The sensitivity of predicted final grain yield to changes in the mean and variance of daily temperature and daily log(radiation) was studied for the arcwheat1 crop model of winter wheat. These two climatic variables were each simulated by each of two stochastic models, the parameters of which were estimated from 12 years' data from Rothamsted Experimental Station.

When arcwheat1 was run with systematic changes in daily temperature from – 2 °C to +2 °C in steps of 0·1 °C, there were abrupt changes in predicted final grain yield which coincided with predicted increases in leaf number. These effects were smoothed out when the stochastic climate models incorporating simulated daily variation were used as inputs, in multiple runs of arcwheat1.

In such runs, the response of predicted yield to changes in the means of temperature and log(radiation) was studied both for individual developmental stages and over the entire growing season. Yield was insensitive to changes in temperature and radiation during the stage between sowing and emergence, and to changes in radiation before terminal spikelet formation.

Field experiments were conducted in Scotland between 1985 and 1987 to examine the responses of mean grain weight and nitrogen content of triticale cultivars to levels of applied nitrogen from 0 to 180 kg N/ha and the plant growth regulator chlormequat. Cultivar differences were seen for both these characters. Mean grain weight generally declined as yield increased, whether with nitrogen or with chlormequat. Nitrogen content of the grain decreased as grain size increased. Nitrogen recovery (g/m2) generally increased with applied nitrogen and was unaffected by chlormequat application. Within a grain sample from an individual treatment, however, grain size was not related to nitrogen content.

The response of nitrogen content is interpreted as differential dilution of nitrogen in the grain by different amounts of carbohydrate. This is probably related to the frequent occurrence of shrivelled grain in triticale.

Field scale variability in the grain yield of barley in 1989 was investigated in 62 field plots in a Dutch polder area, and compared to soil- and simulation-type characteristics. Total grain mass varied between 3409 and 6019 kg/ha, and grain moisture content between 131 and 14·7%. Soil profile descriptions and soil characteristics were used as basic input data for simulations. Soil water flow was simulated at 119 locations with the LEACHM model, for the purpose of quantifying spatial variability in transpiration deficits in the growing season. Both soil- and simulation-type characteristics were translated from point values to spatial averages for the harvested fields, using kriging. Kriged characteristics were correlated with yields, and used to construct transfer functions. Simulated transpiration deficits during sensitive crop development phases showed negative correlations with grain yield. Transfer functions explained at maximum 68·2% of the variance in the yields.

The effects of varying the timing of nitrogen application and the frequency of fungicide sprays on the incidence of foliar disease and on the grain yield of winter barley (cv. Panda) were investigated at two sites in Ireland over three years, 1986–88. Nitrogen application timing had little effect on the amount of foliar necrosis due to disease but delaying application of all the nitrogen until April significantly reduced grain yields in two of the three years when compared with standard split dressings in March and April. The reductions in yield reflected small differences in 1000-grain weight.

The number of fungicide sprays applied had significant effects on the amount of foliar necrosis and on grain yields. One-spray and two-spray programmes increased average yield by 16 and 32%, respectively. The yield increases were attributable to more ears/m2 and larger grains (greater 1000-grain weight). Fungicides also delayed the onset and significantly reduced the amount of brackling. Delaying nitrogen application in the spring did not decrease the number of fungicide sprays required to achieve maximum yield.

In two field experiments in Suriname, competition between weeds and sorghum (Sorghum bicolor (L.) Moench) was studied in the rainy seasons of 1982 and 1983. The crop was kept either weed-free or without weed control for each of six different periods of time from planting. Observations made at the end of each period allowed an analysis to be made of the growth and development of a crop with and without weed control.

Due to the crop canopy structure and fertilizer placement near the row, weed growth was concentrated in the rows. Starting at c. 20–30 days after planting, competition with weeds reduced ground-cover and leaf area index of the crop. Competition reduced growth rates, leading to lower yields. Plant population density was not affected, but competition reduced the number of leaves present. Stem length initially increased with competition in one season, but was retarded in another. Competition for nutrients was strong and was found as early as 15 days after planting. Nitrogen was the element most competed for initially. Competition for water occurred, but competition for light seemed unlikely. About 20 weed-free days after planting were necessary to avoid yield losses and around 30 weed-free days to attain negligible weed growth at harvest. Yield reduction was mainly due to a decrease in number of grains per panicle. Competition during floret establishment (c. 30–40 days after planting) should be avoided.

The influence of four seeding times on herbage dry matter (DM) yields and clover content of white clover (Trifolium repens L.)/orchardgrass (Dactylis glomerata L.) mixtures was evaluated at Truro, Nova Scotia and Charlottetown, Prince Edward Island from 1985 to 1988. Sacramento, Sonja and Milkanova white clover/orchardgrass mixtures were assessed under simulated grazing (four or five harvests per year) over two production years at each location.

Delaying seeding from May to August reduced total herbage DM yields significantly in the first production year, from 8·1 to 3·3 t/ha in Truro and from 11·0 to 7·2 t/ha in Charlottetown. Late seeding significantly reduced clover content in the herbage of the first two harvests in the first production year but, by the mid to late-season harvests, white clover content had increased to levels similar to those of the May seeding. Estimated white clover DM yields were highest in June, and dropped in the second production year at both locations. Sonja and Milkanova white clovers consistently outyielded Sacramento in herbage DM yields and clover content in both locations irrespective of seeding dates.

Seed is often stored in warehouses where the temperature may drop below freezing or increase to 40°C depending on the time of year. Survival of rhizobia on lime-coated alsike clover (Trifolium hybridum L.) seed stored in polypropylene bags was monitored under various temperature regimes ranging from –10 to 35 °C at Agriculture Canada Range Research Station, Kamloops, British Columbia, Canada during 1990 and 1991. Rhizobia were applied ata range of initial concentrations. Seed was inoculated with a peat-based clover inoculant (‘B’ inoculant, Nitragin Ltd, Milwaukee, Wisconsin, USA), and then given a commercial polymer-based lime coat (GNR™, Grow Tec Ltd, Nisku, Alberta, Canada). Rhizobia died continuously at all temperatures within the range —10 to 35°C. The dependence of Iog10(number of viable rhizobia/seed) on storage time was best described by a linear equation: Iog10(viable rhizobia/seed) = a + b (time). Coefficient a providedan estimate of the initial concentration of rhizobia. Coefficient b provided a measure of how rapidly rhizobia died. The death rate of rhizobia was the same during storage at 5 or 20 °C, but increased at a storage temperature of 35 °C. Storage at freezing temperatures did not increase the rate of rhizobial death but repeated freezing and thawing resulted in an increase. As the rate of rhizobial death was similar at constant temperatures from — 10 to 20 °C, temperature requirements are not stringent. Nevertheless, some temperature control is required to maximize the legal storage life of preinoculated coated seed, which in this study was estimated to be 96 days.

Clones from the potato species Solanum phureja and 2x and 4x hybrids between S. phureja and S. tuberosum were tested for the culinary quality of their tubers following steaming, frying and baking. The quality of S. phureja tubers was high but material from the F 1 hybrids showed more disintegration or blackening after cooking than either parental species. Tetraploids produced by backcrossing 4x Fl hybrids toS. tuberosum cultivars showed less of these defects.

Fourteen S. phureja and 2x F1 hybrid clones selected for their unusual tuber skin pigmentation or shape were found to have a variety of baked flesh colours from orange-yellow to cream with red marbling. Their cooked flesh texture was generally floury and often crumbly. It is suggested that S. phureja material could be exploited as a novel food source for specialized use in North European countries.

The response of low glucosinolate, low erucic acid (double low) cultivars of oilseed rape to spring nitrogen application was examined at Cockle Park, Northumberland in three successive seasons (1987–90). Seed yield and protein content increased in response to increasing nitrogen application. In each season over 85% of the maximum recorded yield was obtained with an application of 150 kg N/ha. In the absence of spring nitrogen, seed yield varied considerably over the three seasons. The variation in seed yield and protein content between 1987/88 and 1988/89 can partly be explained by differences in the availability of soil nitrogen in the different seasons. Seed glucosinolate concentration was significantly increased withnitrogen applications between 0 and 150 kg/ha. Increasing nitrogen beyond 150 kg/ha hadlittle or no effect on seed glucosinolate concentration. The results are examined with reference to the varying effects of increasing nitrogen application rates on seed glucosinolate concentrations reported previously.

Effects of diseases on growth and yield of linseed (cv. Antares) were assessed by controlling diseases with fungicide treatments in field experiments at Rothamsted from 1988 to 1990. Fungicide seed treatments decreased the incidence of Alternaria lesions on cotyledons and stem bases of emerging seedlings in 1989 but decreased emergence in 1990. The incidenceof leaf browning, associated with Alternaria spp. and Botrytis cinerea, was less in 1989 and 1990 than in 1988 when the period, in July, between flowering and harvest was wet, but the incidence of powdery mildew was greater in 1989 and 1990 than in 1988. Fungicide spraysdecreased leaf browning in 1988 and powdery mildew in 1990. In 1988 there were more capsules per plant and the crop was taller than in either 1990 or 1989, when July and August were hot withperiods of dry weather. The incidence of plants with dark brown stems, associated with Verticillhun dahliae, was greater in 1989 and 1990 than in 1988, but was not greatly affected byfungicide treatments. The incidence of Alternaria linicola on sepals, capsule cases and seed from capsules sampled before harvest was decreased by fungicide treatments. Other fungi isolated from these tissues included A. alternata, A. infectoria, B. cinerea, Fusarium spp. and V. dahliae. Yields of grain and oil were increased by fungicide treatments in all three years, but the yield increases were greatest in 1988 when fungicide treatments also increased 1000-grain weight. The incidence of fungi on the harvested seed was not greatly affected by fungicide treatments.

Stages in the diagnosis of an interveinal leaf chlorosis in bean in the Usambara Mountains of northern Tanzania are described. Leaf tissue analysis, soil analysis, a 25 factorial trial with treatments of nitrogen, phosphorus, potassium, the trace elements copper and zinc and lime at one location and data from a series of 43 factorial trials of N, P and K demonstrated the leaf condition to be due to potassium deficiency. Large growth and yield responses to N, P and K were recorded. The responses were accompanied by greater numbers of pods and seeds/pod. The application of N and K increased leaf concentrations of the respective elements but depressed the concentrations of other major and minor elements in leaves. There were no effects of trace elements or lime.

Sixty-four lactating buffalo cows (24 normal cycling, 8 pregnant and 32 repeat-breeder), selected from two buffalo farms near Cairo during 1987 and 1988, were studied during thefirst 26 days after oestrus (day 0). Plasma progesterone concentrations were significantly (P < 0·01) higher in pregnant than in cyclic (between days 3 and 5) and repeat-breeder (between days 0 and 8) animals. Concentrations of total unconjugated oestrogens were also highest (P < 0·01) in the pregnant group between days 6 and 16. Cyclic and pregnant cows had higher (P < 0·01) concentrations of plasma calcium between days 3 and 7, inorganic phosphorus at all times and glucose between days 2 and 8 than repeat-breeders. Plasma protein concentrations were greater at all times, except between days 6 and 8, in the first two groups. Analysis of the uterine fluid collected from cyclic and repeat-breeder buffalo cows revealed that concentrations of all biochemical components, except for calcium, were significantly (P < 0·01) higher in flushings from the uterus of cyclic animals than from repeat-breeders at alltimes for inorganic phosphorus, between days 6 and 12 for glucose and on day 2 as well as between days 8 and 12 for protein. Large differences were found in calcium levels, especially on day12 when flushings from repeat-breeder cows contained more than six times the concentrations of this metabolite in uterine flushings from cyclic animals. The results suggested that reduced luteal function, related to atypical profiles of plasma biochemical components, during the oestrous cycle in repeat-breeder buffalo cows might provide the basis for altered syntheses and secretions of uterine calcium, phosphorus, glucose and proteins which are needed for embryo development.

The effects of two diets formulated to be either synchronous or asynchronous with respect to the hourly supply of energy and nitrogen on rumen fermentation and microbial protein synthesis were studied in sheep.

In Expt 1, the in situ degradation characteristics of nitrogen (N), organic matter (OM) and carbohydrate (CHO) fractions were determined in winter wheat straw, winter barley, malt distillers dark grains rapeseed meal and fishmeal. The feeds exhibited a large range in degradability characteristics of the nitrogen and energy-yielding fractions.

A computer program was developed based upon the raw material degradation characteristics obtained from the above studies. The program was used to formulate two diets with similar metabolizable energy (9·5 MJ/kg DM) and rumen degradable protein contents (96 g/kg DM) but to be either synchronous (diet A) or asynchronous (diet B) with respect to the hourly rate of release of N and energy. The program was used to predict the hourly release of N, OM and CHO and the molar production of volatile fatty acids (VFA).

In Expt 2, the two diets were fed to four cannulated sheep at the rate of 1 kg/day in four equal portions, in two periods, using a change-over design. Rumen ammonia concentrations followed the predicted rate of N degradation. A maximum concentration of 10·5 and 7 mM for diets A and B respectively was achieved within the first hour of feeding which then fell to 7 and 3 mM respectively. Rumen VFA proportions were more stable for the synchronous diet (A) than the asynchronous diet (B) and were more stable than predicted for both diets. True ruminal degradation of OM and CHO was similar for both diets and close to that predicted, although fibre degradability in diet A was 30% lower than predicted due to a reduction in both cellulose and hemicellulose digested. Microbial protein production was estimated simultaneously with L-[4,5–3H]leucine and a technique based on cytosine. Estimates varied with marker but mean values indicated a 27% greater production of microbial N (g N/kg DM I) with the synchronous diet (A) and an average improvement in microbial protein efficiency (g N/kg OM truly degraded or CHO apparently degraded) of 13%, although neither difference was significant. There was evidence of a greater recycling of N in the animals and a significantly lower content of rumen degradable protein when the sheep were fed the asynchronous diet (B).

The results are consistent with the view that synchronizing the rate of supply of N and energyyielding substrates to the rumen micro-organisms based upon ingredient in situ degradation data can improve microbial protein flow at the duodenum and the efficiency of microbial protein synthesis.

An experiment was conducted at Toorak Research Station, Julia Creek, in semi-arid northern Australia (141° E, 21° S) during 1990 to determine the relationship between placental and fetal weight in sheep after placental growth had been restricted by chronic heat stress during mid-pregnancy. Placental and fetal weight were measured in single bearing ewes housed either in a thermoneutral environment throughout pregnancy, or in a heated room between the 30th and 80th days of pregnancy followed by a thermoneutral environment until the 140th day of pregnancy. The placental weight of the heat-treated ewes was lower than that of the control ewes at the 80th (P < 0·05) and 140th (P < 0·01) days of pregnancy. Fetal weight and dimensions did not differ significantly between control and heat-treated ewes at the 80th day of pregnancy, although fetal weight (P < 0·01) and fetal dimensions (P < 0·05) for the previously heat-treated ewes were lower than those for the control ewes at the 140th day of pregnancy. Placental and fetal weight at the 140th day of pregnancy were correlated (P < 0·05) with the rectal temperature of ewes measured at 08.00 and 16.30 h during the period of heat-treatment, but not with the change in rectal temperature between 08.00 and 16.30 h. It was concluded that restricted placental growth in heat-treated ewes retarded fetal growth during late pregnancy even in the absence of heat treatment, and it is suggested that selection of ewes which can maintain normal rectal temperatures during periods of heat stress would produce lambs of normal birthweight in a hot climate.