In water, oxamide was sparingly soluble and released ammonia slowly at 25" C. In an uncropped soil, conversion of the nitrogen in oxamide to ammonia and nitrate was essentially complete in 1 week with -60-mesh oxamide, but much slower with -4 + 6-mesh oxamide. Nitrogen uptake by one crop of corn forage in greenhouse pots from -4 + 6-and -2 8 + 35-mesh oxamide was approximately 22 and 89y0, respectively, of uptake from ammonium nitrate or 60-mesh oxamide. Nitrogen recoveries by three successive corn crops from 800 mg. of nitrogen applied as oxamide ranged from 44 to 64% on unlimed Hartsells fine sandy loam (pH 5.2) and from 61 to 82% on this soil limed to pH 7.5. These recoveries were similar to those from ammonium nitrate and considerably higher than those from an equal application of nitrogen as urea-formaldehyde.

A method has been devised which permits measurement of P absorption by plants during relatively short periods of root‐soil contact. Plants are grown without added P in sand during which time a mat of roots develops at the bottom of the container. The exposed root mat with plants intact is then placed in contact with the soil or soil‐fertilizer system. Results obtained using oats as the principal crop and concentrated superphosphate applied to Hartsells fine sandy loam support the following conclusions: (1) P uptake by oats from applied fertilizer increased linearly with time between 1 and 7 days and increased linearly with rates of applied P ranging from 0 to 50 mg. or more per 200 g. soil. (2) Moisture equivalent was approximately the optimum soil moisture level for P absorption. (3) Recovery of applied P commonly ranged from 2 to 5% after absorption periods of 3 to 7 days. The method holds considerable promise as a means of studying the influence of various factors on P absorption by plants. These include environmental factors as well as soil and fertilizer characteristics.

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The method previously reported for measuring short‐term P absorption by plants has been adapted to studies of K uptake in relation to various factors. K‐deficient oat or corn plants, grown in sand cultures, were placed in contact with soil or soil‐fertilizer mixtures for periods of 1 to 14 days. Recovery in oat tops from applications of 10 to 120 mg. K ranged from 25 to 7% in 3 days to 63 to 30% in 14 days. When K content of roots in sand and in soil also was taken into account, 14‐day recoveries from 30‐ and 120‐mg. K additions were 85 and 43% respectively. Despite the wide range in K content of plants, growth differences among treatments were not apparent for at least the first week, as had previously been observed in studies with P. Unfertilized soils supplied significant amounts of K to plants in 3 days. At 7 days, rather wide differences in K content of plants were evident among soils, indicating the possible utility of the method in assessing the K status of soils. Moisture contents of soils were important in relation to K uptake. Moisture equivalent for each soil appeared to be the near‐optimum level. Availabilities of K in potassium calcium pyrophosphate (KCP), potassium metaphosphate (KMP), and KCl to corn plants were compared in soil and sand. During 1‐ and 3‐day absorption periods, KCl was more available than KMP and KCP in both media. The data suggest that contact with soil increased dissolution of the KMP and KCP. KCl was less available in soil than in sand. Very high correlations were found between uptake of K by tops and whole plants for a wide range of K rates, absorption periods, and soils. Thus, K content of plant tops is a suitable criterion for assessing relative effects of treatments on K nutrition of the plants.