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.

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.

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 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.

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.

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.

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.

In a 2-year field experiment at Hohenheim in 1987–88, with an intact or partly deflowered indeterminate cultivar and a determinate cultivar, light interception and dry matter production were highest in crops grown in isometric stands (equal distances between plants), lowest in double rows and intermediate in single rows. Dry matter production was greater at high than at low population density and in the wetter and cooler weather of 1987. Population density had a greater effect on DM production than on light interception. The greater leaf canopies under high density and in 1987 (Stützel & Aufhammer 1991) reduced light extinction coefficients. In the determinate cultivar, light extinction coefficients were consistently higher and light use efficiencies were consistently lower than in the indeterminate cultivar. Deflowering the indeterminate genotype and different planting designs did not change light use efficiencies and light extinction coefficients. In general, differences in light use efficiencies were inversely related to differences in light extinction coefficients.

In studies of two indeterminate cultivars in field experiments in 1985 and 1986 at Hohenheim University, the hierarchy within the reproductive storage system of field bean plants was manipulated by removal of inflorescences at various growth stages and nodes. Shading reduced pod set and seed weight mainly at basal nodes. Increasing plant population density reduced seed yield traits at all nodes. Removal of basal inflorescences increased pod set and seed weight at the remaining nodes, especially the lower ones. The favourable effects were greater under high light intensities and in sparse stands. The growth stages at which the basal inflorescences were removed and the removal of apical inflorescences were of minor importance.

An experiment was carried out in Normandy between 1986 and 1988 over c. 6 months in each year, using a simplified rotational grazing technique (two paddocks in spring, four in autumn) with a total of 162 high-yielding cows (mean milk yield of 30·0 kg/day at turn-out). Three stocking rates, designated control (C: 2·3 cows/ha over the total area of the system), moderate (M: 2·6 cows/ha = 115% of C) and high (H: 3·0 cows/ha = 130% of C), were compared at two rates of concentrate supplement, 3·7 kg/cow per day and 0·5 kg/cow per day. Individual milk yield differed by a non-significant 5% between the extreme stocking rates (21·3 v. 20·3 kg fat-corrected milk (FCM) for treatments C and H, respectively). Milk production/ha was 23% greater in the H treatment (9816 v. 7970 kg FCM for H and C, respectively). Concentrate supplementation led, on average, to a 9% milk yield improvement (21·8 v. 20·0 kg FCM for high and low rates, respectively), i.e. a mean efficiency of 0·6 kg FCM/kg supplement. This response tended to be greater in the higher-yielding cows and for the high stocking rate. The sward measurements contributed to a better understanding of herbage utilization by the cows.

In three experiments, carried out in 1985 and 1986 in the Netherlands, the effects of herbage maturation and rate of nitrogen fertilization on rumen degradability of organic matter (OM) and crude protein (CP) in fresh herbage (Lolium perenne) were studied using the nylon bag technique. Experimental farms at Lelystad and Swifterbant (clay soil) and Achterberg (sandy soil) provided the herbage samples. From the results, the content of digestible CP entering the small intestine (DPI) was estimated.

Crude protein content and in sacco degradability of OM and CP decreased with increasing grass maturity and with decreasing rate of N application. With every 100 g/kg DM decrease in CP content, the estimated content of DPI decreased by 19 g/kg DM, no matter how the CP content was manipulated.

Two groups of nine wethers, three of which were fitted with rumen cannulas, were used in a digestion trial at the INRA centre in Theix, France, in 1988. Group 1 received 65% maize silage and 35% concentrates; group 2 received 65% hay and 35% concentrates. Concentrates were based on either cereals rich in starch, or by-products rich in fibre and were given either alone or supplemented with lipids as calcium soaps. The fatty acid content of lipid-supplemented diets was c. 9·5 and 8·5% of dry matter, of which 85 and 89% was provided by calcium soaps, for maize silage and hay diets, respectively. For each group, the four diets were tested in four successive periods from January to June 1988.

Total digestibility of dry and organic matter, acid detergent fibre (ADF) and neutral detergent fibre (NDF) was measured in six wethers of each group by total faeces collection. On cannulated wethers, volatile fatty acid content and composition, pH and NH3-N in rumen liquor were determined four times a day; in sacco degradability of dry matter, ADF and NDF of the forage eaten by the wethers was estimated by the kinetics of incubation in the rumen.

In vivo and in sacco results showed that dry matter and organic matter digestibilities were not modified by the nature of concentrates. Cell wall digestibility was higher for fibre concentrates than for starchy concentrates, by 4·1 and 6·2 percentage units for NDF in maize silage and hay groups, respectively. Volatile fatty acids (VFA) and ammonia concentrations were higher and pH was lower with the maize silage than with the hay diet.

Lipid supply slightly increased cell wall digestibility in the group fed maize silage by 7·5 and 2·0 percentage units for starch and fibre concentrates, respectively. This surprising increase was related to an improvement in in sacco degradability. In all diets, lipid supply increased pH, but variations in VFA concentration and pattern were low. Interactions between the nature of concentrate and lipid supply were moderate, but were higher in the group fed maize silage than in the group fed hay, especially for total digestibility.