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 (Ze a mays), but will the use of chlorophyll meters decrease total N use or inc rease corn grain yield? Use of a fully fertilized reference strip with a ch lorophyll meter (SPAD 502) is an accepted management strategy. The critical level of relative chlorophyll necessary to trigger supplement N is uncerta in. To determine the impact of using a 96 or 92% critical level of chloroph yll 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 ferti lized 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 wat er contained nitrate ranging from 20 to 38 mg L-1. Irrigation water supplie d 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.