As a prerequisite for developing crop-yield/water-use functions for potatoes using the results of historical irrigation experiments, it was necessary to develop a water-use model which could operate with a limited data set. The general form of this model has been reported by Wright et al. (1994), and its application to the sugarbeet crop by Hamer et al. (1994). In this paper the development and validation of the model for potatoes is described.

The canopy was modelled in terms of intercepted incoming solar radiation using functions based on thermal time and time. Four phases of growth were identified: emergence, expansion, plateau and senescence. An empirical drought factor was included to allow for the effects of water stress on canopy development during the expansion phase. Root development was described using a two-phase model: linear and maximum depth (both time dependent).

Independent data from various sources were then used to validate the model in terms of its capacity to predict crop canopy development, with and without drought stress, soil water extraction at different depths and soil water deficits during the season. The study confirmed the validity of the model for predicting the water-use of potatoes.

The progenies of six crosses, made in 1987, between the best available hooded barley line and six selected awned barley lines were used to study the effect of the hooded gene on the performance of barley under rainfed conditions in Cyprus. A single dominant gene was found to control the hooded character. Awned genotypes on average outyielded hooded genotypes by 17%, but the difference between the two genotypes was smaller in the central plain than in the coastal area. The effect of the hooded gene on yield varied also with the combination of parents, as the superiority of the awned genotypes varied with cross from 13 to 30%. Hooded lines giving a higher grain yield than their hooded parent were identified. On average the awned genotypes had higher 1000-grain weight (5·0 g), were slightly later in heading date (1·1 days), had slightly higher volume weight (1·3 kg/hl) than hooded genotypes, but had similar plant height. The 1000-grain weight of most hooded lines was significantly higher than that of their hooded parent.

In spite of the negative effects of the hooded gene on grain yield, it was concluded that it is possible to increase the yield of hooded barley for hay production by continued crossing and selection (with special emphasis on 1000-grain weight), by selecting special combinations of parents through the Bulk-Pedigree method and by growing hooded barley in suitable areas, making use of the locationdependent performance of the hooded gene.

Three rates of phosphate (0, 25 and 60 kg/ha P2O5) were applied for 7 years to phosphate-deficient grassland at Tel Hadya, north Syria. Liveweight, milk yield, wool production and supplementary feeding of Awassi sheep were monitored for six seasons (1985/86 to 1990/91). The experiment was grazed at low (0·8 sheep/ha per year) and high (1·7 sheep/ha per year) stocking rates from the second to the fourth season, while in the fifth to seventh seasons stocking rates were increased to 1·1 and 2·3 sheep/ha per year, respectively. The experimental site was typical of communally owned, degraded grasslands within the cereal zone of west Asia, where cropping is not possible because of shallow, stony soils and steep slopes.

The results showed that annual applications of phosphate, even at 25 kg/ha, improved pasture and sheep productivity. Liveweights were higher on fertilized plots in five out of six years, significantly so in the last three. Milk production was also higher on phosphate-treated plots, and the need for supplementary feeding was reduced, especially in the last three years, when rainfall was below average. The results suggest that stocking rates can be significantly increased by annual applications of small amounts of superphospate, and that doing so is profitable.

Use of the results depends on the presence of native legumes, the level of soil phosphate, and the ability of farmers to control grazing of these communally owned grasslands. A strategy to fulfil these criteria is suggested.

At the research farm of the Swedish University of Agricultural Sciences, Uppsala, above- and belowground production and changes with time in root length, mean root radius and root surface area of spring oilseed rape were studied during the growing seasons 1987 and 1990. In both years, the highest root growth rate was recorded during the stem elongation phase, and the highest shoot growth rate during flowering. The root: shoot ratio decreased throughout the whole period of root sampling, from 0·64 to 0·16, during the cool and wet first year. In the warmer and drier second year, the ratio increased to a maximum of 0·72 when flowering started, and thereafter decreased. More than 80% of the root dry matter was found in the topsoil. Roots were longer and thinner in the dry and warm 1990 than in the wet and cool 1987. Maximum root length was c. 4·9 km/m2 in 1990, and mean root radius varied between 01 and 0·7 mm. Increases in root surface area during periods of root growth were due to increased root length rather than to increased mean root radius.

The developmental phase in which photoperiod sensitivity for podding occurs was determined for two bambara groundnut genotypes grown in 1987 and 1990 in glasshouse experiments in the Netherlands, namely genotypes ‘Tiga Nicuru’ from Mali (day-neutral for flowering and photoperiod-sensitive for podding) and ‘Ankpa 4’ from Nigeria (photoperiod-sensitive for both flowering and podding). Eighteen photoperiod treatments were given to each genotype. Two treatments consisted of a constant 12 or 14 h photoperiod and started 21 days after sowing for ‘Tiga Nicuru’ and 18 days after sowing for ‘Ankpa 4’. Eight treatments were introduced by transferring plants with at least 20 flower buds (33-day-old plants of ‘Tiga Nicuru’ and 35-day-old plants of ‘Ankpa 4’) from a 12 to a 14 h photoperiod or vice versa. In ‘Tiga Nicuru’ transference was for 4, 8, 12 days or until harvest, and in ‘Ankpa 4’ it was for 8, 12, 16 days or until harvest. Another eight similar treatments were given to plants transferred after having had at least 20 open flowers (48-day-old plants of ‘Tiga Nicuru’ and 62-day-old plants of ‘Ankpa 4’). Transferring plants of ‘Tiga Nicuru’ to the 12 h photoperiod for at least 8 days induced podding. Plants were susceptible to podding induction for nearly 4 weeks: podding was induced in plants which had been in the natural photoperiod (≥ 15·5 h) for 21 days, followed by 12 days in the 12 h photoperiod and subsequently in the 14 h photoperiod until harvest, and it could still be induced in 48-day-old plants that had had > 20 open flowers. However, transference to the 12 h photoperiod for 16 days did not induce podding in ‘Ankpa 4’. Transferring plants from the 12 to the 14 h photoperiod or vice versa caused differences in the number of flowers and pods/plant, petiole length and leaf area. The influence of photoperiod was most obvious on the number of pods/plant. Leaf area and number of pods/plant seem suitable parameters for modelling crop growth under different photoperiods. Leaf area development correlated with the number of developing pods/plant, but was also more directly influenced by the prevailing photoperiod.

Early reports on new, nutritionally superior, white-flowered (zero-tannin) faba bean cultivars indicated that they may show poor emergence under field conditions. The field emergence of 23 winter and spring type white and coloured-flowered lines and cultivars was investigated in relation to fungicidal seed dressing in 1989/1990 and 1990/1991 in the UK. These trials showed no definite emergence problems in white-flowered faba beans, probably because of favourable soil and weather conditions. Further experiments were therefore conducted in relation to emergence under controlled environmental conditions. The emergence of lines near-isogenic except for flower colour (the coloured line SCI v. the white line SWI) was investigated in relation to a range of soil moisture levels (soil water potential (SWP) ranging from −1·02 to 0·0 MPa (waterlogged)) and to three temperatures (22, 12 and 5°C) in a clay loam soil. Emergence was rapid and high at the SWP range from −0·52 to −0·24 MPa in both lines, depending on temperature. Any decrease or increase in SWP beyond this range resulted in a substantial reduction and delay in emergence in both lines. Emergence of SWI was more adversely affected than SCI when the temperature decreased from 22 to 5 °C. The emergence of six winter and six spring lines/cultivars was tested in relation to fungicidal seed dressing using wet soil (-0·06 MPa) at 5 °C under controlled environmental conditions. White-flowered winter lines (WWI, Polar and WD) and the spring line, SWI, had poor emergence (56–85%) compared to coloured types (86–98%). In some lines there was a slight improvement when using a fungicidal seed dressing.

The effect of breeding for the absence of condensed tannins in the testa of Vicia faba L. on resistance to foot rot, Ascochyta blight and chocolate spot diseases was investigated in 1988–92 at Wageningen, The Netherlands. For this purpose the disease development in tannin-free and tannin-containing partners of six near-isogenic pairs was compared after exposure to causative pathogens. Except for one near-isogenic pair, in which both partner lines showed a relatively high resistance, the tannin-free lines were more susceptible to foot rot than the tannin-containing partners of the same pair. This observation indicates that the presence of condensed tannins in the testa prevents infection of the plant by the causative pathogens. Fusarium oxysporum and F. solani, isolated from faba bean tissues showing foot rot symptoms, were shown to be primary foot rot pathogens, while F. avenaceum caused wilting of young plantlets. No pathogenic isolates were obtained from F. tabacinum. Resistance to Botrytis fabae (chocolate spot disease), scored on leaves and stems under glasshouse and field conditions in 1992, was not influenced by selection for the absence of condensed tannins which occur in the testa of mature seeds. Under the same environmental conditions, leaves, stems, pods and seeds of tannin-free lines showed similar levels of damage due to Ascochyta fabae (Ascochyta blight) as the tannin-containing partner lines of the same near-isogenic pair. These results indicate that condensed tannins do not play a role in resistance to both B. fabae and A. fabae, probably because, except for the seeds, these polyphenols do not accumulate in the tissues affected by these pathogens.

In 1991 and 1992, four sets of isogenic lines and eight released cultivars of pea (Pisum sativum L.) differing at the loci af (normal leaflets are converted to tendrils) and st (reduced stipule size) were grown in conventional plot stands at Göttingen, Germany. Crops were either supported by wire netting, to avoid the negative effects of lodging on yield, or were unsupported, thus permitting natural lodging, in order to study the effect of both genes on yield.

The conventional, normal-leafed plant type (AFAF STST) exhibited the highest yield potential, but also the largest yield reduction due to natural lodging. Yield potential of the ‘semi-leafless’ plant type (afaf STST) was less than that of the conventional type but, due to its better standing ability, the yield of the unsupported, ‘semi-leafless’ crop, on average, was less reduced by lodging than was the yield of the conventional one. With the additional reduction in stipule size by the gene st, the decrease in yield potential was too large to be counterbalanced by the positive effects of an improved standing ability. For the released cultivars, the effects of both genes on crop performance were smaller than for the isogenic lines.

The ability of 12 Scottish Blackface ewes to discriminate and concentrate grazing activity in nitrogenfertilized heather patches was determined. The nitrogen content of a stand of heather (Calluna vulgaris) was increased and the fibre content decreased by adding ammonium nitrate fertilizer (7·5 g N/m2) 3 months prior to grazing, in Scotland during August 1991, to selected areas within a patchwork array. The sheep were offered either a high protein (300 g soyabean meal) or low protein (285 g ground barley) supplement daily before being allowed to graze within the heather mosaic during November 1991. The proportion of time spent grazing in fertilized and control patches (patch selection) and the proportion of daylight hours spent grazing (proportion of time spent grazing) was estimated for individual sheep for 6 days. Rumen ammonia concentrations were determined at the end of the grazing period. All animals spent approximately twice as much time grazing in fertilized as in control patches. About half of the daylight hours were spent grazing. The nature of the supplement did not influence patch selection, the proportion of time spent grazing or rumen ammonia concentrations. It was concluded that sheep are able to discern differences in the chemical composition of heather on a fine scale and that their foraging behaviour is not influenced by the type of supplement offered.

Fine wool in China is characterized by severe dust contamination and substantial tip weathering. In an attempt to improve wool quality, synthetic rugs were fitted to ewes and a range of raw wool characteristics was monitored. Two trials were carried out in successive years: a pilot trial (June 1985 to June 1986) involving 100 ewes wearing rugs and 75 controls, and a main trial (June 1986 to June 1987) involving 250 ewes with rugs and 250 controls. The rugs were fitted to ewes after shearing and remained on until shearing the following year. Wool from ewes with rugs was significantly better in almost all the characteristics measured (P <0·05) than wool from sheep without rugs. Clean fleece weight was improved by 15% over the two trials, yield and wax content were increased, and dust content and dust penetration were substantially reduced. Staple length and strength were increased, and dust content and dust penetration were substantially reduced in the main trial. Several style characteristics were measured using a prototype image analysis system and these also showed wool from sheep wearing rugs as being of better quality than wool from sheep in the control group. The only negative result was an increase in yellowness, in the greasy state only, due to the higher wax content in the sheep wearing rugs and the yellow nature of the wax of Gansu Alpine Finewool sheep – probably due to their genetic background. Wool from sheep wearing rugs would be expected to perform better in processing than wool from unrugged sheep.

The effects of infection with T. vivax in mid- or late pregnancy on food intake and utilization, liveweight changes, abortion rate and lamb growth rate were investigated in West African Dwarf ewes at lbadan, Nigeria in 1990. Rate of liveweight gain by ewes infected during mid-pregnancy (IMH) was16 g/day compared with 33 and 37 g/day for the uninfected ewes offered medium (CM) or high (CH) plane diets. Although digestibility coefficients were not affected, intake of digestible organic matter was higher in CH ewes than in IMH and CM ewes. Nitrogen retention at mid-pregnancy on a metabolic size basis was higher in CH ewes than in CM and IMH ewes.

Lamb birth weight and survival rate were lower in infected ewes. Ewes infected in mid-pregnancy (IMH) and in late pregnancy (ILH) had mean birth weights of 1·4 and 1·0 kg compared with CM and CH ewes, which had mean birth weights of 1·9 and 2·0 kg respectively. Observed survival rates were 63, 15, 75 and 80% for lambs nursed by IMH, ILH, CM and CH ewes respectively. During the first 6 weeks postpartum, lamb growth rate in all groups did not differ. However, during weeks 7–12 postpartum, lambs nursed by IMH ewes had significantly lower growth rates. Weaning weight was also lower in lambs from IMH (5·0 kg) dams than in lambs from CM and CH dams (7·1 kg). Infection during late pregnancy was more severe and all infected ewes lost weight due to reduced feed intake and fever. T. vivax infection in sheep is responsible for reproductive wastage, abortion, poor lamb growth and ewe mortality.

The effects of trypanosomiasis on digestible organic matter intake, milk yield and composition, dam liveweight changes during lactation and lamb growth rates were investigated at Ibadan, Nigeria 1991/92, using 20 West African Dwarf sheep nursing single lambs. Although digestibility coefficients were neither affected by infection nor by level of feed intake, organic matter intake during early and late lactation was significantly lower in infected dams. Nitrogen retained in late lactation was lower in infected animals due to reduced feed intake. Mean daily milk yields were not affected by the infection during early lactation; however, during the second half of lactation, average daily milk yields were significantly lower in infected animals than in uninfected controls. Variations in milk component concentrations between experimental groups did not attain statistical significance throughout lactation. While control ewes on a high plane of nutrition (CH) gained 12·1 g/day, infected ewes (IH) and uninfected control ewes on a medium plane of nutrition (CM) lost 45 and 5·4 g/day respectively during lactation. Liveweight gain in the lambs was not affected by infection in the dams.

This study demonstrated reduction in feed intake, late lactation milk yield and dam liveweight gain with no adverse effect on digestibility coefficients, milk composition, early lactation milk yield and lamb weight gain during T. vivaxinfection of lactating ewes.

Three experiments were conducted in Mérida, Mexico, between 1987 and 1990 in which jack beans, treated in various ways, were included in chick diets at the rate of 300 g/kg diet. The diets were balanced by appropriate supplementation to provide the same concentrations of energy, minerals, vitamins and principal essential amino acids as control diets based on maize or sorghum and soyabean meal. Boiling jack beans or soaking and shaking them and the combination of boiling with soaking and shaking were studied with a view to removing or inactivating toxic factors and enhancing the utilization of the beans as a livestock feed. A fourth experiment was conducted to evaluate the contribution of canavanine to the deleterious effect observed when broiler chicks are fed diets containing treated jack beans and to examine the effect of canavanine on the efficiency of protein retention of broiler chicks.

Boiling for 1 or 2 h reduced the toxicity of jack beans, but chick growth rate was only half that of controls. The combination of boiling, followed by soaking and shaking, removed most of the jack beans’ anti-nutritional factors, but some toxic effects were left in the beans, causing a depression of c. 10% in feed intake and growth rate. Growth, feed intake and protein utilization of chicks were not affected when canavanine was added to a sorghum-soyabean diet at a level (3·5 g/kg diet) which matched the canavanine present in a diet containing 300 g/kg boiled jack beans.

It was concluded that boiling was a satisfactory procedure for the inactivation of the heat-labile lectins in jack beans and that soaking and shaking was an effective method of reducing canavanine and the haemolytic activity of the saponins in jack beans. However, canavanine was found not to be the main toxic or anti-nutritional factor present in jack beans.

Four experiments were conducted in the Yucatán, Mexico, in 1991 and 1992 to study feed intake in 24 h trials with chicks and pigs fed diets containing either raw or treated jack beans or conventional diets with added canavanine.

Feed intake of chicks in the first hour was markedly reduced and feed intake of pigs was severely reduced when raw jack beans (300 g/kg for chicks, 250 g/kg for pigs) were included in their diets. Feed intake of pigs diminished to a greater extent than that of chicks when treated beans (300 g/kg) were included in the diet. Short-term feed intake of chicks was not affected when canavanine (3·5 g/kg) was added to a sorghum-soyabean diet. However, pigs showed a large drop in feed intake when canavanine was added to a maize-soya diet at only 0·8 g/kg. It was concluded that in both species the anti-nutritional factors in jack beans cause a rapid reduction in feed intake which precedes a depression in growth rate. The initial feed intake depression in pigs could be partly attributed to canavanine remaining in the jack beans after treatment. In the chicks' case, however, rejection of a diet containing treated jack bean was due to anti-nutritional factor(s) other than residual canavanine.