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Fluid Journal : Fluid Journal 1996-1998
2 Fluid Journal Winter 1996 WF WCF WCMF Rotation 170 150 130 110 90 70 50 30 N App lb/A (4yrs) Resid lb/A NO3- 6 ft. lb grain/in precip Gross Income $ Figure 2. Influence of dryland rotation on income, water use efficiency, and residual N, Westfall, et al., 1991. WF = wheat-fallow; WCF = wheat- corn-fallow; WCMF = wheat-corn, milo, fallow. SA WS BS CS CB Placement 100 80 60 40 20 0 Yield - bu/A Phosphate Sulfur Nitrogen Figure 3. Winter wheat yield response to fertilizer placement averaged over N rates (1983-84) and P and S rates (1985-86) at three locations in northern Idaho. SA = surface-applied, WS = with seed, BS = below seed, CS = row centered-seed depth, CB = row centered-below seed. crop and a 120-bu/A-plus irrigated crop are obvious. Davis sees the trend to residue management continuing. Weed/disease management. As reported by Veseth, early control of volunteer grains and weeds between harvest and spring planting has been identified as another important component in crop health management strategies under no-till in the Pacific Northwest. Research has shown that roots of volunteer grain and weeds growing between harvest and planting of the spring crop can serve as a 'green bridge" host for root diseases to attack spring crops under conservation tillage, particularly with direct seeding. In the past, a common practice with seeding of spring cereals in conservation tillage in the Northwest has been to spray volunteer grain and weeds shortly before seeding with a non-selective herbicide such as glyphosate. The short interval served to increase the potential for some root diseases, particularly Rhizoctonia root rot, Pythium root rot, and take-all. Researchers are finding that earlier control of the "green bridge," beginning ideally in the fall after harvest and at least two to three weeks before spring seeding, sharply reduces root disease potential and commonly increases yields 20 to 50 percent, compared to letting the "green bridge" grow until shortly before planting. Continued R & D research in weed control needs to be coupled with an evaluation of the potential for disease levels and the subsequent design of control measures that are tailored to crop residue management systems. The importance of controlling root pathogens, in conjunction with weed control, is amply demonstrated in Figure 1. Note how placement makes a big difference in spring wheat yield where there is root disease and virtually none where a soil fumigant is used to eliminate root pathogens. Crop rotation. Reduced tillage acres serviced from Blackfoot have been mostly continuous grain. However, some progressive growers are evaluating reduced tillage options and residue management for other crops, including potatoes. Growers of row crops under irrigation have some interesting crop residue management hurdles to overcome. For example, Shane Boden, a Simplot unit manager who works the Rockford area, which has little or no dryland grain, finds that residue management for his customers is confounded by row crop rotations. The nature of seedbed preparation and harvest of potatoes and sugar beets means that soil disturbance is inevitable and crop residues are reduced, compared with continuous grains.
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