The effects of a range of environmental factors on the performance of six varieties of sugar beet at 62 trial sites are considered with special reference to the identification of those environmental factors important in explaining observed variety × environment interactions.

Soil-water profiles are often calculated using models based on the application to successive soil layers of an approximate formulation of Darcy's Law. An arbitrary decision is usually made concerning the magnitude of the layer thickness, Δz, and time increment Δt, a decision often based on the intuitive criterion that both should be as small as possible. An unsuitable choice can either give rise to oscillations in the solutions that can be eliminated only by recalculation using different increments, or can culminate in an accuracy unjustified by the precision of the data, both cases resulting in unnecessarily lengthy and wasteful computing. However, mathematicians have shown, for problems which are analogous to particular soil-water models, that oscillations will not occur if τ = D(Δt)/(Δz)2 ≥ 0·50 (where D is the soil-water diffusion coefficient, assumed constant).

This paper considers the development of moisture profiles in soils with a constant rate of loss (e.g. evaporation) or entry (e.g. irrigation) of water imposed at the surface, and demonstrates that the criterion τ ≥ 0·50 can be extended to apply to waterdependent diffusion coefficients by re-interpreting D as the maximum value occurring in the profile. Examples for 10-layer models suggest that it is sufficient for practical purposes to start with Δt values that give τ-values close to 0·50, and to proceed to smaller Δt-values only when necessary. The total gain or loss of water given by integrating the calculated profiles is compared with the known amount entering or leaving at the surface.

The profiles for both evaporation and irrigation are found to advance too rapidly.

The potential yield of the best varieties of winter wheat currently grown in eastern England is estimated to be in the range 12–14 t/ha (15% moisture, 10% protein, freshweight basis).

Increases in the leaf area index at anthesis, in the duration of the grain-filling period and in the light-saturated rate of photosynthesis of the leaves, slower decline in their photosynthetic capacity, and decreases in the respiratory losses of assimilated carbon would increase this potential yield. Such changes might be brought about by breeding or by improved agronomic practices.

The grain growth rates predicted by several published simulation models are shown to be in reasonable agreement with each other.

The effects of white clover mosaic virus infection on the yield of two red clover varieties grown alone and in mixtures with either perennial or hybrid ryegrasses were examined. The spread of this virus within the pure clover plots was rapid. Clover drymatter yields were reduced and these losses were greater in the grass–clover mixtures than in the pure clover plots. Reductions in yield of about 70% were recorded at the first cut in mixtures of Sabtoron and Sabrina. The response of the clover to different levels of virus infection was best described by a negative linear relationship.

Yields of Sabrina hybrid ryegrass increased as the levels of virus infection in the clover increased. This compensated for the losses in yield of the legume, leaving total sward yields unaffected by the virus.

The genetic parameters of lifetime production traits and their relationship with milk yield in first, second and third lactations were estimated from information on 753 Tharparkar cows. The heritability estimates for milk yield in first, second and third lactations were 0·22 ± 0·10, 0·33 ± 0·14 and 0·49 ± 0·17 and for number of lactations completed, lifetime milk production, number of days in milk and herd life 0·58 ± 0·23, 0·51 ± 0·22, 0·54 ± 0·22 and 0·34 ± 0·20 respectively. The genetic and phenotypic correlations among the four lifetime production traits were in the range of 0·83–1·0 and 0·84–0·85 respectively. The phenotypic correlations of milk yield in first, second and third lactations with lifetime production traits were significant and ranged between 0·15 and 0·56. The corresponding genetic correlations ranged between 0·26 and 0·83. For the first three lactations, the genetic correlations of lifetime traits with the third lactation were high and that between lifetime milk yield and yield in third lactation the highest (0·83 ± 0·17). The direct and correlated responses from single trait selection were also estimated.

Wheat production in Australia relies heavily on superphosphate to maintain maximum grain yields. The current rock-phosphate supplies for superphosphate manufacture are derived from Nauru and Christmas Island in the Pacific Ocean; these supplies are anticipated to last only for the next 10–20 years. The supplies of ‘A’ grade ore (apatite) which can be used directly for superphosphate production are greatly overshadowed by large amounts of lower grade rock phosphate which is high in total phosphate but low in apatite. This material is termed ‘C’ grade rock and, to date, it has found little use in Australian agriculture.

One of the major limitations of white clover in Britain is the delay in commencement of spring growth compared with companion grasses (Williams, 1970) and the delay is further increased. by the resulting competitive disadvantage (Davies & Young, 1967; Spedding & Diekmahns, 1972). Thus there is a need to increase growth of white clover at low temperatures particularly in the uplands where the season is short (Ollerenshaw & Baker, 1981). However, the work of Cooper (1964) suggests that increased spring growth rate will be detrimental to survival. Small-leaved cultivars, e.g. S.184, have been favoured for upland use because they are well able to survive. This paper presents a study of the survival and early spring growth of 13 commercial varieties of white clover. Early spring growth was described by the increase in numbers of leaves per growing point and lamina length. The density of growing points was not recorded as previous field studies (Haycock, 1980, 1981; Davies & Evans, 1982) showed this variable to be of minor importance in spring yield increase.