Multifactorial experiments at Rothamsted Experimental Station in two contrasting seasons, 1985/86 and 1986/87, tested the effects of treatment combinations that varied the supply of nitrogen at important stages of crop development in autumn and spring on the grain yield and nitrogen content of September- and October-sown winter wheat. Treatments that altered the nitrogen supply in autumn were an application of winter fertilizer N and sowing the wheat after rape or oats, which left different amounts of residual N. These were combined with treatments which tested the effects of 200 kg N/ha in spring applied as early or late dressings and as single or divided dressings. The effect of applying an additional 50 kg N/ha in summer was also tested in 1985/86.

In both experiments, larger yields were obtained from sowing in September than in October. The September-sown wheat grew better over winter in 1986/87 than in 1985/86 but the early advantage in size and N uptake resulted in enhanced production of straw rather than grain. Residues of N from previous crops were smaller after oats than rape in both years. This difference in soil N did not affect the over-winter growth and N uptake of the October-sown wheats. Neither this difference in residual N nor an application of fertilizer N in winter affected the yield of the following September-sown wheat in 1985/86 because autumn growth and N uptake were restricted by adverse weather. In 1986/87, however, wheat that followed oats yielded 0·42 t/ha less grain than wheat that followed rape, and the deficit in yield was removed by an application of fertilizer N equivalent to the deficit in soil N.

Yields were decreased when the spring N was applied as a delayed, single dressing in April especially if the wheat was sown in September after oats, or was not given winter N. Yields were not affected by any of the other combinations of single v. divided dressings or early v. late applications of spring N, despite these being given at very different stages of apical development.

The percentage of N in the harvested grain was greatly increased by winter applications of fertilizer N, especially to wheat grown after oats, by applying the spring N as a late, single dressing and, in 1986, by applying N in summer.

The phenotypic stability of seven Finnish and Nordic oat cultivars and 12 breeding lines developed at the Hankkija Plant Breeding Institute, Finland, was studied using the Finlay–Wilkinson regression method, Eberhart–Russell stability analysis, principal component analysis (PCA) with biplot presentation, canonical variate analysis (CVA) and Procrustes analysis. Comparison of stability analyses was based on four dissimilar growing seasons. In addition to the measurement of phenotypic stability of grain yield, the performance of 12 morpho-physiological traits was evaluated, including maturity class and structure of canopy and plant stand.

The different stability analyses examined produced uniform results and ranked the cultivars and breeding lines without major disagreements. Lines with exceptionally stable yield performance over the different growing seasons were identified. In general, there was an association of high yielding ability with poor stability. However, some cultivars deviated from this tendency and showed high grain yield production and average stability of yield performance.

A series of 240 thin-layer drying runs carried out in 1988 and 1989 at the Scottish Centre of Agricultural Engineering were analysed to find out which factors influenced the rate of drying of grass mixtures. The grass used in the experiments was cut by hand, by a mower without conditioner or by a mower with conditioner. The experiments covered a range of air conditions from 16·0 to 40·4 °C temperature and 24·4 to 82·8% relative humidity. By fitting curves to the experimental data it was shown that the drying curves could be simulated by a two-parameter, exponential equation. Analysis of the data showed that the experimental results could be adequately represented by holding one of the parameters fixed and fitting the curves with only one parameter varying. The variable parameter, called the drying coefficient, was dependent on harvesting method and related to drying air temperature, initial moisture content and ratio of leaf area to stem area. A regression equation relating the drying coefficient to these variables for conditioned and unconditioned grass is presented.

Predictions from the regression equations indicated that the temperature of the drying air had a major effect on the drying coefficient. Both the initial moisture content of the samples and ratio of leaf to stem had a smaller influence on the coefficient over their likely range.

All combinations of five cutting heights (2, 4, 6, 8 and 10 cm), two rates of P application (0 and 100 kg P/ha per year) and two irrigation treatments (0 and maximum soil water deficit 35 mm) were compared on field plots sown with a mixture of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) in Wales. The cutting and P treatments were applied for 4½ years (1986–90) and the irrigation treatments for 2 years (1987 and 1988). The plots were cut at 4-week intervals from April to October each year.

Applied P and irrigation had only a small effect on the productivity and composition of the swards. The proportion of white clover in the sward was inversely related to the height of cutting, so that clover was almost eliminated by 3 years of 10 cm cutting. This reduction in clover content led to a 50% reduction in herbage yield. Close cutting increased the tiller density of ryegrass in May and June of the first harvest year, but this effect was subsequently reversed as clover competed more strongly with ryegrass under close cutting. The proportion of unsown species, predominantly Agrostis tenuis, was much higher in the third and fourth than in the first and second harvest years and was positively related to the height of cutting. Close cutting depleted soil K and soil water.

All combinations of five cutting heights (2, 4, 6, 8 and 10 cm) were compared, for 3 years (1986–88), on field plots sown with a mixture of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) in Wales. The plots were cut at 4-week intervals from April to October each year.

A reduction in cutting height reduced the length, width and weight of clover leaflets, petiole length, stolon diameter, the length of stolon internodes and the height of stolons above ground level, but increased the length of clover stolon/m2, the number of stolon nodes/m2 and the proportion of stolon nodes which produced branches. The latter factors out-weighed the former, leading to the inverse relationship between cutting height and the proportion of clover in the sward previously reported (Acuñia & Wilman 1993).

A reduction in cutting height reduced the following attributes of ryegrass: the height of the shoot apex, the length and width of leaf blades, sheath length, leaf extension rate, the death rate of leaves and the net gain in blade length.

Cutting height had little effect on either the thickness of clover leaflets or the rates of leaf emergence in clover and ryegrass.

Field experiments with the potato variety Desiree at Cambridge, UK, in 1988–90 examined the effects of windrowing on the development of blemishing diseases during storage on tubers from crops grown with differing irrigation regimes and dates of defoliation and harvest. Irrigation reduced levels of silver scurf (Helminthosporium solani) at harvest in all three years and increased black dot (Colletotrichum coccodes) in one year. Early crop defoliation slightly increased silver scurf at harvest in one year only. Silver scurf developed less during storage at 3 °C than at 7 °C and disease levels on tubers after storage were related to levels present at harvest. The effects of leaving tubers for up to 6 h in a windrow at harvest on silver scurf after storage were small and inconsistent between years despite similar drying conditions. The results suggest that windrowing may be of little practical use in controlling silver scurf during storage.

A 2-year study conducted in Salinas, California in 1989–91 showed that soil nitrate (NO3–N) concentrations were reduced by cover crops during a short winter fallow period and that this practice can be compatible with year-round vegetable crop production schedules by planting and incorporating cover crops directly on the beds into which the lettuce crop will be direct seeded in the early spring. Cover crops grown the first year were oilseed radish (Raphanus sativus cv. Renova), white senf mustard (Brassica hirta cv. Martigena), white mustard (Brassica alba), Phacelia (Phacelia tanacetifolia cv. Phaci), rye (Secale cereale cv. Merced) and annual ryegrass (Lolium multiflorum). Only phacelia and Merced rye were included in the second year. In both years, all of the cover crops depleted soil NO3-N and soil moisture relative to the fallow control. Estimates of cover crop root length, based on core sampling to 60 cm soil depth, averaged 18800 m/m2 after 17 weeks of growth the first year and 12500 m/m2 after 13 weeks of growth the second year. Above-ground dry matter production averaged 449 g/m2 (12·8 g N/m2) the first year and 161 g/m2 (61 g N/m2) during a shorter growing period and under the more adverse growing conditions of the second year. Following cover crop incorporation with a rotary tiller, soil ammonium (NH4-N), N03-N and net mineralizable N (anaerobic incubation) peaked after c. 1 week, then gradually declined for 1 month. Cover-cropped plots sustained higher net mineralizable N levels than the fallow control after incorporation. Nitrate concentrations after spring rains were lower in soils left fallow during winter. The subsequent lettuce crop was not affected by cover crop treatment.

Gaseous NH3 losses from pig and cattle slurry stored in eight storage tanks were measured simultaneously using wind-tunnels. The slurry was either stirred weekly (uncovered), or was allowed to develop a natural surface crust. Oil, peat, chopped cereal straw, PVC foil, leca® (pebbles of burned montmorillonitic clay) and a lid were tested as additional covers. Convective transport of ammonium to the surface layers caused NH3 volatilization losses of 3–5 g NH3-N/m2 per day from the stirred, uncovered tanks. The loss of NH3 from the stirred slurry was related to air temperature. The development of a natural surface crust reduced NH3 losses to 20% of those from stirred slurry. NH3 losses from slurry not developing a natural surface crust layer and left undisturbed were similar to the losses from stirred slurry. A 15 cm layer of straw was as effective as a surface crust layer in reducing NH3 losses. In one experiment, cracks developed in the oil cover and losses were therefore only reduced to 50% of those of uncovered slurry. Apart from this experiment, NH3 losses from slurry covered with oil, leca®, peat and foil were small.

The concentration of N in samples of urine from dairy cattle fed on grass herbage, or grass or maize silage, sometimes with additional concentrate feeds, ranged from 6·0 to 13·8 mg N/l with 67–91% of the total N being present as urea. The concentration of N in 11 samples of dung was 0·32–0·52% on a fresh weight basis (2·74–3·82% N in dry weight). About 18% of the dung N was contained in particulate material of > 0·2 mm diameter, c. 72% in fine particulate plus colloidal material, and c. 10% was soluble in the presence of A12(SO4)3.

When urine was stored for 3 weeks, the urea component was hydrolysed with the formation of ammonium. The rate at which hydrolysis occurred was greatly influenced by temperature. Hydrolysis of urea was complete within 2 days at 35 °C, within 7 days at 20 °C and within 21 days at 10 °C, but was only c. 90% complete after 21 days at 5 °C. The rate of hydrolysis of urinary urea-N at 20 °C was increased slightly by inoculation with slurry, dung or soil, and was also increased slightly by the greater aeration resulting from a continuous stream of bubbled air. No nitrification was detected, even in urine that was aerated for 6 weeks, probably because the process was inhibited under the conditions of high pH (9–10) and high concentrations of ammoniacal N.

When dung was stored for 3 weeks at 5 or 10 °C, there was little change in the amount of organic matter or in the form of N. However, at higher temperatures, some mineralization occurred and the amount of organic matter declined by 8% at 20 °C and by 17% at 35 °C. About 10% of the organic N was converted to ammonium during 3 weeks at 20 °C, and c. 18% at 35 °C.

With a slurry prepared from approximately equal amounts of urine, dung and water, more of the dung material was mineralized than with the dung stored alone: c. 15% of the organic matter was lost during 3 weeks at 5 °C and c. 34% at 35 °C. Despite this loss of organic matter, there was net immobilization of soluble N during the 3-week period by the solid fractions of the slurry, at all four temperatures.

The fate of 35S-labelled sheep urine sulphate in the soil and its plant uptake were measured in field experiments over a 12 month period in 1990/91 in Canterbury, New Zealand. Urine was applied in either summer or winter. After the summer application, there was a marked increase in pasture growth and S uptake which lasted for a period of c. 90 days. Plant uptake of applied 35S was very rapid and c. 11% was recovered in the pasture herbage within 65 days of application. By the end of the experiment, c. 80% had been recovered in the herbage. A portion of applied 35S was incorporated into soil organic forms mainly as C-bonded S. After 86 days, 30% of the applied 35S was in the C-bonded form but during the rest of the experiment this declined to 17% as the 35S was remineralized and absorbed by the growing pasture plants.

Following the winter urine application, the increase in pasture dry matter production and 32S uptake was much less marked than that for the summer application. Twenty five percent of the applied 35S was recovered in pasture herbage within 65 days and this increased to 70% by the end of the experiment. Some of the applied S was incorporated into soil organic forms and, by 83 days, 20% of the applied 35S was present in C-bonded form. Through mineralization this declined to 7% by the end of the experiment. Over the initial 41 days of the experiment, c. 25% of the 35S was lost due to leaching.

Copper deficiency in cattle is a world-wide problem. A deterministic digital computer simulation of copper metabolism was applied to cattle and especially to their response to dietary copper. This simulation was verified by comparison with published data on copper metabolism of cattle. Copper loss under conditions of dietary deficiency was governed largely by the rate of hepatic loss of copper. Copper stores were replenished gradually when the animal was returned to a normal diet. The increased copper consumption associated with increased total digestible nutrients (TDN) during lactation compensated for loss of copper in milk. Cattle have a very efficient mechanism for extrahepatic copper homeostasis by storage of excess copper in the liver, which can then be withdrawn in future deficiencies.

The lactation curve may be represented mathematically by the general equation Y = Aϕ1(t)ϕ2(t), where A is a positive scalar, ϕ1,(t) is a positive monotonically increasing function with an asymptote at ϕ1 = 1, and ϕ2 is a monotonically decreasing function with an initial value of unity and an asymptote at ϕ2 = 0. Functions considered as candidates for ϕ1 were: (Mitscherlich), (Michaelis-Menten), (generalized saturation kinetic), 1/(1 + b0 (logistic), b0 exp (Gompertz) and [1+ tanh(b0 + b1t)]/2 (hyperbolic tangent). Candidates for ϕ2 were e–ct (exponential) and 1/(1 + ct) (inverse straight line). The 12 models thus obtained and Y = Atb e–ct (Wood's model) were fitted to whole-lactation data from 23 animals. Mitscherlich x exponential, Michaelis-Menten x exponential, logistic x exponential, logistic × inverse straight line and Wood's model all fitted well. For these models, expressions for time to peak, maximum yield, total yield over a finite lactation and relative decline at the midway point of the declining phase were obtained. The Mitscherlich x exponential model generally fitted better than Wood's model and, unlike Wood's model, gives simple algebraic formulae for all these summary statistics.

Beef cows in the 14 weeks before calving and during the first 12 weeks after calving were fed one of three diets based on 15, 30 and 45 % broilers poultry litter (PL), 20 % maize grain (MG) and 65, 50 and 35% wheat straw (WS) on a DM basis, respectively. They were housed from June to November in individual open pens. Four weeks before and 9 weeks after calving, in vivo digestibility, fibre and fluid mean retention time (MRT) were measured. The intake of all diets before calving was low. Nine weeks after calving the intake of DM increased 2·1 times on the 15% PL diet, and 1·6 times on the two other diets. The in vivo digestibility of the 15% PL diets was lower than that of the two other diets before calving, and increased after calving, in spite of the doubling of its intake, while that of the 45% PL diet decreased. The mean retention time of fibre in the digestive tract was not affected by the increase in DM intake after calving on the 15 % PL diet and was shortened on the two other diets. It seems that the combination of the volume taken up by the gravid uterus and the bulkiness of the 15% PL diets (65% WS) reduced the intake and impaired the digestibility of that diet before calving. After calving, the fibre pool increased considerably and consequently both intake and digestibility were increased.

Infusion of [35S]-labelled cysteine into the jugular of Romney sheep of different ages was used to estimate the extent of combined cysteine and cystine (cyst(e)ine) and glutathione (GSH) interchange in various tissues, including skin, and to measure whole body irreversible loss rates (1LR) for cyst(e)ine. The studies were undertaken at Palmerston North, New Zealand during 1990 and 1991.

Reverse phase HPLC using a fluorigenic reagent, 7-fluoro-2,1,3-benzoxadiazole-4-sulphonate (SBD-F) was used for the simultaneous determination of thiols (cysteine and GSH) in whole blood (bound and free fractions), liver, kidney, small intestine, muscle, pancreas and skin. The appearance of [35S]-label in thiol compounds and their oxidation products was determined by ion-exchange HPLC. Specific radioactivities (SRA) for cyst(e)ine and GSH derived from this data showed equivalence for cysteine and GSH SRAs in all tissues, except for whole blood, indicating rapid withintissue interconversion between these thiols. In whole blood, however, the very low SRA for GSH (< 4 DPM/nmol) compared to cyst(e)ine (250 DPM/nmol) indicated markedly slower or negligible exchange with red blood cell GSH, and hence little inter-organ transport of [35S]-label as GSH.

Close infusion of [35S] cysteine into a defined patch of skin and collection of the venous outflow permitted direct in vivo measurement of the proportional uptake of cysteine by the skin. Results indicated considerable variation in the uptake of cysteine per se (20–40%) but no, or very little, oxidation of cysteine in the skin and no net export of GSH.

The combination of whole body, tissue and skin specific studies of [35S]-labelled cysteine metabolism quantitatively confirmed the very high proportion of circulating cyst(e)ine in sheep which is directed to skin and wool protein synthesis alone, and highlighted those aspects of this metabolism which are of most importance to wool production.

The effect of rumen fermentation on the relationship between urea and glucose kinetics was examined in sheep fed chopped lucerne hay with intraruminal infusions of water, urea, sucrose, or urea plus sucrose at Palmerston North, New Zealand in 1986. Sheep were fed hourly and infused intraruminally with water (1200 m1/day), or a similar volume containing either urea alone (13·7g/day), sucrose alone (178·2 g/day) or urea (14·6 g/day) plus sucrose (175·0 g/day). The added sucrose resulted in a lower rumen ammonia concentration (P < 0·05), lower plasma urea concentration (P < 0·05) and reduced urinary urea excretion (P < 0·05). Urea recycled to the gut tended to increase with the sucrose, urea or sucrose plus urea treatments compared with the water treatment. The fermentation of sucrose in the rumen resulted in decreases in ruminal pH (P < 0·05) and in the ratio of acetate to propionate (A:P) (P < 0·05). The infusion of sucrose also increased the concentration of propionate in rumen fluid (P < 0·05), tended to increase the plasma glucose level and increased plasma glucose irreversible loss (P < 0·05). The infusion of urea resulted in an increase in the plasma urea level (P < 0·05), urea pool size (P < 0·05) and urea irreversible loss (P < 0·01). However, urea infusion did not affect glucose metabolism or volatile fatty acid (VFA) fermentation. The effects of sucrose infusion on glucose and urea kinetics were broadly similar when given alone or with urea, apart from changes in the urea degradation rate. It was concluded that the additional fermentative activity resulting from sucrose increased propionate production which, in turn, was available for glucose production, thus ‘sparing’ amino acids for tissue protein utilization and reducing urea excretion.

The Agricultural and Related Industries Study Group of the Operational Research Society held a one-day meeting on ‘Decision Support Systems for Profitable Livestock Production’ on 18 November 1992 at the Meat and Livestock Commission, Milton Keynes, UK. The Group promotes the use of the scientific method in solving management problems. The aim of the meeting was to look at the contribution of advances in modelling towards improving management and hence profitability in livestock production. The first four papers concerned feeding and the remaining two breeding. A large part of the discussion could perhaps best be summed up by the regression equation which related dry matter intake and waste output from a cow. When the output was zero, the intake was reduced by 50%!