Sign up for email alerts of new Fluid Journal issues!
Fluid Journal : Fluid Journal 1996-1998
2 Fluid Journal Summer 1996 12.8 bu/A under wheat-corn-fallow (Figure 1). The greater yield response in wheat-corn-fallow occurred because greater residual soil NO3 depletion in the check treatments (0 N rate) of the more intensive cropping system. Dryland corn yields in these systems were increased with N fertilizer rates up to 105 lbs/A. Yields were increased from 55 to 73 bu/A on the Weld soil and from 41 to 80 bu/A on the Keith soil as N fertilizer rate increased from 0 to 105 lbs/A (Figure 2). Yield increased linearly up to the 105 lb/A rate, but this rate was the point of diminishing return. The wheat-corn-fallow cropping system required 73 to 90 percent more N fertilizer compared to the wheat-fallow system. In western Kansas, wheat-sorghum- fallow cropping systems required 40 to 80 lbs/A of N for maximum economic winter wheat yields. Higher fertilizer N rates were needed in higher rainfall years or wetter locations. Havlin has reported that fertilizer N rates between 75 to 125 lbs/A were needed to optimize dryland corn yields in wheat-corn-fallow rotations. Similarly, 80 to 100 lbs/A were required to maximize sorghum yields in no-till wheat-sorghum-fallow rotations. The key means of determining N quantity remains soil testing. Placement/timing. The two placements that usually ranked highest for the wheat crop were 100 percent urea preplant broadcast and 30 percent UAN banded below the seed plus 70 percent surface banded at planting. In a higher rainfall environment, Carlson et al. showed 15 and 10 bu/A no-till corn yield increases for preplant banded N as compared to broadcast at 75 and 150 lbs/A rates, respectively. In the same environment, Lamond et al. reported 28 and 13 bu/A sorghum yield increases for preplant banded N as compared to broadcast at rates of 50 and 100 lbs/A, respectively. Although we appear to have flexibility in N placement recommendations, additional research is needed to develop precise fertilizer N placement recommendations. Farmer practice Wheat-fallow, with mulch tillage, is still the most common cropping system in the plains. The more intensive cropping systems are being used on less than 20 percent of the cultivated areas. Alternative cropping systems, which include various legume crops, seem to be most diverse in the northern plains. In the central Great Plains, corn and sorghum are most common. In the southern plains grain sorghum is the most common crop grown in rotation with wheat. UAN is applied in a variety of ways ranging from injection to use as a herbicide carrier. Using UAN as a herbicide carrier for preplant applications is reported to be effective and cost conserving. Why sidedressing has not been widely used is not clear. It may be farmers lack suitable injection equipment that won't handle surface residue. It may also be that sidedressed N gets stranded in dry soil, which is of natural concern to farmers who are always looking for the cheapest, most efficient way possible to apply nitrogen. More research is obviously needed to improve uptake efficiencies of N. Dr. Peterson is professor of soil and crop sciences at Colorado State University, Fort Collins, Colorado.
Fluid Journal 1993-1995
Fluid Journal 1999-2001