Showing papers in "The Journal of Agricultural Science in 1998"

Nitrogen and organic matter losses during storage of cattle and pig manure

Abstract: Solid pig manure (240 g kg 1 DM) and solid cattle manure (150-180 g kg 1 DM) were stored in an open storage facility during spring-summer and autumn conditions for periods of 9-14 weeks during 1994 and 1995. Concentrations of C, N, P and K were determined prior to and after storage, corrected for dry matter losses and distance from the surface. Temperature and, in experiments with pig manure, gas phase composition inside the manure heap were monitored during storage. Nitrogen losses as ammonia volatilization, nitrous oxide emission and leaching were measured, while total denitrification was estimated from mass balance calculations. For both cattle and pig manure there was little difference between seasons with respect to the pattern of decomposition, as reflected in temperature dynamics and C/N turnover. In contrast, there was a distinct difference between manure types. Pig manure was characterized by maximum temperatures of 60-70°C, although the concentrations of oxygen and methane clearly demonstrated that anaerobic conditions dominated the interior parts of the heap for several weeks. Losses of C and N from pig manure both amounted to c . 50%. In contrast, the temperature of cattle manure remained close to the air temperature throughout the storage period and cattle manure had lower, not significant losses of C and N. Leaching losses of N constituted 1-4% with both manure types. Ammonia volatilization from cattle manure constituted 4-5% of total N, and from pig manure 23-24%. In pig manure a similar amount of N (23-33%) could not be accounted for after storage, a loss that was attributed to denitrification. Nitrous oxide emissions amounted to <2% of estimated denitrification losses.

The feeding value of chicory (Cichorium intybus) for ruminant livestock

Abstract: Chicory (Cichorium intybus) is perhaps best known for the extract of its roots used as an ingredient in ‘coffee substitute’ beverages. It is less well known as a grazed forage for ruminants. Thomas et al. (1952) reported the high content of some major and minor trace minerals in chicory grown in the UK, and commented on its use in pasture mixtures as a source of these minerals. Chicory was first mentioned in New Zealand (NZ) literature as an animal forage by Cockayne (1915), but a long period then elapsed before Lancashire (1978) reported its excellent value for forage production under rotational grazing in dry summer conditions. Plant selection then followed and the cultivar ‘Grasslands Puna’ was approved for commercial release as a grazed forage plant in 1985 (Rumball 1986). The use of Puna chicory has now spread throughout NZ and the variety is also being used commercially in Australia, North America and South America and is being evaluated in parts of Europe and Asia (W. Green, personal communication). Chicory is a herb, whereas other temperate forages used for ruminant production are either grasses or legumes. This paper reviews work on the chemical composition, nutritive value and feeding value of chicory relative to perennial ryegrass (Lolium perenne) and to red clover (Trifolium pratense), a legume that, like chicory, is used as a forage for dry summer conditions. Throughout this paper, feeding value is defined as the animal production response to grazing a forage under unrestricted conditions (Ulyatt 1973), with its components being voluntary feed intake (VFI), the digestive process and the efficiency of utilization of digested nutrients; the latter two comprise nutritive value/dry matter (DM) eaten.

Evidence for differences between winter wheat cultivars in acquisition of soil mineral nitrogen and uptake and utilization of applied fertilizer nitrogen

Abstract: The response of cultivars to applied nitrogen was examined in 11 seasons, 1982-92, in two experiments per year, normally testing seven cultivars at seven rates of fertilizer nitrogen. In all, 27 cultivars were tested in 22 experiments throughout Nottinghamshire, Lincolnshire, Northampton-shire and Suffolk. Cultivars ranged in their date of introduction from Maris Huntsman (1969) to Hereward (1988). For each cultivar in each experiment, the economic optimum yield (Y opt ), the amount of fertilizer N needed to produce it (N opt ), the grain % N at N opt , the offtake of N in the grain at nil N (N off(NO) ) and N opt (N off(opt) ) and the estimated recovery of fertilizer in the grain at N opt (AFR opt ) were estimated by fitting linear plus exponential curves to data for grain yield and two-straight-line models to data for grain N offtake. From cross-site analysis, normalized cultivar means were calculated for each variate. Over the 20-year period relating to the cultivars in the trial, the contribution of new genotypes to grain yield improvement was 1.92 t/ha, Y opt increasing by 96 kg/ha per year. There was no change in grain % N at N opt . The effect of changes through breeding from 1969 to 1988 was to increase N off(opt) by 42 kg/ha (2.1 kg/ha per year), that was associated with a decrease in N off(NO) (equivalent of soil N offtake) of 15 kg/ha (0.77 kg/ha per year). Part of the increased requirement for fertilizer N was fulfilled by an increase in AFR opt of 18 % over the 20-year period. The net effect was for N opt itself to increase by 56 kg/ha (2.8 kg/ha per year). Since survey evidence indicates no general increase in N use on wheat by farmers since the mid-1980s, it appears that current fertilizer use by farmers may be underestimating the requirement for N now. Alternatively in previous years N requirements may have been overestimated. The change in N available for loss to the environment, from the balance of grain N off(opt) and N opt , was from 11 kg N/ha in 1969 compared to 25 kg N/ha in 1988. It seems possible that the potential increase in nitrate levels in groundwater associated with plant type may not have been realised because farmers have conserved the amount of N they use.

Influence of xylanase-supplemented feed on the development of selected bacterial groups in the intestinal tract of broiler chicks

Abstract: 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.

Biophysical interactions at the root–soil interface: a review

Abstract: Soil close to roots generally has chemical, physical and biological properties which are significantly different from those of soil located some distance away (Jenny & Grossenbacher 1963; Hawes & Pueppke 1986; Young 1995). The root–soil interface is defined as soil near to or adhered to the root surface to some small distance into the soil matrix. This distance may vary between <1 mm and c. 10 mm. Working definitions include rhizosphere, where ‘zones of influence’ are inferred, and rhizosheath, when soil adhered to the root is discussed. Most work carried out at the root–soil interface has concentrated on biological or chemical processes, due both to the fact that the relevant techniques required to examine these processes have been more advanced than the physical techniques, and also because the farmer is generally offered either biological or chemical solutions to his everyday problems, as these are readily accessible, easy to use and cheap. The main manipulation of soil physical conditions occurs during cultivations, and the addition or removal of water from the soil profile. Intensive cultivations are a regular occurrence in many farming systems, despite the potential drawbacks: damage of the soil structure, leading to reduced crop yields and an increased risk of erosion.The main aim of this review is not to cover all the complex issues related to the root–soil interface. Instead, it concentrates on the biophysical processes which, compared with conventional plant physiological and soil microbiological research, have attracted relatively limited attention (e.g. see Waisel et al. 1996). The review examines small-scale (μm-mm) interactions and, where possible, links their impact to the larger scale. Three interacting areas are investigated: the physical structure of the soil and root growth, water dynamics and microbial dynamics.

Cultural control of volunteer oilseed rape (Brassica napus)

Abstract: Laboratory studies on the biology of oilseed rape (Brassica napus L.) showed that the induction of secondary dormancy is influenced by light environment, time of exposure to light and darkness, temperature regime and genotype. Seeds did not become dormant while exposed to light but were increasingly likely to become dormant the longer they were exposed to water stress and darkness. Dormancy was broken by alternating warm and cold temperatures. Conclusions from results obtained in Petri dishes have been tested in the field and hypotheses regarding the effects of post-harvest cultivation have been proposed. In July 1995, field experiments were initiated on a flinty silty clay loam and a sand to test the implications of post-harvest cultivation on the development of a persistent seedbank. The results largely confirmed assumptions made on the basis of laboratory findings. Seeds that had been exposed to water stress and darkness for longest, by cultivating the soil at the beginning of the experiment, immediately after seed distribution, exhibited the highest persistence rates. Seeds that were exposed to light for 4 weeks and then incorporated into the soil built up a much smaller seedbank. The seedbank was very small or nonexistent in plots that had not been cultivated at all.

Selection of diets by dual-purpose Mamber goats in Mediterranean woodland

Abstract: The feeding behaviour of Mamber dairy goats grazing on Mediterranean woodland in the Upper Galilee mountains of Israel was studied throughout a year (1991/92). The percentages of crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL) and condensed tannins (CT) were determined in samples collected by hand to simulate the plant parts selected by the goats. Total feed intake was evaluated by using Cr-sesquioxide as an external marker to determine the amount of faeces excreted, and 48 h in sacco degradability to assess the digestibility of samples. Overall, more time was spent by goats in feeding on ligneous material (tree and shrub foliage) than herbaceous vegetation (60 and 40 % of total feeding time, respectively, P < 0.05). The main ligneous species consumed by the goats were Quercus calliprinos, Sarcopoterium spinosum and Calico tome villosa (20, 13 and 7% of total grazing time, respectively). There was considerable variability in the 48 h dry matter (DM) in sacco degradability, and in the concentration of CP, NDF, ADF, ADL and CT, within and between seasons and plant species. Although requirements for nutrients varied according to the physiological stage of the goats, 48 h in sacco DM degradability and the concentration of non-ADF linked (available) CP, NDF, ADF, ADL and CT in the diet did not vary greatly: respective ranges were 45.0-49.4; 9-12.5; 44-53; 33-39; 12-17 and 3.5-4.7%. It is concluded that Mamber goats (i) may not select the best quality diet available, but may avoid wide variations in nutrient content of their diets throughout the year; and (ii) may not select a diet consistent with maximization of milk yield, but rather with optimization of body condition at the onset of the mating season.

The effect of winter cover crop management on nitrate leaching losses and crop growth

Abstract: Two field experiments in Canterbury, New Zealand, were conducted during 1993–95 following the ploughing of temporary pasture leys. These experiments investigated the effects of cover crop management on the accumulation of soil mineral N and nitrate leaching during winter, and the growth and N uptake of the following spring cereal crop. The cover crops used were ryegrass ( Lolium multiflorum L.), oats ( Avena sativa L.), lupins ( Lupinus angustifolius L.), mustard ( Sinapis alba L.) and winter wheat ( Triticum aestivum ). Ploughing of temporary pasture in autumn (March) resulted in extensive net N mineralization of organic N by the start of winter (June). In fallow soil, mineral N in the profile in June ranged from 98 kg N/ha in 1993 to 128 kg N/ha in 1994. When cover crops were established early in the autumn (March) in 1993, both the above-ground dry matter production (1440–3108 kg DM/ha) and its N content (50–71 kg N/ha) were substantial by the start of winter. In 1994, establishment of cover crops one month later (April) resulted in very little dry matter production and N uptake by June. In both years, compared with fallow soil, winter wheat planted in May had little effect on soil mineral N content by the start of winter. Compared with fallow, cover crops had little effect on soil drainage over winter. Cumulative nitrate leaching losses from fallow soil were much smaller in 1993 (23 kg N/ha) than in 1994 (49 kg N/ha), mainly due to differences in rainfall distribution. Cover crops reduced cumulative nitrate leaching losses in 1993 to 1–5 kg N/ha and in 1994 to 22–30 kg N/ha. When cover crops were grazed, soil mineral N contents were increased due to the return of ingested plant N to urine patch areas of soil. Elevated soil mineral N contents under grazing persisted throughout the winter. Grazing had little effect on cumulative nitrate leaching losses, mainly because of the small amount of drainage that occurred after grazing in either year. Compared with fallow, incorporation of large amounts of non-leguminous above ground dry matter depressed the yield and N uptake of the following spring-sown cereal crop. Where cover crops were grazed, yields of the following cereal crops were similar to those for soil fallow over the winter.

Yield, N uptake, and apparent N-use efficiency of winter wheat and winter barley grown in different cropping systems

Abstract: Increasing the efficiency with which crops use supplied nitrogen (N) can minimize the impact on the environment. In the growing seasons 1990/91 to 1992/93, the effects of different cropping systems on yield, N uptake by the grain and apparent N-use efficiency (NUE) of the grain of winter wheat and winter barley were investigated in a factorial field experiment at Hohenschulen Experimental Station near Kiel in NW Germany. The crop rotation was oilseed rape-winter wheat-winter barley, and soil tillage (conservation tillage without ploughing, conventional tillage), application of pig slurry (none, autumn, spring, autumn + spring), mineral N fertilization (0-240 kg N ha -1 ) and application of fungicides (none, applications against pathogens of the stems, leaves and ears) were all varied. Each year, the treatments were applied to all three crops of the rotation and were located on the same plots. Averaged over all factors, wheat yield was > 7 t ha -1 dry matter in all years and N uptake of the harvested grain varied between 140 and 168 kg N ha 1 . Pig slurry application in autumn increased grain yield and N uptake more than spring slurry in two out of three years. Mineral N unfertilized wheat yielded only 5.3-6.3 t ha depending on the year, mineral N fertilization increased wheat yield up to 8 t ha -1 . Barley yield was lower than wheat yield, ranging from 4.5 t ha -1 in 1993 to 6.3 t ha -1 in 1992. Unlike wheat, spring slurry N affected barley yield and N uptake more than autumn slurry. Wheat apparently utilized 12-21 % and barley up to 13% of the applied slurry N for its grain development. In 1991, the highest apparent slurry N-use efficiency (SNUE) of wheat and barley occurred after the late spring slurry application. However, in the following years, autumn SNUE of wheat was similar to (1992) or higher than (1993) spring SNUE, presumably because of vigorous tiller growth before winter. Additionally applied mineral fertilizer N decreased SNUE. Apparent mineral fertilizer N-use efficiency (FNUE) was higher than SNUE and ranged in wheat from 40 to 59% and in barley between 19 and 37% of the applied mineral fertilizer N. FNUE decreased with increasing N fertilization. To improve the N-use efficiency of both slurry N and mineral fertilizer N, more information is needed about the combined use of both N sources, with special emphasis on split applications of slurry as is common practice for mineral N fertilizer.

Yield and partitioning in crops of contrasting cultivars of winter wheat in response to CO2 and temperature in field studies using temperature gradient tunnels

Abstract: Diverse cultivars of winter wheat (Triticum aestivum L.) were grown in the field in 1993/94 and 1994/95 at Reading UK in temperature gradient tunnels at normal atmospheric (c. 370) or elevated CO2 concentration (c. 700 μmol CO2 mol−1 air). In 1993/94, grain yield of cv. Avalon was insensitive to mean temperature (between 8·8 and 10·9°C), while elevated CO2 increased yield by 1·3 t ha−1 (12·6%). In all other cultivars, warming reduced grain yield and CO2 increased grain yield. In 1993/94, in cvs Galahad and Mercia the effects of CO2 and temperature on yield were additive. However, for cv. Hereward in both years and for cv. Soissons in 1994/95, there were negative interactions between the effects of CO2 and temperature on yield: the maximum benefit of doubling CO2 to grain yield, 4·5 and 2·7 t ha−1 (65 and 29%) respectively, occurred at cooler temperatures; there was no benefit from doubling CO2 (i.e. 0%) once the temperature had increased above the seasonal mean by 2·2–2·6°C in cv. Hereward and by 1·3°C in cv. Soissons. The beneficial effect of doubling CO2 on grain yield in cvs Galahad, Hereward, Mercia and Soissons was negated by an increase in mean seasonal temperature of only 0·7–2·0°C. Warming decreased root dry mass at anthesis in 1994/95 while it increased at elevated CO2 (49 and 186%, coolest and warmest regime, respectively). Carbon partitioned to roots declined progressively with warming, while at elevated CO2 there was an average of 56% increase in allocation to roots. The relative impacts of both CO2 and temperature were greater on root dry mass than on either grain yield or total above-ground biomass, while the effects on grain and biomass yield varied considerably between cultivars, suggesting that the impact of rising CO2 and temperature are likely to be dependent on cultivar.

The relative effects of drought stress and virus yellows on the yield of sugarbeet in the UK, 1980-95.

Abstract: 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.

Controlled-temperature effects on cotton yield and fibre properties

Abstract: 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.

Survey of vesicular-arbuscular mycorrhizae in lettuce production in relation to management and soil factors

Abstract: The occurrence of vesicular–arbuscular mycorrhizae (VAM) root colonization and spore number in soil was assessed for 18 fields under intensive lettuce (Lactuca sativa L.) production in California during July and August of 1995. Data on management practices and soil characteristics were compiled for each field, and included a wide range of conditions. The relationship between these factors and the occurrence of VAM in these fields was explored with multivariate statistical analysis. VAM colonization of lettuce tended to decrease with the use of chemical inputs, such as pesticides and high amounts of P and N fertilizers. Addition of soil organic matter amendments, the occurrence of other host crops in the rotation, and soil carbon[ratio ]phosphorus and carbon[ratio ]nitrogen ratios, were positively associated with VAM colonization of lettuce roots. The number of VAM spores in soil was strongly correlated with the number of other host crops in the rotation, the occurrence of weed hosts and sampling date, but was more affected by general soil conditions than by management inputs. Higher total soil N, C and P, as well as CEC, were inversely related to soil spore number. A glasshouse study of the two primary lettuce types sampled in the field showed no significant differences in the extent of root colonization under similar growing conditions. The results of this study are compared with other studies on the effects of management and soil conditions on mycorrhizal occurrence in agriculture.

REVIEW A review of some studies into tuber initiation in potato ( Solanum tuberosum ) crops

Abstract: Despite the importance of potato tubers as a source of food and a means of propagation, the initiation, growth and development of tubers and the factors affecting these processes are not well understood. There are many reported studies of the effects of various factors on the initiation of tubers but, for a number of reasons, few have sought to understand the initiation of tubers under field conditions. Most reports are concerned with experiments carried out in growth-rooms, which often used very short stem sections as planting material and in which environmental conditions, especially light intensity, differed greatly from those normally prevailing during the period of initiation in the field. In almost all field experiments, the timing of initiation was not defined or properly assessed; number of tubers was recorded infrequently and maximum number of tubers was rarely, if ever, established. Despite these deficiencies, the initiation of tubers is still widely regarded as a key developmental stage in the crop's life, having profound implications for subsequent growth and development (Ewing 1990; Ewing & Struik 1992). This view was first expressed 30 years ago (Ivins & Bremner 1965; Bremner & Radley 1966) and its general acceptance has greatly influenced studies of the growth and development of the crop. During the intervening years, the study of tuber initiation has been an important aspect of research programmes at the University College of Wales (UCW) Field Station, Tenby, Pembrokeshire (1972–84) and Cambridge University Farm (CUF), Cambridge (1982–95), which have now produced sufficient data for a re-evaluation of the significance of tuber initiation in field-grown potato crops.

Dietary manipulation as a means of decreasing N losses and methane emissions and improving herbage N uptake following application of pig slurry to grassland

Abstract: Slurry was collected from two groups of finishing pigs fed either a standard commercial diet (containing 205 g/kg crude protein (CP)) or a specially formulated lower CP content diet (140 g/kg CP). The slurries were surface applied to grass/clover plots on a freely draining soil in SW England in mid-March 1995 at three application rates: 25, 50 and 70 m 3 /ha. Measurements were made from the 50 m 3 /ha plots of ammonia volatilization, denitrification, nitrous oxide and methane emissions and nitrate leaching. Measurements of herbage yield and apparent N recovery (ANR) were made from all plots. Decreasing the CP content of the pigs' diet reduced N excretion by the pigs and also changed other characteristics of the slurry. Slurry from pigs fed the lower CP diet (the slurry referred to hereafter as LS) had a higher dry matter (DM) content, lower pH, lower total ammoniacal N (TAN), total N and VFA content with a similar total C content compared with slurry from pigs fed the standard commercial diet (the slurry hereafter referred to as CS). From the 50 m 3 /ha treated plots, losses by ammonia volatilization represented 38 and 58 % of the applied TAN and net losses through denitrification represented 5.3 and 12% of the applied TAN for LS and CS respectively. Nitrous oxide emission was similar from the two slurries, with net emissions of c. 0.5 % of the applied TAN. Methane emission was significantly less from LS. No nitrate leaching was detected either in spring or in the following autumn. Yield and ANR increased with increasing slurry application rate up to 50 m 3 /ha. The best % N recovery was from the 50 m 3 /ha application rate with 58 and 47 % of the applied TAN being recovered from LS- and CS-treated plots respectively. Changes in the slurry characteristics due to the lower CP diet resulted in lower losses to the environment and an improved utilization of the slurry N by the herbage.

Cell wall thickness and cell dimensions in plant parts of eight forage species

Abstract: To appreciate more clearly some of the physical characteristics of forages which may be important in relation to digestibility and structural integrity, different parts of eight plant species were examined for the proportion of thick-walled, thin-walled and epidermal cells, the thickness of the cell walls and the diameter, length and volume of the cells. The eight species were: Trifolium repens L., Medicago sativa L., Desmodium intortum (Mill.) Urb., Lolium perenne L., Festuca arundinacea Schreb., Chloris gayana Kunth, Cenchrus ciliaris L. and Zea mays L. Early harvesting was compared with later harvesting in each of two years. The plants were grown in a heated glasshouse in spring–summer.The plant parts with the lowest proportion of thick-walled cells (3–6% of cross-sectional area) were the legume leaflets and those with the highest proportion (47–57%) were the leaf blades and stems of C. ciliaris. The plant parts with the highest proportion of thin-walled cells were the legume leaflets and petioles and the Z. mays stems and leaf sheaths. The walls of the cells categorized as thick-walled were thinnest (0·9 μm) in L. perenne leaf blades and T. repens leaflets and thickest (2·0–2·3 μm) in the leaf blade midribs, leaf sheaths and stems of Z. mays and in the stems and petioles of T. repens. The thinnest outer walls of epidermal cells (0·9 μm) were recorded for the leaf blades of L. perenne.The largest cells within the categories and plant parts examined (1 100000 μm3) were thin-walled cells in the stems of Z. mays. The longest cells recorded (180 μm) were thin-walled cells in the petioles of T. repens. The thick-walled cells were particularly small (1800–2600 μm3) in L. perenne leaf blades and sheaths and in T. repens leaflets. The largest thick-walled cells in the study were in the stems and petioles of T. repens. The epidermal cells of D. intortum leaflets, petioles and stems were particularly small (2000–3000 μm3).

Effects of long-term fertilizer phosphorus application on soil and crop phosphorus and cadmium contents

Abstract: The effects of four rates of fertilizer phosphorus (P) application (0, 9·8, 19·6 and 39·2 kg P/ha per year) on soil and crop P and cadmium (Cd) contents were measured in a field trial begun in 1968 and cropped each year with barley in south west England In 1996, available and total soil P and Cd were measured in seven soil layers (0–20, 20–25, 25–30, 30–35, 35–40, 40–45 and 45–50 cm) Offtake of P in the crop was measured, or could be estimated, throughout the trial period There was a linear relationship between P balance (total applied − total offtake) and P application rate with a balance of zero at a rate equivalent to 17 kg P/ha per year The rate of P required for the economically optimum grain output was equivalent to 30 kg P/ha per year No evidence was found for available P enrichment of soil layers below 25 cm There was no evidence of Cd enrichment of either soil or crop after 29 years of P applications

A comparative study on growth, body composition and carcass tissue distribution in Omani sheep and goats

Abstract: Growth, body composition and distribution of carcass tissues were compared in Omani sheep and goats. Animals had ad libitum access to Rhodes-grass hay (8 % CP) and a concentrate diet (16 % CP) from weaning until slaughter. The two species had similar birth weights but sheep had higher preweaning (181 g/day), postweaning (175 g/day) and overall (179 g/day) growth rates than goats (120, 102 and 111 g/day, respectively) and thus they reached slaughter weights earlier. Sheep had higher slaughter weight (22.26 kg), empty body weight (20.39 kg), hot carcass weight (12.48 kg) and dressing out percentage (55.94%) than goats (21.17, 18.82, 11.48 kg and 53.97%, respectively). Sheep also had higher proportions of skin, liver and lungs and trachea (P < 0.01) than goats, which had higher proportions of head, feet and gut contents. As proportions of carcass weight, sheep had higher fat (25.08%) but lower muscle content (57.24%) than goats (15.72 and 65.88 %, respectively). There were no significant differences between the two species in proportion of carcass bone (13.76 and 14.17%). These effects resulted in sheep having a lower muscle:bone ratio (4.19 and 4.68) and higher fat:muscle ratio (0.44 and 0.24). Sheep had higher proportions of non-carcass, carcass and total body fat in the empty body weight (EBW) than goats. However, sheep had less non-carcass but more carcass fat than goats when fats were expressed as proportions of total body fat. Sheep had higher proportions of muscles in the proximal hind limb, distal hind limb (P < 0.01), around the spinal column, connecting forelimb to thorax and high-priced muscle group (P < 0.05), but lower proportions of muscles in the abdominal wall, proximal forelimb (P < 0.05), distal forelimb (P < 0.01), connecting neck to forelimb, intrinsic muscles of neck and thorax (P < 0.05) and total forequarter muscles (P < 0.01) than goats. As proportions in carcass bone, sheep had higher axial skeleton (P < 0.05) but lower forelimb than goats. Among species/sex/slaughter weight groups, castrated male and female goats had the lowest growth rates. Castrates and female sheep, particularly at heavier liveweights, had higher carcass and non-carcass fat contents than intact males and goats of all sexes. Although Omani goats produced leaner carcasses and had higher proportions of some non-carcass offals than Omani sheep, they had slower growth rates and a less attractive muscle distribution. This may negatively affect their potential for large scale meat production under Omani conditions.

Influence of dietary energy and nutrient concentration on the growth of body weight and of carcass components of broiler chickens

Abstract: The influence of dietary nutrient concentration on performance and the growth of fat depots, breast meat and leg muscles was examined in five groups of male broiler chickens fed ad libitum with combinations of high (H), commercial (C) or low (L) energy and nutrient concentration in starter and finisher diets Diets were changed from starter to finisher at 3 weeks of age giving 200 birds on each of five treatments: HH, HL, CC, LH and LL Ten birds per treatment were slaughtered at weekly intervals from 0 to 70 days Five of these were dissected into component lean tissues of breast muscles (white meat) and thigh+leg muscles (dark meat) and fat depots, and the other five carcasses were minced for chemical analyses Data were analysed by fitting Gompertz functions to each componentAnalysis of body weight, carcass components and feed intake revealed that at 70 days birds on LH approached similar liveweights to those on HH with lower overall food intakes, comparable feed conversion ratios but slightly greater fat depots The HL birds had less fat but achieved specific weights over longer periods of time with greater feed intakes and poorer feed conversion ratios Content of white and dark meat was always greater in HH birds, with differences between treatments being greater for white meatDecisions on which conditions are most appropriate will be influenced by time taken to reach specific liveweights if whole birds are marketed, or the rate of growth of individual portions if further processing is considered, together with feed conversion efficiency and the relative costs of diets varying in energy and nutrient concentration

Arbuscular mycorrhizal associations of plants colonizing coal mine spoil in India

Abstract: A survey of soil and root samples collected beneath some pioneering plants colonizing reclaimed mine spoil at an opencast coal mine site at Chandrapur, Maharashtra State, India, was conducted in October 1994 to examine the possible host and edaphic influence on the occurrence of arbuscular mycorrhizal (AM) fungi. Thirteen plant species were sampled to determine the mycorrhizal root colonization and the number of spores of individual AM fungal species in the rhizosphere. Typical AM fungal infection was observed in roots of all the plant species examined. Mycorrhizal infection ranged from 20 to 95%. Sampled soils contained six spore-forming species of AM fungi (Acaulospora scrobiculata, Entrophospora colombiana, Glomus aggregatum, Glomus ambisporum, Scutellospora calospora and a previously undescribed species of Glomus). Fungal spore densities were not related to the mycorrhizal infection levels. E. colombiana and G. ambisporum were the leading species in terms of spore densities and frequencies. Phenotypic variations in spores of AM fungi were possibly related to the physical and chemical properties of the mine spoil. It is concluded that the pioneering plant species on mine spoils can cause the development of different populations of AM fungi. The study also indicates that certain species of AM fungi have broad environmental requirements.

In vitro digestibility and neutral detergent fibre and lignin contents of plant parts of nine forage species.

Abstract: 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

A comparative study of nitrate leaching from intensively managed monoculture grass and grass-clover pastures

Abstract: Nitrate leaching losses from intensively managed monoculture grass and grass-clover pastures were measured during 1994-96 at a long-term experimental farm in south-west Scotland. Field-size lysimeter plots were established in 1993 on the existing pastures on a silty clay loam non-calcareous gley. No fertilizer-N was applied to the grass-clover, while the monoculture grass was fertilized with c.240 kg N ha-1 year-1, but both swards received 2-3 cattle slurry applications annually (120-390 kg total N ha-1 year-1). The pastures supported 2-3 cuts for silage conservation, and were grazed by dairy cattle and stocked with sheep during the winter months. Initially, leachate nitrate concentrations from the fertilized grass were considerably larger than those from the clover-based pasture, but became similar with time. The annual nitrate leaching losses from the grass-clover (24-38 kg NO3-N ha-1) were less than that from the monoculture grass (30-45 kg NO3-N ha-1), but the differences were not large considering the additional fertilizer-N applied to the latter treatment. Results also suggested that greater leaching losses occur during a warmer, drier year, compared to a cooler, wetter year, regardless of the source of N-input.

Mineral and slurry nitrogen effects on yield, N uptake, and apparent N-use efficiency of oilseed rape (Brassica napus)

Abstract: In NW Europe, autumn-grown oilseed rape normally receives nitrogen (N) in autumn as seedbed N and in the spring as a split application at the beginning of growth and at stem elongation. In the growing seasons 1990/91 to 1992/93, the effects of slurry and mineral N fertilization on yield, N uptake by the seed and apparent N-use efficiency (NUE) by oilseed rape (Brassica napus) were investigated in a factorial field experiment at Hohenschulen Experimental Station near Kiel, NW Germany. The crop rotation was oilseed rape–winter wheat–winter barley, and soil tillage (conservation tillage without ploughing, conventional tillage), application of pig slurry (none, autumn, spring, autumn+spring) and mineral N fertilization (0 to 200 kg N ha−1) were all varied. Each year, the treatments were applied to all three crops of the rotation and were located on the same plots.Between the years, average seed yield ranged from 3·04 to 3·78 t ha−1, while the corresponding N uptake by the seed varied from 107 to 131 kg N ha−1. Slurry application in spring increased the seed yield and N uptake by the seed in all years, whereas the effect of autumn slurry alone or in combination with spring slurry was negligible. Mineral N fertilizer increased seed yield and N uptake by the seeds except in 1991/92, when N amounts exceeded 160 kg N ha−1. No significant slurry×mineral N interaction occurred. Apparent NUE of mineral N was larger than that of slurry N, but decreased with increasing mineral fertilizer N rates. Only 5% of the autumn slurry N was apparently utilized by the seeds, compared with 24% of the spring slurry N.Despite its ability to take up substantial quantities of N before the winter, oilseed rape utilized very little autumn slurry N for seed production. To minimize environmental impacts, slurry should be applied in the spring, when plants are more able to use N for yield formation, even if NUE of slurry N is lower than that of mineral N. However, since NUE changes with the amount of applied N, it is difficult to find the best combination of slurry and mineral N fertilization to avoid negative environmental effects.

Quantification of the recycling of microbial nitrogen in the rumen using a mechanistic model of rumen fermentation processes

Abstract: The effects of dietary variations on microbial N turnover and recycling related to protozoal activities in the rumen were examined using a previously described model of rumen fermentation processes. Simulations were performed with diets containing variable proportions of concentrate (between 0 and 1 kg/kg diet dry matter) at a rate of daily dry matter intake (DMI) by cattle of between 5.3 and 21.0 kg/day. The roughages examined were hay, fresh grass and maize silage, and the concentrate supplements included molasses, barley, maize grain, untreated and formaldehyde-treated soyabean meal. The simulated fractional turnover rate of microbial N varied between 0.416 and 1.556/day, and simulated microbial N recycling ranged from 34.9 to 76.2% of gross microbial N synthesis. High turnover rates and recycling were observed particularly for diets containing maize silage as roughage and molasses and maize grain as concentrate supplements. Increased DMI generally resulted in reduced turnover rates with high-roughage diets, but increased turnover rates with high-concentrate diets. These responses of microbial N turnover and recycling were related to substrate availability and the substrate preferences of protozoa and, consequently, protozoal activities in the rumen. The large impact of recycling on the amount of organic matter required per unit of microbial protein washed out of the rumen was demonstrated. Thus, by quantification of the interactions between microbial populations in the rumen, the model can help to interpret the differences in microbial N recycling observed in the experiments and provide an improved understanding of the efficiency of microbial protein synthesis.

Estimation of maintenance energy requirements of beef cattle and sheep.

Abstract: Metabolizable energy intake and heat production were measured in a series of calorimetry experiments carried out at the Agricultural Research Institute of Northern Ireland, Hillsborough, between 1993 and 1996 with beef cattle and sheep. A total of 75 estimates were made with cattle: 23 with Charolais cross steers; 16 with Simmental cross steers and 36 with Angus cross steers (450–628 kg liveweight). Fifty-six estimates were made with lambs: 24 with Blackface cross, eight with Suffolk cross and 24 with Texel cross (23–53 kg liveweight). The diets offered to both cattle and sheep contained proportionately 0·0–0·8 cereal-based concentrates, the remainder being grass silage. Linear regressions of energy retention (measured by calorimetry) against metabolizable energy intake were produced for the cattle and sheep studies. From these linear regressions an estimate of metabolizable energy required for maintenance (MEm) was obtained. For cattle, the derived MEm was 0·614 MJ/kg LW0·75 per day, and for sheep the derived MEm was 0·460 MJ/kg LW/kg LW0·75 per day. The estimates were proportionately 0·34 higher in cattle and 0·32 higher in sheep than the 1990 values of the UK Agricultural and Food Research Council.

Evaluation of sorghum root branching using fractals

Abstract: Root branching and architecture play a significant role in water and nutrient uptake, but description of these parameters has not been easy due to the difficulty of observing roots in their natural arrangement. Fractal geometry offers a novel method for studying the branching patterns of roots. Plants of ten diverse sorghum (Sorghum bicolor (L.) Moench) genotypes (five of African origin, three of US origin and two hybrids composed of African×US lines) were grown in root boxes containing 80% sand and 20% fine-textured Sharpsburg silty clay loam topsoil. The root fractal dimension (D) and abundance (log K) were determined at nine regions within the profile. Roots were washed free of growth media and photographic slides were taken of each region. Values of D and log K were determined by projecting photographs onto grids of progressively increasing sizes. The number of intersects was regressed on log grid size. Differences in D were found among genotypes (1·44[les ]D[les ]1·89) suggesting that these sorghum genotypes may be associated with greater root branching patterns. Greater fractal dimension (branching) and abundance values occurred in the 0–35 and 35–70 cm depths of the soil profile within the root box, indicating a greater root distribution in that part of the profile. Significant differences were also noted in branching patterns for sorghum genotypes derived from different sources. In general, the African sorghums were more branched and deeper rooted than the US-derived genotypes. Results indicated that fractal dimension can be used for the description of sorghum root system morphology and provides a good measure of branching patterns which can be distinguished.

The response to fertilizer nitrogen of cereals grown on sandy soils

Abstract: The responses to fertilizer N of winter wheat and winter barley grown on sandy soils were measured in 74 experiments in England from 1991 to 1994. A series of curves was fitted to the data from each of the experiments to determine which best described the yield response to fertilizer N. The linear plus exponential model, adopted for data from a range of other soil types, with the rate parameter (r) determined for each experiment, proved to be the most satisfactory for these data. The median value of r at 0.987 was less than has usually been determined for other soil types, and was reduced by increasing moisture stress in June, suggesting that the reduced efficiency with which recovered N produces assimilate is partly a result of moisture stress. The model produced a mean N opt of 143 kg/ha following cereals. Soil N supply in spring (SNS s ) was small at c. 45 kg/ha and commensurate with a large requirement for fertilizer N. Apparent fertilizer recovery (AFR) at 0.70 was greater than that previously measured on clay or chalk soils, suggesting that AFR was not restricted by lack of soil moisture. The larger AFR is considered to be a consequence of more rapid remobilization of fertilizer N in these sandy soils. The greater recovery of fertilizer N reduced the optimum requirement for fertilizer N. Nitrogen harvest index (NHI) was decreased from 0.76 to 0.70 as fertilizer N increased from 0 to 300 kg/ha, whereas dry matter harvest index (HI) decreased from 0.53 to 0.50. The economic optimum requirement for fertilizer N, at 143 kg/ha, was less than reported for other soil types. The increase in grain yield from applied fertilizer N was less in these experiments than in those reported on other soil types in the UK. However, this overall observation masks two counterbalancing differences. Fertilizer N was recovered more efficiently on these soils: the recovered fertilizer N was used with similar efficiency to produce grain dry matter. The explanation proposed is that on these soils a large proportion of soil water is readily available to crops. and this was taken up rapidly in May accompanied by fertilizer N. However, shortage of water in June restricted the ability of the crop to produce assimilate from fertilizer N applications > c. 150 kg/ha.

A 6-year comparison of nitrate leaching from grass/clover and N-fertilized grass pastures grazed by sheep

Abstract: 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/1 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.

Contribution of dietary sulphur to the interaction between selenium and copper in sheep

Abstract: The effect of concentration of sulphur (S) in a diet on the interrelationship between copper (Cu) and selenium (Se) metabolism was investigated in sheep The animals received a sheep finishing diet in individual feeding pens for a period of 74 days The minerals were included in the diets according to a 3 x 2 x 2 factorial experimental design The final mixtures contained three concentrations of Se; 035, 088 and 134 mg Se (Se added as Na 2 SeO 3 ) ; two concentrations of Cu; 67 and 170 mg Cu (Cu added as CuSO 4 ) and two concentrations of S; 215 and 397 g S (S added as Na 2 SO 4 )/kg dry matter (DM) An increase in dietary Cu resulted in a significant (P < 001) increase in liver Se concentration; 230 v 343 mg Se/kg DM for the low v the high Cu treatments The addition of S reduced the hepatic Se concentration significantly (P < 001) This was most pronounced at the high Cu intake, resulting in a significant (P < 005) three-way interaction between the three minerals, ie the hepatic Se concentrations were 253, 208, 407 and 279 mg/kg DM for the low Cu-low S, low Cu-high S, high Cu-low S and high Cu-high S treatments, respectively Dietary S reduced (P< 001) the concentration of Cu in the liver from 678 mg/kg DM at the low S to 305 mg/kg DM at the high S intakes Dietary Se did not change the concentration of Cu in the liver significantly Adding S to the diet caused a reduction (P < 001) in the Se concentration of rumen bacteria, ie from 348 mg/kg DM in the low S to 196 mg/kg DM in the high S treatments Selenium concentrations in rumen bacteria and the liver were the most sensitive to changes in Se intake, followed by the heart, muscle, plasma and whole blood It was concluded that an increase in S intakes would decrease the accumulation of both Cu and Se in the liver of sheep, resulting in a diminishing degree of interaction between Cu and Se

Integration of nitrate cover crops into sugarbeet (Beta vulgaris) rotations. I. Management and effectiveness of nitrate cover crops

Abstract: Between 1989 and 1993, 17 experiments tested the effect of cover crop species, sowing date and destruction date on cover crop dry matter (DM) yield, N uptake and on soil mineral nitrogen (SMN) content. All the experiments were carried out in Suffolk, Norfolk, Lincolnshire and Yorkshire on sandy-loam textured soils after crops of cereals or oilseed rape had been harvested. The largest DM yields were obtained with early sowings and averaged 1·6 t/ha. Cover crop N uptake was less dependent upon sowing date and averaged 35 kg N/ha. The average reduction in SMN was from 46 to 32 kg N/ha. Differences between cover crop species were small when compared with season/site variations.Cereal cover crop DM yields were closely related to the thermal time accumulated from the first significant rainfall after sowing, whilst the yields of non-cereal cover crops were more affected by the moisture content of the soil at sowing. The amount of SMN in the soil at sowing had little or no effect on cover crop yield. The yields of cereal cover crops were much more predictable than those of non-cereal cover crops. Water usage by cover crops was estimated to be 20 mm/t DM and large cover crops delayed the onset of leaching and reduced the amount of water leached. However, even in dry autumns and winters, soils are likely to reach field capacity before the following beet crop is sown. Due to their large C[ratio ]N ratio (20[ratio ]1) little N would be mineralized after cover crop destruction. Cover crops comprising volunteer cereals and weeds often performed as well as the other cover crops and in most cases will be the most cost-effective cover crops.