simple colorimetric kit using pH indicator solutions is satisfactory, fast, and inexpensive. These kits, available at most local extension offices and lawn and garden stores, do not determine lime requirements.
If the pH of the surface soil is less than 6.2, take a standard soil sample for laboratory analysis and lime requirements. The recommended lime should be applied as early as possible before corn planting. If the standard test does not call for any lime but the surface pH is less than 6.2, apply 2,000 pounds of limestone per acre.