The effects of inoculation with the vesicular-arbuscular mycorrhizal fungus Olomics mosseae(Nicolson & Gerdemann) Gerdemann and Trappe, fumigation of soil with methyl bromide, and addition of superphosphate (up to 60 kg P/ha) on growth and phosphorus nutrition of spring wheat (Triticum aestivum L. cv. Highbury) were investigated in two experiments (in 1980 and 1981 respectively) on plots that had been fallowed and recently limed.

Fumigation severely reduced natural levels of infection, and slightly reduced yield of above-ground dry matter in both years. In 1981 a decrease in grain yield of about 25% was accompanied by an increase in growth of straw. Plants on fumigated plots contained appreciable amounts of bromine in shoot tissue.

Inoculation increased and added P decreased infection in all treatments. In 1980 inoculation had little effect on above-ground dry matter, but it increased concentration of P in shoots especially on plots without added P. In 1981 added inoculum increased yield of grain on fumigated plots by about 0·75 t/ha at all levels of added P, but had little effect on non-fumigated plots, though responses in grain production to added P were similar with and without fumigation. Increases in yield resulting from inoculation were generally accompanied by increases in concentration of P in plant tissue.

Winter barley was sown on the plots after their use for spring wheat, without further application of the fumigation, inoculation or phosphorus treatments used in those experiments, to determine any residual effects on mycorrhizal infection and on growth. The levels of mycorrhizal infection on non-fumigated, inoculated plots were relatively constant in successive crops, although numbers of propagules of mycorrhizal fungi increased significantly with time for all treatments. Infection levels on fumigated and non-inoculated plots increased in successive crops, so that the relative effects of fumigation and of inoculation declined with time.

The effects of inoculation on infection levels persisted for longer than those on yields, suggesting that maximum effects of mycorrhizal infection on growth did not require the maximum levels of infection found in the roots. Harvest yields continued to respond to applied phosphorus even when uniformly high levels of infection had been established, suggesting that the ability of the root system to absorb phosphate was not greatly increased by mycorrhizal infection.

Young Lean And Obese Mice given diets containing, respectively, 5% reducing to 3% and 5% rising to 7% of typical alkaloid-containing ergot (Claviceps purpurea) showed inappetence, failed to grow during the period of 19 days and some individuals died. In contrast, ergot of a strain which cannot biosynthesize ergoline alkaloids was generally well accepted in dietary proportions, rising stepwise from 5 to 12% over the same period; growth rates of animals on control and alkaloid-free ergot diets did not differ significantly. The findings provide a context in which to discuss differentiation of ergoline alkaloids from the inappetence which is a prominent feature of ergot poisoning.

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.

Over five growing seasons (1976–80) experiments were carried out using at least three contrasting sites per season to study the relationship between growing conditions and storage losses in Pentland Crown potatoes. Crops were harvested by hand and storage was carried out in a single environment over a period of 6–7 months without sprout suppressants. The range in growing conditions was great and reflected in the pattern of leaf growth and range in yields of the stored crops (30–90 t/ha). Crops from Tenby (S. W. Wales) produced the most consistent and frequently the highest yields and usually lost the least weight during storage. Although the range in total weight loss over all experiments was large from 5·4 to 16·3%, treatment effects were much smaller than in field growth and yield. Delaying the date of harvest usually increased weight loss and tubers harvested in early August stored at least as well as late-harvested tubers. Tubers harvested without prior defoliation stored as well as tubers harvested on the same day from crops defoliated at least 2 weeks previously. Lengthening the interval from defoliation to harvest usually increased weight loss in storage. Although the tubers were hand harvested effects on saleability were found at the end of storage and there was no evidence that earlier harvesting, which may involve some loss of field yield, would result in any loss of saleable yield out of store.

The results provided no evidence to support the widely-held view that the suitability of a tuber for harvesting improves during maturation associated with natural or imposed crop senescence. It is therefore suggested that the use of the term maturity be avoided as it is wholly unhelpful in studies of the relationship between field growth and storage losses in potatoes.

The importance of mycorrhizal infection for the growth of wheat and barley sown in winter and spring was assessed in two field experiments. Low temperatures during winter restricted the development of mycorrhizal infection, and calculations of ‘thermal time’ indicated that the percentage of root length infected did not increase when mean temperatures were less than 5 °C. Hence infection was less in the winter-sown crops than in the spring-sown crops at early stages of plant development. However, the effects of mycorrhizal infection on growth were greater in winter-sown than in spring-sown wheat.

At all levels of applied phosphorus up to 60 kg P/ha, artificial inoculation with mycorrhizal fungi increased the yields of both cereals at each sowing date by 17–25% after indigenous mycorrhizal fungi had been removed by fumigation, but the effects were smaller on non-fumigated plots. The results confirmed the potential importance of mycorrhizal infection for the growth of cereals.

Mycorrhizal infection increased the phosphorus concentration in the plant tissue at very early stages of growth, but the effect generally declined with time.

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.

Inheritance of resistance to leaf curl disease in tomato (Lycopersicon esculentum) was studied in F1F2 and F3 generations in a cross between a cultivated tomato variety and a related wild species (L. pimpinellifolium). The wild species carries a dominant factor for resistance. Other useful variation was also observed in plant size, leaf characters and fruit size. The implications of these variabilities for tomato improvement are briefly discussed.

The interaction of water stress and time from sowing to floral initiation was investigated in the field with pearl millet hybrid BJ 104. Extended daylength was used to delay panicle initiation (PI) and flowering (FL) of crops exposed to single periods of mid-season drought. Growth, yield and yield components were related to the number of days for PI and FL in both irrigated and water-stressed treatments. Delay in PI resulted in more leaves and tillers per plant, and greater leaf area, height and total dry matter. Grain yield, however, was not affected resulting in lower ‘harvest index’. There was, however, an increase in the grain yield of main shoots which was offset by a proportional decrease in the grain yield of tillers.

Water stress effects were dependent on the physiological stage of the crop at which stress occurred, as a result of the photoperiod treatments. Water stress prior to panicle initiation did not affect the grain yield of the main shoot but increased tiller grain yield, resulting in a higher total (crop) grain yield. Water stress during panicle development reduced the grain yield on the main shoot but this loss was compensated by the grain from the increased number of tiller panicles which reached flowering. Water stress during flowering and grain filling reduced grain yields of both main shoot and tillers, making this the most sensitive stage. Photoperiodic control of floral initiation can provide an escape mechanism to avoid the coincidence of mid-season water stress with sensitive periods of growth.

The number of kernels per m2 (K) in well managed and watered wheat crops was studied using results of experiments in Mexico and Australia in which short spring wheat cultivars were subjected to independent variation in radiation, largely via artificial shading, and in temperature. Also crops subjected to differences in weather (year), sowing date and location within Mexico, revealed responses to the natural and simultaneous variation which occurs in radiation and temperature. Responses in K were interpreted in terms of spike dry weight at anthesis (g/m2) and number of kernels per unit of spike weight.

K was linearly and most closely related to incident solar radiation in the 30 days or so preceding anthesis, herein termed the spike growth period; for the cultivar Yecora 70 with full ground cover the slope was 19 kernels/MJ. This response seemed largely due to a linear response of crop growth rate to intercepted solar radiation. The proportion of dry weight increase partitioned to the spike increased somewhat with reduced radiation. Also increasing temperature in the range 14–22 °C during this period reduced K (slope approximately 4% per CC at 15 °C). The cause appeared to be lower spike dry weight due to accelerated development. The number of kernels per unit spike weight at anthesis was little affected by radiation or temperature, and averaged 78±2/g for the cultivar Yecora 70.

With natural variation in radiation and temperature, K was closely and linearly correlated with the ratio of mean daily incident or intercepted radiation to mean temperature above 4·5 °C in the 30 days preceding anthesis. As this ratio, termed the photothermal quotient, increased from 0·5 to 2·0 MJ/m2/day/degree, K increased from 70 to 196 × 102/m2. These responses of K to weather, sowing date and location were closely associated with variation in spike dry weight.

It was concluded that the ratio of solar radiation to temperature could be very useful for estimating K in wheat crop models. Also the analysis of K determination in terms of spike dry weight appeared promising, and suggests that wheat physiologists should place greater emphasis on the growth period immediately before anthesis.

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.

The digestive efficiency, rumen fermentation pattern, nitrogen balance, water intake and urine excretion were compared using four mature vasectomized Chios rams and four Damascus goats for each of five roughages (barley, lucerne or sudax hay, barley straw and leaves and twigs of acacia) offered alone or with concentrates (1:1 ratio), at approximately the maintenance energy level.

There were no species differences in the apparent digestibility of nutrients when the roughages were offered alone except for the significantly higher digestibility of dry matter, organic matter (OM), and gross energy (GE) of straw by goats. Sheep exceeded goats significantly in the digestibility of D.M., OM, GE and crude protein (CP) of lucerne hay plus concentrate and of CP when barley hay or sudax hay were supplemented with concentrate.

Compared with sheep, goats tended to consume more D.M. per kg W0·75 and drink less water and excrete less urine, but significant differences for water were obtained only with barley straw plus concentrate and for urine with barley hay and acacia.

Daily protein retention (g/kg W0·75) was consistently lower in goats than sheep but significant difference was obtained with acacia and with lucerne hay or straw plus concentrate. These results would suggest that Damascus goats require more protein for maintenance than sheep.

Compared with sheep, goats had significantly higher rumen NH3·N concentration with both acacia diets but lower with lucerne hay.

Total VFA concentration tended to be higher in sheep with all diets, but significance was observed only with barley hay although rumen pH was lower (acacia diets) or similar compared with goats. The molar proportion of acetic was significantly higher in sheep than goats with barley hay plus concentrate. Goats exceeded sheep significantly in the proportion of propionic with straw, of butyric with both barley hay and sudax hay plus concentrate diets, and of isobutyric with barley hay or acacia plus concentrate; with the other diets goats tended to have higher proportions of butyric and isobutyric.

Transpiration rate, diffusive resistances, canopy conductances and water potentials were determined at three canopy positions in non·stressed and stressed plants of sunflower hybrid BSH·1 and five other cultivars of sunflower under field conditions. The leaf area (LA) and stomatal frequency (f) was determined at the three canopy positions in field·grown plants and the total number of stomata per plant was calculated as the product of LA and f. These variables were then related to the dry·matter accumulation and seed yield in these cultivars. Cultivars with either a high leaf area or high number of stomata per plant were more productive under non-stress conditions. Under stress conditions, cultivars differed in the extent of change in conductance (g) and transpiration rate at different canopy positions. In the hybrid BSH·1, g was low at all levels in the canopy associated with a higher (less negative) water potential and this hybrid had lower transpiration rates at all canopy levels under stress although the number of stomata per plant was high. Stomatal sensitivity associated with a higher threshold water potential for stomatal closure is discussed as a possible explanation for the higher dry·matter accumulation and productivity of hybrid sunflower BSH·1 under moisture stress conditions.

Eighteen growing cattle with a mean live weight of 180 kg were used to study the influence of restricted water on feed intake, nutrient utilization and nitrogen metabolism in Zebu cattle in the Sudano–Sahelian ecological zone of Nigeria.

Feed intake and water consumption were negatively correlated (r = 0·63). As the amount of water intake was reduced from 15·8 to 11·91/day, the mean feed intake increased from 5·6 to 6·8 kg D.M./day; water to feed ratios decreased from 2·83 to 1·75 and average daily live-weight gain as well as apparent feed utilization efficiency improved significantly from free-choice water to 50% of free-choice water treatments respectively.

Apparent digestibility coefficients of almost all the nutrients from the 75 and 50% of free-choice water treatments indicated progressively higher (though not significant) values than those of the free-choice water treatment. Nitrogen metabolism did not indicate any difference in the nitrogen intake in any of the three treatments; however, nitrogen balance and nitrogen retained as a percentage of nitrogen intake were significantly (P < 0·05) higher on the 50% of free-choice water treatment.

The survival ability of these Zebu breeds of cattle under water stress during the acute water scarcity of the protracted dry period of the Sudan–Sahelian zone of Nigeria could probably be attributed to increased recycling of nitrogen as well as a reduction in nitrogen loss during the period.

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.

Oestroua activity of three flocks of Ossimi (O) and Rahmani (R) subtropical fattailed and imported Finn (F) ewes was followed over a calendar year under the prevailing subtropical conditions in Egypt.

Rahmani had quite consistent oestrous activity throughout the year, with a slight drop in March and June, and may be regarded as a non-seasonal breed. Oestrous activity of the O ewes was lower than the R at different times of the year. They showed high individual variation. Most of the O ewes had an anoestroua period during July–September but had regular oestrous activity during their breeding season.

Overall number of oestruses per ewe per year was 15·9, 13·0 and 10·3 for R, O and F, respectively. Normal cycle length tended to be longer, though not significantly so, in both R and O subtropical breeds than the F (17·8 and 17·6 v. 17·1 days). Heat duration was significantly longer in F (47·0 h) than in both local breeds (37·7 and 37·5 h for R and O, respectively).

Development of the fibrous root system of sugar beet was studied by washing soil samples taken from field experiments through the growing season. At the beginning of June the root system was still poorly developed but during June there was rapid proliferation. In the top 70 cm there was only little further increase in root density after the end of June. Below 70 cm root density increased up to the end of August. Throughout the season fibrous root density decreased with depth. Despite the origin of the lateral roots from two grooves on the storage root, fibrous root distributions at each depth around individual plants were essentially uniform from mid-June onwards. In the absence of nitrogen fertilizer, fibrous root development exceeded that of a crop given fertilizer, particularly at depths greater than 50 cm early in the season. The maximum value of root density was 2·8 cm/cm3 soil recorded in the top 10 cm in mid-September. Compared with published data for other crops, the sugar-beet root system was sparser than that of winter wheat or maize but denser than that of a soya bean or cassava.

Soil water content was measured with a neutron probe. Inflows to roots were calculated from soil water content changes in different soil layers. In the top 30 cm, inflows ranged up to 10·8 μl water/cm root.day and were up to five times higher than published inflows for winter wheat. At 30–100 cm sugar beet and winter wheat inflows were generally similar. The 0–30 and 30–120 cm layers contributed about 80 and 20% respectively of the total water use by sugar beet while no uptake was recorded below 110 cm. Previous studies have shown that sugar beet often takes up water from soil deeper than 110 cm, although it is not unknown for the depth of water removal to be restricted.

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.

The response of cotton (Gossypium hirsutum L.) to chilling temperatures has been documented mainly for germinating seeds and young seedlings (Christiansen, 1963; Christiansen & St John, 1981; Guinn, 1971; Sellschop & Salmon, 1928). Ratoon (known also as stub or biennial) cotton offers an opportunity to study the chilling injury of mature plants under field conditions. Observations showed that ratooning plants suffer stand loss during the winter. However, the surviving plants recover and start growing vigorously when temperatures rise, early in the following spring (Ellern, 1966; Evenson, 1970; McClintic, 1981).