CHEMICAL WEED CONTROL ON SUMMERFALLOW

Use of residual and contact herbicides was compared with cultivation for weed control on summerfallow on Regina heavy clay from 1964 to 1967, inclusive. A single spring application of desmetryne (2-isopropylamino-4-methylamino-6-methylthio-s-triazine) at 3 kg/ha gave 77 to 90% weed control without reducing wheat yields the following year. Disadvantages were incomplete weed control, and herbicide persistence in the soil with thinning of the following wheat crop in some years.Three or four applications of paraquat (1,1′-dimethyl-4,4-bipyridinium (salt)) at 1 kg/ha gave weed control equal to cultivation of summerfallow. Chemical summerfallow was equal to cultivated summerfallow in its effects on soil moisture conservation, NO3-N accumulation and crop yields. Chemical summerfallow conserved 91% of the original crop residues compared with 24% for cultivated summerfallow. This extra crop residue was sufficient to prevent serious soil erosion from wind. Paraquat is currently too expensive to compete with cultiva...