A field trial on alley-cropping was conducted at the University of Ibadan research farm in the 1990/91 cropping season to assess the contributions of arbuscular mycorrhizal (AM) fungi and hedgerow woody legumes to the yield and nutrient uptake of cassava (Manihot esculenta Crantz) as an intercrop in an infertile soil. The trial also investigated the influence of AM fungi on the interplanting of a non-nodulating woody legume Senna siamea (syn. Cassia siamea) with a nodulating woody legume (Leucaena leucocephala).

AM contributions to cassava were greater than the hedgerow contributions, which demonstrated that AM associations are an essential component in the nutrition of cassava. In contrast to cassava, AM inoculation only influenced the leaf dry weight and uptake of nutrients of non-interplanted woody legumes but not the above-ground biomass and P uptake of interplanted woody legumes. However, non-inoculated interplanted Leucaena benefited more from indigenous AM fungi than the competing Senna. The negative contributions to the nutrient uptake (K, Ca and Mg) of cassava by hedgerows and the lack of response to AM inoculation in interplanted hedgerow woody legumes could be attributed to root competition among the different plant species growing in close proximity to each other. The present results show that cassava benefits more from AM association than Leucaena which in turn benefits more than Senna in an alley-cropping system.

In order to understand better some of the reasons for differences between forage plant species in digestibility, different parts of nine plant species in either milled or chopped (1 cm lengths) form were examined for in vitro digestibility and in milled form for neutral detergent fibre and lignin. The nine species were: Trifolium repens L., Medicago sativa L., Desmodium intortum (Mill.) Urb., Brassica napus L., Lolium perenne L., Festuca arundinacea Schreb., Chloris gayana Kunth, Cenchrus ciliaris L. and Zea mays L. In each case early harvesting was compared with later harvesting in each of two years. The plants were grown in spring–summer in a heated glasshouse.

The forage at the early harvest was, on average, 1–4% units more digestible in vitro than that at the later harvest and generally slightly lower in lignin and neutral detergent fibre content. However, the stems of Z. mays were higher in neutral detergent fibre at the early than at the later harvest.

The leaf sheaths of L. perenne and F. arundinacea were more digestible than the leaf blades. L. perenne was more digestible than F. arundinacea in both sheaths and blades. The sheaths and blades of C. gayana and C. ciliaris were less digestible and had a higher neutral detergent fibre content than those of L. perenne and F. arundinacea. The leaf blades, excluding the midribs, and the stems and leaf sheaths of Z. mays were all rather high in digestibility when milled and moderately low in neutral detergent fibre and lignin; the leaf blade midribs of Z. mays were less digestible and higher in neutral detergent fibre than the stems and similar to the stems in lignin content. The leaflets of T. repens had an appreciably lower neutral detergent fibre content than the stolons and petioles and a rather lower lignin content in dry matter and yet were, if anything, less digestible than the stolons and petioles. The stolons of T. repens were much more digestible than the stems of M. sativa and D. intortum. The digestibility of D. intortum was low in all the plant parts examined, leaflets, petioles and stems. In both D. intortum and B. napus, the leaflets or leaf blades were much lower than the stems in neutral detergent fibre and lignin and yet they were no more digestible than the stems when milled.

The digestibility of chopped leaflets and leaf blades was similar to that of milled leaflets and leaf blades, but chopping rather than milling reduced the digestibility of stems (particularly of those of Z. mays), petioles, the leaf blade midribs of Z. mays, and, to some extent, leaf sheaths.

Nitrate leaching was measured over a 3-year period from rotationally grazed perennial ryegrass (Lolium perenne L.) pasture receiving 200 kg fertilizer-N/ha and from similarly grazed ryegrass/white clover (Trifolium repens L.) pasture that received no N fertilizer. The results are discussed together with those from the same plots in the preceding 3 years when they were stocked continuously. Under both managements, the numbers of grazing sheep were adjusted on the basis of the quantity of herbage available on the plots. During the whole 6 years, mean nitrate concentrations in soil water collected by porous cup samplers remained below the European Union limit of 11·3 mg N/l except for the fertilized grass plots in year 5 of the study. Quantities of nitrate leached ranged from 6 to 34 kg/ha per year from the grass/clover plots and 2·46 kg/ha from the fertilized plots. Leaching losses from both types of pasture were positively correlated with the numbers of lamb grazing days in the later part of the grazing season. This relationship and the high spatial variability associated with the measurements indicated that N derived from excreta was the main source of leached nitrate. It was concluded that, where pastures of equal productivity are compared, similar quantities of N are likely to be leached from grass/clover swards as from grass swards receiving N fertilizer.

The effect of a comprehensive (three-spray) fungicide programme on yield, specific weight (SW), 1000-grain weight (TGW), nutritive value and yield of both winter and spring oat grains was investigated over a 3-year period (1989–91). With winter oats, four cultivars (Aintree, Image or Pennal, Solva and Kynon), were tested at each of three sites (Gwent, Hereford and Kent). Similarly for spring oats, four cultivars (Dula, Keeper, Rollo and Rhiannon) were tested at each of three sites (Cornwall, North Yorkshire and Wales).

On winter oats, fungicide treatment produced a significant increase (P<0·05) in grain yield, but did not on spring oats. Fungicide treatment produced no significant effect on SW, TGW or nutritive value of the winter or spring oats. With winter oats, but not with spring oats, fungicide treatment produced a significant increase (P<0·05) in the yield of digestible (DE) and metabolizable (ME) energy for pigs and ruminants respectively.

The naked oats, Kynon and Rhiannon, had a significantly lower yield, higher SW and lower TGW than the other conventional cultivars (P<0·05). Their oil, fatty acid, protein, DE and ME contents were also significantly higher than the other cultivars (P<0·05). Nevertheless, the yield of protein, DE and ME tended to be less from naked oats than from some of the other cultivars tested.

On winter oats, TGW, protein content and protein yield, dry matter (DM) and fatty acid content and on spring oats, yield, TGW, ME yield, DM, oil, fatty acid, protein, DE and ME all varied between years. With winter oats, oil content and energy values were negatively correlated with yield and positively correlated with SW. With spring oats, DE and ME were positively correlated with SW.

It was concluded that, on winter oats, fungicide treatment was worthwhile in terms of grain yield, but this was not the case for spring oats. Also with winter oats, but not spring oats, fungicides gave useful increases in the yield of energy. The naked oats, Kynon and Rhiannon, had a distinct advantage in terms of nutritive value, but their low yield compared with the conventional cultivars tended to negate this benefit.

The growth and development of cotton was studied on cotton plants grown in pots in growth rooms under constant day/night temperature (C) and varying temperature regimes throughout the day and/or night (V) The V-treatments had a common mean temperature of 22°C. The objectives were to determine the thermal requirements of three cultivars and to observe the extent of genotype×thermal environment interactions throughout the entire growth period.

Vegetative growth was found to be almost exclusively time and temperature dependent, varietal differences being largely insignificant. Plant material was found to accumulate four times faster under the warmest C-regime, which was 7°C warmer than the coolest. The C-treatments caused variation in the number and size of lateral shoots and leaves, causing leaf area to be larger at the squaring stage in cool environments but at maturity in warm regimes. Relatively cool nights lowered the position of the first floral or fruiting branch, whereas warm days shortened flowering intervals and thus promoted earliness. However, the effect of temperature in altering the position of the first floral branch seems to be less important than its effect on the shedding of early squares.

The effects of fluctuating temperature (V) on vegetative growth and earliness were similar to those from constant temperature environments. Growth and development rates were low in the low minimum V-regimes, especially when the maximum temperature was also low. Temperature variation affected vegetative growth to a greater extent in the early than in the later stages of development. At squaring, leaf area and dry weight were lowest under the regime with the highest minimum and maximum temperatures. Later on, only leaf area at flowering and total dry weight at maturity significantly differed between treatments. High maximum or minimum temperatures produced effects similar to a higher or lower mean temperature, respectively. The low minimum raised the node number of the first floral or fruiting branch, whereas in the case of boll dry weight it acted in the same way as a further drop in temperature, decreasing the weight, regardless of the maximum temperature. Boll period was affected mainly by the temperature variation itself rather by than the type of variation.

The inverse of time to a certain stage and the corresponding mean temperature were linearly related and allowed threshold temperatures (T0) and thermal time requirements to be estimated. T0=12°C, except for the initial stage, when it was lower. A cotton growing season cooler on average by only 1°C will considerably delay maturity.

Different management regimes for 1-year rotational set-aside were tested in three experiments that followed winter wheat and started in autumn 1988–90. The regimes included operations that prevented the establishment of volunteers or allowed them to establish and persist until either spring or summer, and also altered the distribution of debris from the winter wheat that preceded the set-aside. For comparison, treatments in the set-aside year also included winter wheat.

Samples taken in spring from the first test crop showed that there were few significant or consistent effects on leaf diseases of growing the wheat after different set-aside treatments or after winter wheat. There were significant effects of the set-aside treatments on root and stem base diseases but some of the effects, and the apparent absence of others, are not easily reconciled with current understanding of the biology of the pathogens concerned. In summer, eyespot (Pseudocercosporella herpotrichoides) was most severe after winter wheat and least severe after ryegrass. Severity after the other set-aside treatments did not differ significantly. There was more sharp eyespot (Rhizoctonia cerealis) in plots that had been ploughed at the start of the set-aside year, including those sown with winter wheat, than in those that had not. Brown foot rot (Fusarium spp.) was equally severe where the wheat followed wheat or where it followed set-aside treatments that allowed volunteers to develop, and less so where the development of volunteers was prevented. Take-all (Gaeumannomyces graminis var. tritici) was most severe after winter wheat and more severe after set-aside treatments that allowed volunteers to develop and survive through the winter than after those that did not. Effects of ryegrass (Lolium perenne ssp. multiflorum) on take-all in the following wheat were particularly variable, perhaps because ryegrass is a host of both the take-all fungus and of Phialophora graminicola, one of its principal antagonists.

Studies of soil erosion in upland and marginal upland Britain are reviewed. Processes affecting soil erosion and runoff are described in marginal upland improved pastures of differing age in the Clwydian Hills, including one which was cultivated twice during the study period. A Gerlach-type trough was designed for trapping sediment and filtered runoff from bounded plots and for operating under grazing. Erosion and runoff amounts are interpreted in the light of ground cover, rainfall amounts and intensity, the action of grazing stock and other animals, and other influences. The chief erosion processes are the action of animals and surface wash by unconcentrated overland flow; no rilling occurred. The significance of particle size of eroded sediment is discussed.

Twelve field experiments, carried out over 7 years, examined effects of shading and seed tuber spacing on plant growth, initiation and retention of tubers in four cultivars: Estima, Maris Piper, Maris Peer and Record. Ten of the experiments were carried out at Cambridge and two near Valencia, Spain. Other treatments included in some experiments were floating polythene mulch and planting date.

Shading by up to 75% did not affect the timing of onset or cessation of tuber initiation in Estima but shading by 50% or more delayed the completion of tuber initiation in Maris Piper compared with less severe shading. Except for intensely shaded treatments (50% or more), the majority of tubers were initiated in a very short period (4–7 days). Shading by 37% or more during the period of tuber initiation and increasing planting density, decreased number of tubers per stem initiated in all experiments, but number of tubers was not affected by shading at other stages of growth. At Cambridge, effects of shading on number of tubers >10 mm retained later in growth from normal planting dates (March to early May) were similar to effects on number of tubers initiated, but effects were much reduced or absent following later plantings at Cambridge and in both experiments in Valencia. The decreased effects of shading on number of tubers >10 mm at late plantings at Cambridge were associated with the initiation of fewer tubers at these plantings. Effects of shading, planting density and planting date on number of tubers were a consequence of changes in the frequency of occurrence and tuberization of different stolon types. Increasing shading and planting density and delaying planting reduced the number of lateral and branch stolons and the frequency of their tuberization but there were no effects on number of primary stolons or their tuberization. Consequently, at Cambridge a similar number of tubers was borne on primary stolons in shaded and unshaded crops. In Valencia a greater proportion of initiated tubers was retained at final harvest from shaded treatments than at Cambridge, which accounts for the absence of effects of shading on number of tubers >10 mm. The greater retention of tubers late in growth in Spain may have been associated with the higher peak growth rates achieved in higher radiation fluxes than at Cambridge.

Linear regressions of the data for normal planting dates at Cambridge and from Valencia indicated that the number of tubers >10 mm late in growth was dependent on the radiation environment during the period of tuber initiation. Radiation flux during the brightest period of the first few days of initiation appeared to be the most crucial aspect of radiation affecting number of tubers. As incident radiation can vary greatly over the short period of tuber initiation, it is potentially an important factor affecting number of tubers in field crops.

Fourteen rice accessions resistant to bacterial leaf blight (BB), caused by Xanthomonas oryzae pv. oryza (Xoo) and belonging to nine wild Oryza species representing three genomic groups: AA (O. nivara, O. barthii, O. longistaminata, O. rufipogon and O. meridionalis), BBCC (O. punctata, O. malampuzhaensis and O. minuta) and CCDD (O. latifolia) were used to produce hybrids with two O. sativa (2n=24, AA) cultivars PR 106 and Pusa Basmati 1 (PB 1). The seed set in similar genome crosses ranged between 1·4 and 79% depending upon the rice cultivar used. In general, PR 106 showed better crossability with the wild species. Hybrids were obtained from intergenomic crosses with O. malampuzhaensis, O. latifolia and O. punctata, using embryo rescue. Morphologically, the hybrids were more vigorous than their parents and tended to resemble their male parent. Intragenomic hybrids showed little fertility (0·24–8·04%), while the intergenomic hybrids were completely sterile. Meiotic studies revealed irregularities in cell division, with a high frequency of univalents (12·17–18·75), fewer bivalents (2·43–5·80) and occasional multivalents, in intragenomic hybrids. The intergenomic hybrids were characterized by a very high frequency of univalents (34·98–35·35). The reaction of the hybrids to BB revealed the presence of both dominant and recessive genes in the wild gene pool. The hybrids with O. longistaminata, O. punctata, O. latifolia and O. malampuzhaensis showed resistance in the F1 generation, and hence they were likely to carry dominant genes for resistance, while the hybrids with O. barthii, O. nivara, O. meridionalis and O. rufipogon were susceptible and hence carried recessive genes for resistance.

Temperature effects on cotton yield and fibre properties of three cotton cultivars were determined. Plants were grown in pots maintained in growth rooms at varying day and night temperatures representing seasonally constant or varying (C) or daily varying (V) regimes.

Yield and fibre characters responded to variation of daily mean and amplitude of temperature. Mean temperature reduction improved yield components, but fibre length, uniformity, strength and micronaire were increased by high, particularly high day, temperatures. A large daily temperature amplitude produced an intermediate number of flowers and the lowest retention percentage.

Fruiting and yield were increased by reduction in temperature down to the threshold mean temperature of 22°C. However, V-regimes with a low minimum temperature acted as a further drop (below 22°C) of temperature and adversely affected these characters. An adverse effect of low minimum temperature combined with a moderate day temperature was observed also on lint percentage and fibre properties.

Varietal differences were more pronounced for highly heritable characters such as fibre properties, for which significant interactions between varieties and temperature also occurred. Differences in reproductive development were not sufficient to be of much practical importance.

A series of three experiments on loam to sandy loam soil at Woburn, all following winter or spring wheat, tested the effects of six different 1-year set-aside treatments and crops of winter wheat in 1989, 1990 and 1991 on two following winter wheat test crops. Effects of the treatments on overwinter changes in soil mineral nitrogen (SMN) and plant N in the set-aside years and in the first test crops were measured, as were the grain yields of both the first and second test crops.

Differences in net overwinter changes in SMN plus plant N between set-aside treatments were variable and dependent on rainfall. During a wet winter, SMN plus plant N losses were large under fallow and natural regeneration, intermediate under winter wheat and small under Italian ryegrass (Lolium multiflorum). Ryegrass restricted the growth of the following wheat but yields were unaffected where fertilizer N was applied. Ryegrass proved difficult to control in the subsequent wheat test crops. Forage rape (Brassica napus) took up large amounts of N but after topping did not compete well with weeds.

Yields of the first wheat test crops after winter wheat were smaller than after the set-aside treatments, take-all was probably the cause of this yield depression. No consistent yield differences were recorded in the second wheat test crops.

The colonization of Lactobacillus spp., enterobacteria and facultatively anaerobic gram-positive cocci was monitored in intestinal samples of growing broiler chicks from 24 h to 28 days of age. Rapid bacterial growth occurred within the first week, followed by stabilization and decline of colony forming units (CFU). Xylanase supplementation led to significantly lower CFU per gram of wet weight for total presumptive enterobacteria and total gram-positive cocci in luminal and tissue samples in the first 3 weeks. Lactobacillus spp. colony counts from tissue samples were higher for animals with the xylanase-supplemented diet, but luminal CFU were not. The composition of dominant Lactobacillus spp. strains was different in duodenal and jejunal tissues, but distribution of Lactobacillus spp. colony forms was unaffected by xylanase treatment. Mucosa-associated Enterococcus spp. displaced the dominant gram-positive cocci in the jejunal samples. d- and l-lactic acid and acetic acid concentrations were significantly higher in ileal samples from the control group on days 7 and 14, while butyric acid concentrations were higher in the xylanase-treated group. It is concluded that the less viscous intestinal environment caused by the xylanase slowed proliferation of gram-positive cocci and presumptive enterobacteria in enzyme-supplemented animals in the first 3 weeks of life.

Six management regimes for 1-year set-aside were compared with continuous winter wheat for their effects on weed control in two following test crops of winter wheat. The experiment was repeated in each of three years (1989–91) on predominantly sandy loam soils in eastern England. The weed flora was dominated by Poa spp., Stellaria media, Matricaria spp., Chenopodium album and volunteer crops, predominantly wheat.

Managing set-aside by allowing natural regeneration and cutting it 2–4 times during the growing season resulted in fewest weeds in the following wheat crop. It was also a low cost option. Winter wheat, despite the application of herbicides, was not as effective in minimizing weeds in the winter wheat test crops as the best set-aside options.

An Italian ryegrass cover crop set seed despite being cut 2–4 times per year. The only serious weed infestation arising in following wheat crops was from volunteer ryegrass in the second wheat following set-aside. The effects of management in the set-aside year were generally greater in the second of the following wheats than in the first.

Drought stress and virus yellows disease are two of the major problems of sugarbeet crop production in the UK. We have calculated the annual national drought losses from 1980 to 1995 by using long term data sets for two sites (IACR-Broom's Barn, Suffolk and ADAS Gleadthorpe, Nottinghamshire) to relate yield loss to cumulative potential summer moisture deficit, and combining these relationships with regional meteorological records, soil type and crop distribution data.

Experimentally measured relationships between yield losses and the timing of virus yellows infection were combined with annual survey data of the extent of the problem, and calculated infection dates from the UK aphid suction trap network, to calculate actual national annual losses to the disease. Potential losses in the absence of control measures were then calculated by use of data from trials and surveys of pesticide use.

The results showed a mean annual loss of production to drought stress of 141000 t/year of sugar, 10·5% of production, with a loss to the industry of £27·9 million. Losses in individual years varied from zero to 2·5 times the mean figure. Actual losses to virus yellows were much smaller, due to the efficacy of treatments, averaging 24700 t/year of sugar (1·8% of national yield, financial loss £5·5 million). Average potential virus yellows losses in the absence of control measures were approximately double this.

Control of virus yellows is a major, cost-effective contributor to rising and consistent sugarbeet production. Nationally, irrigation has made little impact on drought losses and, due to constraints in surface water supply, this situation appears likely to continue. Improved drought stress tolerance represents the largest single opportunity for yield and profitability improvement of the sugarbeet crop in the UK at present. Predicted climate change appears likely to increase the severity of both drought and disease stresses. Drought stress appears relatively less important in other NW European sugarbeet-growing areas.

The effects on succeeding crops of nitrogen in residues returned to the soil of brassica vegetable crops (Brassica oleracea) were studied on a nitrogen-retentive silt loam soil at Horticulture Research International, Kirton, Lincolnshire, UK. A sequence of four crops was started in 1988 and again in 1989. In the first sequence, two successive cauliflower crops (Brassica oleracea cv. botrytis L.), crops 1 and 2 in the first year, were followed by Brussels sprouts (Brassica oleracea cv. Gemmifera D.C.), crop 3, in the second and spring barley (Hordeum vulgare), crop 4, in the third year. The second sequence, started in spring 1989, was on an area adjacent to the first, but with spring wheat (Triticum aestivum) as crop 4. The sites followed an unfertilized, 1-year grass ley (1987) or spring barley (1988) with 73 and 107 kg N/ha soil mineral nitrogen (SMN, NH4+NO3) in the 0–90 cm soil profile at the start of each sequence. The marketable yield of the first cauliflowers in both sequences increased with fertilizer nitrogen up to 240 or 300 kg/ha. The response of the second cauliflower crop to fresh N declined with increasing amounts of SMN (0–90 cm) at planting, with no response when SMN exceeded c. 270 kg N/ha. Crop 3 apparently responded to fresh N in sequence 1 but not in sequence 2 even though SMN at planting ranged up to c. 400 kg N/ha. This difference in response was largely explained by the amount and distribution of SMN in the 0–30 and 30–60 cm layers when the sprouts were planted. Soil mineral N to 90 cm when the cereals were sown was only c. 100 kg N/ha, which did not reflect the large amounts of N applied to the previous crops. In spite of this, barley yield without any fresh fertilizer N did vary with the amounts of N applied to the previous crops. The results showed that SMN was a useful predictor of fertilizer response in some, but not all, situations. To use SMN more generally requires interpretation using dynamic simulation models.

The effect of four seed rates on the grain yield, grain N content and grain size of Blenheim malting barley sown on two dates in the spring was tested on three different soils over a 4-year period (1991–94). The four seed rates (120, 160, 200 and 240 kg/ha) gave mean plant populations of 222, 308, 374 and 430 plants/m2, respectively, for the first sowing date (February to early March) and 235, 340, 405 and 470 plants/m2 for the second sowing date, 3–5 weeks later (late March to mid-April). The earlier-sown crops generally gave greater yield, lower grain N and smaller amount of screenings, but in two of the twelve experiments, the first sowing gave lower yield and greater grain N.

The influence of seed rate on yield and quality depended on sowing date. The three higher seed rates (160, 200, 240 kg/ha) had little influence on yield or grain N, irrespective of sowing date, and there was no significant difference in yield between the lowest (120 kg/ha) and the three higher seed rates when the crop was sown in February and early March. But when the crops were sown in April, the lowest seed rate (120 kg/ha) gave the lowest yield in all seven comparisons and gave significantly reduced yield in three of the seven comparisons. There was a significant increase in grain N in three of the comparisons. Seed rate had little effect on grain screenings or 1000-grain weight. Soil differences did not influence the effect of seed rate on the yield and quality of the grain.

The progress of leaf emergence, external morphology and apical development stages were recorded in sowings of triticale (cv. Lasko) made from February to November 1990 at Aberdeen (57° N). Leaf appearance and the number of primordia were related to thermal time (above a base of 0°C) except when photoperiods were <c. 11 h. The thermal time per phyllochron varied between leaves and the combined times for all the phyllochrons at a particular sowing accounted for the apparent response of average phyllochron to sowing date. The thermal time requirements for progression to the double ridge stage, terminal spikelet stage, onset of stem elongation and anthesis were similar except where photoperiods of <11 h occurred. The rate of grain primordium production was constant when photoperiod had been increasing at seedling emergence but the rate was reduced when the seedling experienced shortening photoperiods at emergence.