Fifty-nine full-sib progenies produced in a North Carolina Model I design were assessed fortotal yield (sum of three harvests) under four treatments differing in plot size and density. The treatments were: swards of 0.25 m2, spaced plants at 0.6 x 0.6 m and single and double rowswith 0.3 m betweenrows and 0.15 m between plants, with ten plants per row. Estimates of plot heritabilities ranged from 0.24 for spaced plants to 0.59 for double rows. Heritability in the sward was 0.35. Additive genetic correlations between the sward and the other treatments were surprisingly high: about + 0.86 for the spaced plants and between +0.8 and +0.9 for the row plots. The implications of these estimates for the relative selection efficiencies of the non-sward treatments are discussed.

A condition known as ‘scorch” with symptoms similar to copper deficiency often occurs in dry weather on cereals grown on a sandy soil (at Woburn) with an unstable structure. Plants with symptoms contained more sulphur than normal and sulphur/ copper interactions were suspected.

Sulphur fertilizers tested in two pot experiments with this soil did not induce copper deficienciesbut increased grain and straw yields of spring wheat especially at higher nitrogen rates. Yields were increased when the mature grain contained less than 0.12% S and the straw less than 0.5% Sin the dry matter. Sulphur concentrations were larger in plants grown in the greenhouse rather than in growth cabinets and in plants grown in oven-dried rather than air-dried soil.

Soil-applied copper sulphate slightly increased grain yields in pots but in one experiment there were no corresponding increases in copper contents of the crop. In a field experiment where ‘scorch’ symptoms occurred in 1972, copper oxychloride sprays increased copper concentrations but not yields of the grain.

These results suggest that copper deficiency is unlikely to be a primary cause of ‘scorch’ symptoms.

The studies were designed for breeding resistant varieties of rice to bacterial leaf blightcaused by Xanlhomonas oryzae (Uyeda et Ishiyama) Dowson with induced mutations. In 1971, seedlings of irradiated lines (X$) originated from treatments of 60Co γ-and X-radiation and control (C6), which were propagated in bulk up to X6(C6) generations after the treatments, were inoculated with highly virulent isolates.

The results showed that the variability of disease reaction within the irradiated lines increased in both resistant and susceptible directions from the control mean. It was assumed from these results that the irradiation treatments could induce polygenic mutations to give both germ types more resistant and those more susceptible to bacterial leaf blight, suggesting that such treatments might be an effective approach for breeding varieties resistant to the disease.

Food utilization by lactating dairy cows was studied in a randomized experiment covering the first 24 weeks of lactation, with further observations on performance over the remainder of the lactation under farm conditions. Over a 3-year period 90 firstcalf cows each took part in the experiment for one lactation, making six groups of 14–16 animals.

For the experimental period a fixed basal diet was given of hay, concentrates, and wet brewer's grains. One group received only the basal ration. Four groups received in addition a fixed concentrates supplement for 4, 8, 12, 16 weeks from calving onwards respectively. The sixth group also had supplementary concentrates for 16 weeks but for weeks 5–12 inclusive the amount was doubled so that this group's diet simulated broadly ad libitum feeding in early lactation.

Milk yield was increased by extra concentrates. The greater part of the effect was apparent in the first 2 weeks of different levels of intake, with a further build-up over the next 6–8 weeks. The size of the response fell as time from calving to initiation of different intakes increased. Additional food increased and delayed peak yield level. Persistency of milk yield was not affected by fixed differences in intake. Rate of liveweight change was improved by extra concentrates, less so in the third compared with the first month on treatment.

A higher level of feeding in early lactation led to a greater partition of nutrients in mid-lactation to milk at the expense of gains in body reserves. This advantage to milk production extended to the end of lactation. In it the greatest response per unit concentrates was obtained from supplementation in the first 4 weeks of lactation but the total effect was increased by giving a double allowance of concentrates, and by extending the period of extra feeding to 8 weeks after calving.

Solids-not-fat content and yield, and fat yield but not fat content, showed a similar response pattern to milk yield.

Animal-to-animal variation in output on constant diets was characterized by negative regressions of live-weight change on milk yield. The regression coefficients were greater in early than in mid-lactation but they were constant in size at any one time for the various groups. A change in ration induced a change in output of the individual in which that production pathway favoured naturally by the animal was the more affected.

The rate of change in the test weight of four winter wheat varieties, with changing grain moisture content, was greater when the grain was wetted than when it was dried. The test weight of grain which had been dried and returned to its original moisture content was lower than that of the original sample.