SummaryIn experiments at Sutton Bonington between 1967 and 1970, which tested 0–300 kg N/ha applied in spring, maximum oil yields of both autumn- and spring-sown oilseed rape were obtained by applying 200 kg N/ha. The seed-oil content was reduced by nitrogen application but only seriously when 300 kg/a was applied. Responses to high levels of potassium (180 rather than 60 kg K20/ha) were only obtained at 200 kg N/a. Successive increments of nitrogen from nil to 300 kg/ha improved plant growth, increasing leaf area and the dry weight of leaves and stems. The last increment from 200 to 300 kg N/ha was less effective and either reduced or did not affect pod production.In one experiment 300 kg N/ha stimulated husk growth, apparently at the expense of seed growth, with 200 kg/ha giving the highest proportion of pod dry matter as seed. More nitrogen always raised number of seeds per pod, but only increased seed weight in one autumn-sown experiment.Serial harvests of one experiment indicated that the maximum seed and oil yield was obtained by cutting plants before they were fully ripe, thus avoiding seed loss through pod shatter. The oil content of the bulk samples reached a peak about a week before maximum oil yield, probably because later-ripening seed did not reach full maturity. All nitrogen levels delayed flowering, but only the highest delayed maturity in the autumn-sown crop.

THE SIGNIFICANCE OF PALATABILITYUnder the definition of Tribe and Gordon (41) palatability, being the sum of the factors which operate to determine whether and to what degree the food is attractive to the animal, can be held to constitute the connecting link between grass and the grazing animal and is regarded by Stapledon (31), Grazier (9) and Cockayne (3) to be of greater importance than nutritive value. Necessarily relative, it is influenced by such variables as the animal itself, stage of growth and development of the herbage, alternative foods and the management and manuring of the herbage. (1, 3, 4, 11, 13, 20, 24, 27, 28, and 41).The significance of palatability in relation to animal nutrition is obscure and whilst Stapledon (31) and (32) and Ellison (6) claim that the grazing animal has an instinct to select those species which are of most value to it. Tribe and Gordon (41) renounce this suggestion and quote the results of experiments with rats to prove their point.It would be dangerous to dismiss categorically the importance of palatability in animal nutrition, particularly in the case of such a delicately physiologicaUy balanced animal as the dairy cow and considering the evidence of Hignett (12) concerning the factors affecting fertility of dairy cattle. It is therefore suggested that until such time as the theory of nutritional wisdom (6, 31 and 32) is conclusively confirmed or disproved for such an animal as the dairy cow, then the selection of herbage by the animal is a factor which must be respected by both grassland and livestock authorities alike.It is generally agreed (15, 34 and 41) that palatability has an important influence on the quantity of material consumed by the grazing animal and also on the rate of consumption and hence palatability gains an added importance in relation to the systematic evaluation of grassland.The fashionable simple seeds mixture responding to the specific management as demonstrated by Stapledon and Davies (33) is undoubtedly capable of extremely high productivity in terms of total green material, stock carrying capacity and yield of nutrients as determined by chemical analysis or on a utilized starch equivalent basis (14), but such consideration do not take fully into account the grazing animal, for as Brynmor Thomas (39) contends, palatability has not received sufficient consideration in the design of modern seeds mixtures and he quotes the work of Milton (19) to demonstrate that many miscellaneous herbs and some reputedly inferior grasses are highly palatable and in certain circumstances much sought after by stock.Concerning inter-strain and inter-species competition in the sward, it is agreed (16, 22, 36 and 37) that unpalatabiiity will favour persistency and ultimate domination over more palatable and hence more severely grazed associates. Furthermore, manuring and management, whilst materiaUy and directly affecting the yield of grasslands, affect the botanical composition of the sward with subsequent repercussions on the yield and quality of herbage (10, 17, 3...

SummaryExperiments made between 1967 and 1970 tested the effects of sowing oilseed rape on different dates in autumn and spring. Much greater oil yields were obtained from autumn sowings, due to higher seed yields and oil content, but the effect varied considerably between experiments, varieties and seasons. Autumn-sown crops flowered in late April or early May, and by the time pods were developing rapidly in June the leaves had senesced almost completely. Spring-sown varieties followed a similar pattern but about a month later, and did not reach the same peak in pod growth.There was a major effect of sowing date, late-autumn sowings (after mid-September) giving lower yields than early-spring sowings. The best autumn sowings (early September) gave about 3 t/ha of seed, but late sowings less than half this; oil content also decreased with delay in sowing – from 45% to as low as 38%. Delayed sowing restricted growth, leaf area and pod production, and also had a slight effect on seed weight. Frost damage on flower buds appeared to be the cause of reduced yield from early sowing (August) in one experiment. In spring, the earliest sowing (late March) gave the best yields. Vigorous but late vegetative growth from the latest sowing (end of April) did not lead to high yields, possibly due to pest and disease effects.

In field trials in 1971-73, perennial ryegrass cv. S23 and S24 were given up to 200 kg ha" n itrogen (N) and dry weight, seed yields and seed yield components measured. Optimum levels of applied N ranged from 80 kg ha"', where livestock had grazed the crop in the establishment year or where residua! N levels were about 70 kg ha"', to 120 kg ha"' where residual N was low. Application of more than 120 kg ha"^ did not increase yields further because of increased lodging and increased production of vegetative tillers. Seed set was 37-55% in S24 and 25-29% in S23 and was decreased by lodging.

In the potato plant there is competition for assimilates between foliage and tubers, and the balance can swing in one direction or the other depending on the treatments received. Skill in crop husbandry has found ways by which the crop can be manipulated towards higher returns. Growth analysis studies have now provided some understanding of the factors involved, better knowledge of which could lead to greater control over crop yields.

SummaryIn these experiments lodging not only decreased the number of seeds harvested, but also had an effect in determining which spikelets on the ear set most seed. These data have also shown that many more seeds are set than are harvested, even when the crop is not lodged. It is suggested that there is a lack of assimilate supply to fill the developing seeds, some of which abort, allowing the remainder to attain a viable seed weight. Mechanical support of the crop may increase the assimilate supply to the seed thus allowing seed further up the ear and spikelet to develop fully.

Research conducted on sowing dates has shown a trend towards increased yield as sowing is advanced for winter wheat (Darwinkel, Hay & Kuizenga, 1977; Walker, 1980) and winter barley (Selman, 1980; White, 1981). Green & Ivins (1985) have quantified the rate of yield decline for winter wheat as sowing is delayed after mid-September, giving a mean value of 0–35% per day. For a similar study on winter barley (Green, Furmston & Ivins, 1985) a yield decline of 0–43% per day delay in sowing was attributed to reductions in the number of ears per unit area as planting was delayed.

Research conducted on sowing dates for wheat shows a trend towards increased yield as sowing is advanced (U.K.: Walker, 1980; Bingham et al. 1983; the Netherlands: Darwinkel, Hag & Kuizenga, 1977; Canada: Nass et al.1975; Briggs & Aytenfisu, 1979). In a review of the influence of drilling time on winter wheat in the U.K. McLean (1981) suggested October planting as the optimum. However, sowing before this time often results in increased yield (Bingham et al.1983).