Effect of Fumigation on Soil Aggregation

Abstract

AbstractA study was made of the effects of several soil fumigants in moderate and high dosages and of steam sterilization on the aggregation of the <50 µ particles of five soils. The fumigants were injected into dry soil in large screw cap bottles, water sufficient to bring the moisture content of the soil to 50% of capacity was immediately added, and the lids tightly secured. After 3 days the soil was air‐dried, placed in 16‐ounce jars in 420‐gram portions, adjusted to 50% moisture capacity, and incubated. Microbial counts and aggregate analyses were made after 0‐, 10‐, 20‐, 50‐, 100‐, and 250‐day incubation periods.The fumigation treatments markedly affected the microbial population of the soils but had little or no effect on aggregation. In high dosages, D‐D, chloropicrin, and ethylene dibromide slightly increased the aggregation of one soil, namely, Yolo loam at the 0‐day incubation period only. Steam sterilization increased the aggregation of Yolo loam, an unnamed mountain soil, and Hanford sandy loam. In the latter two soils, the effect was not significant after the 0‐day incubation period. Increased aggregation was associated with decreased wettability of the soil.The study indicates that aggregation is influenced more by products of microbial activity during the decomposition of organic waste material than by numbers of microorganisms. Fumigation apparently does not provide sufficient energy material in the form of dead microbial cells and adsorbed fumigant to change the aggregation status of a normal soil significantly, or destruction of organic cementing materials by increased microbial activity counteracts any aggregating effect.