Nitrogen and Water Interactions in Subsurface Trickle‐Irrigated Leaf Lettuce II. Agronomic, Economic, and Environmental Outcomes

Abstract

AbstractEvaluation of trickle‐irrigated crop production systems should address agronomic, economic, and environmental outcomes. The objectives of this research were to: (i) determine plant N uptake, residual soil inorganic N, unutilized fertilizer N, and unaccounted fertilizer N for subsurface trickle irrigated leaf lettuce (Lactuca sativa L. cv. Waldmann's Green), and (ii) use spatial analysis techniques to simultaneously evaluate agronomic, economic, and environmental production criteria for leaf lettuce within one growing season. Field experiments were conducted using buried trickle irrigation during three winter growing seasons in southern Arizona. Deficient to excessive N (35–300 kg ha‐1) and target soil water tension (SWT) treatments (12.0–4.0 kPa) were applied in factorial combinations each year. Fertilizer N recovery was determined by the difference method. Spatial analysis of response surfaces was used to determine overlap of zones with acceptable values for marketable yield, net economic return, and unaccounted fertilizer N for leaf lettuce during 1992–1993. Maximum unutilized fertilizer N was 216 kg ha‐1 for leaf lettuce, and maximum unaccounted fertilizer N was 149 kg ha‐1. Unutilized fertilizer N and unaccounted fertilizer N increased sharply when adequate N and water rates were exceeded. Spatial analysis of response surfaces for 1992–1993 showed a small region bounded by 6.6 to 7.3 kPa SWT and 238 to 252 kg N ha‐1 that would have resulted in >95% of maximum predicted marketable yield and net return while limiting NO3‐N concentrations in drainage water to ≤10 mg L‐1.