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DIVISION S-4 - SOIL FERTILITY & PLANT NUTRITION

Subsurface Drip Irrigation and Fertigation of Broccoli

II. Agronomic, Economic, and Environmental Outcomes

^a Dep. of Soil, Water, and Environmental Science, University of Arizona, 429 Shantz Bldg. #38, Tucson, AZ 85721
^b Pioneer Hi-Bred International, Inc., P.O. Box 1150, Johnston, IA 50131
^c Colorado State University, Rogers Mesa Research Center, 3060 Highway 92, Hotchkiss, CO 81419

* Corresponding author (thompson{at}ag.arizona.edu)

Subsurface drip irrigation offers potential for increased water and N fertilizer use efficiency, and decreased groundwater NO₃ pollution. Replicated factorial experiments consisting of four rates of N fertilizer application (60–500 kg ha^-1) and three target soil water tensions (SWT) (low, medium, and high) were conducted on subsurface drip-irrigated broccoli (Brassica olearacea L. Italica) during three winter growing seasons in southern Arizona. Objectives were to (i) determine effects and interactions of irrigation water and N inputs on net economic return, residual soil NO₃-N, and unaccounted fertilizer N, and (ii) use abstract spatial analysis techniques to simultaneously evaluate agronomic, economic, and environmental production functions during three growing seasons. Spatial analysis was used to identify overlap of acceptable zones of marketable yield, net return, and unaccounted fertilizer N. Acceptable yields and net return were defined as 95% of maximum predicted response within the range of the treatments, and acceptable unaccounted fertilizer N was defined as 40 kg ha^-1. During this study, >95% of maximum net return encompassed N rates of 300 to 500 kg ha^-1, and SWTs of 7 to 25 kPa. There was little accumulation of NO₃ in the top 0.9 m of soil when 350 kg N ha^-1 were applied. Unaccounted N increased with excessive N and water inputs, and accounted for as much as 46% of N applied. Overlap of acceptable zones of agronomic, economic, and environmental production criteria was achieved in each year. Areas of overlap were bounded by 300 to 325 kg N ha^-1 and 8.5 to 12 kPa in 1993–1994, 350 to 500 kg N ha^-1 and 11 to 14 kPa in 1994–1995, and 340 to 410 kg N ha^-1 and 11 to 24 kPa in 1995–1996.

Abbreviations: SWT, soil water tension

This article has been cited by other articles:

				T. L. Thompson, S. A. White, J. Walworth, and G. J. Sower Fertigation Frequency for Subsurface Drip-Irrigated Broccoli Soil Sci. Soc. Am. J., May 1, 2003; 67(3): 910 - 918. [Abstract] [Full Text] [PDF]