Influence of steam/air mixtures, when used for heating soil, on biological and chemical properties that affect seedling growth

Abstract

SUMMARY An apparatus for heating small quantities of soil with steam/air mixtures, at temperatures from 50 to 100d̀ C., is described. Heating naturally infested soils at 60d̀ C. for 10–30 min. eliminated attack by Rhizoctonia solani Kuhn and pathogens causing brown root rot, so increasing survival and growth of lettuce and tomato seedlings respectively. Growth in soils heated at temperatures above 80d̀ C. was often less, however, than in soils heated at 60–75d̀ C. Decreases were associated with relatively high soil concentrations of (1) soluble and exchangeable manganese and (2) nitrite. Amounts of ammonia were greatly increased at 52d̀ C., compared with the unheated controls, but those of manganese (water‐soluble and exchangeable) and nitrite were not significantly increased at temperatures less than 65d̀ C. The damage done to lettuce by R. solani when inoculated to preheated soils usually increased with increasing treatment temperatures. Fewer seedlings survived in soils preheated at 60d̀ C. than in the unheated controls but usually more than in soils preheated at 100d̀ C.