Effect of Tansy Mustard (Descurainia intermedia) on Moisture Storage during Fallow

C INCE the work of Cox and Cates (2) in 1912, it had been shown 3 repeatedly that weeds growing in competition with crops decrease yields. These results lead to the general assumption that weeds are detrimental anytime, including a fallow period for moisture conservation. In fact many farmers in the Great Plains area still plow during the winter or when there are no weeds to promote a dust for moisture conservation even though this practice has been shown to be of little value (6, 7). Recent research has shown that where runoff is prevented and weed control is adequate during the fallow period, type of tillage or amount of mulch does not greatly affect moisture storage in the Southern Great Plains (8). Finnell (5) stated that on the heavy soils of the Southern Great Plains 65.8 percent of the rainfall was evaporated, 13.5 percent was runoff, 2.7 percent was lost in tillage operations and 18.0 percent was stored in the soil.