1. Ten experiments were carried out on grassland in various parts of England and Scotland to compare ammonium nitrate, ammonium sulphate, urea with less than 1% biuret and urea with about 4% biuret. The grass was cut a number of times during the season and each nitrogen fertilizer was applied at rates supplying 30 and 60 lb. per acre of nitrogen in spring and after each cut except the last.2. Total yield and yields at most individual cuts of both dry matter and nitrogen in the herbage were increased by each increment of applied nitrogen.3. Ammonium nitrate and ammonium sulphate gave similar dry-matter yields at all cuts in six experiments, while in four on calcareous soils ammonium sulphate gave lower yields than ammonium nitrate at one or more cuts. Ammonium sulphate gave lower yields at the second or third cuts in more experiments than at the first cut.4. Urea with < 1% biuret gave lower dry-matter yields than ammonium nitrate at one or more cuts in eight of the ten experiments. Urea became less efficient relative to ammonium nitrate as the season advanced.5. The efficiency of urea with < 1% biuret relative to ammonium nitrate in each experiment was positively correlated with the ammonia absorption potential of the soil.6. Urea with < 1% biuret and urea with about 4% biuret gave similar yields.

1. Fifty-one experiments on the nitrogen, phosphate and potash requirements of maincrop potatoes were carried out in Great Britain in 1956–62. Each experiment tested four rates of each nutrient in all combinations and both total and riddled yields and quality data were obtained.2. Nitrogen requirement was influenced by previous cropping and the rainfall during the preceding winter. 50–80 lb/acre of N are recommended in mixed farming rotations depending on winter rainfall, and 120–150 lb/acre of N in arable rotations.3. Yield increases from phosphate were usually larger on soils with low citric-soluble phosphate. Nevertheless, irrespective of soil phosphate status, optimum rates of application were at least 120 lb/acre of P2O5 which was the highest rate tested in most of the experiments.

The changes in phosphate availability that occurred when fertilizer phosphate was incorporated in moist uncropped soil were examined by storing fertilized soil in the open for periods up to 3 years before a final test crop was grown. Superphosphate was the standard source as it was fully available initially and therefore provided a measure of the rate of immobilization of phosphate on the four soils used. The extent to which this rate was modified by slower rates of dissolution of non-water-soluble sources was examined, using dicalcium phosphate (powder and granular), basic slag and ground North African rock phosphate (GNAP).Powdered dicalcium phosphate and basic slag in general behaved similarly to superphosphate, indicating very rapid dissolution. The only exception was a slightly lower rate of dissolution of slag on the calcareous soil. Other than in the very acid soil, the rate of dissolution of GNAP was slow so that the available phosphate was not similar to the superphosphate treatment until after at least the second year. On the calcareous soil GNAP was practically inert. Granular dicalcium phosphate was the only consistent slow-release source. It gave available phosphate levels which were initially lower, but subsequently higher, than those from superphosphate. In the absence of a crop, cumulative assessments of phosphate availability were not possible.The pertinence of these results to the problem of maintaining a high soil phosphate status is discussed.

1. Urea containing less than 1% biuret was compared with ammonium nitrate in field experiments on barley, sugar beet, winter wheat and grassland, and with ammonium sulphate on potatoes, in various parts of Great Britain in the years 1957–61.2. When broadcast on the seed-bed for barley at rates supplying 25–45 lb./acre of nitrogen in twenty-five experiments, urea and ammonium nitrate gave similar mean increases in grain yield on acid soils, while on alkaline soils urea gave smaller increases than ammonium nitrate. The relative effect of the two sources was similar on light and heavy soils and in the east and west of the country.3. When broadcast on the seed-bed for sugar beet at 50–60 lb./acre of nitrogen in nineteen experiments, mostly on alkaline soils in eastern England, no difference was detected between the mean increases in yield of sugar and tops from urea and from ammonium nitrate.4. In twenty-two experiments on potatoes urea gave slightly smaller mean increases in yield of tubers than those from ammonium sulphate when applied at 40–60 lb./acre of nitrogen, with a larger difference at 80–120 lb./acre. No influence of soil pH, soil texture, region of the country or method of application (broadcast on the flat or over the open ridges) was detected.5. When broadcast as spring top dressings in seventeen experiments on winter wheat, mostly in western England and Scotland, at rates supplying 34–45 lb./acre of nitrogen, urea and ammonium nitrate gave similar mean increases in yield of grain.

1. Ten experiments were carried out on winter wheat in various parts of England in 1959-61, to compare 60 lb./acre of nitrogen broadcast as ammonium sulphate, ammonium nitrate and calcium nitrate (a) all in autumn, (6) one-third in autumn and two-thirds in spring, (c) all in spring. The winter rainfall was high in four experiments and moderate in six.