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.

The moisture content of soils is frequently reported to have an important effect upon the phytotoxicity of herbicides. Yet, specific experimental results establishing such relationships are, for the most part, lacking. Most moisture studies with herbicides have been designed to evaluate the effect of applied water on leaching and its indirect effect on volatilization and breakdown by exposure to sunlight. Some studies have shown the effect of moisture content on the rate of herbicide breakdown. Research on the fate of herbicides in soils has been summarized by Hill et al. and Ogle and Warren. The experiments reported here were designed to establish the effect of soil-moisture content per se upon the response of cotton to 3–(3,4–dichlorophenyl)–1,1-dimethylurea (diuron), isopropyl–N–(3–chlorophenyl) carbamate (CIPC) and 4,6–dinitro ortho secondary butylphenol (DNBP) as the alkanolamine salts.

When a small seed is covered with an inert material which makes it relatively large and round, it is called a pelletized seed. The main advantage in using pelletized vegetable seeds is that they can be planted at regulated distances from each other. This decreases the number of doubles and makes thinning easier and cheaper. If perfect seed germination and seedling survival were possible, pelletized seed could be planted at the distance required for each crop and thinning could be eliminated. This is impossible in practice, however, and more seeds than are required for final stand must be planted. As a result, thinning is necessary. This is usually done by hoeing out the extra plants. Weeds in the rows are removed at the same time.

In symptomatological studies with 3–(p-chlorophenyl)–1,1–dimethylurea (monuron2 or CMU) it was found that light intensity had an effect on the type of symptom and on the extent of the injury produced by this chemical. This note is published to direct attention to the influence of light in the herbicidal action of monuron.

Bear oak (Quercus ilicifolia Wang.) is widely recognized as difficult to eradicate. Burning, cutting, and routing, while killing the original stems to the ground, have caused dormant buds on the root collar to become active and produce fast growing sprouts which soon replace the original plant. In fact, single-stemmed plants so treated can produce as many as 40 or more new stems. Moreover, this species has been difficult to control chemically owing to resurging growth from the root collar and lower stem after a kill of original stems. Bear oak is widely distributed as an understory tree in the eastern United States extending from Maine to North Carolina and from the Atlantic Coast to Ohio and Kentucky. Often it develops into dense thickets on burned-over forest land or abandoned fields so that it monopolizes the site, crowding out other more desirable species and making planting of other trees an expensive operation. One hundred and fifty to two hundred thousand acres of such “scrub oak barrens” occur in Pennsylvania.

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.

Maleic hydrazide (MH) or 1,2–dihydropyridazine–3,6–dione is an organic plant growth regulator which has been found useful in preventing sucker formation in flue-cured tobacco, in preventing sprouting of stored vegetables, and in inhibiting the growth of some weeds and grasses. The compound can be synthesized from hydrazine and maleic acid or by reacting hydrazine hydrate and maleic anhydride. The commercial product, MH–30, is made by reacting MH with diethanolamine (DEA), and contains 58 per cent active ingredient, the remainder being classified as inert ingredients.

Since 1951 a number of reports on the use of pre-emergence herbicides for cotton have been published, and in several cases, these reports included data on the reduction of hand labor following the use of chemicals. In 1956, McWhorter et al. reported that combining chemical treatments with cross-plowing resulted in even greater reductions of hand labor than by the use of chemicals alone. They also reported that even though the amount of hand labor was reduced, both by the use of chemicals alone and by a combination of chemical and mechanical means, a corresponding reduction in the overall weed control cost did not always occur.

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.

The average annual celery production in Florida for the last five years has been 10,080 acres, most of which is grown in organic soils, with a value of 14 million dollars. Florida produces approximately 54 per cent of the celery marketed in the nation during the winter and spring months.

The use of pre-emergence herbicides to aid in the control of weeds in cotton has become an accepted production practice during the last ten years. In the process of becoming an established practice, this use of herbicides has created several new problems of a temporary nature and has been associated with stand losses in isolated cases.

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.

The present paper is supplementary to one previously published which received more comment than had been expected. In the meantime Salisbury's book appeared in which reference was made to the paucity of data on the subject and many records from the previous paper were quoted. Salisbury made statistical and ecological studies of various species in Great Britain.

The use of 2,4–dichlorophenoxyacetic acid (2, 4–D) for weed control in irrigated regions, especially on ditch banks, provides possibilities of contaminated irrigation water. A series of investigations has been conducted in the field to determine the response of certain crop plants to applications of 2,4–D in irrigation water, particularly at rates totaling herbicidal dosages. The first investigation dealt with Red Mexican beans and the results were published in 1954. This report deals with sugar beets, a root-type of crop plant.