SPRING WHEAT AND BARLEY RESPONSE TO LONG-TERM FALLOW MANAGEMENT

Crop rotations with a high frequency of fallow remain the dominant cropping practice in the semiarid northern Great Plains. Tillage to control weeds during fallow periods increases soil exposure to erosion by wind. A fallow management study, initiated on a clay loam soil in 1955, has been used to compare tillage alone, herbicides alone, and combinations of tillage and herbicides on the yield and quality of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). From 1977 to 1991, average spring wheat and barley yields were similar regardless of fallow treatment, with a 3.1 bu/acre difference between highest (31.4 bu/acre) and lowest yielding (28.3 bu/acre) treatments for wheat, and a 4.1 bu/acre difference for barley (54.4-58.5 bu/acre). Fallow with summer herbicides and cultivation with wide blade in fall resulted in the highest grain and grain N yields for wheat and barley, and highest soil nitrate-N concentration. The use of herbicides atone resulted in the highest level of crop residue conservation and plant-available water (PAW) at seeding. When tillage was used alone, only the wide blade cultivator maintained sufficient crop residue cover to protect against wind erosion. Grain yields on fallow increased with precipitation in May and June, the period of tiller formation and stem elongation, and decreased with increasing evaporative demand in June and July, during grain filling. Environmental conditions prevailing from May to July explained 67% of the yield variability observed in spring wheat and 83% in barley, Producers using a cereal-fallow rotation are encouraged to explore herbicide-tillage combinations for fallow as a means of ensuring erosion protection and optimizing grain yield potential.