ALBERT

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Description: An approximate, conveniently applied theory with corresponding experimental data is presented concerning the changes in momentum and mass transfer produced by a ridge of small slopes in a flat-surface quasi-stationary turbulent boundary layer. A first-order mean velocity perturbation solution is found to be in good agreement with measured velocities on the up-slope side of a two-dimensional ridge, of length 20 cm and height 1 cm, fixed on the floor of the working section of an open-circuit wind tunnel. A vapour-transfer eddy-diffusivity distribution is then calculated for the inner boundary-layer region and solutions of the consequent vapour-transfer equation give the variation of rate of evaporation from surfaces of varying lengths placed at different positions on the up-slope region of the ridge. Corresponding measurements are found to be in good agreement with the theoretical calculations, and show that, even over small slopes (of 1 in 10), the evaporation rate varied with position by 25% from maximum to minimum. This method of calculation is extended to examine the effect of surface curvature on diffusion of gas from an upstream line source in a turbulent boundary layer over the ridge; experimental and theoretical concentration profiles compare extremely well over the leading slope. © 1981, Cambridge University Press. All rights reserved.

Description: SummaryDespite much experimental evidence showing that sodium fertilizer increases sugar–beet yield and decreases need for potassium, there is resistance to its use on some soil types through fears of deterioration in soil structure. Twelve field experiments with sugar beet were made in Eastern England, testing all combinations of autumn and spring applications of 0, 150 and 300 kg Na/ha and 0, 83 and 333 kg K/ha. Fields were chosen with soils of loamy very fine sand, very fine sandy loam, sandy clay loam and clay loam textures. Micro–plot and controlled environment studies were also made with the same soils to examine effects of sodium on seedling emergence and growth.Visual assessments of soil physical state following sodium application revealed no effect in the year sugar beet was grown nor in the following spring when cereals were grown. Measurements of physical properties of soils treated with sodium suggested that applications of several times the recommended amounts of sodium fertilizer would not damage soil structure. However, sodium fertilizer increased the osmotic suction of soil solution which, under some circumstances, e.g. dry springs or giving the fertilizer close to the time of sowing, decreased germination and seedling growth. For this reason and not because it has a detrimental effect on soil physical condition, sodium fertilizer best given in the autumn or some weeks before sowing.

Description: SUMMARYThe effects of overwinter cover cropping, delayed ploughing and method of straw disposal on the quantities of nitrate leached (averaged over three winters during 1989–93) from a chalk loam in Eastern England were examined. The recovery of ‘retained’ nitrogen (retained through cover crop uptake, delayed ploughing and immobilization by straw) in a following spring crop was also assessed. In the first two winters, the rye cover crop decreased nitrate leaching by 〉 90% (28 kg N/ha per year), as compared with bare fallow treatments. In 1992/93 this decrease was only 23% (10 kg/ha), due to the early onset of drainage before cover was well established. Delayed ploughing on bare treatments, to decrease autumn N mineralization and subsequent nitrate leaching, was ineffectual in 1989/90 but had substantial effects in 1990/91 and 1992/93; N mineralization, inferred from soil mineral nitrogen content, and nitrate leaching were decreased by 31 and 35% in 1990/91 and by 36 and 61% in 1992/93, respectively. Nitrate leaching (averaged over three winters) was unaffected by straw incorporation. There was no evidence of recovery of cover crop N in the spring sown test crops (barley or sugarbeet). In the low soil N input situation encountered in this experiment, it was unnecessary to sow cover crops before early September in years of average or below average rainfall to ensure that the average soil solution concentrations remained below the EU drinking water limit of 11 mg NO3-N/1. However, in wetter seasons substantial N leaching occurred before cover had taken up much N. In 1992/93 N retained against leaching by a rye cover crop in previous years was apparently being remobilized and lost through leaching, although if cover was grown again there was less leaching than from bare land. In the future, an increase in the extent of cover cropping might increase transpiration rates and therefore lead to a decrease in aquifer recharge.

Description: The recovery of nitrogen ‘retained’ through cover crop uptake, delayed ploughing and immobilization by straw was assessed in a spring cropping rotation on a chalk loam in Eastern England (1989–96). The effect of annual cover cropping on yield of the subsequent spring crops and on the soil N balance was also investigated. The recovery of retained N was in part dependent upon cover crop management. Late August-sown cover crops which were incorporated in February/March tended to reduce spring crop yields and crop N offtake. Adverse effects on soil N supply, seedbed conditions and soil water reserves were not in evidence and so an allelopathic effect from the decomposition of the rye cover crop, previously reported by others, may be responsible for the reduction in yield of spring crops. When the cover crops were drilled later and their early destruction was followed by a short fallow period, spring crop yields and N offtake were increased. The soil N balance indicated that over the course of the experiment there was a positive N input to the system due to continuous cover cropping. This input may be held as immobilized organic N, in which case it could be made available to subsequent crops over a number of years or lost via other routes. Nitrate concentrations in drainage water increased with the number of years under cover cropping.

Description: SUMMARYAn appraisal of the value of S. 59 red fescue (Festuca rubra L.) for grazing was made using ewes and lambs (Clun Forest in 1969, Welsh Mountain in 1970) at a site 305 m O.D. in mid-Wales. S. 23 perennial ryegrass (Lolium perenne L.) was used as a control, and the value of S. 184 white clover (Trifolium repens L.) in conjunction with both grasses was examined.In the first year, under a rotational grazing regime at a fixed stocking rate of 22 ewes and single lambs/ha, lamb live-weight gains were significantly poorer on S. 59/S. 184 and significantly better on S. 23/S. 184 than on either of the pure grass swards. For the 130 days grazing season, mean daily lamb live-weight gains were 157, 126, 78 and 120 g on S. 23/S. 184, S. 23, S. 59/S. 184 and S. 59 treatments respectively.During the second year lamb growth rates on S. 59/S. 184 improved by 59%, whereas those on the other treatments were marginally lower than in 1969. Stocking rates were increased on the grass swards and decreased on the grass/clover swards for most of the grazing period in the second year in accordance with herbage availability. No significant difference was detected between the four treatments in total lamb liveweight production as a result of better individual growth rates on the grass/clover swards.In both years wide variations were recorded between treatments at different periods within the grazing season. Red fescue swards maintained superior lamb production in early spring and late autumn, but were inferior to ryegrass in mid-summer.

Description: SUMMARYHerbage characteristics of perennial ryegrass (Lolium perenne L.), cocksfoot (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb.) and timothy (Phleum pratense L.) pastures were obtained whilst rotationally grazed by ewes and their single lambs at a fixed stocking rate of 25/ha on an upland site (305 m O.D.) in mid-Wales. Drymatter production of cocksfoot averaged 32·1 kg/ha/day over the 3-year duration of the trial (1975·7) and was 13·3 kg/ha/day lower than that of the other three grass species. This resulted in a 8 kg/ha/day reduction in dry-matter intake on cocksfoot; this was significantly lower (P 〈 0·05) than that achieved on the other grasses, which were similar to one another around 36 kg/ha/day.In vitro digestibility of the herbage ranked in the order perennial ryegrass 〉 timothy = cocksfoot 〉 tall fescue. Intake of digestible organic matter (DOMI) was lower on cocksfoot than on perennial ryegrass and timothy. Differences were also detected in crude protein, water-soluble carbohydrates and sodium composition between species.Dry-matter intake was positively correlated with herbage growth rates (r = 0·95, P 〈 0·001) but not to digestibility of herbage on offer (r = 0·18). Both ewe and lamb live-weight gains were positively related to intake of dry matter and DOMI.Reference is made to comparative yield data between the grasses obtained under cutting trials. In the 2nd and 3rd harvest years (1967–1967) growth rates in the grazing experiment were 76, 61, 81 and 80% of the 66·2, 66·7, 67·8 and 65·0 kg D.M./ha/day obtained under a cutting regime on perennial ryegrass, cocksfoot, tall fescue and timothy swards respectively. This illustrates the danger involved in assessing the potential of grasses based on such information.The results are discussed in relation to the value of the species for use under grazing in the uplands.

Description: SUMMARYThe performance of Welsh Mountain ewes and their single Clun-cross lambs on swards of perennial ryegrass (Lolium perenne L.), cocksfoot (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb.) and timothy (Phleum pratense L.) was studied over 3 years (1975–1977) at a site 305 m O.D. in mid-Wales. Under a rotational grazing regime at a fixed stocking rate of 25 ewes and lambs/ha, mean daily lamb live-weight gain over the 84 days experimental period from early May to late July was 24 g higher on timothy than on perennial ryegrass and tall fescue and 35 g higher than on cocksfoot. Averaged for the 3 years the mean daily lamb live-weight gains were 194, 170, 170 and 159 g on timothy, perennial ryegrass, tall fescue and cocksfoot respectively. There were, however, marked interactions with years.Ewe live-weight change varied considerably between grasses and years with cocksfoot poorer than timothy and perennial ryegrass. Mean ewe live-weight change ranged from an overall loss of 39 g/day in 1975 to a gain of 34 g/day in 1977.Differences detected in animal performance between the four grass species altered during the 84 days of the experiment. Timothy and to a lesser extent tall fescue produced better animal performance early in the season whereas perennial ryegrass came into prominence during July.The results are discussed in relation to the present and potential use of the grass species under upland conditions.

Description: SummaryThe effects of controlled grazing, application of N, P, K, Ca, and Mg and the introduction of grasses and white clover, with and without cultivations, on Molinia caerulea dominant rough hill grazing were studied over 19 years in mid-Wales. Nutrient concentration in, and uptake by, the herbage and changes in soil physical, chemical and biological characteristics were monitored periodically. Concentrations and uptake of N, P, K, Ca, Mg and Na were highest on the reseeded pastures. Nutrient balance sheets showed that the nutrients applied were most efficiently utilized on reseeded swards. They also highlighted the considerable losses of applied Ca and Mg that occurred.Implications of the results are discussed in relation to both future agricultural use of such areas in the hills and the effects on the environment.

Description: 1. A study of grazing intake and efficiency was carried out on eighty-one ewes suckling twin lambs during early lactation.2. A method of estimating comparative grazing intake is described involving the administration of Cr2O3 and sampling from the pasture with the minimum of labour. The results indicated that reasonable precision was achieved with a method suitable for studying large numbers of animals. 3. The efficiency of production of lamb up to 5 weeks of age was not associated with the body weight of the ewe nor with the wither height. It was, however, negatively associated with grass intake by the ewe and to some extent with the gain in body weight by the ewe during lactation. Only in two of the four experiments was efficiency associated with lamb production up to 5 weeks.