Elliott (1962) estimated that the average grain yield of wheat in the United Kingdom increased by 6·1 cwt per acre between 1947 and 1957. By considering results of yield trials carried out by the National Institute of Agricultural Botany he attributed 3·8 cwt of this increase to greater yielding ability of new varieties and the remainder to ‘other factors’, including the increased use of fertilizers, chemical weed control, better seed dressings and combine harvesters. The genetic improvement obtained by breeding new varieties is due partly to the incorporation of characters which are comparatively easily recognized, such as resistance to various diseases and lodging. However, even when these major limiting factors are absent from the environment the new varieties give higher yields, presumably due to physiological superiority. Many investigations, reviewed by Thome (1966), have sought to identify and establish the relative importance of the responsible physiological characters, but the information is still far from complete. This shortcoming is now the chief hindrance to more efficient choice of varieties for use as parents and selection of improved genotypes by the breeder. The objective of the three experiments reported here was to provide further information on the physiological basis of varietal differences in yield in wheat.

The rotation responses of unfertilized cotton were investigated using data obtained over a 28-year period from an experiment comparing ten rotations in various combinations of cotton with fallow and an alternating crop of dura (a sorghum millet) and lubia (a legume).

Experiments were carried out in dry, nonpregnant cows by varying dietary concentrations of calcium and phosphorus. Calcium and phosphorus absorption were measured by balance and isotope techniques. It was found that absorption of calcium or phosphorus increased when the dietary intake of the element increased, but only for a few days.

Three field trials with Italian ryegrass showed that solid N fertilizers usually gave larger yields than solutions containing 5% N but the differences were significant in only three of thirteen comparisons. More N was taken up from solid fertilizers than from solutions; the differences were not significant at 561b N/acre but were at 1121b N/acre. Grass given solutions had smaller percentage of N and the differences in the percentage of N were significant in eight of ten comparisons. In pot experiments with Italian ryegrass, solutions containing 3.3% N were less effective than solid fertilizers, but solutions containing 1.8% N were equally effective. Possible causes of solutions being less effective are discussed.

Calcium nitrate, or ammonium sulphate without or with 1% of the nitrification inhibitor 2-chloro-6 (trichloromethyl) pyridine were applied in the spring to winter wheat growing on clay- and sandyloam soils; 50 or 100 lb N/acre was applied on the clay-loam and 75 or 150 lb N/acre on the sandyloam. On permanent grassland ammonium nitrate or ammonium sulphate without or with 1 or 2% of inhibitor were broadcast to supply 100 or 200 lb N/acre. Winter wheat was sampled 32 days, and grass 68 days after applying fertilizers. Ammonium sulphate increased nitrate in the wheat on the clayloam soil but significantly less with than without the inhibitor. On the sandy-loam, wheat given ammonium sulphate with and without the inhibitor contained similar amounts of nitrate-N. The double amount of ammonium sulphate without inhibitor increased the nitrate content of grass most, and the nitrate content decreased with increasing amount of inhibitor.

1. In a 3 x 2 x 2 factorial experiment forty-eight Large White type pigs (twenty-four hogs and twenty-four gilts) were individually and restrictedly fed, at either a 3:1 or 2:1 ratio of water to dry food, a diet containing 70% wheat prepared in either crimped, rolled or ground form. A further six litter-mate Large White type hog pigs were used in digestibility and nitrogen retention studies.

1. Over 3 years monogerm sugar beet seed spacings of up to 5 in apart produced sufficient plants to form an adequate plant population for maximum yields. In the first two seasons the braird from a 5 in seed spacing did not need to be thinned; but in the third it contained over 50,000 seedlings per acre and so had to be reduced by thinning to approximately 30,000 per acre.

1. The nutritive value and chemical composition of hybrid Napier, Napier and Jowar grasses and also a leguminous fodder, berseem, were studied using adult kumaoni steers.

1. The flow of digesta in the duodenum and the changes in the lipid composition of ruminal and duodenal digesta of sheep accustomed to receiving hay and oats, hay and palm oil and hay and tallow have been studied.

1. The rate and pattern of water extraction from the soil by grass swards were examined.

2. Under a continued drought water was removed progressively down the soil profile. The rate of removal of water was similar from all horizons to a depth of over 3 ft in these conditions.

1. Calorimetric experiments on the utilization of dietary energy by the laying White Leghorn hen are described.

1. From 1960 to 1964 an experiment at Woburn, Bedfordshire, measured yields and the amounts of N, P and K removed by five arable crops (barley, grass-clover ley, potatoes, oats and sugar beet) and by a long ley; each was manured with all combinations of N, P and K fertilizers and with farmyard manure (D) and with both fertilizers and farmyard manure (DN1PK and DN2PK).

Various carcass measurements were obtained from 216 Hereford steers and evaluated in an attempt to find traits or combinations of traits which accurately estimate carcass composition. Carcass weight and trimmed retail cuts from the round proved to be the best single estimators of kilograms of retail cuts. Prediction equations were developed using carcass weight, trimmed retail cuts from the round, longissimus dorsi area, measures of fat thickness at the 12th rib, untrimmed round weight and weight of kidney, heart and pelvic fat in various combinations. Eighty-four to 94 % of the total variation in actual kilograms of retail cuts could be accounted for by using these equations.

Net assimilation rate (E) was measured in three experiments involving related species and cultivated varieties with increasing grain yield potential in the genera Hordeum, Avena and Triticum. No consistent differences in E between the barley varieties were found, but in the oat and wheat experiments, Abundance and Atle respectively had lower values of E. However, these differences did not suggest that E had been influenced in selecting for grain yield. The relationship of E to dry-matter production was calculated and discussed.