Areas of sulla (Hedysarum coronarium) and pasture (Lolium perenne/Trifolium repens/Holcus lanatus) were grazed by young sheep (29.5-34.8 kg initial liveweight) in four experiments, and effects upon body growth, wool growth and rumen metabolism were measured. Sulla contained 40-50 g condensed tannins (CT)/kg DM, whilst the pasture contained small amounts of CT (2-6 g/kg DM). After chewing during eating, a lower proportion of total CT was readily extractable and greater proportions were protein-bound and fibre-bound. Nutritional effects attributable to CT were assessed by oral administration of polyethylene glycol (PEG), which binds and inactivates CT, to half the animals grazing each forage. Rates of body growth were consistently higher for lambs grazing sulla than those grazing pasture, with the CT concentration in sulla being neither stimulatory or inhibitory to body growth or voluntary feed intake (VFI). The action of CT reduced carcass fatness in sheep fed both diets, in the one experiment where this was measured. CT present in both sulla and pasture decreased rumen ammonia concentration and decreased molar proportions of iso-butyrate and iso and n-valerate. During spring and early summer, when wool growth rates were highest, CT present in both pasture and sulla increased wool growth rate; when wool growth rates were low during winter, CT had no effect upon the wool growth of sheep grazing either forage. Numbers of protozoa and molar proportions of n-butyrate in rumen fluid were increased by CT in sheep grazing sulla but not pasture. It was concluded that the higher rates of body growth and VFI in lambs grazing sulla was most likely to be due to its very high ratio of readily fermentable: structural carbohydrate. Nutritional effects due to CT need to be established using plants with intermediate CT concentrations (10-20 g/kg DM), when grazed by sheep in physiological states where protein supply is more likely to limit productivity.
Several previous studies have shown that the proportion of clover in sheep diets was greater than the proportion of clover in the mixed species swards being grazed. Various hypotheses have been put forward to explain this observation. One widely held hypothesis is that sheep prefer (actively select) clover to grass. This hypothesis was tested by offering 12 sheep, six that had been recently grazing perennial ryegrass and six that had recently been grazing white clover, the choice between foraging on grass or clover provided as turves. It was found that, rather than prefer clover, the sheep preferred the opposite species to the one they had previously grazed. From these observations, alternative hypotheses are proposed to explain the disparity in composition of the diet relative to the swards observed in previous studies, and the evidence for a constant preference for clover and its basis in grazing behaviour is reconsidered.
N-15-labelled fertilizer was applied, in spring, to winter wheat crops in nine experiments in eastern England over a period of 4 years. Five were on Batcombe Series silty clay loam, two on Beccles Series sandy clay loam (with a mole-drained clay subsoil) and two on Cottenham Series sandy loam. In three of the experiments, different rates of fertilizer N were applied (up to 234 kg N/ha); in the others, a single rate (between 140 and 230 kg/ha) was used. Recovery of fertilizer N in the above-ground crop (grain, chaff, straw and stubble) ranged from 46 to 87% (mean 68%). The quantity of fertilizer N retained in the soil at harvest was remarkably constant between different experiments, averaging 18% where labelled N was applied as (NH4NO3)-N-15-N-15, but less (7-14%) where (KNO3)-N-15 was applied. Of the labelled N present in soil to a depth of 70 cm, 84-88% was within the cultivated layer (0-23 cm). Loss of fertilizer N from the crop: soil system (i.e. labelled N not recovered in crop or soil at harvest) varied from 1 to 35% (mean 13%). The magnitude of loss was influenced much more by weather than by soil type or past cropping. Combining data from these and earlier experiments, the regression L70 = 5(+/- 1.63) + 0.264(+/- 0.0352) R3 accounted for 73% of the variation in the data where: L70 = percentage loss of fertilizer N from the crop: soil system, defined as percentage of labelled N not recovered in crop or in soil to a depth of 70 cm at the time of harvest; R3 = rainfall (in mm) in the 3 weeks following application of N fertilizer. There was a tendency for percentage loss of fertilizer N to be greater when a quantity of N in excess of that required for maximum grain yield was applied. However, a multiple regression relating loss both to rainfall and to quantity of N applied accounted for no more variance than the regression involving rainfall alone. In one experiment, early and late sowing were compared on the first wheat crop that followed oats. The loss of N from the early-sown crop, given fertilizer N late in spring, was only 4% compared with 26% from the later-sown crop given N at the same time, so that sowing date had a marked effect on the loss of spring-applied fertilizer N. Uptake of unlabelled N, derived from mineralization of organic N in soil, autumn-applied N (where given) and from atmospheric inputs, was 130 kg/ha when wheat followed potatoes or beans on soil containing c. 0.15% total N. Unlabelled N accounted for 20-50% of the total N content of fertilized crops at harvest. About 50% of this unlabelled N had already been taken up by the time of fertilizer application in spring and the final quantity was closely correlated with the amount present in the crop at this time. Applications of labelled fertilizer N tended to increase uptake of unlabelled N by 10-20 kg/ha, compared to controls receiving no N fertilizer. This was probably due to pool substitution, i.e. labelled inorganic N standing proxy for unlabelled inorganic N that would otherwise have been immobilized or denitrified.
The effect of maternal undernutrition between the 30th and 96th day of pregnancy on placental growth in single-bearing ewes was determined separately in two experiments in consecutive years (1986 and 1987) at Mount Derrimut Field Station, Deer Park, Australia. In the first experiment, placental growth measured on the 96th day of pregnancy was reduced (473-nu. 596 g) by maternal undernutrition, while in the second, placental growth was increased (600-nu. 496 g). Foetal weight and its linear dimensions on the 96th day of pregnancy were not significantly affected by maternal undernutrition in either experiment. The only significant difference in the animals and experimental conditions between the two studies was the liveweight of the ewes at mating, which was c. 10 kg higher in the second experiment compared with the first (P < 0.01). Body condition score and the change in condition score during the respective nutritional treatments were not significantly different between the two experiments. The results suggest that maternal liveweight, possibly body reserves not quantifiable by condition score, protects and even enhances placental growth during a period of maternal undernutrition.
Simulation models are heuristic tools for integrating diverse processes and help to increase our understanding of complex processes and systems. Models that predict crop development can serve as decision-support tools in crop management. This paper describes a phenology simulation model for the winter wheat shoot apex and reports validation and sensitivity analysis results. The complete developmental sequence of the winter wheat shoot apex is quantitatively outlined and correlated with commonly recognised phenological growth stages. The phyllochron is used to measure the thermal time between most phenological growth stages, thereby increasing the flexibility over the growing degree-day (GDD) and photothermal approaches. Nineteen site-years covering a range of climatic conditions, cultural practices and cultivars across the Central Great Plains, USA, are used to validate the model. Validation results show that the predicted phyllochron (108 GDD) agrees well with the observed phyllochron (107 GDD) for ten cultivars. Mean seedling emergence is predicted to within 2 days in almost all of the 19 site-years. The ability of the model to predict growth stages accurately increased successively from jointing to heading to maturity. Maturity is generally predicted to within 5 days of the observed day. After validation, recalibration of the phyllochron estimates between growth stages are provided, and corrections for mesic and xeric conditions are suggested. Further validation of the entire developmental sequence of the shoot apex is recommended.
When N-15 is used to trace the fate of N fertilizer applied in spring to winter wheat crops, some is not recovered in the crop or the soil and has to be presumed lost. In 13 experiments made from 1980 to 1983 on three widely differing soils, these losses ranged from 1 to 35%. We partitioned them between leaching and denitrification by using models to estimate the loss by leaching, taking into account the N absorbed by the crops, and subtracting this loss from the total loss to obtain the apparent percentage loss by denitrification, L(DN). An analysis of variance showed that L(DN) increased significantly with the quantity of N applied, so the study considered L(DN) values for a standard N application of 150 kg/ha subsequently. Regressions showed that L(DN) was better related to the wetness of the soil during the 3 weeks after fertilizer application than to the corresponding amount of rain, as would be expected for denitrification. Values of L(DN) could not, however, be satisfactorily related to soil temperature, probably because the range of temperatures was too narrow. The apparent losses by denitrification were, on average, nearly twice as large as those by leaching, but the ratio varied greatly between experiments.
Nitrate leaching from sheep-grazed pastures was measured over three winters between 1987 and 1990 at a lowland site in Wales. Losses from replicated plots of ryegrass/white clover (Lolium perenne/Trifolium repens) pasture that received no N fertilizer and from pure ryegrass pasture receiving 150-200 kg fertilizer-N/ha per year were determined using suction cup samplers. In Year 1, the average clover content of the grass/clover swards (April-September) was equivalent to 35 % of total dry matter but declined during the course of the experiment and was only 4 % in Year 3. Concentrations of nitrate and quantities of N leached from separate sampling positions exhibited a wide range of values and conformed to a log-normal distribution. In the first two winters, mean nitrate concentrations in soil water and quantities leached from grass/clover plots were greater than those from fertilized grass plots. In Year 3 the loss from the N-fertilized plots was higher and exceeded that from the grass/clover treatment. Total quantities of N leached during the three winters ranged from 6 to 33 kg N/ha from grass/clover plots and from 2 to 24 kg N/ha from fertilized grass plots. At no time did mean nitrate concentrations from either treatment exceed 11 mg N/litre. These values probably underestimate the true loss as the distribution of the main sets of water samplers did not provide adequate coverage of those areas of the plots where sheep congregated and which received high returns of excreta. These positions were characterized by particularly high leaching losses. Differences between losses from the two treatments and between years could only be partly explained by the decline in clover content and differences in stocking rates.
Treatments which lowered the rate of ammonia volatilization from surface-applied cattle slurry were evaluated in three field experiments during 1989/90 at the Agricultural Research Institute of Northern Ireland. The relative effects of separation, dilution with water before application and washing with a water spray after application, on ammonia volatilization rates were compared over 4 days using ventilated enclosures. As the loss rate of ammonia during the first 4 days after application was highly correlated with the loss rate over the first 4 hours after application, the loss rate in the first 4 hours was used as a rapid method to assess the efficacy of various combinations of separation, dilution and acidification. Ammonia volatilization loss rates from treatment combinations were compared to the loss rate from whole slurry. A 50 % decrease in ammonia volatilization was achieved by separation through a 0.4 mm mesh, separation through a 10.0 mm mesh plus dilution with 86 % by volume of water, or separation through a 2.0 mm mesh plus washing with 53 % by volume of water. A 75 % decrease in ammonia volatilization was achieved by acidification to pH 6.5, or combinations of separation and dilution, namely separation through a 0.4 mm mesh plus 50 % dilution or separation through a 5.0 mm mesh plus 100 % dilution. A 90 % decrease in ammonia volatilization was achieved by acidification to pH 6.0, dilution by 50 % plus acidification to pH 6.5, or separation through a 0.4 mm mesh plus acidification to pH 6.5. The effects of separation and acidification on ammonia volatilization were cumulative. There was a highly significant inverse linear relationship between ammonia volatilization rate and volume of nitric acid used. Adding 10 m nitric acid at 1.4 % by volume lowered volatilization by 75 % of that from whole slurry and increased the nitrogen content of the slurry by 2 g N/l, making it a more balanced NPK fertilizer for cut swards. Because the variable value of cattle slurry is due to loss of nitrogen as ammonia and smothering of the sward with slurry solids, a combination of separation or dilution to lower sward contamination and acidification with nitric acid to lower volatilization may be the best practical option for improving cattle slurry as a fertilizer for cut grass.
Four Friesian bulls with ruminal and duodenal cannulae were used in a 4 x 4 Latin square experiment to study the effects of lactic acid (LA) on rumen fermentation and microbial protein synthesis. On a dry matter (DM) basis (g/kg), the basal diet comprised grass silage (700), barley (240) and rapeseed meal (60) and it was given at the rate of 7.1 kg DM/day. LA was infused continuously into the rumen at the rates of 0 (L0), 40 (L40), 80 (L80) or 120 (L120) g/kg basal diet DM. The molar proportion of propionate in the rumen volatile fatty acids (VFA) increased linearly (P < 0.001) and that of acetate, isovalerate, caproate (P < 0.01) and isobutyrate (P < 0.05) decreased linearly with an increasing rate of LA infusion. At the same time there was a linear decrease (P < 0.05) in the number of rumen protozoa. When the metabolic fate of infused LA was calculated on a molar basis, 0.21 of lactic acid was converted to acetate, 0.52 to propionate and 0.27 to butyrate. Infusion of LA into the rumen had no effect on the site or extent of the digestion of basal diet organic matter (OM) and neutral detergent fibre (NDF). LA diets tended to have a lower microbial N flow at the duodenum (71.4 v. 85.8 g N/day) and lower synthetic efficiency in the rumen (14.4 v. 20.4 g N/kg OM apparently fermented) when compared with the control diet. The ratio of duodenal non-ammonia N to N intake was highest with the control diet and lowest with L40, the effect of the LA rate being quadratic (P < 0.05). The results suggest that propionate was the main end-product of lactic acid fermentation in the rumen with the grass silage based diet. Lactic acid had no value as an energy source for microbial protein synthesis.
Twelve yearling Droughtmaster heifers were grazed on a tropical grass/legume pasture in north-east Australia for 1 year in four paddocks, each of 4 ha. One paddock was fertilized annually with 10 kg P/ha (treatment HPF). The other three paddocks had low soil P and low pasture P status. In one of the low soil P paddocks, P was added to the drinking water (treatment HPS) but no supplement was provided in the other two paddocks (treatments LP1 and LP2). In February, May and August 1989, the P kinetics of the heifers were monitored following oral administration of ruminal chromic oxide capsules and i/v injection of P-32. At the same times, oesophageal-fistulated steers were grazed in the paddocks to obtain extrusa samples to estimate the P content and digestibility of selected forage. The liveweight gain per heifer was higher in the HP treatments (196 kg) than in the LP treatments (152 kg). The intake, absorption and excretion of P were closely related but the faecal excretion of P relative to P intake was less in heifers with than without P supplement. The P intakes of the LP heifers were about half the quantities recommended in the nutrient feeding standards for the observed food intakes and weight gains. The coefficients of P absorption in the LP heifers in May and August were high ( > 0.8) and did not decrease with age or liveweight. The coefficients of P absorption of heifers given supplementary P were as high as those for LP heifers, but those of heifers on the fertilized pasture were significantly lower in May and August. The endogenous faecal excretion of P was related to P intake but more closely to dry matter intake and plasma inorganic P together. The reasons for the difference between observed P intakes of LP heifers and recommended requirements are discussed in relation to the assessment of P requirements of grazing cattle. The results from this experiment suggest that recommended P requirements are higher than necessary to sustain the measured liveweight gains of cattle on grass/legume pastures in the tropics.
Twenty genotypes of chickpea, selected according to their performance in trials conducted during 1988/89 in saline fields having equal concentrations of SO4 and Cl, were studied during 1989/90 at Karnal, India. The Cl-dominated soils were divided into microplots with ECe values of 2, 4, 6 and 8 dS/m. Germination, although delayed at ECe 6 and 8 dS/m, was not inhibited up to ECe 8 dS/m. The sensitivity of all genotypes increased with plant growth and greater salinity. Plant growth was most adversely affected by a salinity of ECe 8 dSm. 100-seed weight was less affected by salinity than other yield components, namely, number of pods/plant, number of seeds/plant and seed yield/plant. Chlorides had a more severe toxic effect when present in domination than when they were balanced by an equal concentration of sulphates. Genotypes varied in their tolerance of Cl-dominated salinity. Cultivars ICCC32 and ICCL86446 showed the most tolerance to Cl-salinity, having > 0.75 Mean Tolerance Index values for all eight characters, followed by ICC5003, ICC10575, ICC12908 and ICC12926. ICC12928 had the highest mean tolerance index value for number of pods/plant and highest threshold value and ICC4953 the highest mean tolerance index for 100-seed weight, indicating their better tolerance at flowering and maturity respectively. Therefore, crossing genotypes of the latter with the former group should produce some recombinants with improved tolerance to salinity at all growth stages and at maturity.
Phosphorus (P) cycling and losses in irrigated, sheep-grazed pastures receiving superphosphate (SP) applications for 35 years at annual rates of 0, 188 and 376 kg/ha were studied using a mass-balance approach which accounted both for P inputs to and outputs from the soil-plant-animal system. Total recoveries of applied P in the soil-plant-animal systems in the 188 and 376 kg SP/ha treatments were 94 and 83 % respectively. Approximately 52-53 % of the applied P was recovered in the soil within the major plant rooting zone (0-300 mm soil depth). These data suggest that P leaching losses from SP fertilizer, plant litter, root residue and sheep faeces were unlikely to occur beyond the major plant rooting zone. However, the transfer of excretal P to stock camps and the transport of P from SP fertilizer, plant litter and sheep faeces via the irrigation water along the border from the top to the bottom of the irrigated border strip accounted for less than 6% of the applied P. Superphosphate applications resulted in the accumulation of both soil inorganic and organic P fractions to a depth of 225 mm. The accumulation of soil inorganic P was most pronounced when SP was applied annually at the rate of 376 kg/ha, which was in excess of pasture P requirements.
The number of leaves formed on the main shoot of a wheat plant is an important developmental feature, and a method of predicting this is essential for computer simulation of development. A model function was used to estimate vernalization from simulated sowing dates throughout a season. When expressed in terms of thermal time, it was estimated that a plant might be fully vernalized soon after seedling emergence or take up to about 1000-degrees-Cd, depending on sowing date. When the simulated progress of vernalization was related to main shoot development (primordium initiation and leaf emergence) it was found that there were substantial differences between sowings in the rate of vernalization at comparable stages of apex development. A number of field experiments done in Britain from 1980 to 1984 with prominent commercial varieties, sown at various times from September to March, were analysed in terms of the thermal time to full vernalization and the photoperiod at the time of full vernalization. with vernalization simulated by the model function. In both winter and spring varieties, both of these variables significantly affected the number of main shoot leaves. Multiple linear regression using these two variables accounted for between 70 and 90% of the variance in leaf number, depending on variety..
Four swamp buffaloes (Bubalus bubalis) and four crossbred Bos indicus x B. taurus cattle, fistulated at the rumen and abomasum or duodenum, were offered rice straw with mineral supplements in two experiments. In Expt 1, the straw was supplemented with 5 % of leaf of Leucaena leucocephala, and in Expt 2 with either urea or urea with sunflower meal and rice grain. Intake of supplements of urea or urea/sunflower/rice respectively was 935 and 681 g/kg offered in buffaloes and 566 and 789 in cattle. Buffaloes ruminated longer than cattle (Expt 1, 635 v. 452 min/day; Expt 2, 626 v. 466 min/day, P < 0.01). In Expt 1, voluntary intake and frequency of 'A' sequence forestomach contractions of both species was not affected by species, but buffaloes had a greater (P < 0.05) contraction force in the rumen and omasum, lower rate of 'B' sequence rumen contractions, and faster (P < 0.001) rate of gastrointestinal passage than cattle. In Expt 2, voluntary intake of both species was similar, and addition of concentrates did not affect voluntary roughage consumption, nor in situ rate of digestion of rice straw. Rate and predicted extent of digestion of dietary materials did not differ between species in Expt 1, despite lower concentrations of ammonia in rumen fluid in cattle than buffaloes; however in Expt 2, the rate of digestion of rice straw was higher (P < 0.05) and predicted extent of digestion was 14-20 % (P < 0.05) lower in buffaloes. Digestibility of cell wall constituents was lower (P < 0.05) in buffaloes than in cattle in both experiments, but in Expt 2, provision of concentrates reduced (P < 0.01) the proportion of digestible cell wall constituents digested in the forestomach of buffaloes, but not of cattle. Plasma urea concentrations were higher (P < 0.05) and transfer of urea to the rumen tended to be higher (7-4 v. 3.7 g N/day; P < 0.10) in buffaloes. Faster fractional outflow rates of microbes and of small digesta particles from the rumen were observed in buffaloes in Expt 1. In Expt 1, more microbial N left the abomasum (35 v. 30 g per kg organic matter apparently digested in the forestomach; P < 0.05) of buffaloes than cattle, and in Expt 2 more non-ammonia N (43 v. 31 g per kg organic matter apparently digested in the forestomach) flowed into the intestines of buffaloes. In Expt 1 microbial retention time was shorter (26 v. 47 h; P < 0.01) in the rumen of buffaloes. Patterns of appearance of plastic particles with time after dosing indicated faster escape from the rumen of buffaloes of non-chewed particles, and a greater proportion of particles subjected to ruminative chewing, than in cattle. Ruminative chewing of plastic particles in buffaloes was progressively more efficient than in cattle with increasing particle length and decreasing specific gravity. Analysis of faecal particle distribution indicated buffaloes tended to excrete smaller particles than cattle. The adaptive significance of faster digesta passage in the buffaloes appeared to derive from a more balanced supply of absorbed protein relative to digestible energy.
The effects of a preceding (1986/87) season's crop of vetch (Vicia sativa) or oats (Avena sativa), either singly or as two different mixtures, on the nitrogen uptake and growth of a succeeding barley crop (Hordeum vulgare) were examined in Cyprus in 1987/88, on field plots previously labelled (1984/85) with N-15 enriched organic matter. Grain as well as the vegetative material were harvested before planting the barley. Barley after vetch accumulated 61 % more nitrogen than barley after oats, while, for the mixtures, the nitrogen yields in the succeeding barley crop did not differ significantly from those of barley grown after oats. The N-15 enrichment in barley indicated that fixed N2 from vetch contributed little nitrogen to the available soil nitrogen pool and to the nitrogen in barley. Most of the increased assimilation of nitrogen in barley following vetch (compared to barley after oats) was attributable to a greater availability of soil nitrogen arising from the lower soil nitrogen uptake by the preceding vetch than oats. The dry matter yield of barley following vetch was 84 % higher than for barley after oats, while barley after the vetch-oats mixtures yielded 38-54 % higher than barley following oats. It was concluded that greater nitrogen availability to the cereal following the legume was not the sole cause of the dry matter yield responses observed.