A field experiment was carried out at the Wye College Farm during 1988 and 1989. The aim was to study the effects of three rates and timings of nitrogen fertilizer application on the grain protein content of spring wheat cv. Axona. Results demonstrated that timing of fertilizer application was more important than the rate of nitrogen used. Grain protein development and final grain protein contents are discussed in relation to the seasonal variations experienced during the 1988 and 1989 growing seasons in South East England. Due to the early February sowing in 1989, grain protein content was not affected by the summer drought. Thus, the advantage of early sowing of spring wheat to reduce the detrimental effect of early summer drought on the grain protein content is emphasised.

The number of leaves formed on the main shoot of a wheat plant is an important developmental feature, and a method of predicting this is essential for computer simulation of development.

A model function was used to estimate vernalization from simulated sowing dates throughout a season. When expressed in terms of thermal time, it was estimated that a plant might be fully vernalized soon after seedling emergence or take up to about 1000 °Cd, depending on sowing date. When the simulated progress of vernalization was related to main shoot development (primordium initiation and leaf emergence) it was found that there were substantial differences between sowings in the rate of vernalization at comparable stages of apex development.

A number of field experiments done in Britain from 1980 to 1984 with prominent commercial varieties, sown at various times from September to March, were analysed in terms of the thermal time to full vernalization and the photoperiod at the time of full vernalization, with vernalization simulated by the model function. In both winter and spring varieties, both of these variables significantly affected the number of main shoot leaves. Multiple linear regression using these two variables accounted for between 70 and 90% of the variance in leaf number, depending on variety.

An experiment, carried out over a 5-year period (1984–88) on medium–heavy textured soil at Athy (Ireland), tested the effect of five sowing dates (early September–early December) and four seed rates (c. 100, 150, 200 and 250 kg/ha) on the grain yield and protein content of winter barley (cv. Panda).

September-sown plots gave the greatest yields in all years. Plots sown in mid-October and later gave significantly reduced yields. Yield reductions over the 5-year period averaged 15, 24 and 34% for the mid-October, November and December sowing dates, respectively. Significant differences in yield between the smaller and larger seed rates were obtained, with the latter giving the greatest yields at all sowing dates from late September to December. Increasing the seed rate, however, did not compensate for the yield reduction due to delayed sowing. In the early September-sown plots, the higher seed rates gave reduced yields in four of the five years (1984–87) with the opposite result in 1988. In 1988 the early September-sown plots gave greater yields than the late September-sown plots.

Regression analysis showed a strong relationship between yield and log(ears/m2) in four of the five years (1984–87) but the relationship was poor in 1988 primarily due to the inexplicably low ear population of the early-sown plots. The inclusion of 1000-grain weight in the model gave a better fit and accounted for a high proportion (62–80%) of the yield variation.

The late September sowing date and the higher seed rates gave slightly lower protein levels in four of the five years. There was an inverse relationship between grain yield and protein for the same four years (1984–87).

Fourteen experiments which studied effects of date of planting in July, date of harvesting and seed rate on seed tuber yields (10–51 mm) of several potato varieties were carried out in four seasons in East Anglia. Seed tuber yields of c. 30 t/ha in Estima, Wilja and Maris Piper and 20 t/ha in Record were produced from the early planting and in all varieties c. 20 t/ha were produced from planting in late July. For maximum seed yield in all varieties, seed rates of 1·5–2 t/ha were sufficient for most harvests from both dates of planting but for the earliest harvest of the late-July planting, seed rates of only 1–1·5 t/ha were required. The value of seed crops was assessed as the number of ware hectares that could be replanted from the seed yield of one hectare graded 10–51 mm. In all varieties, the number of seed-size tubers and replantable hectares increased with increasing seed rate over most of the range, but numbers were close to the maximum at the early harvests. With delay in harvesting, the number of seed tubers and replantable hectares decreased in many experiments, especially from low seed rates, as more tubers exceeded the upper seed size limit. Maximum numbers of replantable hectares of 15, 15, 20 and 25 were found in Record, Estima, Wilja and Maris Piper, respectively.

The monetary value of seed crops of Record and Maris Piper was calculated using (i) a fixed price per tonne of seed and (ii) cost of seed per replantable ware hectare. Sale values from the latter were substantially higher than from the former at early harvests in Record and at all harvests in Maris Piper. In Record, differences in sale value between the two pricing methods decreased with delay in harvesting as yields increased while number of replantable hectares varied little. The results showed that high multiplication rates and monetary returns can be obtained from short-season seed potato crops which may follow crops harvested earlier in the same season. The implications for potato production in the UK are discussed.

Patterns of assimilate distribution in single plants of winter oilseed rape (Brassica napus L.) cv. Mikado, following a reduction in sink capacity at flowering were investigated in two field experiments during the 1985/86 and 1986/87 growing seasons at Cockle Park Experimental Station, Northumberland. Plants demonstrated considerable compensatory growth following the removal of flowers from the terminal raceme and primary branches.

Flower removal from lower branches did not significantly reduce total seed weight. Plants with a pod-bearing terminal raceme and one, two or three productive higher-order branches yielded a similar amount of seed. When seed production was confined to the terminal raceme and first four primary branches, seed yield per plant was greatly increased. Removal of flowers from the terminal raceme and uppermost branches of plants increased the number and productivity of lower-order branches but not enough to offset the overall loss in seed yield potential per plant. Indeed, when flowers were removed from higher-order racemes, the reduction in total seed weight per plant, was directly related to the degree of flower removal. The additional seed yield obtained from individual branches of modified plants in both experiments arose largely through an increase in fertile pod number and seed number per pod. Flower removal treatments did not greatly influence mean seed weight.

The results clearly demonstrated that the loss of flowers from lower-order branches could be tolerated and may even be beneficial. Conversely, the removal of flowers from higher-order branches resulted in significant yield reductions. The production of lower branches should be restricted, therefore, in order to increase the superiority of the terminal raceme and uppermost branches and to increase the overall production efficiency of the crop canopy.

Different geranium (Pelargonium graveolens L. Herit) clones differed in susceptibility to root rot and wilt caused by Rhizoctonia solani Kuhn. Reactions were consistent when assessed either by standardized laboratory tests or by pot experiments using 60-day-old well-rooted plants. Plants of an Algerian-type clone (Kd) had a lower survival rate and higher root rot index values than those of a Reunion type (Lo) and an Egyptian type (Eg). Field studies conducted in naturally-infected plots in southern India from 1987 to 1990 showed that summer planting resulted in higher plant losses of all clones than winter planting. As in the laboratory and pot experiments, the Lo and Eg clones sustained less plant loss and produced higher herbage and oil yields than the Kd clones in both field experiments.

Five potting media components mixed in various combinations and in various percentages of one with another (0, 14·3, 29, 42, 57, 71 and 100% by volume of the second component with the first) were inoculated with Glomus intraradix in six experiments. Seedlings of citrus rootstocks were grown from seed in these mixes. Sour orange in inoculated peat plus vermiculite, Astatula fine sand plus vermiculite, and peat plus Perlite® in all percentage combinations grew c. two- to threefold taller than noninoculated control plants. Up to twofold growth increases of sour orange occurred in vermiculite amended with wood shavings. The best evidence for fungus-mediated plant growth occurred in Astatula fine sand amended with 29–71% Perlite, and the roots in that combination had the highest percentage of infection. In another experiment in which Astatula fine sand was amended with up to 16% of an acid peat, ratios of inoculated rough lemon plant growth to controls decreased as the peat content in the medium increased. Top and root weight ratios of inoculated:control seedlings in the six experiments did not fit four simple linear models.

The potential for grain yield and nitrogen fixation by faba bean (Vicia faba L.) cultivars of contrasting plant types was studied at ICARDA's main research station at Tel Hadya in northern Syria during 1985–88. The cultivars included indeterminate landraces, determinate and independent vascular supply (IVS) plant types sown at two seeding densities.

In 1985/86, the cultivars with indeterminate growth habit (ILB 1811, ILB 1819, ILB 1814), which are adapted to the Mediterranean basin, produced the highest grain yield, followed by the determinate cultivar FLIP 84–230F and the lowest yield was obtained from IVSFG–IVS 6, a cultivar with an independent vascular supply to each flower. In 1986/87, ILB 1814 again outyielded two determinate faba bean cultivars (FLIP 84–230F and FLIP 84–239F) and IVSFG–IVS 6. Similarly, in 1987/88, ILB 1814 significantly outyielded the determinate faba bean cultivars FLIP 84–239F, FLIP 84–240F and FLIP 84–241F; and also the indeterminate cultivar IVSFG–IVS 6.

Seeding at 44 plants/m2 as opposed to the recommended rate of 22 plants/m2 gave a slight but non-significant reduction in grain yield for the indeterminate cultivars from the Mediterranean environment (ILB 1814, ILB 1811, ILB 1819). Grain yields were increased significantly in the determinate plant type FLIP 84–39F in 1986/87 and 1987/88, and in IVSFG–IVS 6 in 1986/87.

Grain yield was strongly and positively correlated with total dry matter (r = 0·93) and also to mean weight per bean (r = 0·83) and harvest index (r= 0·47). The correlations between grain yield and pods/m2, seeds/m2 and seeds/pod were negative.

Total nitrogen uptake and nitrogen derived from atmospheric fixation followed a similar pattern to the results for grain yield: high in the high yielding cultivar, ILB 1814, and low in cultivars with low grain yields. In 1986/87, N2 derived from fixation was 77% in ILB 1814, 68% in FLIP 84–239F, 63% in FLIP 84–230F and 62% in IVSFG–IVS 6; and in 1987/88 the values were 88% in ILB 1814, 86% in FLIP 84–239F and 82% in IVSFG–IVS 6.

Field experiments were conducted at Tel Hadya, Syria during 1985–1988 using faba bean (field bean) cultivars of three different plant types – independent vascular supply to each flower (IVS), determinate and indeterminate, sown at 22 and 44 plants/m2. The objective of the study was to determine whether yields had been stabilized and improved in the newly developed plant types.

Both determinate and indeterminate cultivars continued producing nodes late into the season, the former by producing new branches and the latter on the existing branches. Late formation of branches in determinate lines was suppressed by sowing at a high seeding density of 44 plants/m2 in contrast to the usual density of 22 plants/m2. Indeterminate lines, e.g. ILB 1814, produced the highest leaf area index (LAI), intercepted the highest photosynthetically active radiation (PAR) and produced the highest total dry matter (DM). Among the determinate lines, FLIP 84–239F had a high LAI, intercepted a high PAR and produced a high DM. The IVS line, IVSFG–IVS 6, had a low LAI, intercepted a low PAR and attained a low DM. Sowing at a high density of 44 plants/m2 rather than 22 plants/m2 increased LAI and intercepted PAR, resulting in a higher DM production. Determinate lines partitioned proportionately more of the DM to the reproductive parts.

Dry matter production was strongly correlated with cumulative intercepted PAR; with r ranging from 0·90–1·00 in both 1986/87 and 1987/88. The variation in the efficiency of conversion of intercepted PAR into DM amongst cultivars was low (1·309–2·017 g/MJ in 1986/87 and 1·191·2·057 g/MJ in 1987/88). ILB 1814 (an indeterminate cultivar) and FLIP 84–239F (a determinate cultivar) had higher light use efficiencies than the other cultivars. The range in cumulative intercepted PAR was, however, high; 224·8–417·8 MJ/m2 in 1986/87 and 118·4–369·1 MJ/m2 in 1987/88. Differences in DM at maturity were mainly due to differences in cumulative intercepted PAR.

The relationship between DM at different growth stages and DM at maturity was strong; with the DM values at flowering showing the greatest correlations (r values of 0·93 in 1986/87 and 0·96 in 1987/88).

A determinate and an indeterminate cultivar of Vicia faba were grown in the field to study the effects of two different plant densities and three plant distribution patterns on yield formation. The relationship between crop growth rate during flowering and the number of pods produced was identical in both cultivars. The higher growth rates of the indeterminate cultivar and of dense stands were associated with higher pod numbers. Average crop growth rates in the period between flowering and 30 days thereafter were related to the number of mature seed-containing pods. This relationship was similar in both cultivars except that the determinate cultivar aborted seed-containing pods as late as 40–45 days after flowering when grown at the low density. Rates of seed filling for both cultivars were similar at the low density (c 1·4 mg per °C per day per pod), but were larger for the determinate cultivar at the high density. The annual differences in seed weights per pod were not related to seed filling rates. Grain yields and harvest indices were generally lower in the determinate than in the indeterminate cultivar, but high plant density increased seed yields of the determinate more than of the indeterminate, because of an increase in harvest index. Plant distribution pattern had no significant effect on the above characters.

Two grazing experiments in New Zealand, using newly weaned red deer stags, assessed methods of maximizing growth over winter and spring, with the objective of attaining a slaughter weight of 92 kg liveweight (> 50 kg carcass) at the end of spring, by 12 months of age. Perennial ryegrass/white clover pastures, and the same direct-drilled with an annual ryegrass, were grazed at two surface heights (5 cm and 10 cm; Experiment 1; 1988) or at similar pasture mass (Experiment 2; 1989). Balanced groups of stags grazing each forage were immunized against melatonin, commencing at 3 months of age (Expt 1) or at birth (Expt 2). Moata annual ryegrass comprised 19–46% of the feed on offer in Expt 1 and 65–82% in Expt 2. Perennial ryegrass comprised 79–89% of control pastures and white clover generally comprised < 10% of all pastures. Organic matter digestibility of both the feed on offer and diet selected, determined with deer fistulated in the rumen or oesophagus, was 75–80%.

In Expt 1, rates of body growth during winter were greater for stags grazing at 10 cm than at 5 cm pasture height, with no effect due to the inclusion of annual ryegrass. During spring, growth rates were similar for stags grazing 10 cm pastures and the 5 cm pasture containing annual ryegrass, but were lower on 5 cm pasture based on perennial ryegrass. Inclusion of annual ryegrass slightly increased winter rates of herbage dry matter accumulation, animal carrying capacity and the proportion of stags attaining target slaughter weight.

In Expt 2, annual ryegrass pastures were of higher organic matter digestibility than perennial pastures during winter, and supported greater rates of liveweight gain (LWG) and voluntary feed intake (VFI) than the perennial ryegrass. During spring, LWG increased in both groups of stags although the difference between the two groups ceased to be significant. More of the animals grazing annual ryegrass pastures attained target slaughter weight than those grazing perennial pasture. Rumen acetate: propionate ratio, measured in fistulated stags, was similar for both groups of animals. Relative to perennial ryegrass, pastures containing high proportions of annual ryegrass resulted in similar animal carrying capacity during winter but substantially lower carrying capacity in spring.

Antibodies binding melatonin were detected in 75% of immunized animals, with higher and more persistent titres being obtained using Freund's than using Dextran adjuvant and titre being much higher in stags immunized at birth than at 3 months of age. This was associated with a small and variable increase in plasma prolactin concentration, but had no effect upon plasma concentrations of LH or testosterone or upon LWG.

It was concluded that the small increase in deer production attributable to annual ryegrass was mainly due to higher VFI, and that grazing perennial ryegrass/white clover pastures at 10 cm surface height resulted in higher levels of deer production than grazing at 5 cm surface height. These studies emphasise the feasibility of early venison production from grazed pastures in New Zealand, and show that the young deer were growing close to their genetic potential under this system.

The effects of immunization against luteinizing hormone releasing hormone (LHRH) and melatonin were studied during autumn and winter 1989 in yearling red deer stags initially aged 14 months and weighing 90–96 kg. Four out of five stags immunized against LHRH and six out of eight stags immunized against melatonin developed detectable levels of antibody titre. Immunization against LHRH reduced plasma LH concentration and both delayed and reduced weight loss associated with the rut (autumn); however, it had no effect upon carcass weight and dressing-out percentage was slightly lowered, showing that non-carcass components had been affected. Immunization against melatonin had no effect either on weight loss during the rut or on the rate of liveweight gain during winter and spring. Plasma concentrations of LH and testosterone were not affected by melatonin immunization; however, plasma prolactin concentration was consistently, but non-significantly, higher in immunized than control animals.

During weeks 3–23 of lactation, 63 multiparous and 28 primiparous Friesian cows were offered ad libitum access to grass silage of either average (A)(ME 10·6 MJ/kg DM; CP 158 g/kg DM) or low (L)(ME 9·9 MJ/kg DM; CP 154 g/kg DM) energy value, either alone or in mixtures consisting of one of these grass silages with 25, 50 or 75% of the forage DM as maize silage. In addition, all cows received 7·2 kg DM/day of concentrate (ME 12·9 MJ/kg DM; CP 202 g/kg DM). There was a significant (P < 0·001) linear relationship between silage DM intake and percentage maize inclusion with grass silage. For grass silage A, DM intake of the mixture of grass and maize in a 1:1 DM ratio was significantly (P < 0·001) higher that at other inclusion levels. There was a significant (P < 0·05) overall linear effect of proportion of maize on milk yield, with a regression coefficient of 0·022 ± 0·009 kg/day per percentage maize proportion. Although milk composition was unaffected by treatment, there was a significant (P < 0·01) linear effect of maize proportion on protein yield for grass silage L, the regression coefficient being 0·8±0·03 g/day/percentage maize proportion. The mixture of grass silage A and maize silage in a 1:1 DM ratio produced the highest yield of milk protein.

Groups of six single- and six twin-rearing ewes were continuously stocked on five pastures with sward surface heights (SSHs) of 3·5, 5·0, 6·0, 7·0 and 8·5 cm from week l until week ll of lactation. Herbage intake, estimated from faecal chromium concentrations and the in vitro digestibility of herbage samples collected from oesophageal-fistulated wethers, was lowest on the 3·5 cm sward but was not significantly different between SSH treatments during weeks 5, 8 and 9 of lactation. Twin-rearing ewes consumed 0·9–17·6% more herbage than single-rearing ewes did. By week ll, ewe liveweights showed increases of 2–4 kg/ewe on all except the 3·5 cm sward, where the ewes lost a similar amount of liveweight. From week 4 of lactation, twin-rearing ewes had a lower body condition than ewes raising a single lamb on all except the 3·5 cm sward, where the body condition of both rearing ranks was similar. Lamb growth rates during the first 6 weeks were similar for each SSH treatment but from days 46–76 of lactation, lambs on the 5·0 cm and longer swards grew faster (240 g/day) than those on the 3·5 cm sward (197 g/day). Lamb weight on day 76 ranged from 21·5 kg on the 3·5 cm sward to 23·0 kg on the 5·0 cm sward, but was not significantly affected by SSH. Similarly, midside wool growth of ewes and lambs was not significantly influenced by SSH during the period of continuous stocking. The results indicate that farmers should aim to provide swards of 5–7 cm height during lactation to maximize production in both single- and twin-rearing ewes.

The Agricultural and Related Industries Study Group of the Operational Research Society held a one-day meeting on ‘Modelling Approaches to the Control of Agricultural Pollution’ on 12 November 1991 at Silsoe Research Institute. The group promotes the use of the scientific method in solving management problems. The aim of the meeting was to look at different ways in which modelling could contribute to the understanding and hence control of different types of pollution. Contrasts were the order of the day, with the first talk being a complex mass of differential equations and the second talk describing an expert system with a few simple design equations. Model dimensions ranged from point sources for silage effluent to several farms for invertebrate populations. A common theme was the difficulty of validating models faced with the extremely variable and difficult-to-obtain experimental data.