Nitrate production in the field by incubating the soil in polyethylene bags.

Nitrate production was studied in the field by incubation of the soil in pint polyethylene bags during the 1958–59 winter season. This technique permits the diurnal changes in soil temperature to be taken into consideration in studying microbial processes, such as nitrification. Laboratory studies showed that the rate of nitrification in soil contained in the bags was equal to that contained in ventilated bottles. The bags were tightly closed against the soil and secured with rubber bands. Only slight losses in soil moisture occurred during a 6-week period of incubation. Polyethylene is permeable to oxygen and carbon dioxide. No nitrate difused through the polyethylene bags in a 24-week period. Field studies were made using bags of soil buried at a depth of 4 inches for periods of 1 to 6 weeks. Although soil temperatures at this depth were never below freezing, they varied sufficiently to result in considerable changes in the rate of nitrate production. This technique should also prove to be of considerable value in evaluating nitrification in climates where the soil is frozen or at a temperature near freezing during a portion of the year.