Shoot and root growth and associated leaf and soil water potential relations were compared in three consecutive crops of winter wheat grown in the same field. Despite a profuse root system the crop grown in the second drought year (1976) failed to dry the soil as throughly as the crops in 1975 and 1977. Measurements of plant water potential showed that the restricted utilization of soil water reserves by this crop was associated with failure to make any significant osmotic adjustment, leading to premature loss of leaf turgor and stomatal closure. The implications of these results for models to estimate actual crop evaporation from values of potential evaporation are discussed.

The effects on dormancy of post-harvest application of growth regulators to bulbils, tubers and tuber pieces of tropical Dioscorea species were examined. Abscisic acid, kinetin, indole acetic acid and 2-chloroethyltrimethylammonium chloride were found to have little or no effect on either shoot or tuber-root production, while ethrel greatly promoted tuber-root production with little or no effect on shoot development. The germination of slices of tubers of D. alata was delayed by maleic hydrazide but there was no effect on intact tubers of D. alata and D. esculenta. Treatment with 2,4-dichlorophenoxyacetic acid caused massive root and callus development along with delay in shoot development, while gibberellic acid occasioned marked extensions in the dormant period.

The effects of post-harvest application of gibberellic acid on dormancy of tubers of Dioscorea alata and D. esculenta were examined. In both species, gibberellic acid extended the dormancy of immature and mature tubers but when GA3 application was made after storage for varying lengths of time, there was a decreasing effect with increased storage time. Dormancy was also reinduced in germinating tubers, that had gone through a normal dormant period, as a result of gibberellic acid treatment. A possible mechanism of dormancy in tropical yams is discussed. It is concluded that use of gibberellic acid as a means of extending the storage life of yam tubers by post-harvest application is a distinct possibility.

When pre-harvest foliar applications of growth regulators were made to vines of Dioscorea esculenta cv. Chinese Yam and D. alata cv. White Lisbon there were no obvious effects on tubers of D. alata, but dramatic effects on tuber development, storage and germination were obtained with D. esculenta tubers. Gibberellic acid caused marked extensions in tuber dormancy, 2,4-dichlorophenoxyacetic acid resulted in marked callus development, delayed germination and abnormal shoot and root development and indole acetic acid resulted in fingering of the tubers. It was concluded that there was potential for commercial exploitation of pre-harvest gibberellic acid treatments in extension of dormancy in Chinese Yam tubers and that the lack of response of D. alata tubers to foliar application of growth regulators warranted further investigation.

Isogenic fertile and sterile forage maize (cv. LG 11) grown in separate fields were harvested at regular intervals during growth between mid-July and early October 1979. Leaf, stem and ear components and whole plant (before and after ensiling) were examined for changes in the concentration of dry matter (D.M.), soluble sugars, starch, hemicellulose, cellulose, neutral detergent fibre (NDF) and acid detergent fibre (ADF). In vitro digestibility values for D.M., organic matter (OM) and OM in the D.M. were also determined in fresh and ensiled whole crops.

Prior to ensiling the concentration of non-structural carbohydrates in the two crops was markedly different. Fresh fertile plants contained (as g/kg D.M.) 369 and 101 of starch and soluble sugars respectively. Corresponding values for sterile plants were 54 and 343 respectively. Sucrose was the most abundant soluble sugar present and contributed 64 and 74% of the totals in fertile and sterile plants respectively, prior to ensiling. Increases in plant D.M. during growth were significantly affected by the deposition of starch and are described by the following equation:

y = 13·6 + 0·49 (±0·073) x(r = 0·93)

where y = whole-crop D.M. concentration and x = starch concentration in D.M. The concentrations of hemicellulose and cellulose of both types of fresh plants were similar but those of ADF and NDF were lower in sterile plants. Xylose was the major constituent neutral sugar in the hemicellulose fraction and formed 68 and 76% of the total hemicellulose in the fertile and sterile plants, respectively. In vitro digestibility values of sterile plants tended to be higher than their fertile counterparts.

After ensiling, the concentration of soluble sugar in the sterile and fertile crops decreased from 343 to 8 g/kg D.M. and 101 to 5 g/kg D.M. respectively. The in vitro DOMD values of the sterile and fertile crops decreased by 16 and 11 percentage units respectively; both final values were recorded as 61.

In vivo digestibility values determined in 18-month-old wether sheep fed at maintenance, for NDF, ADF, cellulose, hemicellulose, nitrogen, OM, D.M. and OM in D.M. were 60·2, 58·0, 65·8, 64·1, 32·9, 66·6, 65·4 and 63·7 respectively for fertile plant silage. These were all markedly lower than the corresponding values for the sterile plant silage which were 68·3, 70·3, 74·8, 73·3, 60·3, 71·3, 69·6 and 67·7 respectively. Within the hemicellulose fraction the digestibility values for xylose in both sterile and fertile plant silage were considerably lower than the values recorded for either arabinose or galactose. In vitro digestibility values for D.M., OM and OM in the D.M. were similar to in vivo values for fertile plant silage but were lower than in vivo values for sterile plant silage.

Dairy herd replacement heifers (aged 3–6 months) had higher D.M. intakes when given fertile plant silage ad libitum than with sterile plant silage. However, the liveweight gains of the heifers on sterile and fertile plant silage differed little.

S.184 white clover was established on an unimproved brown earth hill pasture using both surface seeding techniques and conventional cultivation. Inoculation with selected Rhizobium trifolii improved clover dry-matter production by 0·017 t/ha on the cultivated trial in the establishment year and by 0·13 t/ha in the first harvest year. On the uncultivated site, clover dry-matter production was increased 1·88 t/ha by the best inoculation treatment in the first harvest year and 1·01 t/ha in the second harvest year. Rhizobium strains differed in their ability to promote clover growth. Clover yields were substantially better on the uncultivated than on the cultivated trial. The implications of the results for hill land pasture improvement are discussed.

The seedling emergence from fluid-drilled germinating and natural onion seeds was compared at five sowing dates between 10 February and 18 May on irrigated and unirrigated plots in two experiments. In the second experiment fluid-drilled seeds selected for uniform germination were also included. There were few significant differences between the emergence of seedlings from germinating and natural seeds in the field sowings of Expt 1. However, a reduction in mean emergence time at the earliest sowing led to an increase in bulb weight while a reduction in the spread of emergence at sowing 3 led to a reduced coefficient of variation of bulb diameter at harvest. Under the less variable conditions on the irrigated plots of Expt 2 germinating seeds reduced mean emergence time and increased percentage emergence compared with natural seed at some sowings. Fluid-drilled selected germinated seeds, however, reduced mean emergence time and increased percentage emergence at every sowing and reduced the spread of emergence at all but the first sowing compared with natural seed.

Low soil moisture content made seedling emergence more unpredictable and reduced the benefits gained by sowing germinated seeds. The results presented suggest that techniques to increase the proportion of germinated seeds at the point of sowing and economical methods of applying water during periods of low soil moisture following sowing are needed if the full benefits of fluid drilling are to be realized.

Three composite populations of oats were grown at contrasting sites in the north, east and west of Scotland for four successive generations from F3 to F6. Analyses of variance and canonical analysis both showed that the genetic constitution of the composites was responsible for a greater proportion of the variation than locations (sites). This suggests that either natural selection was not operating to any great extent or the effect of natural selection was very similar at the three sites. These findings were supported when selections were taken from one of the populations and subjected to canonical analysis. The implications for oat breeding in Scotland are discussed.

A field experiment was conducted for 3 years to study the effect of Rhizobium inoculation, mulch and N and P fertilizers on soya bean. The application of wheat straw mulch helped greatly in lowering the maximum soil temperature but failed to increase the yield, particularly on the fields where soya bean was raised for the first time. Seed inoculation gave significantly greater yield than control (no inoculation and no mulching). The combination of mulch and seed inoculation, on average, produced 0·76, 0·43 and 0·84 t/ha more grain than inoculation alone in 1976, 1977 and 1978 respectively. A basal dose of 15 kg N/ha increased the yield when seed was inoculated but no mulch applied whereas the dressing of N did not prove beneficial when mulching was combined with inoculation. The grain yield, however, increased up to 180 kg N/ha in the case of mulch alone and control treatments. The response of soya bean to phosphorus application was inconsistent.

Apparent digestibility of forage kale (cv. Maris Kestrel) was compared with that of mixed perennial ryegrass (0·85) and clover (0·15) herbage in two experiments. In a third experiment measurements were made of the partition of digestion between the reticulo-rumen and post-ruminal regions of the digestive tract in sheep fed kale, using intra-ruminal infusion of inert ruthenium phenanthroline and chromium-EDTA markers and time sequence sampling from the duodenum. Results in Expt 3 were compared with predicted values for a range of ruminant diets, including digestion of fresh perennial ryegrass and white clover.

In Expts 1 and 2 the ratio of readily fermentable to structural carbohydrate (CHO) was much higher in kale (2·6–3·2) than in mixed ryegrass and clover herbage (0·6), and showed little difference between kale leaf and stem components. Apparent digestibilities of organic matter (OM), cellulose and hemicellulose were 80–90% for kale diets, varied little with changes in leaf/stem ratio, and were generally slightly higher than for mixed ryegrass and clover herbage. Calculated metabolizable energy (ME) concentrations were 12·0 and 11·7 MJ ME/kg D.M. for kale and mixed ryegrass and clover respectively.

Despite large intakes of water-soluble CHO and pectins in kale-fed sheep in Expt 3, duodenal flows were small and respectively 92 and 98% of the total amounts digested were digested in the rumen. Ruminal cellulose digestion (95% total digested) was as predicted for normal ruminant diets, but less hemicellulose was digested in the rumen (71% total digested) than predicted. Total N flow at the duodenum was 5 g/day less than N intake, and respectively 27 and 66% of the N apparently digested was accounted for as total N absorption from the rumen and post-ruminal absorption of NAN. Calculated absorption of amino acids from the small intestine was less for the kale diet (14% ME intake) than for diets of fresh perennial ryegrass and white clover (20% ME intake). Possible reasons are that 10% more of the OM ingested was digested in the rumens of sheep fed kale than was predicted, that the ratio of dietary total N/100 g digestible OM was much less for kale (3·7) than for perennial ryegrass and white clover (5·6) diets, and that protein formed a lower proportion of the total N in kale diets (75%) than in diets of ryegrass and clover (90%). Despite 3·3 g of S-methyl-L-cysteine sulphoxide (SMCO) being consumed per day, none was detected in either rumen or duodenal contents or in faeces.

In was concluded that complete conversion of SMCO to dimethyl disulphide occurred in the rumen, that dimethyl disulphide may have caused the depression in ruminal digestion of hemicellulose, and that the digestion products of kale are deficient in absorbed amino acids relative to other forms of energy, thus explaining responses to essential amino acid supplementation in lambs grazing kale.

Variation in infestation of S. avenae on plots of wheat was assessed by combining techniques of enhancing field infestations with scoring individual shoots according to the number of aphids on them, using a logarithmic scale with base 2. The mean score appeared the most useful way of describing the aphid infestation on each plot.

In 1982, the sampling effort required for assessment of S. avenae on many plots was considerably reduced by this approach. The artificial increase in numbers of aphids avoided problems associated with sampling small populations, and the logarithmic classification of shoots reduced the time needed to assess large numbers. Scoring plots as a whole, although much quicker, gave results that differed from the assessments based on shoot sampling, and should be used with caution. The differences observed among cultivars in infestation of adult plants in the field in 1982 were not always the same as those observed on younger plants in the glasshouse.

Geranium (Geraniaceae) is an important aromatic plant grown for its light yellow to light brown or green coloured volatile essential oil obtained bysteam distillation of the green overground biomass. Geranium oil is extensively used in many perfumery formulations. The crop is generally raised from rooted cuttings whose initial slow growth leaves a large portion of land uncovered. Under identical situations in many other crops, it has been observed that growing grain or fodder legumes as intercrops resulted in monetary or yield advantages (Willey, 1979a,b; Mead & Willey, 1980; Rajeswara Rao & Singh, 1982, 1983; Rajeswara Rao & Sadaphal, 1983). The objective of the present investigation was to study the feasibility of growing a short-duration leguminous intercrop during the initial lag phase of geranium in such a way as not to affect the yield of geranium.

A number of factors affect predictions of rumen degradability of feedingstuffs when using the in sacco technique (Lindberg, 1983). One factor which exerts a great influence is the bag cloth aperture (Lindberg & Knutson, 1981; Lindberg & Varvikko, 1982). Without doubt part of the difference in degradation between pore sizes can be explained by differences in particulate matter losses (Lindberg & Knutsson, 1981; Lindberg & Varvikko, 1982). It has, however, also been suggested that the differences between pore sizes are due to the combined effect of differences in liquid exchange between the bags and the rumen contents and on the selection of microbes entering the bags (Lindberg & Varvikko, 1982).

Groundnuts are mostly grown during the rainy season (kharif) in India. Most of the cultivation is without irrigation. Consequently the crop experiences water deficits of different intensities and durations, depending upon the rainfall distribution. Yields are poor under such conditions. In other leguminous species irrigation at flowering usually improves yield, if the pod development period coincides with a break in rainfall or water deficit (Khanna-Chopra, Koundal & Sinha, 1980). Thus, an understanding of reproductive behaviour and reproductive efficiency could be helpful in adjusting planting to coincide with favourable agroclimatic conditions. Alternatively, this understanding could help in scheduling irrigation.

Fruit curvature is a trait which has been little investigated by botanists and horticulturists. The degree to which a fruit is curved can be accounted for intuitively in cases where there are no physical barriers to normal fruit growth, such as obstruction by plant parts or the soil surface. The curvature of pendant, unobstructed fruit, as in the Solanaceae, has received limited discussion in the literature.