Synopsis No appreciable ammonia volatilized when less than 100 pounds of nitrogen per acre as urea was topdressed on soils with pH values below 6.3. Large ammonia losses took place when higher rates of urea were surface‐applied to bare soil and when soil drying occurred shortly after urea application.

Synopsis Most efficient utilization of potassium by alfalfa and alfalfa‐orchardgrass was obtained when potassium was evenly split and applied in early spring and after the first cutting. Efficiency was reflected by (1) less applied potassium needed for maximum yield, (2) good potassium recovery by the plant, and (3) favorable distribution of potassium in the plant throughout the growing season.

Synopsis Annual application of 200 pounds of N and 83 pounds of K per acre resulted in the highest orchardgrass yields and best recovery of N, P, and K by the plant. The K level in the plant at which yields fell below the maximum was positively related to the rate of N applied.

Synopsis Best yield response to 100 pounds of N per acre occurred when the percent legume was less than 20% in a red clover‐orchardgrass association and less than 25% in a ladino clover‐orchardgrass association. Some clover percentages above 25% were reduced when 50 or 100 pounds of N per acre was applied.

There is urgent need for a laboratory procedure capable of determining the status of the soil nitrogen, one which will predict the ability of a given soil to quickly replenish nitrates removed by cropping and leaching. Such a method would be useful in evaluating soil management systems and in determining the need for nitrogenous fertilizers. A laboratory method is described involving incubation under controlled conditions for 12 weeks with bi‐weekly removal of nitrates produced. This method was found to be successful but time‐consuming. Distillation of ammonia from soils in the presence of alkaline permanganate gave recoveries which were well correlated with incubation results. Both procedures showed that from 200 to 400 pounds out of the 2,000 to 4,000 pounds of total nitrogen in soils are biologically active. With these methods it was possible to show that long continued use of manure leads to a backlog of biologically active nitrogen. Acidity likewise favors accumulation while excessive liming without proper provisions for maintenance depletes the active organic nitrogen supply. Prolonged acidity causes a decline in microbiological activity, permitting potentially active forms of organic nitrogen to accumulate. When this acidity is corrected, as in the laboratory procedure described or as in tier II of the Jordan plots, the yields are higher than on the corresponding less acid plots. It is suggested that either method is quite useful in evaluating soils and soil management systems, but of questionable value in determining the nitrogen fertilizer requirements for the current year. Nitrate delivery to a given crop depends, not only upon the presence of easily ammonifiable organic nitrogen in the soil, but also upon the soil conditions prevailing at the moment. The available nitrogen requirement of a given crop depends upon the adequacy of other growth factors. A very poor correlation was obtained in the field between response to nitrogen and the quantity of easily nitrifiable organic nitrogen in those soils.