Toxicity of certain herbicides in soils

Abstract does not appear. First page follows.

Previous publications from this station have described a method for testing the toxicity of chemical sterilants in soils (Crafts, 1935)3 and have presented results from such tests with arsenic, borax, and chlorate (Crafts, 1935); (Crafts and Raynor, 1936). Further studies by this method have provided data on the characteristics of ammonium thiocyanate, sodium thiocyanate, ammonium sulfamate, dinitro-o-cresol, and certain other soil sterilants. At times when arsenic and chlorate cannot readily be obtained, the results of these studies may be especially useful; some of the chemicals tested may offer possibilities as substitutes. Furthermore, the present extensive use of substituted phenols in weed control presents problems concerning the possible deleterious effects of their accumulation in soils. With the introduction of new and more toxic organic herbicides, the possibility of using these as soil sterilants seems worth considering.

Testing Method

Briefly, the testing method involves growing indicator plants (Kanotaoats) in soils moistened with solutions of the chemical being studied. Surface soils are pulverized, screened, and weighed into no. 2 cans. Each culture is then moistened enough to bring it to field capacity, the solutions being made up by diluting a stock solution. After standing overnight the cultures are seeded. The plants are grown for 30 days, being periodically watered by bringing the cultures up to their original moist weight.

In harvesting, a visual estimate is made of the average height of the plants; then they are cut off at the soil surface and weighed. All yield data in this paper are average values for fresh weight of three or more cultures at harvest time.

After weighing, the tops are returned to the can, and all cultures are dried for 30 days. Then the tops are set aside, the soil is removed and pulverized, the tops are placed in the bottom of the can, and the pulverized soil is poured back in and remoistened with tap water. The cultures are seeded, watered, and harvested as before.

The percolation tests are made in special soil tubes. Each tube consists of a celluloid liner supported by hardware cloth bent into the form of a cylinder. The bottom is closed with a circle of filter paper supported by a square of ?-inch-mesh hardware cloth.