Between 1989 and 1999, 33 experiments tested the effects of potassium (K) fertilizer on the yield and quality of potatoes. The experiments were done on a range of soil types and used varieties and management conditions common to modern commercial production. The average yield in these experiments was 48 t/ha. Nearly half of the experiments were done on soils that had exchangeable K values < 120 mg/l (MAFF Indices 0–1) but use of K fertilizer resulted in statistically significant increases in fresh weight yield in only seven experiments. Generally, soil exchangeable K was a poor predictor of the probability of a yield response. Potassium fertilizer caused an increase in dry weight yield in only four experiments and these experiments were characterized by the absence of irrigation, soils with small amounts of exchangeable K and use of determinate varieties. Re-examination of published data supported the findings in the current work: potatoes are not particularly responsive to K fertilizer and the optimal K application rate is rarely > 170–210 kg K/ha. When applied at the optimal rate, the effects of K fertilizer on tuber dry matter concentration were nonsignificant. Exceeding the optimal K application rate caused occasional reductions in tuber dry matter concentrations particularly if potassium chloride (KCl) was used. In the two experiments where it was tested, application rate and form of K had no effect on crisp fry-colour. The effect of K fertilizer on tuber K concentration was measured in 21 experiments and on average each tonne of fresh weight yield was associated with 4·2 kg K. The range in values was large, 2·8–5·7 and related to soil exchangeable K.

For fertilizer recommendations based solely on the probability of a significant yield response to K fertilizer it is suggested that no more than 210 kg K/ha be applied even on soils with < 120 mg exchangeable K/l. For fertilizer recommendations based on crop K removal, an uptake value of 4·8 kg K/t fresh weight (FW), as has been suggested, would be adequate, although errors in the estimation of yield may lead to over or under application of K. Since there was little evidence to support fertilizer policies that apply more K than is removed by the crop a fertilizer recommendation system based primarily on the probability of a yield response would be more than sufficient.

An account has been given of an investigation into the seasonal changes in the productivity, botanical and chemical composition, and nutritive value of pasture grass, the work constituting the initial stage of a comprehensive study of the nutritive properties of different types of pasture. The pasture on which the work was carried out was situated on a light sandy soil of low water-retaining capacity; the pasturage was of medium quality.

Grazing was imitated by the daily use of a motor-mowing machine, the system of cutting being such as to ensure the whole plot being cut over once per week. The season was divided into ten periods, each period corresponding with the duration of a digestion trial carried out on two wether sheep. The main feature of the weather conditions during the season was the extremely low rainfall during the period from early June to mid-July.

The pasture plot results were compared with corresponding results obtained from contiguous plots which were allowed to grow for hay, and from which, after removal of hay, several successive aftermath cuts were taken. The main findings of the investigation are summarised below:

Seasonal changes in the botanical composition of the herbage. Although precise and systematic botanical analyses of the herbage of the pasture were not carried out, yet careful surveys made at an early and a late date in the season, together with general observations made during the whole course of the experiment, enabled interesting conclusions to be drawn in respect of the seasonal activity and persistency of the different species of grasses in the sward. During the spring season, Bromus mollis, Lolium perenne, Poa annua and Poa trivialis accounted for almost 80 per cent, of the herbage.

Stands of bambara groundnut (Vigna subterranea (L.) Verde.) were grown in five controlledenvironment glasshouses at the Tropical Crops Research Unit, University of Nottingham, Sutton Bonington Campus, in 1990. Five soil moisture regimes were imposed (one per house), from fully irrigated each week (treatment A), to no irrigation after crop establishment at 35 days after sowing (DAS) (treatment E). Decreasing the amount of water applied resulted in a decline in total dry matter production and harvest index, and a reduction in pod yield from 412 (treatment B) to 0·041 ha-1 (treatment E) at 125 DAS. A maximum leaf area index of 5–4 was achieved by treatments B and C at 90 DAS, resulting in a fractional interception of c. 0·8 of incoming radiation. Total accumulated radiation interception values were 749, 693, 688, 618 and 554 MJ m-2 for treatments A, B, C, D and E, respectively. The efficiency of conversion of the radiation intercepted into dry matter was reduced from 1·41 to 0·50 g MJ-1 by drought.

Some years before the appearance of Hellriegel and Wilfarth's work on the sources of nitrogen of leguminous plants, and while the part played by atmospheric nitrogen in the nutrition of crops was under active discussion, Berthelot was making some exact observations on the behaviour of uncropped soils towards the free element. He found that when 50 kilograms of air-dry arable soil were exposed to the air and rain in a vessel for seven months a great increase in the nitrogen content could be observed; the total nitrogen of the original soil had increased from 50 grams to 63, or a gain of over 25 per cent, after allowing for the small amount of combined nitrogen brought down by rain; in another experiment where the soil had first been washed free from nitrates, a gain of 46 per cent, of nitrogen was proved. In many other cases, however, the gain was only from 10–15 per cent, of the original nitrogen present in the soil.

Tetraploidy or the use of diploid genotypes with genes conferring high water-soluble carbohydrate concentrations are two mechanisms to increase the nutritive value of perennial ryegrass. This experiment compared the morphology, nutritive value and diurnal variation in water-soluble carbohydrate (WSC) concentrations of 56-day-old plants from six perennial ryegrass cultivars grown under controlled environment conditions. Three of these cultivars were diploid (Melle, Aurora and Cariad) and three were tetraploids (Meltra, Prospero and AberOnyx) which had been derived from the respective diploid cultivars. Two of the diploid cultivars (Cariad and Aurora) had previously been selected for high concentrations of water-soluble carbohydrates. The tetraploid cultivars had fewer (mean 59), larger tillers than the diploids (mean 83). However, with the exception of Melle and Meltra the dry matter yield of the diploid cultivars was not significantly different from their tetraploid derivatives. The effect of tetraploidy on WSC concentrations was dependent on the genetic background of the cultivars. Melle, which had not been previously selected for increased WSC, had a significantly lower WSC concentration than its tetraploid derivative, Meltra. However, tetraploidy did not further increase the WSC concentration in those cultivars previously selected for high WSC concentrations. WSC concentrations in the leaf of both Aurora and Melle rose by 65–70 g/kg throughout the photoperiod, suggesting that differences in the total WSC concentration of these cultivars were not due to any increase in the amount of carbon fixed by Aurora but rather due to differences in the allocation of carbon during growth and development. This experiment demonstrated that tetraploidy was not beneficial in improving the WSC concentration of perennial ryegrass when imposed on two diploid cultivars which had the genetic potential for increased WSC accumulation. However, tetraploidy significantly increased the WSC concentration and by implication the nutritive value of a cultivar derived from a perennial ryegrass cultivar with standard WSC concentrations.

In a cross-breeding experiment involving all types of matings among Friesian, Ayrshire and Jersey cattle, the effect of maternal size has been investigated, based on various comparisons of reciprocal crosses, using data on weight and body size from birth to 2 years of age. Among the thirteen characters analysed, there was a close relationship at I month old between the relative maturity of the characters and the relative extent of their maternal effects. This relationship showed that the more mature characters were the least affected by the maternal environment. Cross-bred calves out of a mother of the larger breed were larger at birth than the reciprocal crosses but in all cases this difference disappeared during the first year's growth.

The early expression of the offspring's genotype for body size depended on whether prenatal growth had been favoured or restricted by the maternal environment within limits. Maternal retardation of growth resulted in neonatal phenotypes closely related to their genetic ranking for mature body size, whereas early expression of the genotype is obscured by lavish prenatal conditions.

A mammalian growth model is presented and the results are interpreted in terms of this model. The explanation assumes that temporary advantage is taken, during growth, of variations in the environment, when the latter exceeds a minimal level demanded by the genotype for stable development to normal mature size. This supply and demand hypothesis of growth is discussed in terms of its implications for genetic selection of different types of body characters. The main conclusion is that an understanding of the early environment, particularly the maternal one, may permit selection for some adult characteristics to be carried out at an early age.

Three experiments were made, in which two, four and three sheep were given rations in which increasing amounts of linseed oil fatty acids or Unseed oil were incorporated.

Although the changes in the rumen fermentation patterns were similar in all sheep, in some sheep the lipid metabolism in the rumen appeared abnormal, inasmuch as there was considerable accumulation of palmitic and smaller amounts of myristic acid.

It was concluded that the increases in the concentration of palmitic acid were due to an increased rate of its synthesis in the rumen, and an attempt was made to calculate these rates approximately.

The significance of these results within the context of rumen fermentation, methanogenesis and its inhibition were discussed.

Electrical conductivity was evaluated for estimating the nutrient content of cattle and pig slurries. Slurry samples were collected in 1991 from the storage tanks of 48 cattle and 10 pig units on commercial farms in Ireland. Samples were analysed for NH4+ and total concentrations of Na, K, Ca, Mg and P. Electrical conductivity (EC) was measured on raw slurries (ECraw) and on slurries diluted by 10 with water (ECdilute). Relationships between EC and nutrient content were examined by correlation and linear regression analyses.

In both slurry types, NH4+ was the dominant cation with K+ second in importance on a molar basis. Within each slurry type, the concentration of each of these cations was significantly correlated with EC. Using ECdilute gave more accurate predictions of concentrations than ECraw, but even ECraw was a better predictor than dry matter (DM) content. The linear relationships between NH4+ or K+ and ECdilute explained > 82% of the variance within each slurry type. The P content in slurries was related better to DM than to EC. Since EC measurement could be by cheap, robust meters, its potential for on-farm use deserves further investigation.

Grass-legume associations may offer a way of improving the N efficiency of dairy farming, but may also have an adverse impact on the environment by increasing leaching losses. Nitrate leaching from four cropping sequences with different grassland frequency and management (long-term grazed, long-term cut, cereals followed by 1 and 2-year grazed leys) were investigated on a loamy sand in central Jutland for both unfertilized grass-clover (perennial ryegrass (Lolium perenne L.)/white clover (Trifolium repens L.)) and fertilized perennial ryegrass (300 kg N/ha) swards during 1997–2002. Furthermore, 1 year (2001) of N2 fixation in 1-, 2- and 8-year-old grass-clover pastures was determined. Nitrate leaching from grazed unfertilized grass-clover was always considerably lower than from grazed fertilized ryegrass. The effect of grassland age on nitrate leaching was insignificant in grass-clover but clear in grazed ryegrass, where levels increased dramatically with sward age. In production years 6–8, leaching from grass-clover was only 9–13% of the comparable losses from ryegrass. Under the cutting regime grass-clover showed a significant reduction in both yield and N-removal with increasing sward age, whereas for ryegrass these figures did not show any decreasing trend. N2 fixation was lower in 8-year-old swards compared with fully established 2-year-old swards as a consequence of lower dry matter production, lower clover content and a lower proportion of clover-N derived from the atmosphere. The results from the present study indicate that the higher leaching losses observed in fertilized grass compared with unfertilized grass-clover systems were caused by (1) a reduction in N2-fixation in grass-clover over time and (2) a reduction in dry matter production in grass-clover over time, lowering the grazing intensity and the recycling of grassland N via animal excreta.

Experiments were devised to establish suitable techniques of screening seedling material of Lolium perenne for cold tolerance under controlled conditions: these techniques were then used to distinguish between varieties and ecotypes from contrasting climatic regions. For the wide range of material used, greatest discrimination was achieved by 14 days hardening at 2 °C and 8 h photoperiod, followed by 2–4 days freezing at -8 °C in the dark. There were indications that the light intensity and/or temperature before and during hardening could considerably modify the cold tolerance.

The most useful criterion of cold tolerance was the percentage of tillers surviving 14 days after thawing. In some instances, death of tillers and whole plants continued after this time, and this tendency appeared to be related to growth habit; southern ecotypes were particularly susceptible.

Varieties from north Europe were generally more cold tolerant than ecotypes from the Mediterranean region, but tolerance depended also on the altitude of the original habitat. The cold tolerance of a population could, in part, be related to the average lowest temperature in the coldest month and in part to environmental conditions of solar radiation and/or temperature during the autumn in its place of origin.

Along with the experiments under controlled conditions, spaced plants of the same populations were grown in the field in order to evaluate winter hardiness under local conditions. The overall correlation between winter hardiness in the field and cold tolerance as assessed in the growth rooms was not high. Results from one year's field testing showed that indigenous varieties such as S. 23 and S. 24 were more winter hardy than foreign ecotypes and varieties, even if these came from colder climates and showed greater cold tolerance in the growth room.

The lack of control of barnyardgrass in flooded rice cultivated with imidazolinone-resistant rice cultivars is challenging the utilization of this system, which is continuously expanding for new rice areas worldwide. The objectives of the present study were to evaluate the frequency, distribution and mechanisms of imidazolinone resistance in barnyardgrass to establish the best practices to control and prevent this problem. The distribution of resistance was evaluated in 624 populations collected in Southern Brazil. The frequency of imidazolinone-herbicide resistance was 0·81, broadly distributed in all sampled regions. Resistance to quinclorac was also found in 0·19 of the populations, but all of the evaluated populations were susceptible to cyhalofop-butyl. Further studies were conducted in six populations. The enhanced metabolism was assessed with the metabolic inhibitors that reversed the resistance to quinclorac from 0·54 to 1·00 in two populations and the resistance to imazethapyr from 0·15 to 0·41 in three populations. The acetolactase synthase (ALS) enzyme activity also indicated the occurrence of altered target site resistance in two populations caused by the ALS gene mutations Trp574Leu and Ser653Asn, which is a novel finding in this species. The herbicide resistance in barnyardgrass in Southern Brazil presented a complex basis of resistance because it is associated with resistance to multiple herbicides due to multiple mechanisms and with multiple mutations of the ALS gene. This indicates that it is necessary to adopt specific measures to prevent and control the evolution of multiple herbicide resistance in this species.

Mouldboard ploughing, deep and shallow tined cultivation followed by conventional seed-bed preparation, and direct drilling were compared from 1972 to 1976 on a calcareous clay soil in two experiments, one on winter wheat and the other on spring barley.

At sowing the moisture content, bulk density and resistance to penetration in the surface layer of soil of uncultivated land were all greater than in soil that had been ploughed or cultivated deeply. Below 10 cm moisture content was less and root penetration was greater in the uncultivated soil. In all years winter wheat established and yielded well following direct drilling and shallow cultivation. In two dry autumns wheat establishment following ploughing was slower and less complete than with direct drilling, and in 1 year the yield was less. Spring barley established and yielded well without consistent differences in all years with all treatments.

1. Forty Large White pigs varying in age from birth to 5 weeks were slaughtered and their carbohydrate digesting enzymes studied for any change in activity with increase in age.

2. Pancreatic amylase, sucrase and maltase increased from low levels at birth to high levels at 5 weeks of age.

3. The total amount of lactase present at birth and of small intestine amylase at 1-week-old was maintained at a constant level up to 5 weeks of age. The increased weight of the intestine with the growth of the pig made the quantity of these enzymes appear to decrease with age when the values were expressed per kg. body weight or per g. dry tissue.

4. Anaemia had no marked effect on the activity of the enzymes though the rate of enzyme development appeared to be retarded in the case of maltase.

5. The quantity of pancreatic amylase present in the pancreas was sufficient at all ages to digest the amounts of starch likely to be included in a synthetic diet. Maltase, on the other hand, appeared to be limiting in early life.

Drought stress and virus yellows disease are two of the major problems of sugarbeet crop production in the UK. We have calculated the annual national drought losses from 1980 to 1995 by using long term data sets for two sites (IACR-Broom's Barn, Suffolk and ADAS Gleadthorpe, Nottinghamshire) to relate yield loss to cumulative potential summer moisture deficit, and combining these relationships with regional meteorological records, soil type and crop distribution data.

Experimentally measured relationships between yield losses and the timing of virus yellows infection were combined with annual survey data of the extent of the problem, and calculated infection dates from the UK aphid suction trap network, to calculate actual national annual losses to the disease. Potential losses in the absence of control measures were then calculated by use of data from trials and surveys of pesticide use.

The results showed a mean annual loss of production to drought stress of 141000 t/year of sugar, 10·5% of production, with a loss to the industry of £27·9 million. Losses in individual years varied from zero to 2·5 times the mean figure. Actual losses to virus yellows were much smaller, due to the efficacy of treatments, averaging 24700 t/year of sugar (1·8% of national yield, financial loss £5·5 million). Average potential virus yellows losses in the absence of control measures were approximately double this.

Control of virus yellows is a major, cost-effective contributor to rising and consistent sugarbeet production. Nationally, irrigation has made little impact on drought losses and, due to constraints in surface water supply, this situation appears likely to continue. Improved drought stress tolerance represents the largest single opportunity for yield and profitability improvement of the sugarbeet crop in the UK at present. Predicted climate change appears likely to increase the severity of both drought and disease stresses. Drought stress appears relatively less important in other NW European sugarbeet-growing areas.

1. An experiment on pullets combining daily calcium and phosphorus balance determinations with carcass analyses is described.

2. It is shown that fat content of pullets is affected by the calcium content of the ration. The fat content was higher on a low calcium ration than on a high calcium ration.

3. The CaO content of pullets was raised considerably by feeding a high calcium ration before laying. This CaO must have been stored in the bones, which contained between 97·2 and 98·7% of all the CaO in the body.

4. The experiment suggests that pullets may use up to about one-quarter of their body calcium at the outset of laying for purposes of shell formation.

5. The composition of the inorganic material of the skeleton of pullets may be modified by alterations in their mineral metabolism due to egg production on diets with and without a calcium carbonate supplement. The nature of these modifications and their relationship to calcium metabolism during laying is discussed.

The present paper reviews some of the high-level challenges facing the global food system over the next 40 years, drawing in particular on the UK Government's Foresight Report on the ‘Future of Food and Farming’, to set the scene for discussions about the sustainable use of nitrogen in agriculture. It reviews the likely demand and supply pressures on the food system, and the pressing requirements to improve sustainability and address the needs of the world's poorest. It argues that the food system is entering a period of radical change, led particularly by growth in demand, which requires action on food production, diet, waste and efficiency, and governance. A key challenge on the supply side is sustainable intensification – producing more from the same amount of land with fewer and less profound negative effects on the environment. Increasing the efficiency of nitrogen fertilizer application will be critical for increasing yields while reducing the many major environmental consequences of leaching and run-off.

Winter wheat cv. Avalon was sown in autumn 1981, 1982 and 1983 on a clay loam soil following two cereal crops. Multifactorial experiments tested the effects of combinations of the following eight factors, each at two levels: rotation, sowing date, timing of nitrogen, amount of nitrogen, growth regulator, pesticide, spring fungicide and summer fungicide.

The best 16-plot mean grain yields in 1982–4 were respectively 8·7, 10·2 and 11·1 t/ha. Rotation had the largest effect on grain yield. Wheat following barley was severely infected with take-all and yielded, on average over 3 years, 2·2 t/ha less than wheat following oats. Take-all was more severe on wheat sown in mid-September than in mid-October; its effects on yield were lessened by early timing of N in 1982. Take-all decreased growth and N uptake mainly after anthesis, and also number of ears and dry weight per grain. Sowing in mid-September compared with mid-October decreased yield of wheat after barley by an average of 0·8 t/ha because take-all was more severe. Early sowing had negligible effects on grain yield of wheat after oats, but increased straw dry weight by 1·1 t/ha.

Spring fungioide increased yield by an average of 0·3 t/ha. Effects were larger after barley than after oats, associated with a greater incidence of eyespot after barley. Summer fungioide increased yield by an average of 0·3 t/ha. Foliar diseases were slight in all 3 years. Fusarium ear blight and sharp eyespot were prevalent in 1982 and were not well controlled by the fungioide treatments. Fungicide temporarily decreased the incidence of some components of the mioroflora on the ears. Pesticide increased grain yield of wheat after oats only in 1984, when aphids on the ears were numerous. Aphids were present on early-sown plots in all three autumns but there was little barley yellow dwarf virus infection even without pesticide. Pesticide always decreased the number of nematodes after harvest to fewer than present before sowing. Populations never approached levels expected to affect yield.

Early N application (main application early March) resulted in a larger grain yield in 1982 than N applied a month later. In 1983 and 1984 grain yield and N uptake by the grain were greater with the late application, especially when wheat was sown early. The soil contained more mineral N in the autumn of 1982 and 1983 than in 1981. Straw weight was always greater with early than with late application. Increasing the amount of N applied from 163 to 223 kg/ha increased N uptake by 40 kg/ha and grain yield by 0·5 t/ha after oats and by 0·6 t/ha after barley. N uptake in grain plus straw by the best yielding crops ranged from 205 kg/ha in 1982 to 246 kg/ha in 1984.

Chlormequat applied at the start of stem extension shortened the stems at maturity by 2 cm each year. In 1984 it inoreased yield of early-sown wheat by 0·3 t/ha and also decreased lodging, which did not occur in the first 2 years.

The incidence of lamb mortality from birth to 8 months of age has been studied over a 6-year period in an upland, grassland flock of sheep comprising the Scottish Blackface, Cheviot and Welsh Mountain breeds and the crosses among these breeds. Each breed and cross-bred type was maintained at varying levels of inbreeding. Approximately half the lambs which died were stillborn or dead on the day of birth, nearly 40% died thereafter but before weaning and about 10% after weaning.

Post-mortem examinations on 586 of the 632 lambs which died from among the 2453 born attributed death on average to two causes per lamb. Approximately 11% of the causes were stillbirths or delayed births; 11% were cases of dystokia; congenital defects of various types accounted for about 10% of the causes; 25% made reference to weakly lamb, exposure or starvation; 14% to infectious diseases and 16% to noninfectious diseases. The extent to which causes of death occur together is examined.

Breeds differed in mortality rate with the Welsh the lowest and Cheviot the highest. Cross-breds were better than the average of the pure breeds but this advantage emerged only in the period between 3 days and. 6 weeks of age. Inbreeding, both of dam and of lamb, increased mortality. Lambs from dams which were crosses of inbred lines had the best survival. Litter size, type of rearing, parity of dam, sex of lamb and birth weight also had significant effects on mortality rate.

A preliminary investigation on interplanting of maize with nine different tropical legumes in the rain-forest zone of the Western State of Nigeria at Ibadan indicated that Popondo (Phaseolus lunatus) and Mucuna (Mucuna utilis) lowered maize yield, while calopo (Calopogonium tnucunoides) Cowpea (Vigna sinensis) and greengram (Phaseolus aureus) had much less effect on maize and were themselves tolerant to maize shade. These three legumes were interplanted with maize continuously for four growing seasons, during which there was a significant response of maize to fertilizer treatment only in the control (no legume) treatment. Maize interplanted with the legumes gave no response to applications of 50 lb N per acre.

High yields of maize were maintained during the four growing seasons in both the fertilized control plots and those interplanted with different legumes without fertilizer, whereas the yield of maize in plots with neither legume nor fertilizer was reduced to half of the yield of the first maize crop.

Starting from the third cropping season, there was a significant interaction between the presence or absence of legume and fertilizer.

The planting pattern of the maize and legumes (intercropping or growing maize after the legume harvest) did not affect the yield of maize.

Legumes tended to compete with maize during the late cropping season. This did not affect the maize yield seriously during the investigation, but legume yield was significantly suppressed by maize shade.

Few methods exist for estimating quantitatively the diet composition of free-ranging herbivores. The current study examined whether long-chain fatty alcohols (alcohols) or long-chain fatty acids (acids) could be used along with n-alkanes to allow reliable diet composition estimates to be made in herbivores consuming complex diets. Twelve Scottish Blackface wether sheep housed in metabolism crates were fed four different mixtures of three plant species (three animals per mixture) for a seven-period experiment. Concentrations of cuticular wax n-alkanes, alcohols and acids were estimated in samples of individual plant species, and the faeces from animals that consumed mixtures of these species. These concentrations were then used to calculate the dietary proportions of each species by a least-squares optimization procedure. To explore the differences between the estimation methods (individual markers and their combinations), the mean squares of errors (EMS) between the actual and predicted proportions of plant species were calculated.

In three out of the four mixtures, alcohols had the lowest discrepancies (lowest EMS values), followed by n-alkanes and then acids. Acids yielded the lowest discrepancy in one mixture and the highest in the others.

It is concluded that, for this particular set of mixtures, alcohols had great potential to estimate composition of complex diets. However, the estimation using acids was less good and n-alkanes were of intermediate potential. Estimation from the combination of the three marker classes was always better than using the poorest individual marker.