Bromide and Nitrate Movement in an Irrigated Cotton Production System

Abstract

A 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.

Application of a 15 N tracer to simulate and track the fate of atmospherically deposited N in the coastal forests of the Waquoit Bay Watershed, Cape Cod, Massachusetts

“…Similar applications were conducted on two separate plots in each experimental site in October of 1994. Bromide (Br A ), considered to be a conservative ion in soil water (Bowman 1984;Silvertooth et al 1992), was used as a reference ion to compare recoveries of 15 N in lysimeter leach-ate.…”

Furrow Irr Igation and N Management Strategies to Protect Water Quality

“…Where we irrigated alternating furrows, we irrigated Furrow A at the first irrigation, then Furrow B on thé opposite side of the row at the second irrigation, then A, etc. Where alternating furrows were irrigated, the nonfertilized furrow was irrigated first because the first irrigation of the season often leaches the most solute from the profile (Tracy and Hefner, 1993;Silvertooth et al, 1992). The subplot treatments (row spacings, Fig.…”

“…1) were a) 50% of the N (always as urea, 0.45 kg N kg-1 ) broadcast pre-plant then 50% sidedressed at the eight-leaf stage 6 wks after planting, b) 50% banded at planting then 50% sidedressed at the eight-leaf stage, or c) no N fertilizer applied. The N application was split to apply the N when it could be best utilized by the growing corn (Silvertooth et al, 1992). Each plot was four rows wide and 102 m long.…”

Surface fertigation: a review, gaps and needs

“…The estimation of fertilizer leaching requires intense experimental work before and after the fertigation event, and is affected by the strong spatial variability of soil water and fertilizer concentration, as well as by the sampling strategy. Field experiments on a sandy loam in Arizona (USA) showed that high potential for solute leaching under furrow-irrigated conditions with a very high degree of spatial variability (Silvertooth et al, 1992). Conducting fertilization experiments, Jaynes et al (1992) found that the average leaching depth of a mobile tracer applied with irrigation water was about 60% deeper than when the mobile tracer was pre-applied to the soil surface immediately before conventional irrigation in a level basin system.…”