A COMPARISON OF THE SORPTION OF INORGANIC ORTHOPHOSPHATE AND INOSITOL HEXAPHOSPHATE BY SIX ACID SOILS

A comparison has been made of the sorption of inorganic orthophosphate and inositol hexaphosphate by six acidic surface soils from arable land in north-east Scotland. The sorption of inorganic P increased with increasing quantities added and tended towards a maximum, but was never complete. In contrast, the organic P was completely sorbed up to an added quantity which varied with the soil, and above this level the absolute sorption decreased, probably due to the formation of soluble complexes involving iron and aluminium. The sorption sites were apparently the same for the two P forms and, particularly at high levels of addition, the organic P depressed the sorption of inorganic P. Inorganic P did not depress the sorption-of organic P, which was preferentially adsorbed. The results help to explain the extreme stability of inositol hexaphosphate in these soils.     

THE INFLUENCE OF TEXTURE ON THE MOISTURE CHARACTERISTICS OF SOIL

A quantitative assessment was made of the effect of the proportion of sand, silt, clay, and organic matter in twenty-six soils on the moisture contents at the upper and lower limits of available-water of the soils. Regression equations were obtained which enabled the moisture contents to be estimated on a weight or volume basis from mechanical analysis data using either International or American size grades. The accuracy of estimating the upper limit of available-water from the various equations ranged from ±9 to 22 per cent: for the lower limit from ±8 to 16 per cent of the measured values. Mean values of the moisture contents at the upper and lower limits of available-water for each textural class were calculated from the average particle-size composition for each class and from the regressions obtained.     

Growth, colonization and productivity of two white clover cultivars strip-seeded into an upland Festuca-Agrostis sward

Small plots of a Festuca-Agrostis upland sward on a peaty gley podsol were strip-seeded during late June 1986 with white clover cvs Aberystwyth S184 or Menna at 4 kg ha⁻¹ and defoliated early (20 August) or late (3 September) and then frequently or infrequently (every 2 weeks or 4 weeks) until the end of September. All plots were defoliated in early November, at 3-weekly intervals during the growing season in 1987 and then grazed rotationally during 1988.
Satisfactory seedling establishment, representing 46% emergence, was achieved 5 weeks after sowing. The differential defoliation regimes had no persistent significant effects on clover development. S184 soon produced more leaves per seedling than Menna and a smaller proportion of its leaf number and weight were removed at each defoliation. Following large losses of leaves over the 1986–87 winter, SI84 had significantly more leaves per stolon than Menna; subsequently it also colonized the sward at a quicker rate. During 1987 amounts of herbage harvested (6.1 t ha⁻¹) were similar with the two clover cultivars, with S184 contributing 47% and Menna 44% of this respectively. SI84 made a larger contribution to yield during May and June but Menna was more productive during September and October. During 1988 clover populations were maintained with rotational grazing without additional fertilizer inputs.
The results show that, despite initial soil and climatic contraints, both small and medium-leaved clovers can be strip-seeded into upland swards with large subsequent benefits to yield and herbage quality. However, they also indicate the need for further experiments to determine the influence of sward morphology and defoliation regime on stolon branching rates and accumulation of growing points which, in turn, govern sward colonization.     

Breeding and evaluation of new white clover varieties for persistency and higher yields under grazing

Two experiments were established in 1989 and 1990 to evaluate the performance of white clover ( Trifolium repens ) varieties under grazing, using sheep and cattle, and also under a 'cutting-only' regime. The three potential medium/large-leaved varieties (AberVantage, AberCrown and AberDai) were selected and evaluated in a breeding programme that emphasized improving yield and persistency under grazing.
In Experiment 1, the potential varieties were sown with two different grass companions, and evaluated under a continuous cattle-grazing system, representative of their future role in actual farm practice, i.e. a set stocking system. Clover yield of the potential varieties in the second harvest year averaged 1–5 t ha⁻¹ more than the control variety Olwen. Total sward production of AberVantage, AberCrown and AberDai was 2.0–1.4 t ha⁻¹ higher than that of Olwen.
In Experiment 2, clover yields of the three potential varieties averaged 2.1 t more than Olwen in the second harvest year under continuous sheep grazing, but all three were lower yielding than Olwen in the cutting regime.
Both experiments illustrate how the use of grazing treatments during breeding and evaluation can improve the role of white clover varieties.     

A comparison of the ensilage, in an anaerobic cabinet, of grass, either fresh or when thawed after deep freezing

The suitability of freezing a large amount of grass from a single harvest for use in a series of experiments to investigate silage fermentation and its manipulation was examined. Perennial ryegrass, harvested in late June, was ensiled in sterile polythene bags inside an anaerobic cabinet; some was also stored frozen at -20°C for up to nine months before ensiling in a similar manner. The course of fermentation was followed using not only conventional chemical and microbiological analyses, but also by measuring microbial metabolic activity in vitro. Freezing and thawing affected the chemical composition and the microbial populations on the grass, and there were differences in the changes occurring in thawed grass during ensilage, probably related to damage to plant cells and impaired microbial activity associated with freezing and thawing. For both the grasses and the silages made from them, it was clear that the number of microorganisms present was not a reliable guide to microbial metabolic activity. Although the fermentation of frozen-and-thawed grass did not simulate precisely the fermentation occurring with fresh grass, it is concluded that, when used judiciously, the ensilage of thawed grass can be a useful experimental tool, particularly in the initial screening of manipulants of fermentation.     

Slot-seeding investigations. 4. Effect of phosphate fertilizer and grass suppressant on the establishment and growth of white clover in permanent pasture

White clover (cv. Grasslands Huia) was slot-seeded in April 1982 into plots of permanent pasture of differing botanical composition and reserves of soil phosphate. In one investigation the short-term effects of placing different amounts of phosphate (P₂O₅) in different positions in relation to the slot were investigated. In another, emphasis was given to effects of a grass-suppressing herbicide, propyzamide, on herbage growth and clover contributon during the second year. Fewer seedlings established on plots with a high initial P status and abundant in Holcus lanatus and Alopecurus pratensis than on plots deficient in P₂O₅ and dominated by Agrostis capillaris and Festuca rubra. P₂O₅decreased numbers of establishing clover seedlings when applied in the slots but not when placed beneath them. Growth was increased most when placement was beneath the slot. Application of P₂O₅to plots previously supplied with it resulted in 7.2 g total above ground and 1.7 g stolon dry weight (m row)^?1compared to 1.3 and 0.1 g respectively in plots with low reserves and DO applied P₂O₅. Propyzamide greatly increased the yield and the contribution of clover in the presence of high initial P status and applied P₂O₅. Without propyzamide, clover made only a small contribution until July, averaging 7% for the whole season with little benefit from residual P. Clover growth in late summer was increased from 41 to 292 kg DM ha^?1 where P₂O₅ was applied to P-deficient plots sprayed with propyzamide in the previous autumn. The large increases in clover contribution following propyzamide application were accompanied by small decreases in total seasonal yield of grass. The proportions of H. lanatus and. F. rubra. were decreased and of A. capillaris, increased. Spread of clover from the slots was slow during the first year but was encouraged by both P₂O₅ and propyzamide during the second year. Factors requiring further investigation are discussed.     

The effect of blending white clover varieties and their contribution to a mixed grass/clover sward under continuous sheep stocking

The effect of blending small- and medium-leaved white clovers together in a mixture of varieties was examined under continuous sheep stocking over a period of three years. Four varieties were used, S184 and Gwenda, small-leaved varieties suitable for intensive sheep grazing, together with medium leaved varieties Menna and Donna, which are mainly used in general purpose seed mixtures for medium term leys. The small-leaved varieties were blended with Menna or Donna, sown with a commercial grass mixture and managed as near as possible to farm practice. Although the leaf size of Gwenda is only slightly greater than that of S184, blends based on these two small-leaved varieties behaved differently. In spring of the first harvest year the yield of Gwenda and of the clover in mixtures containing Gwenda was 27% greater than the yield of the same mixtures which contained S184. As the season progressed this difference decreased. In terms of total annual yields and saving in fertilizer N, the benefits of including white clover in a seed mixture were more pronounced when Menna was mixed with S184 and Gwenda, rather than when Donna was used, although both varieties are in the medium-leaf category. It was concluded that the slower establishment and the lower clover yield of S184, when compared with larger leaved varieties, can be overcome by blending with a variety that is slightly larger in leaf size, such as Menna, although the choice of variety may depend on sward management and its persistency under grazing.