The effects of climate change on crop suitability in England and Wales were estimatedby systematically adjusting agroclimatic data inputs to a land evaluation model. Mean temperature risesof 1 and 2°C increased drought risk and reduced the length of time whe soil was at field capacity over-winter by raising potential evapotranspiration. In eastern England, this change had a detrimental effect on the potential for cultivating winter wheat because of drought stress. In northern and western England and Wales, drier conditions promoted greater opportunities for soil tillage, especially when temperature rises wereassociated with decreased precipitation. The effect of increased temperature was offset by increased precipitation. The magnitude of the drought stress and length of field capacity periods are similar to current mean conditions when a + 1 °C temperature change is coupled with a 10% increase in precipitation. This demonstrates that winter wheat suitability in England and Wales is affected more by changes in precipitation than by changes in temperature. The local limitations of soils and relief notwithstanding, it appears that the northern and western areas of England and Wales are most likely to gain from a warmer, drier climate.

Disposal methods for straw from continuous winter wheat were tested on two soil types, a flinty silty clay loam and a sandy loam, over 7 years (1985–91). The methods tested were burnt or chopped straw in full factorial combination with four cultivation methods (tined to 10 cm, tined to 10 cm then to 20 cm; ploughed to 20 cm; tined to 10 cm then ploughed to 20 cm). Measurements were taken to determine the effects on crop establishment and growth, pest and disease incidence, and the consequent effects on yield. Another experiment (1985–91) on the flinty silty clay loam site, investigated the interactions between straw treatments (burnt, baled or chopped in plots that were all shallow cultivated to 10 cm) and five other factors; namely, time of cultivation, insecticides, molluscicides, fungicides and autumn nitrogen. All the straw x cultivation systems allowed satisfactory crops to be established but repeated incorporation of straw using shallow, non-inversion cultivations resulted in very severe grass-weed problems. Early crop growth, as measured by above-ground dry matter production, was frequently decreased by straw residues, but the effect rarely persisted beyond anthesis. Pests were not a problem and their numbers were not greatly affected either by straw or cultivation treatments, apart from yellow cereal fly which, especially on the heavier soil, was decreased by treatments which left much straw debris on the soil surface. Incorporating straw also caused no serious increases in the incidence of diseases. Indeed, averaged over all sites and years, eyespot and sharp eyespot were both slightly but significantly less severe where straw was incorporated than where it was burnt. Eyespot, and even more consistently sharp eyespot, were often more severe after ploughing than after shallow, non-inversion cultivations. Effects on take-all were complex but straw residues had much smaller effects than cultivations. Initially the disease increased most rapidly in the shallow cultivated plots but these also tended to go into the decline phase more quickly so that in the fourth year (fifth cereal crop) take-all was greater in the ploughed than in the shallow cultivated plots. On average, yields did not differ greatly with straw or cultivation systems, although there were clear effects of take-all in those years when the disease was most severe. In the last 2 years, yields were limited by the presence of grass weeds in the plots testing chopped straw incorporated by tining to 10 cm.

An experiment at Rothamsted in 1985–89 and another at Whaddon in 1986 studied the effects of incorporating straw on diseases of winter barley. Net blotch (Pyrenophora teres) and leaf blotch (Rhynchosporium secalis) were initially less severe where straw was burnt or incorporated by ploughing than where cultivations only partially buried it. However, by summer both diseases were usually more severe where straw had been burnt than where it had been incorporated. At Whaddon, eyespot (Pseudocercosporella herpotrichoides) tended to be less severe in tine-cultivated plots where straw was incorporated than where it was burnt, but at Rothamsted, where the straw treatments were confounded with cultivations, there was no consistent effect. The disease was usually more severe where straw was incorporated by ploughing than where it was incorporated using other methods. In contrast, the severity of take-all was generally decreased by ploughing. Seedlings usually grew better where straw had been burnt rather than incorporated and grain yields were often larger. However, yields at Rothamsted in 1987 were unusually, and inexplicably, smaller after burning the straw so that the 5-year mean yields showed no significant differences between treatments.

The proportion of sward area rejected for grazing under different stocking intensities in grass-white clover (Trifolium repens L.) swards continuously grazed by steers toconstant sward height was determined and the effect of these areas on clover stolon developmentwas investigated.

In a randomized block field experiment, grazing treatments imposed from 1988 to 1991 comprised target sward surface heights (SSH) of 5, 7 or 9 cm from April to July followed by 7 or 9 cm from July to October (i.e. six treatments). The percentage area rejected was higher in 9 cm than in the shorter swards, the proportion of the total areas rejected increasing generally over the year. Within the rejected areas in spring the number of branches on the main axes of white clover plants was only 17% and the mean number of nodes per branch was 14% of those in grazed areas. Corresponding percentages in summer in rejected areas were 56 and 46% compared with grazed areas.

In a glasshouse experiment involving stolons grown for 18–21 days, the difference between those from grazed and rejected areas in branch number per stolon and mean node number per branch was much reduced. Branching and rate of branch development (node number) were slower in stolons maintained under dark conditions.

Mean growing point density over six sampling dates from summer 1990 to autumn 1991 was significantly higher in the 5 cm than in the 9 cm spring SSH treatment. Although rejected areashad only 34% of the growing point density of grazed areas in autumn, the latter comprised the majority of the total area in most sward height treatments and so reduced the overall effect of rejected areas on growing point density.

Under the short-day conditions and cool temperatures prevailing from January to March in the Nile delta, Egypt, potato (Solatium tuberosum) seedlings grown from true potato seed formed tubers in the nursery when the plants were less than 5 cm in height. In order to examine the hypothesis that slow field establishment after transplanting and low tuber yields of these seedlings were caused by premature tuberization, different treatments to delay tuberization were applied in the nursery before transplanting.

Increasing the air and soil temperature in the nursery accelerated both the development of the above-ground and below-ground shoot organs, but did not improve field establishment of the seedlings after transplanting. Extension of the photoperiod with incandescent dim light, exogenous application of gibberellic acid (GA), and removal of the shoot apex to encourage the growth of lateral branches from the leaf buds increased biomass allocation to the above-ground shoot organs, decreased tuberization in the nursery and accelerated field establishment of transplanted seedlings. Extension of the photoperiod was the most effective treatment to delay tuberization, and doubled the final tuber yield from transplanted seedlings.

The results are in agreement with the hypothesis that poor field establishment and low final tuber yields from potato transplants may be caused by the presence of strong tuber sinks at transplanting, which reduce assimilate partitioning towards the roots and above-ground shoots.

The transmission of silver scurf (Helminthosporium solani) disease of potatoes was examined in field experiments at Cambridge University Farm in 1988–90. Treatment factors examined were seed size, seed age, seed incubation, soil moisture regime and planting date. A laboratory experiment investigated the viability of conidia of Helminthosporium in soil stored under different conditions.

Incubation of seed at high humidity before planting increased sporulation of Helminthosporium on seed tubers after planting and fewer conidia were produced from small seed than from larger seed. Delay in planting caused more rapid growth of Helminthosporium on seed tubers after planting.

Early planting and late harvesting increased the severity of silver scurf on progeny tubers. Severity of silver scurf was also increased by ageing seed and by incubating seed. Weight loss of potato tubers during storage tended to be greater from treatments with most severe silver scurf in all years but a significant linear regression of weight loss on silver scurf severity was found in only one year out of three from a late harvest. The viability of conidia added to soil was found to decrease rapidly so that by 10 weeks after addition, < 1% of conidia were apparently viable.

Seed yields of caraway vary considerably between years, indicating that weather affects the yield-determining processes. Pollination could be one of these processes, because pollinator activity and efficiency are negatively affected by cold or wet weather. From 1990 to 1992 at the Research Institute for Agrobiology and Soil Fertility in Wageningen, The Netherlands, field and glasshouse experiments were performed to study the importance of pollination for caraway seed yields and the effects of some environmental factors. Preventing insect pollination by placing gauze cages in field plots reduced the yield of caraway by c. 15–20%, but under normal field conditions > 90% of hermaphrodite flowers were fertilized and additional hand-pollination did not improve yield. Removal of competing umbels enhanced the low seed set percentages in higher-order umbels, indicating that pollination did not limit seed yield in these umbels. Assays suggested that wind transfer, in addition to insects, plays a role in the pollination of caraway. It was concluded that assimilate availability and not pollination limits caraway seed yield.

Assimilate availability may determine seed yield of caraway during three periods: (i) beforeflowering it may determine dry matter allocation to flowers and thereby the number of ovaries; (ii) during flowering it may determine seed set; and (iii) after flowering it may determine seed filling. From 1990 to 1992 in the vicinity of Wageningen, field experiments were performed in which growth, assimilate storage and partitioning, and the effects of shading during various growth stages on seed set and filling, were studied to determine the importance of these three phases. Dry matter production before flowering was correlated with dry mass of flowers, but there was no relationship between the dry mass of flowers and seed yield. Assimilate availability after flowering only slightly affected seed yield, but during flowering it had a strong effect. Shading 50% (during c. 3 weeks of flowering only) reduced yield by 30% whereas 50% shading (after flowering for > 1 month) reduced yield by only 6%. In addition, the main flowering period of biennial caraway over a number of years was estimated and the daily amount of photosynthetically active radiation (PAR) for that period calculated. There was a close linear relationship between light intensity during flowering and yield. The possibilities for yield improvement using these results are discussed.

The effect of sowing date and plant density are modelled in relation to three variables: Ym, the maximum yield the crop can produce; τ, the interval from sowing to Yb/Ym = 0·5 where Yb is the yield of Brussels sprout buttons and Nb, the number of buttons on a plant stem. Ym is well related to the quantity of solar energy which the crop intercepts during the main period of growth. The fraction of radiation intercepted by the crop canopy is related to leaf area index (L) and sub-models relate L to sowing date and plant density. An empirically derived parameter relates the value of τ to thermal time and photoperiod time. The time course of Nb is modelled relative to the number of buttons at the end of the growing season. To overcome influence of site, variety and season, a generalized equation relates Nb, to plant density and a ‘known’ number of buttons at a specified planting density. The yield of buttons in specific size ranges (required for marketing) is described by a normal distribution with the standard deviation (σ) representing the spread of button diameter. There were no obvious effects of sowing date and plant density on σ. The model enables the effects of sowing date and plant density to be simulated using only simple and easily understood parameters. A sample simulation is presented.

Intake and digestion by swamp buffaloes (Bubalus bubalis) and crossbred cattle (Bos indicus × B. taunts) of a range of diets were measured in two experiments conducted in north Queensland in 1988. In Expt 1, four animals of each species were offered rice straw ad libitum with a supplement of minerals and urea. The four dietary treatments were (i) no concentrates, (ii)cracked rice grain (900 g/day), (iii) cracked rice grain (900 g/day) plus sunflower seed meal (900 g/day) and (iv) as for (iii) but with 50% of the sunflower seed meal treated with formaldehyde solution. In Expt 2, the same animals were offered two legumes, lablab (Lablab purpureus) and verano (Stylosanthes hamata cv. verano), and two grasses, sorghum (Sorghum bicolor × S. sudanense) and pangola grass (Digitaria eriantha). In Expt 1, voluntary intake of organic matter of buffaloes was 1·22 that of cattle. Concentrate supplementation increased organic matter digestibility and total intake, but did not affect straw intake. Intake of supplements by cattle was poor in the absence of sunflower seed meal. In Expt 2, intake and digestibility was similar in both species but was higher in animals given sorghum compared with the other forages. Total time spent chewing for both species and all diets ranged between 163 and 244 min/kg intake of plant cell wall constituents. The fractional rate of fluid flow from the reticulorumen and the concentration of propionic acid in the rumen fluid of buffaloes were consistently higher than in cattle in both experiments. Cotton and rice straw, placed in polyester bags in situ in the reticulorumen, were more extensively fermented in buffaloes than in cattle in Expt 1. In contrast, there were no differences between animal species in fermentation rates of cotton and ground diets in situ in Expt 2, but a relationship was observed between the relative fermentation of cotton and the relative digesta retention times in the reticulorumen in the two animal species. Microbial biomass, estimated as microbial dry matter per kg dry matter in the reticulorumen, was less (P < 0·05) in buffaloes than in cattle in Expt 1; higher concentrations of protozoa were observed in buffaloes than in cattle in Expt 2. Digesta load in the reticulorumen of buffaloes was c. 0·88 that of cattle. In Expt 1, digesta load was inversely related to digestible organic matter intake. The results were consistent with the hypothesis that energy metabolism and digesta load in the reticulorumen interact in the regulation of roughage intake, but it appeared that the lower loads measured in both species in Expt 2 indicated the operation of an unidentified limitation to intake.

The buoyancy and distribution within the rumen of feed particles were measured to assess the extent to which particle buoyancy modulated the movement of particles within and from the reticulorumen. Two experiments conducted in north Queensland in 1988 involved swamp buffaloes (Bubalus bubalis)and crossbred cattle (Bos indicus × B. taurus) fed rice straw with various supplements of energy and protein, lablab (Lablab purpureus), verano (Stylosanthes hamata cv. verano) and two grasses, sorghum (Sorghum bicolor × S. sudanense) and pangola (Digitaria eriantha). Apparent passage rate of particles from the reticulorumen bore an inverse curvilinear relationship to particle size. Passage rate of the smallest particles, retained by a cloth of aperture 50 μm, was faster in buffaloes. Mean particle size of total rumen digesta was smaller in buffaloes than in cattle in Expt 1 with rice straw, but there was no difference between the forage diets offered in Expt 2. The large particle content in digesta (dry matter per kg) in the dorsal rumen was greater than that in the ventral rumen, which in turn was greater than that in the reticulum. The sedimentation rate of particles was measured by a procedure designed to interfere as little as possible with microbial fermentation. A curvilinear relationship was evident between sedimentation rate and particle size; the medium particles sedimented faster than the fine and large particles. Sedimentation rates of some particle fractions were greater in buffaloes than in cattle. Between diets there were marked differences in sedimentation rates of large particles, but these differences decreased with smaller particle size. Large particles from the dorsal sac sedimented faster than those from the ventral sac, and there was no obvious dorsal raft. There was no apparent relationship between particle buoyancy and ease of particle escape from the reticulorumen. The results are discussed in terms of current theories of the physical factors involved in the control of voluntary feed consumption by ruminants.

Pure chicory (Cichorium intybus) and perennial ryegrass (Lolium perenne) forages were cut and fed fresh at Palmerston North, New Zealand, during March 1993 to castrated male red deer kept indoors in metabolism crates. Chicory contained lower levels of dry matter, higher levels of ash, and had a higher ratio of readily fermentable: structural carbohydrate than perennial ryegrass. Apparent digestibility of organic matter was highest for chicory (0·81 v. 0·72), but cellulose apparent digestibility was highest for perennial ryegrass (0·71 v. 0·59). Relative to perennial ryegrass, the rumen fluid of deer fed chicory contained higher concentrations of protozoa, ammonia and total volatile fatty acids (VFA) but had a lower pH at 15.00 h. Chicory-fed deer had higher rumen VFA molar proportions of n-butyrate and a higher acetate: propionate ratio. Total eating time and chews during feeding/g dry matter intake were similar for deer fed the two forages, but deer fed chicory spent much less time ruminating (33 v. 270 min/day) and had fewer rumination boluses (38 v. 305/day). It was concluded that the low rumination time may indicate rapid disintegration of chicory in the rumen to < 1 mm critical particle size, and that particle breakdown and rumen fractional outflow rate should be measured in future experiments with deer fed on chicory.

The relationships between body weight, scrotal characteristics and environmental effects (year, birth type and age) and fertility were studied in a total of 254 Horro rams. Fertility varied between years (P < 0·01), but not with body weight at mating within the range (30–55 kg) observed, nor with type of birth (both P > 0·05).

Testicular diameter and circumference were strongly correlated to body weight (r = 0·95 and 0·89 respectively; both P < 0·001), but weight of testes only weakly so (r = 0–28; NS). Scrotal circumference was more highly correlated to body weight in ram lambs (r = 0–85; P < 0–001) than in adults (r = 0·51; p = 0·06).

It is concluded that adequate levels of fertility (82 ± 1·3%) are expressed by 30 kg Horro rams, and that when feed supplies are limited there are no benefits to be gained from maintaining rams of this breed at higher weights.

Two experiments were carried out to study the efficiency of energy utilization by Suffolk × Blackface lambs. In the first experiment, a digestibility trial, the lambs were fed on either a roughage (chopped dried grass), concentrate (whole barley, ground barley and fishmeal), or mixed (roughage and concentrate) diet. The dry matter (DM) and organic matter digestibility coefficients of the mixed diet were slightly, but not significantly, lower than the ‘expected’ values calculated by summation of the separately determined digestibility coefficients of the component feeds. Similarly, the metabolizable energy (ME) value was 1·6% lower than the ‘expected’ value.

In the second experiment, lambs were offered 52·5 kg roughage DM (ME 9·96 MJ/kg DM) and 52·5 kg concentrate DM (ME 11·59 MJ/kg DM) as:(i) a mixed diet (M); (ii) a progressive change from roughage to concentrate (R–C); (iii) a progressive change from concentrate to roughage (C–R); or 105 kg roughage or concentrate DM as either (iv) a roughage diet (R), or (v) a concentrate diet (C). Lambs on treatments R–C, C–R and R and C combined took a similar time to consume their allocation of food and achieved a similar final empty body weight (EBW) and empty body composition. In addition, the total energy retention (ER) of lambs on these treatments was similar to that predicted by a feeding standards model for lambs of a similar liveweight offered diets of the same ME content. Lambs on treatment M consumed their allocation of food faster than those on all other treatments and achieved a slightly, but not significantly, higher final EBW, which contained a higher proportion of fat. The ER was higher than predicted. The higher overall efficiency of lambs on treatment M was attributed to higher daily intakes and differences in the ratio of protein: fat deposited and maintained by lambs on each treatment. The adoption of separate efficiency constants for both deposition and maintenance of protein and fat in current feeding standards would result in a more accurate prediction of animal performance.