|Kitchen, R.L. - COLORADO STATE UNIV|
|Westfall, D.G. - COLORADO STATE UNIV|
|Peterson, G.A. - COLORADO STATE UNIV|
Submitted to: Journal of Production Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 1, 1996
Publication Date: August 1, 1996
Interpretive Summary: Current nitrogen (N) fertilizer recommendations for wheat have been devised under conventional tillage management and may not be suitable in a no-till system. Additionally these recommendations were not formulated using a rotaional approach, i.e. in a mult-year/multi-crop setting. Little work has been done in devising N fertilizer recommendations for dryland corn and sorghum, especially in a no-till rotation. This study was conducted in two lcoations in eastern Colorado near Sterling (northeast) and Stratton (east central) on Weld loam and Keith clay loam soils, respectively, from 1987 through 1992. Crop production and efficiency of N fertilizer use of winter wheat and corn (Sterling site) or grain sorghum (Stratton site) was measured and compared between two rotations (wheat-fallow, WF and wheat-corn or sorghum-fallow, WCF) with every part of each rotation present in all years. Other comparisons were among four N rates and four N fertilizer source/placement/timing treatments in each crop. Current N fertilizer recommendations were not enough to give maximum production in no-till. Wheat yields wre similar between the two rotations when adequate N was applied. Corn averaged 72 bu/acre when adequately fertilized and needed 1 lb/acre of N to produce 1 bu/acre more grain per year than WF. This 70% increase in annual grain production required 44% increase in annual N fertilizer application.
Technical Abstract: Crop N needs are not usually based on cropping intensity or no tillage practice. However, N fertilzer requirements may increase dramatically as less fallow and less tillage are used in semi-arid regions of the Great Plains where summer fallow cropping is common. This long-term experiment was conducted to study the influence of N fertilizer rate, source/placement/timing (NSP), and crop rotation factors on the production of winter wheat (Triticum aestivum L.), corn (Zea mays L.), and grain sorghum (Sorghum bicolor L.), as well as their fertilir N use efficiency (FNUE) for the initial years of conversion to no-till dryland farming. Research was conducted from 1987 through 1992 on two soils (Keith clay loam, a fine-silty, mixed, mesic Aridic Argiustoll and Weld loam, a fine-silty, mixed, mesic, Aridic Argiustoll) in eastern Colorado. Rotations included winter wheat-fallow (WF) and winter wheat-corn or grain sorghum-fallow (WCF). Wheat yields were similar between WF and WCF with adequate N application. Response to N fertilizer at lower rates was greater in WCF than WF because of its greater depletion of soil N. Corn production averaged 72 bu/acre with adequate N and required 1 lb/acre of N uptake to produce 1 bu/acre of grain. Current N fertilizer recommendations for wheat and corn were not adequate to insure maximum production under no-till management. Fertilizer placement significantly affected average annual rotational yield (40 to 70 lb/acre per yr difference) but application rate was more important economically. Grain biomass produce in each rotation per pound of total plant N uptake (GNUE) was 17 lb/acre per yr in WF compared with 29 lb/acre per yr for WCF. This 70% increase in average annual grain production of WCF over WF was accomplished with a 44% annual increase in fertilizer N application.