Chemical Fallow in the Southern Great Plains

Abstract

HE concept of reducing tillage operations with herbicides was 1 first tested in California orchards in 1944 (9). In 1949, Johnston and Sullivan (7) gave a detailed discussion of chemicals and equipment needed for eliminating tillage in orchards. Over a 4-year period chemical weed control proved cheaper than cultural methods. Soil condition and water penetration were improved and soil erosion was reduced by chemical weed control. In the Great Plains area, where residue conservation is needed to control wind erosion, eliminating medhanical tillage operations with herbicides has enormous potential. Recognizing this, T. S. Aasheim started experiments with chemical fallow, i.e. weed control with herbicides during the fallow period in 1948 at the North Montana Branch Station, Havre, Montana. These tests were expanded to 3 locations in Montana and the results were reported by Baker et al. (2) in 1956. They concluded that where chemical fallow controlled weeds, grain yields were comparable to yields from conventional tillage. Reduced yields occurred if chemical residues remained in the soil at planting time. Krall (8) recently noted increased protein content of wheat after using 3-p(chlorophenyl)-l, l-dimethyl urea (monuron) for weed control during the fallow period. Many studies have been conducted to find suitable herbicides for chemical fallow (3, 10, 11, 12, 13). These studies indicate that 2,4-D (2,4-dichlorophenoxyacetic acid) successfully controls broadleaf weeds. However, chemical control of annual grasses or volunteer wheat is often unsatisfactory. Good control of foxtail (Setaria sp.), witchgrass (Panicum capillare), downy brome (Bromus tectorum), and hairy chess (Bromus comutatus) was usually obtained. Stinkgrass (Eragrostis cilianensis) was not controlled with chemicals. Shafer (14) applied 3-amino-1,2,4-triazole (amitrol) and the sodium salt of 2,2dichloropropionic acid (dalapon) with an airplane and observed that a minimum of 5 gallons of carrier per acre was required to obtain control of volunteer wheat and downy brome. In preliminary studies in Wyoming, Barnes et al. (5) observed that water intake rates were higher on chemically fallowed plots than on plowed ground where only a sweepmachine was used. During the second 30 minutes of an hour run, chemically fallowed plots absorbed 0.95 inch of water; an increase of 216%o and 250% over plowed ground and subsurface-tilled plots, respectively. Further studies on fallowed land in Wyoming showed that a chiseling operation in conjuction with chemical fallow gave maximum moisture intake rates (1, 6). Three or four years of fallow with chemicals alone