Solute Movement in an Irrigated Cotton Production System

J.C. Silvertooth, J.E. Malcuit, and J.E. Watson


 
ABSTRACT

A single field experiment was conducted in 1988 on a Mohall sandy loam soil in central Arizona to characterize the solute leaching potential within a furrow irrigated cotton production system. Objectives were 1) to characterize the spatial and temporal variability of solute leaching within a generally uniform field under uniform management conditions, and 2) to develop a characterization of the "worst case" leaching potential of solutes within the system. To facilitate solute leaching measurement, Br- was used as a biologically conserved tracer. Applications of Br- were made as KBr to lm(2) Subplots (20g Br- M-2) within six mainplot areas, which were spaced equidistantly throughout the field (experimental area). Subplot areas were treated separately at five different times in the season, and soil from each subplot area was sampled to a depth of six feet (by one foot increments) after one to three irrigation events. Mainplot arrangement was intended to provide information regarding spatial variability, and subplots provided information describing differences in leaching encountered as a function of time in the growing season (irrigation rates and frequencies, and consumptive use patterns of the crop). Soil samples were analyzed for NO3--N and Br- concentrations from each one foot depth increment, for each subplot area. Amounts of irrigation water and fertilizer N applied in the growing season were recorded. Also, plant tissue analyses (petioles) were used to monitor the crop's N nutritional status throughout the season. Results of this experiment revealed a very high degree of spatial variability associated with both the Br- and NO3-N distributions throughout the soil profiles with any given sampling date. In terms of "worst case" leaching potentials, the Br- data indicated a substantial potential for downward movement through the extent of the profile measured in this experiment (six feet) after approximately 12 - 18 acre inches of irrigation water were applied. These results indicate the importance of proper and thorough soil sampling procedures that are needed for any attempt to monitor or measure the concentration of a given solute (such as NO3 or Br-) within an agricultural production setting. From a management standpoint, these results provide reinforcement to growers to utilize available N management tools for a cotton crop such as: residual NO3--N levels in the soil, NO3--N contributions from irrigation water, N use patterns by the crop, petiole testing, and split applications of fertilizer N over the course of the growing season; in an effort to maintain adequate but not excessive levels of N available to the crop at any given time.



Reprinted from 1990 Proceedings: Beltwide Cotton Production Research Conferences pp. 500 - 501
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998