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Overcoming environmental stresses during seedling establishment is crucial to successful vegetable production. In the irrigated production areas of the southwestern United States, stress most often is related to unfavorable temperature, soil or water salinity, or poor soil structure; it is frequently difficult to separate the effects of these stresses, since they may all be present to some significant degree. Growers use a variety of techniques to ameliorate these conditions. The use of sprinkler irrigation for stand establishment has become a widespread practice; sprinkling moderates soil temperature, minimizes salinity in the zone of germination, and reduces soil crusting. By modifying bed configuration, growers have been able to increase soil temperature to stimulate germination. Various chemical and physical treatments have proven effective in reducing soil crusting. The use of transplants has expanded for many crops, both as a means to circumvent seedling establishment problems and as a technique to obtain earliness.
Drip-irrigation scheduling techniques for fresh-market tomato (Lycopersicon esculentum Mill.) production were compared in three growing seasons (1989-91). Three regimes were evaluated: EPK [reference evapotranspiration (ETo, corrected Penman) × programmed crop coefficients], ECC (ET0 × a crop coefficient based on estimated percent canopy coverage), and SMD (irrigation at 20% available soil moisture depletion). EPK coefficients ranged from 0.2 (crop establishment) to 1.1 (full canopy development). Percent canopy coverage was estimated from average canopy width ÷ row width. Irrigation in the SMD treatment was initiated at -24 kPa soil matric tension, with recharge limited to 80% of daily ET0. The EPK and ECC regimes gave similar fresh fruit yields and size distributions in all years. With the EPK scheduling technique, there was no difference in crop response between daily irrigation and irrigation three times per week. In all seasons, ECC scheduling resulted in less total water applied than EPK scheduling and averaged 76% of seasonal ET0 vs. 86% for EPK. Irrigating at 20% SMD required an average of only 64% of seasonal ET0; marketable yield was equal to the other scheduling techniques in 1989 and 1991, but showed a modest yield reduction in 1990. Using an SMD regime to schedule early season irrigation and an ECC system to guide application from mid-season to harvest may be the most appropriate approach for maximizing water-use efficiency and crop productivity.
A 1993 survey of 50 commercial processing tomato fields in California revealed widespread potassium deficiency, as determined by tissue K levels below existing sufficiency standards and the occurrence of vine necrosis consistent with K deficiency. Soils from these fields were analyzed for exchangeable K by ammonium acetate extraction, and for K release rate by a 7 day incubation procedure (1:10 soil:. 01 M CaCl2 at 25°). Soil K release rate was more highly correlated with tissue K at midseason than was exchangeable K. These soils were further examined for K fixation capacity. Three g soil was blended with 3 ml 10 meq K as KNO3, allowed to dry, incubated for 7 days in a 1:10 soil: H2O solution, then extracted in 1 N NH4Cl; added K not recovered was considered fixed. Percent K fixation ranged from 0 to 82%. These data suggest that the inconsistent response of processing tomato to K application in numerous California trials may be related to a) the reliance on extractable K analysis to characterize soil K supply and b) no consideration of soil K fixation capacity in determining K application timing and method.
Drip irrigation scheduling techniques for fresh market tomato production were compared in three consecutive seasons (1989-1991) in the southern coastal environment of Irvine, California. Three techniques were compared: 1) reference evapotranspiration (ETo, corrected Penman) × programmed crop coefficients (Kc), ranging from 0.2 (crop establishment) to 1.1 (full canopy development); 2) ETo × Kc, based on % canopy cover as estimated by average canopy width per row; and 3) irrigation at 20% available soil moisture depletion (SMD) at 30 cm, with recharge limited to a maximum of 0.8 × cumulative ETo since the previous irrigation. The use of programmed crop coefficients and Kc values based on % canopy cover gave equivalent yields and fruit size distribution in all years; there was no difference in crop response between daily irrigation and irrigation three times a week. Both scheduling techniques maintained soil water content in the top 45 cm near field capacity throughout the growing season. The use of Kc based on % cover required less total irrigation in all seasons, averaging 78% of seasonal ETo vs. 88% with programmed coefficients. Irrigation at 20% SMD required an average of only 66% of seasonal ETo; marketable yield was equivalent with the other scheduling techniques in 1989 and 1991 but showed a modest yield reduction in 1990.
The use of drip irrigation in the production of vegetable crops has expanded rapidly in the Southwest in the last decade. The factors contributing to this conversion are: a) water availability and cost, b) improved design and production of drip irrigation products which has dramatically improved performance and reliability, c) reduced cost of drip irrigation in relation to other crop production costs, and d) development of integrated management practices which maximize crop productivity and system performance. Regionally, more than 30,000 ha of vegetable crops are produced annually using drip irrigation, the majority of which is in California; major commodities are tomato, pepper, melons and salad crops. Many different types of drip installations have been evaluated. The trend in new installations is toward buried systems in semipermanent beds, with multiple crops being produced before system renovation. Specialized management practices are evolving which make such systems highly efficient.
Overcoming environmental stresses during seedling establishment is crucial to successful vegetable production. In the irrigated production areas of the southwestern United States, stress most often is related to unfavorable temperature, soil or water salinity, or poor soil structure; it is frequently difficult to separate the effects of these stresses because they may all be present to some significant degree. Growers use a variety of techniques to ameliorate these conditions. Advances in seed technology have improved seedling establishment under unfavorable temperatures, particularly for lettuce. The use of sprinkler irrigation for stand establishment has become a widespread practice; sprinkling moderates soil temperature, minimizes salinity in the zone of germination, and reduces soil crusting. By modifying bed configuration, growers have been able to increase soil temperature to stimulate germination. Modifying seed placement and furrow irrigation patterns can create zones of lower salinity. Various chemical and physical treatments have proven effective in reducing soil crusting. The use of transplants-has expanded for many crops, both as a means to circumvent seedling establishment problems, as well as a technique to obtain earliness.
Many factors influence appropriate drip irrigation management, including system design, soil characteristics, crop and growth stage, and environmental conditions. The influences of these factors can be integrated into a practical, efficient scheduling system that determines quantity and timing of drip irrigation. This system combines direct soil moisture measurement with a water budget approach using evapotranspiration estimates and crop coefficients.
Trials were conducted under California field conditions examining the impact of drip irrigation and nitrogen fertigation regime on in-season NO3-N leaching losses. Six field studies were conducted, 4 on tomato and 2 on pepper. Seasonal fertigation ranged from 0-440 kg N/ha; irrigation was applied 3X per week, with leaching fractions of 10-25% of applied water. NO3-N leaching losses were estimated both by suction lysimetry and the use of buried anion resin traps. A similar pattern was seen in all trials. From transplant establishment until early fruit set soil solution at 0.8 m had relatively high NO3-N concentration (>30 mg/liter), which declined as the season progressed; in the month before harvest soil solution NO3-N at 0.8 m was consistently below 10 mg/liter (tomato) and 15 mg/liter (pepper) in appropriately fertilized plots. Seasonal NO3-N leaching estimates were generally below 25 kg/ha (tomato) and 35 kg/ha (pepper), with only modest differences among fertigation regimes. These results suggest that well managed drip irrigation can minimize in-season NO3-N leaching.
Overcoming environmental stresses during seedling establishment is crucial to successful vegetable production. In the irrigated production areas of the West stress is most often related to unfavorable temperature, soil or water salinity, or poor soil structure; it is frequently difficult to separate the effects of these stresses since they may all be present to some significant degree. Growers use a variety of techniques to ameliorate these conditions. Advances in seed priming and coating have improved seedling establishment under unfavorable temperatures, particularly for lettuce. The use of sprinkler irrigation for stand establishment has become a widespread practice; sprinkling moderates soil temperature, minimizes salinity in the zone of germination, and reduces soil crusting. By modifying bed configuration growers have been able to increase soil temperature to stimulate germination. Modifying furrow irrigation patterns can create zones of lower salinity. Various chemical treatments have proven effective in reducing soil crusting. The use of transplants is expanding for many crops, both as a means to circumvent seedling establishment problems as well as a technique to obtain earliness.