Some data have already been presented on the kill of blue oak (Quercus douglasii H. & A.) with concentrates of 2,4–dichlorophenoxyacetic acid (2,4–D) and 2,4,5–trichlorophenoxyacetic acid (2,4,5–T) applied to cuts in the trunks. The present paper is concerned with reporting some similar studies on species which are noted for being persistent or vigorous sprouters. Since the sprouting question represented an important part of these studies, it was necessary to make observations for several years after treatment to arrive at some relatively dependable conclusion concerning effectiveness.

The influence of 3–amino–1,2,4–triazole (ATA) and eight of its salts or derivatives on defoliation and secondary growth in cotton, the straight growth and respiration of Avena sections, and the respiration of cotton leaf discs were reported in a previous paper.

The increasing use of dalapon (sodium salt of 2,2–dichloropropionic acid) by farmers and agricultural workers has stimulated interest in its effect upon the soil microflora and soil microbiological processes. Thiegs and Holstun and Loomis concluded that dalapon is broken down by an undertermined fraction of the soil microbial population. Magee and Colmer reported that dalapon at rates higher than those used in field applications, was toxic, as measured by manometric methods, to certain species of Azotobacter. Smith, Dawson, and Wenzel reported the effects of several other herbicides on soil microorganisms under laboratory conditions.

The rate of disappearance of a herbicide from soil is one of the key properties in determining its utility. In some cases it is desirable that a selected herbicidal concentration be maintained in the soil as long as possible. In other cases, rapid dissipation is desirable after a given effect has been produced. Leaching is a primary factor in the removal of many herbicides from soil.

The process of biological nitrification in soil is a two-step oxidation of the ammonium ion to nitrite and thence to nitrate and is largely caused by the autotrophic bacteria in the genera Nitrosococcus, Nitrosomonas and Nitrobacter. The biochemical activities of these soil microorganisms can be studied by using the percolation technique of Lees. When studying the nitrifying organisms, an ammonium salt solution is bubbled under air pressure through a lift tube to the surface of a soil sample in a suitable container from whence it percolates downward through the soil and drains back into the reservoir from which it came. Air and moisture are thus constantly replenished in the soil and water logging is avoided. The value of the method lies in the fact that any substance introduced into the percolating fluid which affects the metabolism of the nitrifying organisms causes a change in the rate of conversion of the ammonium ions to nitrate ions. When the nitrate in the percolating fluid is in equilibrium with the nitrate in the soil, measurements of the nitrate nitrogen in aliquots of the percolating fluid are a measure of the rate of nitrification in the soil.

Forage legumes are often injured when herbicides, such as 2,4–dichlorophenoxyacetic acid (2,4–D), are applied to control weeds in fields of grain containing legume seedlings. At times the legume seedlings are not injured materially but in many instances the herbicide applications result in a moderate or even drastic thinning of the stand. Various factors have been suggested to account for the variability in results observed.

Growth regulating type herbicides have been found to be effective when applied in low volume sprays. Uniformity of spray application has become a paramount requirement because of the high concentration of the spray solution. Volumes of one to ten gallons of solution per acre are not uncommon. Low volume application requires good design, construction, and operation of equipment. Air movement, temperature, and humidity also influence the spray deposition.

One of the major problems in present-day soybean production is weed control. The increased interest in profitable soybean production in recent years has stimulated a demand for a satisfactory and economical means of chemical control to supplement cultural practices. The gradual shift from solid planting to row planting has practically eliminated the problem of weeds between rows, but it has not solved the critical problem of weed growth in the row.