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Fluid Journal : Fluid Journal 1996-1998
Summer 1996 Summary: Trickle irrigation in combination with feedback from in- season nitrogen (N) tissue tests offers almost unlimited flexibilty in developing site-specific nutrient management plans. Field experiments were conducted during 1994-95 in southern Arizona to evaluate the agronomic, economic, and environ- mental response of broccoli and cauli- flower to a factorial arrangement of water and N rates, both ranging from deficient to supraoptimal. Concurrent evaluation of crop response surfaces for marketable yield, net economic return, and unaccounted for nitrogen fertilizer determined that profitable yields of broc- coli and cauliflower could be produced with minimal impact on the environment. _________________________________ California and Arizona are the first and second leading producers of broccoli and cauliflower in the United States. These two crops are harvested from 162,000 acres each year and have a total value of over $457 million. Much of the produc- tion in these two states is accomplished on arid and semiarid soils, and represents about 92 percent of the broccoli and cauilflower harvested annually in the United States. Broccoli and cauliflower are highly dependent on inputs of irrigation water and nitrogen (N) fertilizer to achieve optimum production. Growers realize that these inputs must be carefully man- aged to ensure optimum yields and profits, and minimal environmental impact. Increasingly, growers are adopting production practices that allow them to significantly improve N and water-use efficiency. Two such practices are: 1) conversion to drip irrigation systems, and 2) the use of in-season tissue nitrate tests to monitor the N status of the crop. Used together, these technologies offer almost unlimited flexibility in developing site- specific nutrient management plans. The ability to inject multiple "split" applications of fluid N fertilizers directly through the drip system offers this flexibility in N management. The use of tissue nitrate testing provides the information growers need to avoid N deficiencies as well as unneeded N inputs. Existing plant tissue N testing guidelines for broccoli and cauliflower, however, have two deficiencies. Either they are not calibrated to recommend the amounts of N fertilizer needed, or they contain guidelines for only the latter portions of the growing season when it is too late for remediation. Studies, therefore, were initiated to: 1) develop and calibrate N tissue tests to monitor crop N status as well as predict optimum timing and rates of fluid N fertilizer applications throughout the growing season, and 2) determine the response of trickle-irrigated broccoli and cauliflower to varying levels of N and water inputs to clearly identify best managment practices (BMP). Niskey Yield/return. Pronounced N x water treatment differences were visually apparent beginning at the 6- to 8-leaf stages for both crops, and persisted and intensified as the season progressed. In general, N deficiency had a much greater negative effect on marketable yield and net return than did excessive water ("Wet") for both crops as shown in Figures 1 and 2. A severe N deficiency (89 lbs/A of N) decreased these two yield parameters an average of 50 and 85 percent for broccoli and cauilfower, respectively. In contrast, excessive water application decreased average marketable yield and net return by only 14 and 32 percent for broccoli and cauliflower, respectively. Due to moderately high rainfall during the growth periods, no yield reductions were measured in the "Dry" water treatments for either crop. N loss. In general, unaccounted for N fertilizer values were moderately low for both crops. Only when excessive water and a supraoptimal level of N (267 lbs/A) were applied did unaccounted for N fertilizer amounts exceed 100 lbs/A. It is estimated that the amounts of unac- counted for N below 36 lbs/A per crop would result in NO3-N concentrations <10 ppm in the drainage water passing below the root zone of these crops. Concurrent analysis of crop response surfaces for marketable yield, net return, and unaccounted for N fertilizer revealed that profitable yields for both broccoli and cauliflower can be produced with minimal impact on groundwater. Quality. Broccoli and cauliflower harvest quality and earliness were significantly decreased by a nitrogen deficiency. In contrast, irrigation water treatments (Wet, Optimum, Dry) had no significant effects on these quality parameters. Calibration. The results obtained using the preliminary midrib tissue NO3 test calibration for both crops were quite successful. Cumulative applications of 219 lbs/A of N with broccoli and 260 lbs/A of N with cauliflower were recommended by our preliminary guidelines. For both crops, the yield Drs. Thomas A. Doerge and T. L. Thompson Trickle Irrigation: One Answer To Site-Specific Nutrient Management Practice is combined with tissue nitrate testing used to avoid N deficiencies as well as unneeded N inputs.
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