A method for investigating the thermoperiodicity of crop plants is described. On the basis of our experimental results and published data, crop plants were assessed to establish whether they were thermoperiodic or not. Tomato and maize were classified as thermoperiodic species. Cucumber, beans, peas, oats and wheat were not thermoperiodic. Strategies for climate control based on the estimation of optimum temperature are proposed. These can be used to minimize energy consumption and, together with other environmental treatments, could optimize the yield of glasshouse crops.

A field experiment was conducted at the experimental farm of the Central Soil Salinity Research Institute, Karnal, India during 1992/93 to evaluate the effects of rates and methods of manganese application on the yield and nutrition of wheat on a reclaimed and intensively cropped Mn-deficient sodic soil (pH = 8·7, exchangeable sodium percentage = 18 and DTPA-extractable Mn = 2·7 mg kg-1). There were eight treatments which consisted of a control (no Mn application), three rates of 25, 50 and 100 kg MnSO4. H2O ha-1 each either as a basal or a top-dressing at first irrigation or a foliar spray of 1·0% MnSO4.H2O at crown root initiation (CRI), tillering and jointing stages. Grain and straw yield of wheat increased significantly with increasing rates of Mn application. A foliar spray of Mn produced a significantly higher yield than 25 and 50 kg MnSO4. H2O ha-1 applied either as a basal or a top-dressing but similar to that from 100 kg MnSO4.H2O ha-1. Efficiency of Mn was higher with a foliar spray (82·6 kg grain kg-1 Mn) than with soil application (4·4–6·4 kg grain kg-1 Mn). Application of Mn increased its concentration in the crop but decreased Fe and Cu crop concentrations. Grain yield had a significant positive correlation with the Mn content of the grain (r = 0·72) and straw (r = 0·78). Grain yield was positively correlated with 1000-grain weight (r = 0·90). Recovery of applied Mn ranged from 28·1 to 33·0%.

A field experiment was conducted at nine sites in England (1991–94) to compare six sown species of cover crop and natural regeneration in terms of nitrogen uptake and effect on response to applied N by a subsequent spring barley crop. The success and extent of cover crop establishment varied among sites and was insignificant in two. This may be associated with the relatively late sowing of the cover crops, the earliest site being sown on 27 August and the latest on 19 October. Dry matter (DM) yield of the sown cover crop at time of incorporation was related to sowing date, earlier sowing giving the higher yields. Maximum total DM yield and N uptake by the above-ground portion of cover crops were 1280kgDM/ha and 38 kg N/ha respectively. The extent of N uptake by the cover crops appeared to be related to the success of establishment rather than to the level of soil nitrate-N at the time of their sowing. Effects of cover crop incorporation on the subsequent spring barley were small. There was no evidence for any positive effect of the cover crop on N supply to the barley. In one trial, incorporation of forage rye significantly reduced grain yield of the barley by 0·7–1·2 t/ha compared to other cover crop species.

Two long-term field experiments were conducted on a clay soil near Carrickfergus, County Antrim from 1983 to 1993. The main experiment tested the effects of lime (0,4, 8 and 12 t/ha applied in 1983), N (160 and 320 kg N/ha per year as ammonium nitrate/calcium carbonate), sward type (permanent pasture and perennial ryegrass reseed) and initial soil pH (5·1 and 5·5) on the yield and composition of herbage for 10 years. The secondary experiment studied the interaction between lime (0, 4 and 8 t/ha applied in 1985) and N (80 and 160 kg N·ha per year) for 8 years. In both experiments the plots were fertilized three times each year for three cuts of herbage. In the main experiment, dry matter (DM) yield and N offtake over all 10 years depended little on initial soil pH. Over all cuts and years, DM yields of both sward types increased with lime. Responses peaked after 3 years and were largest with the first cut of the reseed at the lower rate of N fertilizer. Over the first 6 years after lime application, the average responses from the reseed at the lower rate of N fertilizer to 4, 8 and 12 t/ha of lime were 1·02, 1·85 and 1·65 t DM/ha per year respectively at the first cut. At the higher rate of N fertilizer, the response in DM yield of the reseed to lime averaged 0·91 t/ha at the first cut over the same period. In the last 3 years of the experiment, lime had no effect on DM yield even though soil pH ranged from 5·0 to 6·3 A significant response in N offtake due to lime only occurred at the first cut. Responses at the first cut averaged over all treatments were 3·5, 6·5 and 6·6 kg N/ha per year for 4, 8 and 12 t/ha of lime respectively. In the secondary experiment, responses to lime were again mainly at the first cut. There were few lime × N interactions in either experiment. Liming increased N availability either by increasing mineralization of soil N or by improving the uptake of ammonium and nitrate by roots. The effects of soil pH and Ca supply on these two processes are difficult to separate. All rates of liming at both N rates were cost-effective for the reseed, but only the lower rates of liming at 160 kg N/ha per year were cost-effective on permanent pasture. Current recommendations for liming grasslands should continue, particularly for swards reseeded with perennial ryegrass.

A split split-plot experiment was conducted in the 1986 and 1987 cropping seasons in three major yam-growing areas in southeastern Nigeria to assess the performance and yield stability of six cultivars of white yam (Dioscorea rotundata Poir). Location, fertilizer and cultivar, as well as some of their interaction effects, significantly affected tuber yields.

The best location for yam production, based on the overall performance of the cultivars, was the sub-humid Guinea savanna, followed by the humid forest-regrowth and then the transitional forestsavanna zone. Except for two cultivars, which performed best in their source locations, all other cultivars yielded best at a different location. Thus, at present, these cultivars are not grown in those areas to which they are best suited. This makes it desirable to test exogenous cultivars in new areas. In terms of yield stability, however, the two cultivars originating from the humid forest-regrowth area gave the most stable yields across the three diverse environments considered. Although they did not give the highest tuber yields at all the locations, their overall yields were above the mean yields forall the cultivars. The most suitable cultivars were recommended for each ecological zone, on the basis of the observed interaction effects.

Effects of temperature, hydrogen ion and substrate concentrations on conjugation of l-chloro-2,4-dinitrochlorobenzene by glutathione S-transferase from susceptible and dichlorvos-resistant strains of cotton aphid (Aphis gossypii Glover (Homoptera: Aphididae)) were evaluated. Enzymes from both strains had common optimum temperature and substrate concentration values of 30 °C and 10 mM respectively. Also, while enzyme activity of the susceptible strain peaked at pH 7·2, that of the resistant strain showed complete linear dependency up to pH 8·0. Of four subcellular fractions, the 100 000 g supernatant (soluble fraction) gave the highest enzyme activity in both phosphate and Tris/HCl buffers. There was no linear relationship between insecticide application frequency and production of enzyme activity in the susceptible strain but there was a very high positive correlation between these two parameters in the resistant strain.

The effects of different rates of N fertilizer (0–180 kg N/ha) were tested on the growth, yield and processing quality of sugarbeet in 34 field experiments in England between 1986 and 1988. The experiments were performed using soil types, locations and management systems that were representative of the commercial beet crop in the UK. The responses obtained showed that current recommendations for N fertilizer use are broadly correct, but large differences occurred on some soil types, in some years, between the recommended amounts and the experimentally determined optima for yield. The divergence was largest when organic manures had been applied in the autumn before the beet crop. Calculations using a simple nitrate-leaching model showed that much of the N in the manures was likely to be leached, the extent of leaching being much less if the manure application was delayed until spring. In these circumstances, spring measurement of inorganic mineral N in the soil could improve fertilizer recommendations. In situations where higher than optimum rates of fertilizer N were used, the extra N had little effect on yield. Increasing the rate from 0 to 180 kg N/ha increased the amount of nitrate left in the soil at harvest by only 8 kg N/ha. The amount of inorganic N released into the soil from crop residues at harvest increased by 50 kg N/ha with N application rate, and the fate of this N has not been established.

Pod wall photosynthesis is known to contribute to nearly one-third of rape (Brassica napus) seed weight. The relationship between the number of seeds and the growth of the pod wall, and the effects of single and mixed applications of gibberellic acid (GA), naphthyl acetic acid (NAA) and benzyl adenine (BA) on development of the pod wall were, therefore, examined in potted plants of spring rape under glasshouse conditions.

The size and weight of the pod wall were closely associated with the number of seeds per pod, and a stronger development of tissues was observed in the presence of seeds. Application of BA alone or in combination with GA (GA + BA) to emasculated flowers induced the development of parthenocarpic pods similar in size and shape to the untreated seeded pods. NAA applied singly or in mixtures produced abnormal pods. BA enhanced cell division in all tissues while GA and NAA caused expansion of parenchyma in the mesocarp. Application of BA or GA + BA at 1–5 rather than at 11–15 days after flower opening led to the development of bigger pods. Younger pods responded more than the older ones when they were treated simultaneously. BA or GA + BA application to nonemasculated flowers on the terminal raceme delayed senescence in both basal and apical pods but it increased pod size only in the latter. The balance of cytokinins and gibberellins within a pod seems to play an important role in regulating the growth of the pod wall.

In laboratory tests using stable manure consisting of wheat straw and slurry, ammonia emission was found to have two peaks corresponding to the population dynamics of proteolytic bacteria and amino acid-degrading bacteria respectively. Cumulative ammonia emissions over 14 days were 0·8–23·2% of the initial total nitrogen (Nt) and were both abiotically and biotically induced. Changes in pH had the most significant effect on the abiotically induced ammonia emissions. After 14 days of decomposition, at pH values of 6·0 and 7·5, abiotically induced emissions remained close to the limit of detectability, whereas at pH 9·0 as much as 9·8% of the initial Nt was lost. An increase in storage pressure from 0 to 400 and 800 kp/m2 generally decreased the biotic emissions to 9·6, 2·8 and 2·3%; while increasing the amounts of litter (2·5, 5·0 and 15·0 kg straw/LAU per day) led to a decline not only in the biotic (17·1, 12·8, 3·5%) but also in the abiotic emissions (6·1, 5·5, 1·6%). Varying the temperature (20, 30 and 40 °C) resulted in biotically induced emissions of 7·9, 11·7 and 11·6%, respectively, and abiotically induced emissions of 1·1, 1·4 and 2·2% of the initial Nt. At temperatures of 30 and 40 °C, the amount of microbially digested sources of carbon available was obviously sufficient to permit almost total reincorporation of NH4+ from 4 days onwards.

The capacity for gas production by three sources of inocula was evaluated at the University of the Azores between 1993 and 1994. The sources were: liquor from the rumen of sheep and slaughtered cattle and a suspension of sheep faeces. The highest gas production was observed in the liquor obtained from sheep rumen. Lower production(p ≤ 0·05) was observed in the rumen liquor obtained from slaughtered cattle, and the lowest results (p ≤ 0·05) were obtained with the suspension of faeces from sheep.

Reindeer calves(Rangifer tarandus tarandus) were used in parallel feeding trials with two different qualities of round-bale timothy silage in September 1992 (summer) and April 1993 (winter) in northern Norway, to determine the effect of season on their food intake and ability to utilize silage of different fibre contents. The silages were prepared from first-cut (FC) and regrowth (RG) timothy. The FC silage contained (on a dry matter (DM) basis) 12·3% crude protein, 30·4% cellulose and 6·2% water soluble carbohydrates (WSC), whereas the RG silage contained 14·3% crude protein, 18·7% cellulose and 30·0% WSC. For each trial, six male calves were taken directly from a natural range and divided into two groups of three animals. One group was offered FC silage and one RG silage ad libitum, for 46 days. Mean daily DM food intake (g/kg liveweight) was not significantly different in summer compared to winter(P > 0·05), but significantly higher in the animals fed RG silage compared to the animals fed FC silage (P < 0·0001). The apparent digestibility coefficient of DM was high for both silages both in summer and winter, ranging from 74·4 to 86·6%. However, the digestibility in winter was significantly higher than in summer(P < 0·002) and the digestibility of RG silage was higher than that of the FC silage (P < 0·009). The ruminal VFA concentration was significantly higher in winter than in summer (P < 0·03) and in the animals fed RG silage (range 55·3–104·9 mM) compared to the animals fed FC silage (range 35·2–61·7 mM) (P < 0·002). In spite of the high digestibility of both the FC and RG silages, the nitrogen balance was significantly higher in the animals in winter compared to summer(P < 0·0001) and in the animals fed RG silage compared to the animals fed FC silage(P < 0·0001). Thus, utilization of grass silage in reindeer appears to be influenced both by season and by plant quality.

Pure swards of chicory (Cichorium intybus) and perennial ryegrass {Lolium perenne)were grown at Palmerston North, New Zealand. They were cut daily and fed fresh at 2 kg dry matter (DM)/day to ten hand-reared rumen fistulated castrated red deer stags kept in metabolism crates in April and October 1994. The efficiency of particle breakdown during the time allowed for rumination (<C.PART>) to below the critical size required to leave the rumen (passage through a 1 mm sieve) and jaw activities (i.e. eating and ruminating) were measured. Total eating time and the number of eating bouts were similar for deer fed each forage, but deer fed chicory had a greater chewing rate during eating (97·4 v. 81·0 chews/min), and a higher number of chews/g DM eaten (36·2 v. 31·5). Deer fed chicory had lower total ruminating time (30 v. 257 min/22·5 h), lower number of boli ruminated (38 v. 440/22·5 h), lower number of rumination bouts (5·4 v. 16·2/22·5 h) and less chews per minute ruminating (16·5 v. 44·3) than those fed perennial ryegrass. Of the ten deer used to measure (<C.PART>), only four ruminated when fed chicory compared with nine when fed perennial ryegrass.

Deer fed chicory had a higher efficiency of particle breakdown (<C.PART>; 0-64 v. 0·42), higher fractional degradation of particles > 1 mm (9·2 v. 5·1 %/h) and faster fractional disappearance of total DM from the rumen (10·2 v. 5·3 %/h). All three measurements for chicory were similar in deer that did or did not ruminate, but with perennial ryegrass, all values were considerably reduced in the deer that did not ruminate.

It was concluded that chicory can be broken down faster in the rumen, with less rumination being required than for perennial ryegrass, and that some deer (60%) could break down swallowed chicory to below the critical particle size without ruminating at all. The faster clearance of DM from the rumen explains the high voluntary feed intake (VFI) of deer grazing chicory. Future research needs to be done to partition rumen fractional disappearance rate into its components, rumen fractional degradation rate and rumen fractional outflow rate in deer fed chicory and perennial ryegrass.

Genetic variation was analysed in cattle from the central area of Spain, in 1993, for the following microsatellite loci: CYP21, BOVTAU, ETH131, ILSTS002 and ILSTS005. The breeds studied were Morucha (n = 104), Sayaguesa (n = 60), Brown Swiss (n = 90) and two different populations of Avilena-Negra Iberica (n = 134 and n = 104). Morucha cattle showed the largest number of different alleles (66), whereas Sayaguesa exhibited the lowest (38). Values of number of observed alleles, gene diversity, polymorphism information content and effective number of alleles indicated that the microsatellite showing the highest variability was CYP21, followed by ETH131, ILSTS002, BOVTAU and ILSTS005.

The efficiency with which llamas and sheep digest various roughages was compared in France in 1993. Six llamas (three of which were rumen-cannulated) and six rumen-cannulated sheep were simultaneously given three different diets: (i) a grass hay low in N content (HLN), (ii) the same hay with barley, representing 25% of the total dry matter (HLN+B) and (iii) a cocksfoot grass hay, rich i n nitrogen (HRN). Daily forage dry matter intake was slightly, but not significantly, lower in llamas (55·9 g/kg W0·75 ν. 60·3 g/kg W0·75 in sheep). Intake behaviour was similar for the two species except that the number of rumination periods was lower with llamas (P < 0·05). With all diets, the digestibility of both organic matter and cell walls (estimated from neutral detergent fibre) was higher in llamas (Animal Nutrition, 9700 Angra do Heroismo, Azores, Portugal 5+6 and +6+5 units respectively, P < 0·001). The higher digestibility in llamas may be related to the slightly lower level of intake and to the lower dry matter turnover rate in the forestomachs compared to sheep (3·9%/h ν. 5·3%/h, P < 0·01). However, in sacco degradation of both hays were higher in llamas' forestomachs after 24 h of incubation (+6+5%, P < 0·01) and 48 h (+4+3%, P < 0·05) than in sheep. The high microbial efficiency of the llamas can be ascribed to the physical and chemical characteristics of their forestomach contents, which had a higher liquid turnover rate (+1+4%/h, P < 0·05), a lower volatile fatty acid concentration (P < 0·01), a higher and more constant pH (P < 0·01) than in sheep and a greater buffering capacity when pH was close to neutral. These results suggest the greater ability of llamas to control the physicochemical conditions of their forestomach contents to digest cell walls efficiently and to minimize the negative effects of concentrate supplementation.

Two experiments were done in Mexico (1992–93) to determine the response of goats to different periods of feed restriction on liveweight, organ weights and tissue composition. In each, the weight, body condition and daily dry matter intake (DM1) of two groups of 12 female, adult, non-lactating, non-pregnant, Nubian crossbred goats were recorded for 7 weeks (stabilization period; SP), to allow the animals to reach and maintain their liveweight and body condition. At the end of the SP the animals in Expt 1 (RP1) were feed restricted for 18 weeks and for 36 weeks in Expt 2 (RP2). Animals were divided into three groups receiving either 100 (FL1), 80 (FL2) or 60% (FL3) of the levels of DM1 previously observed. At the end of each experimental period all animals were slaughtered, carcass weights were recorded and viscerae were weighed.

A sample of the soft tissues was chemically analysed. There were no significant changes in body condition in either experiment (P > 0·05). None of the feeding levels had an effect on carcass weight or the chemical composition of soft tissues (P > 0·05). Liver weights (as a proportion of slaughter weight) were significantly different among goats fed at different feeding levels in both experiments. The results of this study show the adaptation capacity of adult goats to medium and long term malnutrition, and the importance of the liver as a source for the generation of energy and for sustaining protein turnover. This could be especially important for goats grazing in arid and semiarid zones where dry periods can last for months and feed availability is therefore sometimes limited.

Plant species mixtures vary in total herbage mass (total availability) and the fractional cover (horizontal availability) and bulk density or height (vertical availability) of the component plant species. The expected diet selection response of sheep to changes in these three components of availability was tested in an artificial food environment by releasing flocks (of three ewes) onto a vegetation-free field that contained patches (plastic bowls) of preferred and less preferred sheep pellets for 15 min and observing their behaviour. One hundred patches (bowls) were laid out at equidistant intervals on a 50 × 50 m field. The patches were filled with either cereal (preferred) or lucerne (less preferred) pellets in different amounts to create in a factorial design two levels of total availability (10000 g or 15000 g of pellet in the field), two levels of horizontal availability (20 or 50 of the 100 patches contained cereal pellets, the rest contained lucerne pellets) and two levels of vertical availability (the mass of pellet in the cereal patches was either 10 or 80% relative to the mass of pellet in the lucerne patches). All patches were positioned at random in the field. Although, in all cases, the proportion of cereal pellets in the diet was higher than that expected if the sheep had foraged at random, it was sensitive to the horizontal and vertical availability of the food resource. The proportion declined as the horizontal availability declined from 50 to 20 patches, but only at 10% not 80% vertical availability. The lower proportion for this treatment combination arose because sheep ate from a higher proportion of the lucerne patches that they encountered and rejected more of the cereal patches that they encountered. Total availability did not affect diet selection. From these results it is pointed out why conclusions of diet selection experiments that do not consider how the food alternatives are distributed horizontally and vertically can be equivocal. The effect of variable levels of selective grazing in relation to changing horizontal and vertical availability of plant species on the species composition of plant communities is considered.