Fertilizer 15Nitrogen Recovery by Corn, Wheat, and Cotton Grown with and without Pre-Plant Tillage on Norfolk Loamy Sand

Cropping systems must efficiently use N inputs to be sustainable environmentally and economically. This research was conducted to determine the fate of ¹⁵N fertilizer that was applied to corn (Zea mays L.), wheat (Triticum aestivum L.), or cotton (Gossypium hirsutum L.) grown in a 2-yr, three-crop rotation on Norfolk (Typic Kandiudult) loamy sand. A total of 48, 2.3- by 2.3-m microplots were established, half into plots that received surface tillage (disked) and half into non-disked plots. Corn and wheat received a split application of urea [CO(NH₂)₂] plus ammonium nitrate (NH₄NO₃) solution (UAN) had a 5 atom percent (ATM%) ¹⁵N isotopic label. Cotton was fertilized with NH₄NO₃ containing a 5 ATM% label. The amounts of ¹⁵N removed in the harvested portion of treated and subsequent crops, recycled in crop residues, or remaining in the upper 90 cm of the soil profile were determined. Corn, wheat, and seed cotton yields ranged from 1485 to 7410, 1850 to 2270, and 120 to 2510 kg ha⁻¹, respectively, with significant differences caused primarily by seasonal rainfall or temperature extremes. No-till significantly increased cotton yield, presumably because of water conservation. Crop removal accounted for 20 to 34% of the fertilizer ¹⁵N, while another 20% was accounted for by soil profile analysis to a depth of 90 cm. Approximately 50% of the ¹⁵N was apparently lost through denitrification, volatilization, or leaching below the root zone. Most of this loss appeared to occur during the cropping season in which the ¹⁵N was applied. This suggests that for optimum fertilizer efficiency and environmental sustainability, crop production practices on Coastal Plain soils must account for all N sources that plants can draw upon, and should accommodate several fertilizer N management options including split applications, injection beneath the soil surface, and/or using less mobile forms.