Bromide and Nitrate Movement in an Irrigated Cotton Production System

Abstract

AbstractA field experiment was conducted for the purpose of determining the worst‐case potential for solute leaching under furrow‐irrigated conditions, and to assess the spatial variability associated with solute movement. The experiment was carried out on a Mohall sandy loam soil (fine‐loamy, mixed, hyperthermic Typic Haplargid) within a field of upland cotton (Gossypium hirsutum L.), with uniformity of all management factors including fertilizer N and irrigation water. Six mainplot areas were identified throughout the study area to provide characterization of spatial variability. Within each main plot, five subplots (1 m2 each) were further identified. To each subplot area, 20 g KBr was applied in 500 mL of solution using the Br‐ as a biologically conserved tracer. Soil from each subplot was sampled to a depth of 180 cm and separated into 30‐cm depth increments. Soil samples were then subjected to a 1:1 (soil/water) extraction and analyzed for Br‐ and NO‐3‐N. Appreciable amounts of solute movement were measured, with a very high degree of spatial variability. The highest degree of leaching potentials was measured early in the season, when soil water depletions were the lowest and crop root development would not be extended past very shallow regions of the soil profile. The results reinforce the need to split fertilizer‐N applications throughout the course of a growing season, and to base fertilization rates and frequency on properly calibrated plant‐tissue tests.