Current standard recommendations are based on long-term research throughout the state, but general recommendations fail to take into account variations due to weather, rainfall, manure applications, residual soil nitrogen, and situations where all the nitrogen may be applied prior to planting. To compensate for these uncertainties, growers may apply more nitrogen than is needed by the crop, resulting in increased production costs and potential for nitrates leaching into groundwater or running off in surface water. Several techniques have been used in Alabama and in other parts of the United States to fine-tune nitrogen applications. Multiple or split nitrogen applications help. Fertigation is useful where growers irrigate.
Some growers take whole plant samples early and monitor the ear leaf nitrogen at tasseling.
The chlorophyll meter has shown promise for identifying nitrogen deficient corn at side dressing time and especially at silking. All of these are useful tools, but each has its own limitations. Most tend to encourage over-application of nitrogen fertilizers. Soil nitrogen testing has not proved very useful in the humid eastern United States because most nitrogen fertilizers are mobile in the soil. They don't stay around long following heavy rainfall.