Synopsis Losses of nitrogen as ammonia during 7 days following surface application of 100 pounds of dry urea‐nitrogen were 20 to 30% for 4 different grass sods, and 17 to 59% for acid light sandy soils. Losses from ammonium nitrate or ammonium sulfate were negligible. Losses From urea solution were similar to those from dry urea for turf but much less for soils.

seed (1, 77). However, the inert coating will necessarily make up a greater proportion of the pellet weight and thereby will lower the analysis of the original fertilizer.Optical examinations of fertilizer particles often show extremely' irregular surfaces with evidence of pores, crevices, and many small, exposed crystal forms. The nature of this surface including the aggregation of crystals in mixed fertilizers and its polarity must be studied before adequate coatings can be developed. It is more difficult to prepare coatings for granular, single salt fertilizers such as potassium chloride, ammonium nitrate, or urea than for granules involving mixed salt systems. For instance, a very small imperfection in the coating on a granule of KC1 allows the potassium to diffuse away rapidly in water or moist soil. With an aggregation of small crystals in a matrix which contains partially soluble salts such as calcium phosphates, the dissolution properties are quite different.Experimental work indicates that fertilizers can be coated satisfactorily to change the rate at which they dissolve in moist soils. When large quantities of fertilizer are used under farming conditions, this reduction will help to alleviate seed-fertilizer contact injury, reduce leaching losses of fertilizer nutrients in sandy soils, and minimize luxury absorption of potassium by crops.

The persistence of surface‐applied urea and comparative crop responses to solution and solid N sources including urea were studied on sandy soils of pH 5.4 to 6.0 and 1.7 to 2.5% organic matter. Over 80% of prilled urea applied to a soil with an air‐dry surface under field conditions did not hydrolyze within 14 days, and from 42 to 72% persisted where a soil surface was only temporarily moist from recent tillage or irrigation, even though heavy dews formed nightly. With an exposed surface, continuously moist from a high water table, urea completely hydrolyzed within 7 days, with 65% of the applied N not accounted for as NH4+ and assumed largely lost as NH3 gas. Response of pasture grasses usually showed urea to be inferior to other N sources, with ammonium nitrate being the most consistently superior. Efficiency of urea and solutions appeared to be increased by rain immediately after application. Surface liming depressed responses to urea and materials containing ammonium‐N. Response of sweet corn to side dressings of urea was slightly inferior to responses to solid or solution‐N materials containing nitrate‐N, apparently as a result of faster penetration of NO3‐ as compared to NH4+ when moisture permitted. Covering urea or applying it on a temporarily moist vs dry surface had no differentiating effect. Persistence of urea on air‐dry or temporarily moist soil surface until incorporated by tillage or rainfall vs rapid loss of NH3 if a moist surface persists is a logical explanation of erratic responses to surface‐applied urea.

A five-day, whole plant toxicity test was developed and evaluated. The 18 chemicals tested were primarily substituted benzenes and phenols, although representative herbicides, surfactants, and other industrial chemicals were also tested. The test yields information on root and shoot growth as a function of toxic chemical concentration in the root environment and can also be used to determine the effect on transpiration. The measurement found to be the most sensitive indicator of toxicity was total plant growth. EC50 (effective concentration that reduced growth 50%) values were estimated for each compound using regression analysis. This simple bioassay gives a quick response to an acute exposure and can be used to screen chemicals at various concentrations. The beginning of a unique database comparing species, concentrations, and chemical toxicity are presented, and the results are discussed in relation to other phytotoxicity data.