Studies on the growth rate and nutrient absorption of head lettuce

Two field experiments were conducted with subsurface trickle-irrigated romaine lettuce (Lactuca sativa L. cv. Parris Island Cos) during the 1990–92 winter growing seasons in southern Arizona. The objectives were to determine 1) yield and quality response to varying combinations of soil water tension (SWT) and N fertilizer, 2) seasonal patterns of N uptake, and 3) unutilized fertilizer N. During 1990–91, N rates were 35, 120, and 205 kg·ha–1. During 1991–92, the experiment was factorial with N levels from 50 to 300 kg·ha–1 and target SWT levels of 7.0 and 4.0 kPa. Unutilized fertilizer N was the difference between fertilized and nonfertilized plots in total N inputs not harvested in the crop. When excessive irrigation was not applied (SWT between 6.5 and 7.4 kPa), 95% of the maximum crop yield and yield quality (head length and fresh mass) response occurred at N rates of 156 to 193 kg·ha–1, with unutilized fertilizer N <60 kg·ha–1. Excessive irrigation (4.6 kPa) resulted in lower yields and yield quality and higher unutilized fertilizer N. Romaine accumulated >74% of its total N uptake in the 38 days before harvest. Unutilized fertilizer N increased sharply when adequate N and water rates were exceeded. These results suggest that a target SWT of no wetter than 6.5 kPa is appropriate for subsurface trickle-irrigated romaine lettuce.

Section: Resultssupporting

confidence: 88%

Section: Methodsmentioning

confidence: 99%

Nitrogen and Water Rates for Subsurface Trickle-irrigated Romaine Lettuce

Thompson¹,

Doerge²

1995

“…Furthermore, the large variability among fields suggested that even under potentially N-limited conditions factors other than N availability could confound diagnosis. The midrib samples were taken prior to the second sidedressing, which occurred at approximately the "cupping" stage that initiates head formation, before the rapid growth phase; under California coastal conditions <30% of total seasonal crop N uptake would have occurred at this time (Zink and Yamaguchi, 1962). Pritchard et al (1995) reported that, because of the slow early growth rate of lettuce, well-defined differences in midrib NO 3 -N levels among a range of N treatments did not consistently occur until the last one-third of the season.…”

Section: Discussionmentioning

confidence: 99%

The Value of Presidedress Soil Nitrate Testing as a Nitrogen Management Tool in Irrigated Vegetable Production

Hartz¹,

Bendixen²,

Wierdsma³

2000

The utility of presidedress soil nitrate testing (PSNT) in irrigated lettuce (Lactuca sativa L.) and celery (Apium graveolens L.) production was evaluated in 15 commercial fields in California from 1996 to 1997. Fields were selected in which soil NO3-N (5- to 30-cm depth) was >20 mg·kg–1 at the time the cooperating grower made the first sidedress N application. The grower's N regime was compared with reduced N treatments established by reducing or eliminating one or more sidedress applications. All fields were sprinkler and/or furrow irrigated, with minimal in-season precipitation. Reductions in seasonal N application averaging 143 and 209 kg·ha–1 N in lettuce and celery trials, respectively, had no effect on marketable yield in any field. Crop biomass N at harvest in the lowest N treatment in each field averaged 94% (lettuce) and 88% (celery) of that in plots receiving the full grower N program. Based on controlled-environment aerobic incubation of soil from 30 fields in long-term vegetable rotations, in-season N mineralization averaged 1% to 2% of soil organic N. A soil NO3-N “quick test” procedure utilizing a volumetric extraction of field-moist soil and measurement by nitrate-sensitive colorimetric test strips was evaluated and proved to be a practical on-farm method to estimate soil NO3-N concentration. Lettuce midrib NO3-N concentration at cupping stage was poorly correlated with current soil NO3-N level. We conclude that PSNT can reliably identify fields in which sidedress N application can be delayed or eliminated without affecting crop performance.

“…Groundwater nitrate contamination is of particular concern in the coastal valleys of central California, where many wells now exceed the U.S. Environmental Protection Agency drinking water standard of 10 mg·kg -1 NO 3 -N. Vegetable production dominates agriculture in these valleys, with lettuce by far the most common crop. Seasonal N application >200 kg·ha -1 is common for lettuce production (Hartz et al, 2000), substantially more than crop N uptake, and perhaps three times the amount of N removed in harvested product (Doerge et al, 1991;Zink and Yamaguchi, 1962). Similar imbalance between the amount of N applied and that removed in harvested product exists for the other common vegetable crops grown in rotation with lettuce in this region.…”

mentioning

confidence: 99%

Presidedress Soil Nitrate Testing Reduces Nitrogen Fertilizer Use and Nitrate Leaching Hazard in Lettuce Production

Breschini¹,

Hartz²

2002

Trials were conducted in 15 commercial fields in the central coast region of California in 1999 and 2000 to evaluate the use of presidedress soil nitrate testing (PSNT) to determine sidedress N requirements for production of iceberg and romaine lettuce (Lactuca sativa L.). In each field a large plot (0.2-1.2 ha) was established in which sidedress N application was based on presidedress soil NO3-N concentration. Prior to each sidedress N application scheduled by the cooperating growers, a composite soil sample (top 30 cm) was collected and analyzed for NO3-N. No fertilizer was applied in the PSNT plot at that sidedressing if NO3-N was >20 mg·kg-1; if NO3-N was lower than that threshold, only enough N was applied to increase soil available N to ≈20 mg·kg-1. The productivity and N status of PSNT plots were compared to adjacent plots receiving the growers' standard N fertilization. Cooperating growers applied a seasonal average of 257 kg·ha-1 N, including one to three sidedressings containing 194 kg·ha-1 N. Sidedressing based on PSNT decreased total seasonal and sidedress N application by an average of 43% and 57%, respectively. The majority of the N savings achieved with PSNT occurred at the first sidedressing. There was no significant difference between PSNT and grower N management across fields in lettuce yield or postharvest quality, and only small differences in crop N uptake. At harvest, PSNT plots had on average 8 mg·kg-1 lower residual NO3-N in the top 90 cm of soil than the grower fertilization rate plots, indicating a substantial reduction in subsequent NO3-N leaching hazard. We conclude that PSNT is a reliable management tool that can substantially reduce unnecessary N fertilization in lettuce production.