Two grazing experiments were undertaken to evaluate the effects of sulla (Hedysarum coronarium) which contains condensed tannins (CT) and lucerne (Medicago sativa), which does not contain CT, on the performance of parasitized and non-parasitized lambs. The work was carried out near Palmerston North, New Zealand in 1992 and 1993. Experiment 1 used lambs which were either genetically 'conventional' or 'resistant' to gastrointestinal nematodes and which had a naturally acquired heavy parasite burden (faecal egg count (FEC) 1300-2500 eggs per gram faeces (epg)). They were either drenched to remove all the parasites or remained undrenched when allocated to pure swards of either sulla or lucerne for the 28-day experimental period. Liveweight gains of drenched lambs were higher with sulla (mean 302 g/day) than with lucerne (mean 245 g/day; P < 0.02) and rates of gain were not reduced (P = 0.10) by genetic resistance to nematodes. Undrenched lambs had mean faecal egg counts of 1090-2220 epg after 28 days, with higher counts in lambs grazing lucerne than in those grazing sulla (P < 0.05). Lambs grazing lucerne also had a much lower average daily gain (ADG) (mean 50 g/day) than those grazing sulla (mean 206 g/day; P < 0.0001). Resistant lambs had reduced (P = 0.07) ADG in the sulla treatment only. In Expt 2, lambs with a relatively low worm burden (average FEC 250 epg) were either drenched to remove all worms or dosed with 20 000 Trichostrongylus colubriformis infective larvae and grazed on pure sulla or lucerne swards for 42 days. Drenched lambs had a similar liveweight gain (mean 190 g/day) and wool growth when grazing either sulla or lucerne. Undrenched lambs grazing sulla had a greater ADG (mean 129 g/day) than those grazing lucerne (mean -39 g/day; P < 0.0001) and a higher rate of wool growth from mid-side patches (P < 0.009) and larger wool fibre diameter (P < 0.05) than those grazing lucerne. Undrenched lambs grazing sulla had lower FECs (P < 0.05) on days 14, 21, 35 and 42 than those grazing lucerne and lower (P < 0.05) Trichostrongylus colubriformis worm burdens at slaughter. Undrenched lambs had less perineal faecal contamination when grazing sulla rather than lucerne. Parasite-induced anorexia was evident in the lambs grazing lucerne but not in those grazing sulla. These findings demonstrate that the performance of lambs infected with nematode parasites can vary substantially when given feeds of a similar chemical composition. The superior performance of lambs grazing sulla was probably caused by condensed tannins, which decrease protein degradation in the rumen and can increase post-ruminal protein availability.
Slurry pH is of great importance for the regulation of ammonia volatilization from livestock slurry, and therefore more knowledge of the buffer system controlling pH is urgently needed for modelling ammonia losses from stored and surface-applied slurry. The composition of 17 different Danish cattle, pig and biogas plant-digested slurries was studied. The results were used to describe the main buffer components in the slurries, and to discover the most important chemical components necessary for modelling slurry pH. The results showed that the pH of slurry was mainly controlled by the species NH4+/NH3, CO2/HCO3-/CO3(2-) and CH3COOH/CH3COO-, and that ion pair formation did not change the ionic balance significantly. There were only trace amounts of Ca2+, Mg2+ and inorganic phosphates in solution due to precipitation of CaCO3 (calcite) and MgNH4PO4.6H2O (struvite). Measured electrical conductivities were found to be strongly correlated with the calculated ionic strength.
The possible interacting effects of shading and N supply on number of grains of Triticum aestivum L. (cv. Buck Nandu) were investigated at Balcarce, Argentina, during the 1988/89 and 1989/90 growing seasons. Shading was imposed from c. 13 days before anthesis to 6 days after, and four rates of N fertilization were supplied within each shading treatment around the date of terminal spikelet formation. Water and other nutrients were not limiting. Total grain yield was strongly correlated with grain number/m(2), regardless of shading or N supply. At the highest N rates, grain number and dry weight of spikes at anthesis were linearly related to a photothermal quotient, i.e. the ratio of intercepted photosynthetically active radiation (PAR) to mean temperature minus 4.5 degrees C, during the period from 20 days before anthesis to 10 days after. The response of grain number to the photothermal quotient was interpreted in terms of the supply of assimilates to the spike at anthesis, which determined flower survival. The response of dry weight of spikes to photothermal quotient was interpreted in terms of crop growth rate since there was a linear relationship between crop growth rate and intercepted radiation. The lowest N rates reduced the number of grains/m(2), at any given photothermal quotient. Since the reduction in grain number also occurred at any given dry weight of spikes, it cannot be explained by a reduced supply of assimilates to the spikes. Grain number responded directly to the supply of N to the spike, probably through the survival of differentiated flowers. The relationship between spike growth rate and crop growth rate was not affected by N supply. Crop growth rate was reduced by reduced N supply, because less radiation was intercepted and because radiation-use efficiency was lowered. These results indicate that current models for determining yield and number of grains/m(2), based on crop growth, are not adequate when N is deficient.
In ruminants, the urinary excretion of purine derivatives (PD) reflects the absorption of microbial purines and can be used as an index of microbial protein supply. The objective of this study, carried out in Aberdeen, 1992, was to examine whether PD concentrations in spot urine or plasma samples vary diurnally during a given feeding regime and if they reflect differences in daily PD excretion induced by varying feed intake. Sixteen sheep were offered ad libitum one of four diets (fresh weight basis, the rest of each diet being minerals and vitamins): (1) 99.9 % lucerne (pelleted); (2) 50% hay, 30% barley, 9% fishmeal and 10% molasses; (3) 72% straw, 7% molasses and 20% molassed sugarbeet pulp; and (4) 97 % barley. Measurements were made for 1 week after a 2-week adaptation period. Urine was collected daily on days 1-4 and hourly on days 5-7. Hourly urine collection was achieved using a fraction collector. Plasma samples were collected hourly from 09.00 to 17.00 h on day 4. Feed intake varied considerably (347-1718 g DM/day) between diets and between animals. Daily excretion of PD (7.1-22.6 mmol/day) was linearly related to DM intake (r = 0.85, n = 16), and so was the microbial N supply (3.9-19.5 g N/day) estimated from daily PD excretion (r = 0.87). In hourly urine samples, the ratio of PD:creatinine concentrations showed no significant difference between sampling times, and was linearly correlated with the daily PD excretion (r = 0.92). Similarly, plasma PD concentration also showed little diurnal fluctuation. Glomerular filtration rate (GFR) increased with feed intake. Plasma PD was not well correlated with daily PD excretion in urine (r = 0.57). The tubular load of PD (plasma PD x GFR) was better correlated with the daily excretion (r = 0.80). It appears that when sheep are fed ad libitum, PD in spot urine may provide a practical indicator of microbial protein supply status.
Field experiments were carried out in Brittany (Western France) in 1993 to measure ammonia losses from surface-applied pig and cattle slurry. Experiments were conducted on grass, stubble (wheat and maize) and arable land using a wind tunnel system. Ammonia losses were followed during periods ranging from 20 to 96 h after slurry application. Rates of slurry applied varied from 40 to 200 m(3)/ha. In two experiments, losses from cattle slurry were respectively 75 and 54% of the ammoniacal nitrogen applied in the slurry. Ammonia emissions from pig slurry applied at a rate of 40 m(3)/ha, during spring and summer experiments, were higher on grass (45-63% of the total ammoniacal nitrogen applied) than on wheat stubble (37-45%). On average, 75% of the total loss in all experiments occurred within the first 15h after spreading. Significant correlations were found between ammonia losses (kg N/ha) and mean soil temperature and slurry dry matter content (%) using simple linear regressions and stepwise procedures. The time of application was also found to influence the magnitude of ammonia loss: 83% of the total loss occurred within 6 h when the slurry was applied at midday compared with 42% when it was applied in the evening.
The effects of synchronizing dietary energy and nitrogen supply in diets with a similar carbohydrate composition on microbial protein synthesis and rumen fermentation were examined in sheep. Two diets were formulated to be either synchronous (diet S) or asynchronous (diet A) for the hourly release of nitrogen (N) and energy to the rumen. Diet S contained (g/kg) 425 g wheat straw, 400 g winter barley, 150 g rapeseed meal and 25 g minerals/vitamins and diet A contained 505 g wheat straw, 458.5 g winter barley, 11.5 g urea and 25 g minerals/vitamins. Both diets were fed at the rate of 1 kg/day in four equal portions, to four cannulated sheep, in two periods in a change-over design. Rumen ammonia concentrations followed the predicted hourly trend in N degradation with a peak 1 h after feeding of 10 mM for diet S and 16 mM for diet A before falling within 3 h of feeding to 4 mM in animals fed either diet. Rumen volatile fatty acid (VFA) concentrations followed the cyclical trend predicted by stoichiometric equations, whilst rumen VFA ratios were more stable than predicted in animals fed either diet. The observed content of rumen degradable protein and organic matter truly degraded in the rumen was similar for both diets. The increase in total CHO digested in the rumen observed with diet A (427 g/kg DM) compared with diet S (364 g/kg DM) can be attributed to the greater content of starch in the asynchronous diet, which had a high degradability. The efficiency of microbial protein synthesis (g N/kg OM truly degraded in the rumen) was 11-20 % greater in animals fed the synchronous diet (S) than the asynchronous diet (A). It is concluded that microbial N production was more efficient when dietary energy and N supply were synchronized.
Electrical conductivity was evaluated for estimating the nutrient content of cattle and pig slurries. Slurry samples were collected in 1991 from the storage tanks of 48 cattle and 10 pig units on commercial farms in Ireland. Samples were analysed for NH4+ and total concentrations of Na, K, Ca, Mg and P. Electrical conductivity (EC) was measured on raw slurries (EC(raw)) and on slurries diluted by 10 with water (EC(dilute)). Relationships between EC and nutrient content were examined by correlation and linear regression analyses. In both slurry types, NH4+ was the dominant cation with K+ second in importance on a molar basis. Within each slurry type, the concentration of each of these cations was significantly correlated with EC. Using EC(dilute) gave more accurate predictions of concentrations than EC(raw), but even EC(raw) was a better predictor than dry matter (DM) content. The linear relationships between NH4+ or K+ and EC(dilute) explained > 82 % of the variance within each slurry type. The P content in slurries was related better to DM than to EC. Since EC measurement could be by cheap, robust meters, its potential for on-farm use deserves further investigation.
Nitrate leaching was measured under three pastures - perennial ryegrass and white clover, a herbal ley comprising a mixture of legumes, non-aggressive grasses and deep rooting herbs, and perennial ryegrass fertilized with 400 kg N/ha per year as urea - from 1989 to 1991 at Palmerston North, New Zealand (latitude 40 degrees S). The pastures were regularly mob-grazed by sheep at a stocking rate which varied with the amount of feed available. Drainage was estimated from a daily soil water balance and accumulated over 10 day intervals. Nitrate concentrations in the drainage were measured as the volume-averaged concentrations in the soil solution between 30 and 45 cm depth during these intervals. Although the N applied as fertilizer to the grass was 2.5 times greater than the N estimated to have been fixed by the clover-based pastures, the leaching loss from the former was 6-7 times greater than from the latter. The stocking rate on the grass pasture averaged over each year was only 1.2-1.4 times that on the two clover-based pastures. Leaching from urine patches was estimated to account for 55% of the total N leached from the clover-based pastures, but only 25% of the total leached from the N-fertilized grass. The amount of NO3-N leached should be related to the cumulative drainage to determine whether the average nitrate concentration exceeds the environmental safety limit of 10 mg NO3-N/1. In 1989: when the total drainage was 215 mm, 21.5 kg N/ha would have had to be leached for the concentration to exceed the limit and none of the pastures did so. In 1990, when the total drainage was 270 mm, the critical amount to be leached was 27 kg N/ha which was exceeded by the Grass + N400, but not by either the Grass-clover (5.8 kg N/ha) or the Herbal ley (7.3 kg N/ha). The utilization of N was more conservative in the clover-based pastures than in the N-fertilized grass.
Two field experiments at Canterbury, New Zealand during 1991-93 investigated the effect of the timing of ploughing a 4-year-old ryegrass/white clover pasture and the effect of two winter cover crops on subsequent N mineralization, nitrate leaching and growth and N uptake of the following wheat crops. Net N mineralization of organic N (of plant and soil origin) increased with increased fallow period between ploughing and leaching. The total amount of N accumulated in the profile by the start of winter ranged from 107 to 131 and from 42 to 45 kg N/ha for fallow treatments started in March and May respectively. Winter wheat (planted in May) had no effect on mineral N contents by the start of winter, whereas greenfeed (GF) oats (planted in March) significantly reduced the mineral N content in one year. Cumulative leaching losses over the first winter after ploughing-in pasture varied markedly between years in relation to rainfall amount and distribution. Leaching losses were greater from the March fallow (72-106 kg N/ha) than the May fallow treatments (8-52 kg N/ha). Winter wheat did not reduce leaching losses in either year. GF oats did not reduce losses in 1991/92, but losses in 1992/93, when major drainage events occurred late in the winter, were only c. 40% of those under fallow. Incorporation of a large amount (> 7 t/ha dry matter) of pasture or GF oat residue in spring depressed yield and total N uptake of the following spring wheat, largely due to net N immobilization which could be overcome by the application of fertilizer N. First-year treatments had very little residual effect in the second year. Leaching losses over the second winter (mean 142 kg N/ha) were largely unaffected by the extent of first year leaching losses. Second year leaching losses were greater than first year losses, probably due to the greater amount of mineral N at depth in the soil before the start of the second winter.
In order to determine whether cereal crops require fertilizer sulphur (S) in areas estimated as receiving 10 kg/ha of S as gypsum at these sites. Yield responses were best predicted by a nitrogen:S concentration ratio greater than or equal to 17:1 in leaf tissue at anthesis and a S concentration of less than or equal to 0.1% in the grain dry matter at harvest. Significant increases in total S and sulphate-S concentrations in leaf tissue at anthesis were obtained from increasing the rates of gypsum applied at ten of the sites, but a significant increase in the concentration of S in the grain at harvest was obtained at only one site. There was no difference in effectiveness between gypsum and foliar-applied elemental sulphur when compared at a single rate of 10 kg S/ha. Comparison of the increases in leaf-S status from maximum application rates of ammonium sulphate and gypsum suggested that ammonium sulphate was the more effective S-fertilizer source. The results confirm that S deficiency is starting to appear in cereal crops in England and Wales.
Field experiments were undertaken at the University of Wales, Aberystwyth over two seasons to investigate the effects of N fertilizer rate and timing on the development of Septoria diseases (principally Septoria tritici) in winter wheat and its subsequent effect on crop growth. Rates of 100, 200 and 300 kg/ha N were applied at GS23, GS30, or split (GS23/30/38) in 1985/86 and 100 and 250 kg/ha N at GS23, GS30, GS23/30, or GS23/30/37 in 1987/88. Foliar diseases were allowed to develop or were controlled with fungicide. Early disease levels were temporarily enhanced soon after N application and were greater at the higher rates of N. In April and June a significant correlation between disease infection and concentration of N in leaf tissue was shown. Despite differences in the level of early infection, dry matter production up to and including anthesis was unaffected by disease. Infection during grain filling caused premature senescence of the flag leaf which significantly reduced grain yield, primarily through a reduction in grain size. Loss of yield was directly related to severity of disease on the flag leaf in early July, with a yield loss of 0.45 % for every 1 % increase in disease infection. The severity of Septoria post-anthesis increased with increasing rate of fertilizer N by an average of 11.1 % per 100 kg/ha N (translating to a potential yield loss of 5 % for each 100 kg/ha N given as fertilizer), but was unaffected by its timing of application.
Winter non-leguminous cover crops are included in crop rotations to decrease nitrate (NO3-N) leaching and increase soil organic matter. This study examined the effect of incorporating a mature cover crop on subsequent N transformations. A field trial containing a winter cover crop of Merced rye and a fallow control was established in December 1991 in Salinas, California. The rye was grown for 16 weeks, so that plants had headed and were senescing, resulting in residue which was difficult to incorporate and slow to decompose. Frequent sampling of the surface soil (0-15 cm) showed that net mineralizable N (anaerobic incubation) rapidly increased, then decreased shortly after tillage in both treatments, but that sustained increases in net mineralizable N and microbial biomass N in the cover-cropped soils did not occur until after irrigation, 20 days after incorporation. Soil NO3-N was significantly reduced compared to winter-fallow soil at that time. A N-15 experiment examined the fate of N fertilizer, applied in cylinders at a rate of 12 kg N-15/ha at lettuce planting, and measured in the soil, microbial biomass and lettuce plants after 32 days. In the cover-cropped soil, 59% of the N-15 was recovered in the microbial biomass, compared to 21% in the winter-bare soil. The dry weight, total N and N-15 content of the lettuce in the cover-cropped cylinders were significantly lower; 28 v. 39% of applied N-15 was recovered in the lettuce in the cover-cropped and winter-bare soils, respectively. At harvest, the N content of the lettuce in the cover-cropped soil remained lower, and microbial biomass N was higher than in winter-bare soils. These data indicate that delayed cover crop incorporation resulted in net microbial immobilization which extended into the period of high crop demand and reduced N availability to the crop.
Ammonia volatilization from stored slurry or surface-applied slurry in the field is strongly affected by pH. Thus a simple, iterative model was developed to predict pH changes in slurry. Concentrations of NH4+/NH3, CO2/HCO3-/CO32- and volatile fatty acids were input data to the model. The model was validated by titrating 17 slurry samples collected from four cattle farms, seven pig farms and three biogas plants. Predictions of pH agreed well for 14 slurries with titration data in the pH interval from 4 to 10. Simulations indicated that microbial degradation of VFA to methane and carbon dioxide resulted in a pH increase if the carbon dioxide produced was lost to the atmosphere. There was little change in pH if the produced carbon dioxide dissolved in the slurry.
A feeding trial was undertaken in Palmerston North, New Zealand in 1991, to determine the extent to which condensed tannins (CT) in Lotus pedunculatus were able to affect the nutritive value of ryegrass (which does not contain CT) for sheep. The trial involved three groups of 11 male cryptorchid sheep held in metabolism crates so that intakes, digestibilities and nitrogen balances could be measured over a 42-day feeding period. One group was fed freshly cut ryegrass (Lolium perenne L.) as a sole diet (Grass group) and the other two groups were given a mixture of about one third freshly cut lotus and two thirds ryegrass (dry matter (DM) basis). This mixture contained c. 1.8% CT in the DM. One group given the mixed diet was drenched twice daily with polyethylene glycol (PEG; PEG group) to bind and remove the effects of the CT from the diet, whilst those not drenched were designated the 'Tannin' group. Intakes of all groups were constrained to that of the Grass group of sheep. Condensed tannins in the lotus had a major effect on the digestion of ryegrass. When the forages were immature, apparent digestibility of nitrogen (N) was substantially reduced in the Tannin sheep (65.3%) compared to the PEG (77.5%) and Grass (77.9%) groups (P < 0.001). With mature forages, the respective values were 48.8, 62.5 and 53.7% (P < 0.01). Rumen ammonia concentrations and plasma urea concentrations were also reduced by CT. Condensed tannins reduced DM digestibility by 3-7 percentage units (P < 0.05) mainly through the effects on N digestion. Concentrations of acetate, propionate and butyrate in rumen liquor were not affected by treatment, but CT reduced the proportions of the minor volatile fatty acids (VFA; isobutyrate, valerate and isovalerate). Treatment did not affect liveweight gain (131-164 g/day), or wool growth from mid-side patches, and N retention was not reduced by CT, so that the nutritive value of the forage was maintained despite the reduction in N digestibility. The principal finding was that CT in Lotus pedunculatus were able to affect the digestibility of both grass and lotus when fed together, and that as little as 1.8% of CT in the dietary DM had a substantial effect on rumen function.
The chlorophyll fluorescence parameters Delta F/Fm' and Fv'/Fm', related respectively to the quantum yield of photosynthetic electron transport and to the efficiency of excitation capture by the open centres of photosystem II, have been evaluated as possible indicators of drought tolerance in durum wheat. Delta F/Fm' and Fv'/Fm' measurements were carried out on excised leaves, both control and dehydrated, of 25 cultivars. Delta F/Fm' and Fv'/Fm' values were obtained at two times after the start of fluorescence measurement: at 14 s, i.e. during the induction curve (Delta F/Fm'(14s) and Fv'/Fm'(14s)) and at 200 s, i.e. at steady state fluorescence (Delta F/Fm'(200s) and Fv'/Fm'(200s)). In dehydrated leaves a mean significant decrease of 20 % (P < 0.001) was observed in Delta F/Fm'(14s) values. In contrast, no great differences were observed between control and dehydrated leaves with regard to Delta F/Fm'(200s), Fv'/Fm'(14s) and Fv'/Fm'(200s). The percentage decrease of Delta F/Fm'(14s) after dehydration was correlated with the drought susceptibility index (DSI) of the cultivars, evaluated on a yield basis and a significant correlation (r = 0.72, P < 0.001) was found.