Wheat yield depression associated with conservation tillage caused by root pathogens in the soil not phytotoxins from the straw
1991
Cook, R.J. | Haglund, W.A.
Wheat planted directly into soil mulched with straw of a previous wheat crop (mulch or conservation tillage) typically grows and yields poorly relative to that planted into a prepared seedbed with straw residue burned or buried (clean tillage). This injurious effect associated with straw mulches has been greatest in the higher-rainfall wheat-growing areas, or in wet years in normally dry areas. Researchers have focused for the past 30 yr on putative phytotoxins thought to be liberated during microbial colonization or breakdown of the straw on or near the soil surface when wet. The results of experiments reported herein indicate that the causal microorganisms are in the soil and not the straw as would be required if phytotoxic straw decomposition products were important. The injury in these experiments resulted from at least three root diseases, all favored by the lack of crop rotation. The three root diseases were take-all caused by Gaeumannomyces graminis var. tritici, Rhizoctonia root rot caused mainly by Rhizoctonia solani AG8, and Pythium root rot caused by several Pythium spp. The effect of straw on, or mulched into, the soil surface possibly amounts to no more than helping to keep the top 10-15 cm of soil, the zone occupied by the root pathogens, more ideally moist for their activity. The results suggest that conservation tillage is feasible for wheat in the higher rainfall areas when used in combination with a break from wheat.
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