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Fluid Journal : Fluid Journal 1996-1998
1 Fluid Journal Summer 1996 Summary: Cropping system alternatives to wheat-fallow have become possible in the Great Plains as a result of improved water conservation techniques. Cropping intensification, compared to wheat- fallow, leads to a greater demand on soil N supply, and thus a greater need for N fertilizers. This article reviews N fertilization practices for intensified cropping systems, and provides an update on current farmer Nfertilization practices for each crop grown in the intensified systems. Plant production in the Great Plains always has had two limitations: 1) water supply, and 2) available N supply. These limitations were present even before cultivated agriculture was established in the plains. Prairie plant production was basically in balance with water and N supplies. The prairie plants used most of the water and nitrate supply as soon as it was available. Plowing the prairies changed both the water and N budgets. With respect to water, it encouraged accumulations in the soil profile far beyond those possible with a prairie system. With respect to N, it stimulated a flush of N mineralization as the resident organic matter mineralized after plowing. Dryland cultivated systems in the Great Plains, mostly crop-fallow, were able to exist without addition of N fertilizer and/or legume N inputs for 30 to 50 years after sod breaking. Beginning in the 1970s, it became apparent that wheat produced on many of our soils was responding to N application and that N mineralization no longer met plant demand. Higher wheat yields associated with improved Dr. Gary Peterson N: the Vital Nutrient in the Great Plains Cropping intensification brings greater need for N fertilizers in Great Plains. 14 12 10 8 6 4 2 0 WF WCF N rate - 90 lbs/A Yield increase - bu/A Weld Loam Soil Keith Clay Loam Soil Yield - bu/A Weld Loam Soil Keith Clay Loam Soil 0 105 0 105 N rate - lbs/A 80 70 60 50 40 30 20 10 0 Figure 1. Comparison of average wheat yield increase response to N applid on different soils at rate of 90 lbs/A. WF=wheat fallow, WCF=wheat-corn-fallow. Figure 1. Comparison of corn yield response to N applied on different soils at rates ranging from 0 to 105 lbs/A. soil water conservation and superior yielding varieties accentuated the N deficiency. In efforts to minimize erosion and maximize water storage efficiency, reduced tillage and no-till systems were developed. Scientists soon recognized that the economics of no-till in crop- fallow systems usually were not favorable. Often the cost of saving additional water was higher than the value of the additional crop produced. Scientists from Canada to Texas have subsequently identified cropping systems that efficiently and profitably use water. The new more intensified systems use rotations involving canola, corn, forages, millets, peas, safflower, sorghum, sunflower, and wheat produced with a mixture of no-till and reduced-till practices. Our data show a 28 percent increase in crop production per unit of water by switching from crop fallow to more intense systems. As anyone would expect, increased productivity with intensified cropping systems leads to even greater N demands on the soil system. We'll briefly review how farmers and scientists are addressing N fertilization problems in intensified cropping systems across the Great Plains. N management issues N quantity. Intensified cropping systems would be expected to consume more N than crop-fallow if they produce more grain forage. On an eroded Weld loam soil with a low wheat production potential, Kolberg and Kitchen reported an average yield increase response of 5.5 bu/A to N applied at the rate of 90 lbs/A (Figure 1). However, on a more productive Keith clay loam, N at 90 lbs/A resulted in an average increase of 6.4 bu/A under wheat-fallow and
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