Reduced growth and yield of wheat with conservation cropping, 2. Soil biological factors limit growth under direct drilling
1995
Kirkegaard, J.A. | Munns, R. | James, R.A. | Gardner, P.A. | Angus, J.F. (Commonwealth Scientific and Industrial Research Organisation, Canberra (Australia). Div. of Plant Industry)
Wheat was grown in growth cabinets in intact cores of soil removed from a field experiment in which seedlings had grown more slowly in direct-drilled soil than in cultivated soil. Shallower sowing led to faster emergence and increased seedling growth, but irrespective of sowing depth, direct-drilled plants grew more slowly than plants in cultivated soil. Shoot growth of direct-drilled plants was 25-65 percent less than that of cultivated plants. These growth reductions were largely overcome by sterilizing the soil with gamma radiation or by fumigation with methyl bromide, indicating that biological factors were primarily responsible. Rhizoctonia was implicated as the cause of the reduced shoot growth when infection was severe. There was no correlation between infection severity and shoot growth at moderate levels and significant reductions in shoot growth occurred in the absence of Rhizoctonia. These reductions were evident on the first leaf suggesting a direct influence on shoot growth rather than one mediated through inadequate uptake of water or nutrients. Infection of the germinating seed by Pythium spp. or the effects of phytohormones produced by inhibitory bacteria on the roots are possible causes of reduced shoot growth of direct-drilled seedlings.
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