Some of the factors affecting sulfate adsorption were studied using Cecil, White Store, and Nipe soils and H‐Al‐bentonite. The soils which contained a relatively large amount of 1:1 type clay minerals adsorbed more sulfate than the soils containing predominantly 2:1 type clay minerals. The amount of sulfate adsorbed decreased as the pH of the soil suspension increased from 4 to 6. The amount of sulfate adsorbed was found to be directly related to the concentration of sulfate in solution. For all of the soils studied, increasing the phosphate concentration in the solution reduced the amount of sulfate adsorbed by the soil. The data indicate that less sulfate ion is adsorbed by the clay particle in the presence of phosphate ion.

Sypnosis More organic sulfur than inorganic sulfate was contained in the surface horizons of a Durham and Marlboro soil. In the lower horizons there was an accumulation of sulfate in both soils. On the Durham soil sulfur deficiencies were exhibited. by cotton and tobacco early in the growing season. Only cotton gave a response to additions of gypsum. Cotton and soybeans removed considerably more sulfur than tobacco or corn. Availability of soil sulfur was evaluated by use of yield of sulfur Curves.

No abstract

Nitrification rate is proposed as a procedure for evaluating nitrogen requirements of soils for the production of corn. By the use of a modified nitrification method the rate of nitrate production was compared with the response of corn to nitrogen fertilizer in a series of experiments conducted in Iowa over a period of seven years. A significant correlation was obtained between nitrification rate and the response of corn to the application of 40 to 60 lbs. of nitrogen per acre. The data serve to stress the influence of plant population density on the magnitude of yield response to nitrogen. At comparable rates of nitrification considerably higher yield responses to fertilization were obtained where the plant population was high than where it was low. In all population groups, however, a profitable yield response to nitrogen fertilization was obtained where the nitrification rate was less than 40 ppm. On fields with thick stands, profitable yield increases were generally obtained when the nitrification rate was less than 50 ppm.

In order to adapt nitrate production for use in soil testing laboratories for the purpose of evaluating the capacity of soils to supply nitrogen to crops, a procedure was evolved which is accurate yet inexpensive and can be determined on a mass production basis. The influence of environmental factors on nitrate production during incubation in the laboratory was studied along with methods of sample manipulation to increase the time efficiency in analysis. Ten‐gram samples of soil were found to give accuracy comparable to 25‐ and 100‐gram samples provided moisture was controlled during incubation. Moisture losses can be closely controlled without creating suboptimum aeration by stoppering the sample containers with one‐hole rubber stoppers and incubating in an atmosphere nearly saturated with water. High humidity was maintained by placing flat open ceramic vessels filled with water in the top and bottom of the incubator. Nitrate production took place over a fairly wide range of soil moisture. Adjustment of moisture by tension methods proved more satisfactory than by the addition of constant quantities per sample. Of the tensions studied, 100 cm. water provided the most optimum moisture for the production of nitrates. This resulted in 25 to 35% moisture, depending on the texture of the samples and was a little above the field capacity. Automatic pipettes for adding the leaching solution, a specially constructed shaker for dispersing the soil which accommodated from one to four sample trays, simultaneous filtration of all samples in a tray and adding the solutions for color development by the use of automatic pipettes all served to increase the time efficiency of the nitrate production method and adapt it to soil testing needs.