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Fluid Journal : Fluid Journal 1996-1998
Summer 1996 to maintain average soil moisture tensions at the target levels. Daily readings of tensiometers placed at 12 and 24 inches were used to assist in irrigation scheduling. Plots. Individual plots were 40 feet by 13.33 feet. Tracking. 15N labeled (NH4)2SO4 was applied in two-meter-long microplots to investigate the effects of water level (Dry, Optimum, and Wet) and time of 15N application (4- to 6-leaf and early heading) on N-use efficiency. This experiment was conducted in the broccoli experiment only. Data collected. The following determinations were made in evaluating our '94-'95 field experiments: 1. Total aerial dry matter and biomass N content at final harvest 2. Midrib nitrate concentrations at 4- to 6-leaf, 10- to 12- leaf, head initiation, head development, and final harvest stages 3. Marketable yield and quality 4. Dry matter and total nitrogen content in unfertilized comparison plots to measure apparent nitrogen- use efficiency 5. 15N content (water x N timing) in 18 broccoli microplots 6. Soil nitrate content to a depth of three feet in one-foot increments in all main plots, plus 15N in the 18 microplots in samples taken immediately postharvest. Nitrogen budgets were calculated for all of the main plots by the difference method. For each of the 15N microplots, they were calculated using the isotopic dilution method. Planting. Experiments were established on September 16 by direct seeding with a Stanley precision planter. Irrigation. All plots were irrigated uniformly for 28 days until stands reached the 1- to 2-leaf stage. At this time, daily irrigation was scheduled to maintain the targeted soil water tensions. Total amounts of irrigation water applied (Dry, Optimum, Wet) following stand establishment were 2.8, 3.2, and 14.7 inches for broccoli and 1.4, 2.6, and 17.4 inches for cauliflower. Rainfall. A total of 5.0 and 5.2 inches of rainfall occurred during the broccoli and cauliflower experiments. N content. Water applications contained between 0.6 and 7.9 lbs/A of nitrogen. Refinement The preliminary guidelines used for the 1994-95 crops will be refined as needed and tested again in the 1995-96 season. Planting of both crops went as scheduled on October 2, 1995. All equipment and data-gathering installa- tions are in place and functioning proper- ly. As of mid-December, the experiments were in excellent condition and harves- ting began in February of this year. ________________________________ Dr. Doerge is soils specialist and Dr. Thompson is assistant professor, Department of Soil, Water and Environmental Science, University of Arizona. ! Figure 4. Interpretation of seasonal petiole nitrate levels in the BMP nitrogen treatment for cauliflower, Doerge, et al., University of Arizona, 1994-95. Figure 3. Interpretation of seasonal petiole nitrate levels in the BMP nitrogen treatment for broccoli, Doerge, et al., University of Arizona, 1994-95.
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