Differences in the abilities of crops to utilize fertilizer and soil N can contribute to the establishment of rotation systems to improve the efficiency of fertilizer use and reduce nitrate pollution groundwater. Field studies show considerable site variability in the utilization of fertilizer by individual crops. To compare fertilizer N use by corn (Zea mays L.), sugarbeet (Beta vulgaris L.), and tomato (Lycopersicon esculentum Mill.), several rates of fertilizer N were applied to replicated plots of each crop in the same field at Davis, Calif. A 2nd year study involved only corn and sugarbeet. The experiments were conducted at different sites, but both on the same soil, Yolo silt loam (a fine‐silty, mixed, nonacid, thermic, Typic Xerorthent). Nitrogen‐15 depleted ammonium sulfate was used as a labeled N source in the three‐crop experiment and ammonium nitrate of normal isotopic ratio was used for the two‐crop experiment. In both experiments, N was applied in bands on both sides of crop rows after seedling emergence in 56 kg increments from 0 to 280 kg N/ha. Fertilizer N required for maximum commercial yield in 1979 was: corn 194, tomato 131, and sugarbeet 92 kg N/ha; and in 1980: corn 280 and sugarbeet 70 kg N/ha. Average recoveries of labeled N from fertilizer in 1979 were: corn 57%, and tomato and sugarbeet 27%; and in 1980 without labeled N the apparent recoveries were: corn 52% and sugarbeet 37%. The ratios of fertilizer to soil N in the crops at fertilizer rates giving maximum commercial yields in 1979 were: corn 45/55, tomato 25/75, and sugarbeet 15/85; and in 1980 were estimated by the difference method to be: corn 54/46 and sugarbeet 10/90. Thus corn relied most heavily on fertilizer N, followed by tomato then sugarbeet. On average, over the 2 years, sugarbeet took up 95% more soil N than corn. These data indicate that fertilizer use efficiency may be improved by growing corn when residual N is lowest and tomato or sugarbeet when residual N is highest. With care to avoid residual N too high for depletion prior to harvest, sugarbeet can be used to scavenge soil N and thus conserve the use of fertilizer N.
Nine row‐crop sites, where data for nitrogen fertilizer use, crop yields, and amounts of irrigation water used were available for a number of years, were studied to estimate the N balance as related to NO3− in water in the unsaturated zone from below the zone of root influence to the water table or to the 15‐m depth.The system of predicting NO3− concentrations in drainage waters based on the difference between N inputs and N removal in harvested crop sand the drainage volume in which the excess N, converted to NO3−, is dissolved, was valid in open‐porous soils containing no layers that restrict water movement within the soil profile (0‐ to 2‐m depth). A combination of losses plus net immobilization of up to 56% had to be assumed in some soils to account for all the N loss. In two soils that had been used for disposal of feedlot manure, net mineralization of N from the organic N pool had to be assumed to explain the data obtained.The current fertilization and irrigation practices used for some row crops in southern California leave varying amounts of NO3− in the drainage water. The amounts depend on the total N added, crop removal, drainage volume, net mineralization, and losses.
The present study was designed to provide experimental data which would bear on undocumented claims as to the superior flavor of so called “organic” or “natural” foods. Four vegetables (lettuce, green beans, broccoli greens, and carrots) were grown under three conditions: depleted soil (no additional fertilizer or pesticides); commercially fertilized (plus pesticides), and organically fertilized (manure, no pesticides). Fifty consumer subjects evaluated the four vegetables individually in separate sessions, using a 1 to 9 hedonic rating scale. A fifth evaluation of beans, broccoli and carrots was conducted on vegetables grown under just the commercial and organic conditions, but with products correctly and incorrectly labelled commercial or organic. Analysis of variance indicated no significant differences for lettuce or green beans due to growing conditions. There was a significant preference for the commercial and depleted samples of carrots over the organic sample in the separate sessions, but not in the label study. Organic broccoli was preferred to depleted and commercial samples in the separate sessions study, and to commercial in the label study. In the latter study there was a significant difference for type of vegetable (beans and carrots preferred to broccoli) and for label (organic preferred to commercial). The data indicated that the consumer would not be getting a more acceptable product if organically grown vegetables were purchased.
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