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Effect of different tillage systems on wheat production

E. Davaud1 and G. Wickham2

1School of Wool and Pastoral Sciences, The University of New South Wales
Soil Conservation Service of New South Wales, Wellington Research Centre.

Spiralling fuel prices coupled with an increased need to reduce labour inputs in crop production systems has stimulated research into systems involving reduced cultivation and direct drilling. Since the adoption of these new concepts is very much subject to climatic characteristics and soil properties, there is a need to define tillage systems which are locally optimal and establish the management practices that are necessary.

An experiment was commenced in 1978 on a red brown earth (Northcote: Gn 3.1.2) at Wellington, NSW. Three tillage treatments (conventional cultivation, reduced cultivation. and direct drilling) with three replications were arranged in a latin square having subsoiling treatments superimposed along the length of the plots. Conventional cultivation (CC) consisted of primary (chisel) plus secondary (scarifier) cultivations. Reduced cultivation (RC) had only one shallow scarifying ten weeks prior to sowing. Reduced cultivation and direct drilling (DD) treatments were grazed till four weeks prior to sowing and two weeks after the grazing ceased the plots were sprayed to kill the pasture (mainly lucerne). Subsoiling (SS) was done as early as soil moisture allowed the operation (27 April). Sowing was done with a full Australian standard combine (spring released tynes) on all treatments. Rainfall during the growing season (14 July-20 December) was 322 mm and 797 mm for the whole year.

TABLE 1. Tiller number (til/m). dry matter and grain yield of wheat (kg/ha).

The general response to subsoiling (Table 1) seems to be due to a reduction in soil strength in the deeper soil layers (mainly clay), enabling better and deeper root development which in turn allowed better use of profile nitrogen and moisture (Johnston 1973; Kaddah 1976).

The poorest response was obtained with direct drilling without subsoiling and was mainly due to poor germination and poor vegetative growth in response to restricted root development due to high soil strength. It is apparent that a) cultivations can be drastically reduced without impairing yields and b) a reduction in the number of cultivations with increased depth of cultivation would produce the best results on some soils.

Johnson, J.R. (1973). Soil Conserv. Soc. of America, Proc. Nat. Conf., Des Moines, Iowa, p.125.

Kaddah, K.L. (1976). Agron. J., 68: 36.

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