Reduced growth and yield of wheat with conservation cropping. II. Soil biological factors limit growth under direct drilling

Wheat was grown 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. Experiments were conducted in controlled environments to resolve (1) whether shallower sowing of direct-drilled crops caused slower growth, (2) whether the soil factors causing the slower growth were physical or biological and (3) if biological, whether Rhizoctonia solani was the major pathogen. The conditions of the experiments removed possible constraints of water and nutrient supply but otherwise simulated the environment of wheat seedlings in southern Australia. 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% less than that of cultivated plants. These growth reductions were largely overcome by sterilizing the soil with y 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 (>3 on a 0-5 scale). There was no correlation between infection severity and shoot growth at moderate levels (<3) 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. The dominant role of biological factors in determining plant response to soil management indicates the need for further studies to identify the organisms responsible, to determine the mechanism by which they influence shoot growth, and the effect of management on their populations and activity.

[1]  V. R. Gupta,et al.  Management Practices and Soil Biota , 1995 .

[2]  J. Kirkegaard,et al.  Changes in Microbial Biomass and Organic Matter Levels During the First Year of Modified Tillage and Stubble Management Practices on a Red Earth , 1994 .

[3]  J. Kirkegaard,et al.  Reduced Growth and Yield of Wheat with Conservation Cropping. I. Field Studies in the first year of the Cropping Phase , 1994 .

[4]  R. Stirzaker,et al.  Feedforward Responses of Plants to Physically Inhospitable Soil , 1993 .

[5]  B. Gerhardson,et al.  Characteristics of a plant deleterious rhizosphere pseudomonad and its inhibitory metabolite(s) , 1993 .

[6]  Ky Chan,et al.  Tillage-induced differences in the growth and distribution of wheat-roots , 1992 .

[7]  R. J. Cook,et al.  Influence of wheat chaff and tillage on Pythium populations in soil and Pythium damage to wheat , 1990 .

[8]  Ky Chan,et al.  The effect of soil compaction and fumigation on poor early growth of wheat under direct drilling , 1989 .

[9]  Ky Chan,et al.  Poor early growth of wheat under direct drilling , 1987 .

[10]  P. Cornish,et al.  Reduced early growth of direct drilled wheat in southern New South Wales: causes and consequences , 1987 .

[11]  J. Passioura,et al.  The Effect of Soil Strength on the Growth of Young Wheat Plants , 1987 .

[12]  R. Fischer,et al.  Tillage practices and the growth and yield of wheat in southern New South Wales: Lockhart, in a 450 mm rainfall region , 1986 .

[13]  M. Schroth,et al.  Influence of Bacterial Sources of Indole-3-acetic Acid on Root Elongation of Sugar Beet , 1986 .

[14]  L. F. Elliott,et al.  Pseudomonads as a factor in the growth of winter wheat (Triticum aestivum L.) , 1984 .

[15]  R. Cook,et al.  Evidence for Pythium as a pathogen of direct-drilled wheat in the Pacific Northwest. , 1980 .

[16]  A. Ellington,et al.  Direct drilling experiments with wheat , 1974 .