Chlorate distribution and the effect of nitrate concentration on chlorate toxicity in soil columns

Abstract does not appear. First page follows.

Introduction

Sodium chlorate is widely used in controlling weeds. The fact that it acts most efficiently as a temporary soil sterilant ⁽³⁾, ⁽⁵⁾, ⁽⁶⁾5 emphasizes the need for accurate knowledge of its behavior in soils.

In an attempt to evaluate the effects of soil type and rainfall on the vertical distribution of sodium chlorate in soils, Crafts ⁽²⁾ in 1935 performed experiments on the slow percolation of sodium chlorate solutions into columns of air-dry soil. Enough solution was allowed to drip upon the soil to just wet the entire column. The column of soil was then separated into ten equal fractions, each of which was mixed and seeded with oats. The plants were grown for 30 days. In view of the fact that in some cases the oats grew normally in soil from the bottom parts of the column, but showed high toxicity in soil from the upper parts of the column, he concluded that the chlorate had been fixed in the upper layers of soil and therefore had not reached the bottom part of the column.

In 1939, experiments reported by Crafts showed that chlorate toxicity in soils is reduced roughly in proportion to the nitrate concentration of the soil solution ⁽⁴⁾, p. 655-71). This observation suggests an alternative explanation for the low toxicities occurring in some soils near the bottom of a chlorate-treated column.