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 alone 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. Research Question Fallow is practiced in the semiarid northern Great Plains to increase soil moisture storage, in order to reduce year‐to‐year variation in spring‐seeded cereal yield. Prevention of wind erosion during the 21‐mo fallow period requires conservation of crop residues. This study compared the effects of tillage alone, herbicides alone, and combinations of tillage and herbicides during the fallow period on the production of spring wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). Literature Summary The role of conservation tillage practices in soil moisture storage, crop residue management, and spring and winter wheat yield in the northern Great Plains has received considerable attention from researchers. Replacing tillage operations with herbicides during the fallow period has been shown to improve erosion protection by maintaining crop residues on the soil surface. Soil moisture storage has also been shown to be increased by the use of herbicides for fallow, however little or no response has been recorded in spring wheat yields. Although barley is a major crop in the Canadian prairies, grown for the malting and livestock‐feed industries, its response to conservation fallow has not been reported. Existing research has not addressed the response to barley to fallow management practices. Study Description During a 15‐yr period (1977–1991) spring wheat and barley were grown in a fallow‐crop rotation on a clay loam soil at Lethbridge, Alberta, Canada. Eight fallow treatments were evaluated: One‐way disk (May–Sept.) Glyphosate, metsulfuron, or 2,4‐D (May–Sept.) with no preseeding tillage Heavy‐duty cultivator (May–Sept.) Wide blade cultivator (May–Sept.) 1975–1984: Heavy‐duty cultivator after harvest, herbicides (May–Sept.) 1985–1989: Heavy‐duty cultivator (May–Sept.), trifluralin (June) 1990–1991: Dicamba, 2,4‐D (May), blade (June–Sept.) 1976–1984: Blade after harvest, herbicides (May–Sept.), blade (Oct.) 1985–1989: Heavy‐duty cultivator (May–Sept.), trifluralin (July) 1990–1991: 2,4‐D bromoxynil, MCPA (May), wide blade (June–Sept.) 1976–1984: One‐way disk (May), herbicides (June–Sept.) 1985–1991: Paraquat (May–Sept.) with no preseeding tillage Metsulfuron/glyphosate (May–Sept.), wide blade (Oct.) Applied Question Did fallow management treatment influence spring wheat and barley grain yields? Average spring wheat and barley yields over the 15 yr 1977 to 1991 were remarkably close for the eight fallow treatments (Table ). Average yield for wheat in this study was 30 bu/acre, with a range of 3.1 bu/acre. Average barley yield was 58 bu/acre, with a range of 4.1 bu/acre. Yields were slightly lower on the herbicide‐only system, with tillage/herbicide combinations yielding equal to, or greater than, the tillage alone treatments. For all fallow treatments, spring wheat grain protein was in excess of the 13.5% required for protein premium (Table ). A fallow management system based on herbicides from May to September, followed by wide blade cultivation in the fall, produced the highest wheat and barley grain yields. How did fallow management treatment influence crop residue cover and plant‐available water at seeding? Herbicides used alone, or in combination with fall blade cultivation, can maintain adequate crop residue cover for erosion protection in a fallowcereal rotation (Table ). When tillage (one‐way disk, heavy‐duty cultivator, wide blade cultivator) was used alone, only the blade cultivator maintained adequate surface residue cover. Herbicides alone provided the highest levels of plant‐available water at seeding, reflecting the influence of increased surface crop residue cover with this treatment. Farmers using fallow in their crop production system should consider either herbicides alone, or in combination with wide blade tillage, to ensure adequate erosion protection and optimize soil water storage. Spring wheat and barley grain yield and protein response to 21‐month fallow treatment, 1977–1991. Wheat Barley Fallow treatment Yield Protein Yield Protein bu/acre % bu/acre % 1 29.7 15.7 56.0 12.1 2 28.6 15.5 54.4 12.1 3 30.0 15.9 57.1 12.2 4 30.1 15.6 55.1 11.9 5 28.3 16.1 56.8 12.2 6 30.0 15.8 57.0 12.2 7 29.5 15.8 56.4 12.3 8 31.4 15.9 58.5 12.3 Treatments 1, 3, and 4: tillage only; Treatments 5, 6, and 7: tillage/herbicide combinations; Treatment 2: herbicides only. Average number of tillage operations, spring wheat crop residue cover, and percentage of original crop residues remaining on the surface in spring on five fallow treatments, 1986 and 1988 to 1991. Fallow treatment Tillage operations Total residue cover, lb/acre % original 1 2 364 17 2 0 1352 62 3 3 597 24 4<