Using a chlorophyll meter to manage nitrogen applications to corn with high nitrate irrigation water

Chlorophyll meters can aid in measuring the nitrogen (N) status of corn (Zea mays), but will the use of chlorophyll meters decrease total N use or increase corn grain yield? Use of a fully fertilized reference strip with a chlorophyll meter (SPAD 502) is an accepted management strategy. The critical level of relative chlorophyll necessary to trigger supplement N is uncertain. To determine the impact of using a 96 or 92% critical level of chlorophyll readings relative to a fully fertilized reference strip, 0 and 112 N kg ha(-1) were applied at planting for three years. Specific plots were fertilized with an additional 56 kg N ha(-1) whenever the meter reading on those plots was below either 96 or 92% of the reference area. The experiment was conducted on two Typic Haplustolls and an Entic Haplustoll. Irrigation water contained nitrate ranging from 20 to 38 mg L-1. Irrigation water supplied from 43 to 120 kg N ha(-1) season(-1). For all treatments that received N-supplements based on the chlorophyll meter, yields were statistically the same. The chlorophyll meter is a useful management tool to help schedule N applications, when irrigation water is contaminated with nitrate since use of the chlorophyll meter prevented any yield limiting N deficiencies.