Skeleton weed (Chondrilla juncea) in the Victorian Mallee. 4. Effects of fallowing on wheat yields and weed populations

Abstract

Experiments to compare the duration of fallows and the substitution of a 2,4-D spray for some fallow cultivations for wheat production on skeleton weed land were conducted in the Victorian Mallee from 1962 to 1966. Generally winter fallows outyielded spring fallows, commenced only two months later, and these in turn gave higher yields than an autumn-cultivated treatment. Compared with autumn cultivation, winter fallowing reduced skeleton weed density by an average of 49 per cent. Substituting a 2,4-D spray for some Gltivations had little effect on wheat yield, but improved the control of skeleton weed. Grain yield was determined primarily by the level of nitrate nitrogen in the surface 15 cm of soil before sowing, and this effect was attributed to the low soil nitrogen status found in skeleton weed situations. Soil moisture was conserved only occasionally, owing to the difficulty of controlling weed growth during the summer coupled with the variable rainfall distribution in the Mallee. Although a nitrogen and phosphorus fertilizer interaction was significant at all sites, neither the individual response nor the interaction was affected by fallow treatment.