Rising water costs and concerns about groundwater contamination by NO ‐ 3 are forcing growers in arid regions to adopt practices to improve water and N use efficiency. Subsurface trickle irrigation offers the ability to precisely deliver appropriate amounts of water and N to the crop root zone. The objectives of this research were to: (i) determine the optimum level (with respect to marketable yield) of soil water tension for subsurface trickle‐irrigated leaf lettuce ( Lactuca sativa L. cv. Waldmann's Green), (ii) determine N by water interactions on crop yield and quality, and (iii) determine seasonal patterns of crop N uptake. Three field experiments were conducted during the 1990 to 1993 winter growing seasons on a Casa Grande soil (fine‐loamy, mixed, hyperthermic, Typic Natriargid [reclaimed]) 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. Maximum marketable leaf lettuce yields observed were 54.0 Mg ha ‐1 . Nitrogen rates associated with maximum yields ranged from 120 to 300 kg ha ‐1 , and depended on average SWT. Excessive irrigation (5.3 kPa average SWT) resulted in lower yields, head weight, and head length. Marketable yields showed a pronounced water × N interaction, but yield quality (head length and weight) did not. Maximum N flux was 4.3 kg ha ‐1 d ‐1 , and an average of 75% of total N accumulation occurred in the 38 d prior to harvest. Results suggest that the soil water tension at 0.3‐m depth should be maintained at 6 to 7 kPa for optimum yields of trickle‐irrigated leaf lettuce.
No takes yet. Share an insight, caveat, or question.
Thompson et al. (1996) studied this question.