Rice necrosis mosaic virus infection induced different reactions on monocotyledonous and dicotyledonous plants under field conditions. Under identical conditions virus infection reduced the grain yield of rice by inhibiting plant growth, whereas in dicotyledonous plants like Ludwigia and four fibre crops (including jute infection with sap from rice necrosis mosaic virus-infected rice plants, but not with sap from healthy plants) markedly increased yield, plant height, leaf size, stem diameter, seed weight and number of seeds per capsule.

Reproductive performance, mortality, growth, and culling and replacement rates based on 20000 calving records were evaluated for grade Boran beef cattle maintained with trypanocidal drugs in an area of high trypanosomiasis risk in Tanzania. Under ranching conditions, over a 10-year period in this area of high Glossina morsitans morsitans, G. pallidipes and G. brevipalpis challenge, a calving interval of 15·9 months, pre-weaning mortality of 8%, annual cow mortality of 5·8% and 8-month weaning weight of 133·5 kg resulted in a herd productivity of 96 kg of weaner calf per cow per year. The proportion of heifers required as replacements (45%) and the generation interval (6·9 years) indicated scope for implementation of selection programmes on growth traits. The level of productivity achieved compared favourably with major data sets recently analysed from pure Boran cattle under trypanosomiasis-free ranching conditions in Kenya, and from trypanotolerant N'Dama cattle in West Africa. These results indicate the possibility of improving livestock production in tsetse-infested areas by the rational use of chemoprophylaxis as an integral part of management.

Year, season, cow age, calf sex and location on ranch had significant effects on practically all the traits of calving interval, pre-weaning mortality and growth, and cow productivity. Superior performance where bush clearance and tsetse fly control had taken place suggests that economic evaluation of these interventions should be attempted. The season of calving had a major effect on productivity. Cows of 5–8 years of age were the most productive, as were animals producing male calves, features well recognized in beef cattle production.

An average of 4·4 treatments with Samorin, a prophylactic, and 0·6 treatments with Berenil, a therapeutic, were required per year. The number of treatments varied from year to year and by area, being greater in the south of the ranch where the tsetse challenge was considered higher. However, the age and season of calving had little effect on the number of treatments required. Despite such extensive use of trypanocidal drugs, there was no indication that drug resistance had developed or evidence that repeated inoculation of Samorin had affected productivity.

Grading-up of small East African Zebu cattle to Boran over an 8-year period allowed annual comparison of birth weights, pre-weaning growth and weaning weights of two groups of calves, one having a higher level of Boran genes (varying from 12 to 6% higher annually) than the other. Those with the higher level of Boran genes performed better by 3·3% for all attributes studied, but as the percentage difference in Boran genes decreased, so did this difference. In an environment improved through bush clearance and tsetse fly control, the calves with higher levels of Boran genes were superior, but this superiority was not expressed in the unimproved environment.

A model of a drying swath has been developed and used with 20-year long meteorological data sets from 32 sites in north-west Europe to provide an objective assessment of the influence of weather on field hay drying. The model considered the swath in terms of its bulk properties but incorporated the effects on swath drying of soil evaporation and stubble transpiration: delays in swath drying caused by interception of rain or dew were calculated explicitly.

A cutting season from May to September was assumed, and results given in terms of the number of daily cuts reaching various moisture contents in less than 10 days, and especially those reaching 25% (dry-weight basis) within 5 days so that dry-matter losses were relatively small, and immediate long-term storage was possible. Rainfall amounts on the faster-drying swaths were usually less than 1 mm. A large inter-annual variability in hay-drying prospects was demonstrated, even at sites with fairly good climates for drying on average. The most favourable conditions for field drying were shown to occur substantially earlier in the cutting season at maritime sites than at those with a more continental climate. Conditioning of the swath allowed more cuts to dry to a prescribed moisture content, but with the penalty of larger average rainfall on the swath, and consequent loss of quality.

Recent amendments to European Economic Community Feed Additives Directive 70/524 have lowered the maximum permitted copper content of pig rations because of concern about the environmental pollution risks that may be caused by land application of slurry containing high copper concentrations. The inclusion of copper compounds in pig feed improves growth rates and food conversion ratios, but 80–90% of dietary copper is excreted (Unwin, 1977), although the concentration in slurry varies widely according to diet and water intake. Repeated applications of pig slurry to grassland may result in copper-induced phytotoxicity and, more importantly, toxicity to grazing livestock, particularly sheep. However, the experimental evidence regarding the accumulation of copper in soil and herbage is inconclusive, and there is some difficulty in identifying ‘safe’ levels, as these vary according to soil type, herbage composition and herbage contamination (Batey, Berryman & Line, 1972; Bremner, 1981). Results are presented here on an experimental investigation into soil and herbage copper contents under three different slurry application rates at two permanent grass sites.

Work in controlled conditions (Cooper, 1964; østgård & Eagles, 1971) has indicated that, under short photoperiods and low temperatures, Scandinavian grass varieties tend to grow more slowly than those from lower latitudes, and are, therefore, more resistant to cold and freezing stresses. This has been confirmed in field experiments (Håbjørg, 1979). These grasses would therefore be expected to cease growth earlier in the autumn when grown in the British Isles. However, this mechanism does not appear to operate under lengthening days; indeed, there is evidence to suggest that their growth is particularly stimulated by the combination of cool temperatures and long days (Cooper, 1964; Hay & Heide, 1983, 1984). This raises the possibility that varieties from Norway and Sweden could produce more dry matter than grasses of more southern provenance in the spring in upland areas, when low temperatures are associated with rapidly lengthening photoperiod (12·5–15 h) and moderate to high levels of irradiance (> 200 W/m2) (Hay, 1985).

Previous investigations (e.g. Bates, 1935; Singh, 1952; Bremner & Taha, 1966; Sharpe & Dent, 1968) established that increase in the size of potato seed planted and decrease in inter-sett spaoing increased the number of stems and of tubers, resulting in yield advantage generally, but reduced tuber size in the produce. The use of large seed and of close spacing are, therefore, generally preferred for growing a seed crop. However, their use involves higher seed rates, especially when the two are combined. At high seed rates the improvement in yield with increased seed rate may not be commensurate with the extra investment in seed, beoause of the associated increase in inter-sprout and inter-tuber competition. The severity of the competition may be intensified when some factor, for example water, limits tuber growth (Singh, 1952). As the number of stems is not a simple multiple of seed weight, because of the phenomenon of ‘apical dominance’ in potato tubers, it may be desirable to plant small seed or ‘chats’ closely, without increasing seed rate unduly, to optimize stem density without sacrificing net yield (total yield –seed planted). To investigate this, a seed size and spacing experiment was conducted under irrigated conditions in the autumn crop season.

Lime-induced Fe chlorosis is often a severe problem on calcareous and saline alkali soils. Symptoms of apparent Fe deficiency and responses to its application on several field crops have been observed under such soil conditions (Indian Council of Agricultural Research, 1980–81; Sakal, Singh & Singh, 1982, 1983). Rice varieties exhibit variable reaction to Fe stress when cultivated as an upland crop especially at seedling stage in the nursery (Patel, Ramakrishanyya & Patel, 1977; Singh et al. 1984). Plant analysis is one of the accepted tools for diagnosing nutritional disorders. Chlorotic plants often contain more total Fe than the green plants (Katyal & Sharma, 1.980; Voigt et al. 1982). In order to overcome this elusive behaviour of Fe it has been suggested that in place of total Fe the plants should be analysed for active Fe or dilute HCl-extractable Fe (Machold & Stephen, 1969). Iron is important for chlorophyll biosynthesis and is linked with a number of enzyme systems. The change in the activities of the enzymes has beenused as a yardstick to distinguish Fe deficiency in plants (Del Rio et al. 1978). Wallace (cf. Katyal & Sharma, 1980) and Patel et al. (1977) suggested analysing the plants for that fraction of Fe which correlates well with occurrence of chlorosis.

Sheep are commonly used to graze dairy pastures in the late autumn and early winter, to make use of grass that cows have rejected and to utilize any late growth with a minimum of poaching damage. From late December onwards sheep are less welcome to farmers because of the possible harmful effect on the regrowth of grass in the spring. But if the alternative to grazing from January to March is to bring the sheep indoors and feed them hay or silage, then this cost may be greater than that of the grass lost in the spring. Wilman & Griffiths (1978) concluded that the reduction of yield in spring was directly related to date of last grazing but emphasized that they had made no measurement of herbage remaining at this time. Furthermore, their measurements of subsequent yield were in dry matter to a cutting height of 4 cm with no estimate of the amount of ash or green and dead material.

Interception of rain by the plant canopy and stemflow resulting in non-uniform distribution of soil water beneath the canopy has long been recognized in forest trees (Eschner, 1967). Rutter (1975) stated that stemflow may vary from quite small quantities to as much as 20% of the net rainfall and Geiger (1965) had earlier quoted data both from Ovington (1954), who found stemflow to be 0·1–0·3% of rainfall in seven forest canopies, and from Eidmann (1959) showing that a fir and a beech canopy gave 0·7 and 16·6% respectively of the average rainfall as stemflow. However, there have been few studies of the distribution of rain beneath the canopies of agricultural crops despite the implications which non-uniform distribution might have for studies of crop water and nutrients.

Potassium occurs in soils in four different forms, namely water-soluble, exchangeable, nonexchangeable and mineral (Reitemeir, 1951; Munson & Nelson, 1963). Water-soluble and exchangeable forms are considered to be directly available to plants. Under continuous cropping one may therefore expect depletion of these two forms, but in fact not much discernible difference in the amounts of available K was observed even after a few crops had been grown. Hence several people have stated that there exists an equilibrium among the following forms of K

This equilibrium implies that a change in magnitude of a form is compensated by the movement from, to and among other forms (Reitemeir, 1951; Garman, 1957; Munson & Nelson, 1963; Chevalier, 1971). If water-soluble and exchangeable forms of K are removed by crops more potassium would become exchangeable from non-exchangeable forms (Maurya & Ghosh, 1972). Whether soils when cropped can maintain the level of exchangeable K depends upon the type of soil, nature and intensity of cropping, the relative rate of removal and release from non-exchangeable form. Continuous cropping therefore alters the existing equilibrium of soil potassium in the profile as crop roots penetrate as deep as 2 m. Since all the potassium fertilizer for a crop is applied at sowing, the temporary overloading of the system may cause leaching losses of K in light soils. This may result in the enrichment of deeper layers.

Biomass production in barley is determined by the amount of solar radiation absorbed by the foliage (Gallagher & Biscoe, 1978). As incident irradiance per unit area varies little between neighbouring sites and seasons in the cereal growing areas of the U.K. (Monteith, 1978), biomass production will largely be governed by the size of the canopy, the orientation of canopy constituents and the efficiency of conversion of absorbed radiation into dry matter (Green, 1984). Reviewing the literature, Monteith & Elston (1983) have highlighted the constancy of mean seasonal efficiency, concluding that growth is limited by the ability of the stand to absorb radiation.

Research conducted on sowing dates has shown a trend towards increased yield as sowing is advanced for winter wheat (Darwinkel, Hay & Kuizenga, 1977; Walker, 1980) and winter barley (Selman, 1980; White, 1981). Green & Ivins (1985) have quantified the rate of yield decline for winter wheat as sowing is delayed after mid-September, giving a mean value of 0–35% per day. For a similar study on winter barley (Green, Furmston & Ivins, 1985) a yield decline of 0–43% per day delay in sowing was attributed to reductions in the number of ears per unit area as planting was delayed.