The use of exogenous hormone treatment as a means of increasing the efficiency of animal production has, in general, been rather poorly received by both the public and government agencies. This antipathy towards hormone treatment has tended to direct research effort into finding less contentious ‘hormonefree’ methods of improving animal production. Over the last 10 years, immunological manipulation of the endocrine system has emerged as an attractive possibility in this search. In this review we briefly outline three approaches under current consideration, whereby growth hormone (GH) concentrations or activity are modified. These methods involve immunological manipulation of GH release, use of antibodies as GH mimics and antibody-mediated enhancement of GH action.

Grain sorghum (Sorghum bicolor L. Moench) was grown in Texas in 1985 at a constant population density of c. 6·6 plants/m2 in rows 0·5, 1·0 and 1·5 m apart and with the soil profile at field capacity at planting time. Dry matter production and yield were least at the widest spacing, principally because of a reduction in number of tillers. Dry matter accumulation was in direct proportion to the amount of light intercepted and largely independent of spacing between rows, with a conversion coefficient of 1·71 g dry matter/MJ energy intercepted. The most widely spaced crop used less water but not in proportion to the extent that ground cover was reduced. Water use efficiency was also less in the most widely spaced crop, probably because of heat advection from the bare soil between rows.

Shading treatments of 50% of the incident radiation were applied to the semidwarf wheat cultivar Leones INTA before and after anthesis in two field experiments in Argentina in 1987 and 1988. The treatments reduced biological (above-ground dry matter) yield, grain yield and number of grains/m2. Number of grains/m2 was closely and linearly correlated with ear dry weight at anthesis and with the photothermal quotient, calculated from 20 days before to 10 days after anthesis. Grain yield was sink limited, and the shading treatments reduced sink strength. The contribution of preanthesis assimilates to grain yield was smaller in the shaded crops than in the unshaded controls; in unshaded crops, almost 40% of grain yield was contributed by preanthesis assimilates whilst in preanthesis shaded crops this contribution was negligible. The proportion of preanthesis assimilates contributed to the grain was closely related to the decrease in stem dry weight during grain filling. The effects of shading on main stems and tillers were the same.

Dry matter production, transpiration and transpiration efficiency (DM production: transpiration) were studied during vegetative growth of oats over 4 years (1976–77 and 1982–83) in field experiments on loess-derived soils near Gottingen, Germany, under different weather conditions. Shoot and root dry matter and leaf area were measured or estimated regularly during the season. The rate of evapotranspiration including intercepted rain water by leaves (ET) was determined during five consecutive growth stages from the water balance in the 2 m soil profile. The rate of soil evaporation (E) and the rate at which rain water was intercepted by leaves (I) were estimated separately in order to attain T, the transpiration rate (T = ET–E–I), or IT, the rate of interception of rain water by leaves plus transpiration (IT = ET–E). The potential evapotranspiration rate (ETp) was derived from meteorological parameters.

During the early stages of oat development (seedling growth and tillering), T and IT, related to ETp, were higher than expected from crop growth rate (CGR), calculated for shoot and total dry matter including roots, respectively. It was concluded that, at a leaf area index (LAI) of < 3·4, part of the solar radiation was converted to sensible heat between plant rows, increasing ETp near the ground and hence T, but not CGR. Because of this, LAI influenced IT efficiency and the crop-specific constant m of de Wit's formula. IT efficiency was not only dependent on LAI but also on ETp. Grain yield was related to both cumulative IT (ITC), normalized by ET, and leaf area duration during the period from anthesis to harvest. Increased leaf area duration after anthesis may partly explain the higher yields obtained with modern high-yielding varieties of small-grained cereals.

The minirhizotron technique was evaluated for estimating root length density in potatoes (Solanum tuberosum ‘Record’) by comparing observations in angled 45° glass tubes with corresponding root length densities obtained by (a) destructive core sampling, and from (b) counts of root tips on the soil face of excavated trenches. Measurements were made in a field experiment in Bedfordshire, UK, in 1985, with shallow and deep cultivation as variables, and in a glasshouse trial.

Only at depths below 0·3 m did root lengths observed with minirhizotrons reflect at all closely those estimated from core sampling and even then there was a tendency to overestimate root density. In the surface cultivated layers, where 80–90% of the total root length was present, results from minirhizotrons were unreliable, probably because of poor soil–tube contact and, in soils which shrink on drying, preferential root growth at the interface between the soil and the glass.

Minirhizotrons can provide a realistic estimate of the rate of root growth of potatoes with depth over time when compared with maximum depths of water extraction, but appear to be unreliable for providing a quantitative measure of total root length density.

The effects of deep tillage and no-tillage on soil physical properties and wheat yield following rice were compared with conventional tillage at three irrigation rates (irrigation water:open pan evaporation ratios of 0·6, 0·9 and 1·2) in 1982–85 at the experimental station of the Punjab Agricultural University, Ludhiana. Deep tillage decreased soil bulk density and penetrometer resistance, and increased depth of rooting, profile water use and wheat yield. No-tillage adversely affected all these variables. The tillage effects varied with amount and distribution of rain during the cropping season.

Field experiments in 1987 and 1988 on peaty-loam, Mn-deficient soils of the Adventurers series in Cambridgeshire, UK, tested the response of sugarbeet to three forms of manganese fertilizer supplied as foliar sprays. The influence of a wetter and an adjuvant on manganese absorption and growth was also investigated.

Cutonic and chelated forms of Mn, when applied at standard rates, were inefficient at increasing Mn concentrations in plants and alleviating deficiency symptoms during early summer. Mn concentrations in foliage increased rapidly after spraying with manganese sulphate, and most of the deficiency symptoms disappeared. These benefits were usually enhanced when manganese sulphate sprays were used with an adjuvant.

Averaged over both years, yield without Mn was 8·83 t sugar/ha; the largest yield, 9·56 t/ha, was obtained with manganese sulphate plus adjuvant. Smaller benefits were obtained with the other forms of Mn. The adjuvant, when used with chelated Mn, appeared to depress sugar yields in both years. The likelihood of reducing the number of sprays required to control Mn deficiency on Fen soils was improved by using an adjuvant with manganous sulphate sprays.

A screenhouse study in Haryana in 1986/87 evaluated the effect of boron on the wheat cultivar WH147 grown in pots in a sandy soil at three salinities. Before sowing, 0–9 mg B/kg soil was added. Without added B the crop produced significantly more grain at electrical conductivity of the saturation extract (ECe) 6 dS/m than at other salinities, but at ECe 8 dS/m yields were similar to those in nonsaline (ECe 0·8) soil. Grain yield in nonsaline soil was not affected significantly even at the highest concentration of added B, even though at the boot stage the shoots had accumulated as much as 307 mg B/kg. At ECe 6 and 8 dS/m, grain yield was significantly less with 3 and 1 mg added B/kg, respectively, than without added B, even though the B concentration in the shoots was only 72 and 31 mg/kg, respectively. The results indicated that B tolerance decreased with increasing salinity of the soil, even though B absorption by plants was 24–62% less in saline than in nonsaline soil at similar B concentrations. As B and salinity often occur together, threshold values of B in soil and plants for optimum growth of wheat will differ with the ECe of the soil. The results suggested that Ca:B ratio in wheat straw is not a reliable indicator of B toxicity in the soil.

Applications of nitrogen and a plant growth regulator (mepiquat chloride and ethephon) were used to manipulate stem structure and induce differing degrees of damage due to leaning and lodging in six cultivars of winter barley grown in Belfast, UK, in 1986/87. Weighted incidences of leaning and lodging were combined to give an index indicating damage susceptibility of the cultivars. The index was very high (70) in Pipkin and ranged between 1 and 18 in the other cultivars. Differences between cultivars in number of internodes, plant height and stem weight did not explain their differences in resistance to damage. However, dry weight per unit length ranged from 2·35 and 2·34 mg/mm in the strongest cultivars, Panda and Jennifer, respectively, to 1·75 mg/mm in the weakest cultivar, Pipkin.

Nitrogen application increased plant height but did not affect dry weight/main stem, so that dry weight/unit length of stem decreased. The growth regulator treatments reduced plant height and although dry weight/stem did not decrease significantly, dry weight/unit length of stem was similar in treated and untreated plots.

Dry weight/unit length has potential as an objective indicator of straw strength in winter barley cultivars and could be used in cultivar evaluation in the absence of damage in field trials.

Results are reported from nine field trials carried out in 1985/86 and 1986/87 aimed at identifying plant traits which are associated with high yield in barley in low-rainfall Mediterranean areas. Thirtyseven two-rowed and 35 six-rowed genotypes, representing the known diversity in traits considered to be useful, were compared in trials at three sites differing in expected annual rainfall (212–328 mm) in northern Syria, and in droughted and irrigated trials at Cambridge, UK. Yield, its components and other morphological and developmental traits were measured and correlations calculated.

Grain yields of the two- and six-rowed groups of genotypes were similar at all sites except in the irrigated trial in Cambridge, where the six-rowed genotypes gave the highest yield. Aside from the known difference in number of ears and number of grains/ear between two- and six-rowed genotypes, the simple correlations between grain yield and measured traits suggested that important traits for high yield in two- and six-rowed genotypes in dry environments were prostrate habit, vigorous seedling growth, good ground cover, early ear emergence, many ears/m2 and large grains. In the two-rowed genotypes, short stature and a short grain-filling period were also important, while in the six-rowed genotypes, tall stature, high straw yield, many grains/ear and long peduncles were important. Correlations of these characters with an index of drought susceptibility and with yield adjusted for yield potential and date of ear emergence supported the conclusions based on the simple correlations.

The physiological basis of the correlated traits is discussed and the implications for breeding are considered.

Agronomic research was carried out on upland rice in Toledo District, Belize, in 1979–86, with the objective of improving returns from the traditional system of shifting cultivation and of examining the potential for reducing the demand for new land by cropping for more than one season. The rice was grown in the wet season on land cleared from forest by slash and burn, using a traditional planting technique, placing seed in holes made with a pointed stick.

In a series of fertilizer experiments, in which rice was grown for up to 7 consecutive years, urea and triple superphosphate both increased grain yield, whereas muriate of potash had no effect. Mean yield in the fifth year was 85 % of that in the first. Urea and triple superphosphate both increased the number of full grains/panicle.

A slash and mulch weed control treatment before sowing resulted in low yields of grain in the third year; yield after the use of propanil and 2,4-D (after sowing) was, on average, 77% of the yield after hand weeding; omitting weed control after sowing led to very low yields, particularly in the second and third years.

In the varieties Bluebonnet and C22, grain yield was increased by reducing the distance between stations, particularly where 6, rather than 15, seeds were sown per station. Reducing the distance between stations increased the leaf area index during crop development and the number of panicles/m2, which more than counterbalanced reductions in the number and area of leaf blades per plant, the number of panicles per plant and the number of full grains per panicle. However, the yield/kg of seed sown and per hour spent planting was greatest at the widest spacing. C22 produced more panicles per plant and a greater weight of grain per plant and per hectare than Bluebonnet.

It was concluded that returns from the traditional system can be improved and the demand for new land reduced.

A collection of 168 accessions belonging to 62 species and subspecies was evaluated in Cordoba, Spain, in 1985 for fatty acid composition of the seed oil. Linoleic acid content of seed produced in Cordoba (mean temperature during seed formation 27·9 °C) was compared with that of seed obtained under much cooler environmental conditions in Montpellier, France, (mean temperature 19·5 °C). Linoleic acid content ranged from 27·3 to 83·7% in the warm environment and from 45·9 to 88·7% in the cool environment with average values of 64·3% and 75·0%, respectively. Twenty-three species with linoleic acid values of > 70% in both environments were evaluated again, in 1989 in Cordoba (mean temperature 31 °C). Twelve wild species showed consistently high and more stable linoleic acid contents than the cultivated control and could be readily used in breeding programmes to improve oil quality.

The average yields of a 3-year field experiment (1985/86–1987/88) on a mollisol at Pantnagar showed that, at 87 kg N/ha, applying urea supergranules (USG) gave 0·47 t/ha more rice grain than split application of prilled urea (PU). The data also showed that, at this rate of N, one-third (29 kg N/ha) of inorganic N can be substituted by fresh straw (wheat or rice) applied at planting to give similar rice yields. However, at a total of 58 kg N/ha, 29 kg N/ha applied as straw with 29 kg N/ha of PU or USG reduced yield compared with 58 kg N/ha of PU or USG alone, except in 1986/87. Yield differences were attributed to differences in number of panicles/m2, N uptake by the crop and mean wet soil NH4+-N obtained at various stages of crop growth during 1986/87 and 1987/88. Wheat grown after rice in 1985/86 and 1986/87 showed significant residual effects in plots with straw application and these were correlated with the rate of hydrolysable organic N (HN) obtained after rice.

Three rates of phosphate (0, 25, and 60 kg/ha P2O5) were applied to phosphorus-deficient native grassland at Tel Hadya, in northern Syria, and biomass productivity, botanical composition and number of legume seeds in the soil were monitored for five seasons (1984/85–1988/89). 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 seasons of the experiment; in the fifth season, the low and high stocking rates were increased to 1·1 and 2·3 sheep/ha per year, respectively. The experimental site was typical of native grassland 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 phosphorus, even as low as 25 kg P2O5/ha, alleviated the deficiency in soil P and resulted in improved pasture production, even in dry years. Legume production showed the greatest response to P, increasing by 0·3–3 times the production of the control treatments. By the fifth season, legume seed mass had increased threefold and number of seeds sixfold in the P-treated plots, compared with the first season, while in the control plots there was little change. Rain-use efficiency on the P-treated plots was more than double that of the controls by the fourth and fifth seasons.

Practical application of the results depends on whether (i) legumes are as frequent in native grasslands, as a whole, as they are at Tel Hadya, (ii) the P deficiency observed at Tel Hadya is widespread, and (iii) grazing of communally owned grasslands can be controlled. It is suggested that all three criteria will often be fulfilled and, therefore, that grassland productivity in west Asia could be substantially increased. Furthermore, the results suggest that above-ground cover and soil organic matter will also increase after P application, both of which will help to reduce soil erosion and thereby increase the sustainability of livestock production in west Asia.

Seeds of the Brussels sprout cultivar Asmer Aries having low vigour as a result of ageing emerged more slowly when sown in module trays and had slightly lower final emergences than seeds which had not undergone ageing and were of high vigour. Low seed vigour also resulted in the production of seedlings which were shorter and more variable in height at the first-leaf stage. Once the seedlings reached the transplanting stage there was greater variability in the fresh and dry weights of seedlings produced from seeds having low vigour, although the mean seedling weights differed little from those produced by high-vigour seeds. Similar observations were made for samples of commercial seed of cauliflower, Brussels sprouts, Dutch cabbage, red cabbage and calabrese provided by vegetable transplant propagators and in use in 1988. Low-vigour seeds again emerged more slowly with low final emergence and produced smaller and more-variable seedlings. The implications of these observations for the production of vegetable seedlings for transplanting are discussed.

Components of the N cycle were studied at Hurley, UK, in 1985–87. In grass-clover (Lolium perenne and Trifolium repens) swards, grazed at three intensities, low total inputs of N were associated with low outputs and losses of N. Nevertheless, the flows (intake and excretion) of N through animals were substantial and gave rise, at the higher intensities of grazing, to an acceptably high agricultural output per hectare. This was considered evidence of a fast and efficient recycling of N between plants, animals and soil. The release of N to the environment (as nitrogenous gases and nitrate) was substantially less from the grass–clover swards than from a grass sward fertilized with 420 kg N/ha, and this was at the expense of only 20% loss in production. The mechanisms which might account for the high efficiency of utilization and recycling of N in grass–clover swards are discussed in the context of the balance of the supply of C and N to plant and soil biomasses under grazing. The results confirm that optimizing agricultural output in grass–clover swards has little adverse effect on the environment, but the importance to this end of sustaining a large proportion of N-deficient grass in grass-clover swards is emphasized.

The nodal structure of white clover plants was studied in New Zealand in pastures stocked at 22·5 ewes plus lambs/ha and either continuously or rotationally grazed. Intact plants were sampled every month for a year (1988/89) by removing turves and washing out the plants. Plants were classified according to the degree of branching as first (unbranched, single-stolon plants), second, third or fourth order (plants with at least one quaternary branch). Where possible from each turf, four plants of each of the four branching orders were sampled and, for each stolon of each plant, nodes were ascribed positions numbered from the stolon apex, and the position of nodes with a live branch and the total number of nodes/stolon were recorded.

The mean number (and 5 and 95% quantiles) of nodes/plant was 15·7±0·26 (9, 24) for the firstorder, 42·2±0·90 (18, 81) for the second-, 91–4±2–13 (37, 163) for the third- and 163·7±7·49 (63, 367) for the fourth-order plants. Grazing management and month of sampling had minor effects on these values. The mean number of nodes/stolon within branched plants depended on the category of the stolon within a plant, the presence or absence of an apex and on the branching order of the plant. The first 10,.15, 20 and 25 node positions accounted for, respectively, 64, 79, 90 and 95% of total nodes in the field population and 39, 62, 79 and 90% of all branches. Successful branch initiation occurred at recently formed nodes at positions 3–10, emphasizing the significant contribution of such nodes in growth and persistence of white clover in grazed swards.

Where grazing management allows little consumption of stolon and there is adequate moisture, growth and fragmentation maintain the mean node composition of the branching orders reasonably constant throughout the year. Thus, any seasonal variation in the overall mean number of nodes/plant in a population must be driven by seasonal changes in the distribution of plants among the branching orders. However, there was evidence of mean number of nodes/plant decreasing in the third and fourth orders after dry conditions.

Using an indeterminate cultivar, Bourdon, and a determinate selection, 858 (provided by Plant Breeding International, Cambridge), of winter field bean, the effect of plant population density on yield was investigated in field trials at the University of Nottingham at Sutton Bonington in three consecutive seasons beginning in 1985/86.

Plant morphology had no effect on the optimum plant density, which for both entries lay between 10 and 20 plants/m2. Bourdon yielded significantly more (2 t/ha, on average) than 858 and this was attributable to more pods/pod-bearing stem, more seeds/pod and heavier seeds. Selection 858 was also less winter hardy.

Yield was most closely correlated with number of seeds/plant, but other components were almost as important, highlighting the plasticity of yield in Vicia faba and the difficulties in attempting to increase yield by selecting for particular components of yield.

In contrast to spring beans, the indeterminate cultivar of winter field bean produced as many branches as the determinate entry and both produced fewer branches at higher densities. There was no difference between the two growth habits in the relative contribution of each stem class to the yield of the whole plant. Higher-order branches contributed less than the main stem to final yield.

The assimilation and distribution of carbon in laterally spreading white clover plants was quantified in a controlled environment using CO2 exchange rate measurements and 14C as a tracer. Plants were restricted to three mature leaves on the main stolon apex, and the movement of 14C from these leaves (and one immature, but carbon-exporting, leaf) to meristematic zones throughout the plant was determined by detailed plant dissection.

Sinks throughout the plant drew small to moderate proportions (typically 1–8%) of the 14C exported by all mature leaves. The three mature leaves displayed similar export patterns, and no specific source-sink relationships involving any of these leaves were observed. However, 14C exported by the developing leaf moved predominantly to the main stolon apex, and to adjacent young stolon tissue. Estimated respiratory losses over 24 h accounted for 40–49% of the 14C fixed. Of the total amount of C exported by all four leaves and utilized in new growth or reserve storage, 22% moved to the main stolon apex, 16% to stolon tissue of the main stolon, 34% to adventitious roots on the main stolon (most of which was utilized in older, nodulated roots) and 29% to branches. The apex received the greatest amount of C/unit weight, reflecting its high sink activity, its proximity to the source leaves and, possibly, apical dominance. Subtending leaves provided 46–51% of the C utilized by young branches. Older branches continued to import significant quantities of C from parent stolon leaves despite having their own C sources, though parental support for branches was seen to decrease as branches aged, when the quantity of C they imported was expressed as a function of their weight.

Relative sink strength and distance between sources and sinks contributed to the observed patterns of C distribution. No apparent restriction on C movement was imposed by the vascular architecture of stolons.

In studies at the University of Nottingham at Sutton Bonington in two consecutive seasons beginning in 1986/87, Bourdon, an indeterminate cultivar, and 858, a determinate selection (provided by Plant Breeding International, Cambridge), were compared under six target plant population densities ranging from 10 to 80 plants/m2.

As the season progressed, total dry matter production increased to a maximum and then declined. However, growth rates slowed at pod set because, it is suggested, of the change in the chemical composition of the newly synthesized biomass, from carbohydrate to protein, at that time. Leaf area duration was greater in Bourdon than in 858, especially during pod set, but it bore no relation to seed yield. Specific leaf area was unaffected by competition for light. It is proposed that changes in plant population density affect the competition for assimilates within a plant rather than the competition for light between different plants. Losses of branches and reproductive nodes, with time, are cited as evidence for this. The apparent causes of the lower yield of determinate forms of winter field bean relative to indeterminate forms are discussed.