Attributes related to seasonal herbage growth in white clover
When breeding temperate forage species is investigated, some attributes such as herbage accumulation and seasonal growth patterns have to be considered. To modify some of these traits, knowledge of the detailed process might be useful. In order to evaluate seasonal growth of contrasting white clover populations an experiment was carried out. Treatments were five cultivars and three local populations collected in Argentina. Weekly measures were taken during each season to calculate leaf appearance and flower appearance rates, stolon growing rate and dry matter (DM) net accumulation. Different germplasm of this species have different mechanisms for DM accumulation. Leaf size, more than leaf appearance rate, was the variable with most differences among germplasm and mostly related to dry matter accumulation. During spring and summer, inflorescences production had important effects on growing stolon rate, and differences among germplasm were evident. Some local populations showed favourable attributes that could be useful for breeding.
Estimation of leaf area for clover and lucerne
Summary Photographic standards have been prepared for the estimation of leaf area in clover and lucerne (alfalfa). A wide range of leaf form is covered, and the standards can be used for many trifoliate legumes. The method is rapid and can be used on the intact plant. The need to estimate the leaf areas of experimental plants has led to the development of many devices to reduce the tedium of this process, and comparative information on some of these is given by Milthorpe (1956). Most of these require the removal of the leaves from the plant, and one of the most practical is the airflow planimeter of Jenkins (1959). For some work, however, areas must be determined without damage to the plant. This can be done by using regressions on linear dimensions, especially where the leaf form is relatively simple, but the methods are slow by comparison with direct rating procedures such as that of Williams (1954) for the tomato. Rating procedures are applicable to leaves of complex and variable form if care is taken to cover the range of leaf form to be found in the experimental material. A real obstacle to the use of ratings is the labour involved in setting up the necessary range of standards; an imagined disadvantage is that there is a subjective element in the method. However, Williams (1954) has shown that observers achieve highly reproducible results, in spite of a strong tendency to underestimation. Absolute values can thus be obtained by using a specific observer factor, though such transformations are unnecessary for normal treatment comparisons, and for determinations of relative leaf growth rate. Clearly the same observer should make all the estimates for a given series of measurements. It is thought that, very occasionally, an observer may be unsuited to the method, but this will be evident from a simple test. The trifoliate leaves of many leguminous plants are sufficiently complex to make the use of regression procedures difficult, though Black (1958) used a curvilinear regression of area on midrib length. This depends heavily on the assumption that leaf form is unaffected by stage of growth or treatment, and the regression would certainly differ with strain. The purpose of the present note is to introduce a set of leaf area standards which covers the range of leaf form encountered in clover and lucerne. Original photographs were of individual leaves of several varieties of subterranean clover, Trifolium subterrarzeum L., and of lucerne, Medicago sativa L. However, the standards can be used with a wide range of trifoliate legumes.
Morphology of white clover (Trifolium repens L.) plants in pastures under intensive sheep grazing
Summary There has been little study on the growth and morphology of individual plants constituting the population of white clover in mixed swards under grazing. Such information is required if the mechanisms governing plant productivity and persistence are to be understood. Intact white clover plants were sampled from intensively sheep-grazed pastures under set stocking, rotational grazing, and a combination of both systems, by taking turves (250 × 250 mm), and washing out the plants, every month for a year. Characters measured for every stolon of each plant were: presence of a growing point; numbers of leaves, roots and axillary buds; stolon length. Total plant leaf and stolon dry weight were also recorded. Plants were classified according to degree of branching, and the contribution of each branching order to the population determined. There were strong seasonal variations in plant size (leaf and stolon dry weight, stolon length, and numbers of stolons and leaves per plant) which showed a significant decrease in spring with recovery over the following summer. This was paralleled by a rapid increase in the proportion of less branched plants (1st and 2nd branching order) in the population from 60 to 80% in spring, as higher-order plants broke up into smaller- and lower-ordered plants at this time. Numbers of roots per plant increased over winter to peak in early spring then declined in the following summer-autumn. While system of grazing management had no significant effect on branching structure of plants, it had a large effect on plant dry weight; rotationally grazed plants were 2·5 times larger than set stocked plants (0·182 cf. 0·073 g respectively). Other general features of plant morphology were that each successive order of branch stolons was shorter and length before branching was less than that of their preceding parent stolon. The highest branching order observed was 6th order. There was no relationship between branching and numbers of roots; in branched plants only 55% of stolons were rooted regardless of plant order, but rooted stolons accounted for 85% of total stolon length and carried 62, 48 and 90% of the leaves, growing points and axillary buds per plant, respectively. Comparison with other studies suggests that the processes outlined in this report may be common to white clover growth under grazing over a wide range of favourable environments.