Ammonia losses from surface-applied cattle slurry were measured under field conditions using a wind tunnel system that allows variables affecting ammonia loss to be examined under controlled conditions. The experiments were carried out on a sandy soil with seven different surface covers. This report considers the effect of wind speed, temperature and water vapour deficit on the ammonia loss over a series of 6-day periods. During October 1986 to November 1989 42 treatments were examined, using slurries taken from the same slurry tank to provide slurries of similar chemical composition. When temperatures were near zero, the rate of ammonia loss was generally low. The accumulated loss over 6 days was high, however, because the rate of loss was constant throughout the period. In these experiments the soil was saturated with water and partly frozen, and the infiltration of slurry into the soil reduced. At 19-degrees-C initial loss rates were high but, after 12 h, almost no further loss occurred. Apart from these extremes, the ammonia loss rates within the initial 24 h were significantly affected by temperature and wind speed. Ammonia volatilization after 6 h was exponentially related to temperature (r2 = 0.841) but the correlation weakened with time after slurry application. An increase in ammonia volatilization with increasing water vapour pressure deficit was considered to be an effect of temperature. The ammonia loss rate increased when wind speeds increased up to 2.5 m/s. No consistent increase in ammonia volatilization was found when the wind speed increased from 2.5 to 4 m/s. Ammonia loss after 24 h increased with increasing initial pH of the slurry. A two-stage pattern for ammonia volatilization from slurry is proposed. During the first stage (the initial 24 h) ammonia loss rate is high due to an elevated pH at the slurry surface following application, and temperature significantly affects the loss rate. In the next stage, pH declines and the rate of ammonia volatilization decreases. During this stage other factors, including the dry matter content of the slurry, control the rate of ammonia loss.
Shading treatments of 50% of the incident radiation were applied to the semidwarf wheat cultivar Leones INTA before and after anthesis in two field experiments in Argentina in 1987 and 1988. The treatments reduced biological (above-ground dry matter) yield, grain yield and number of grains/m2. Number of grains/m2 was closely and linearly correlated with ear dry weight at anthesis and with the photothermal quotient, calculated from 20 days before to 10 days after anthesis. Grain yield was sink limited, and the shading treatments reduced sink strength. The contribution of preanthesis assimilates to grain yield was smaller in the shaded crops than in the unshaded controls; in unshaded crops, almost 40% of grain yield was contributed by preanthesis assimilates whilst in preanthesis shaded crops this contribution was negligible. The proportion of preanthesis assimilates contributed to the grain was closely related to the decrease in stem dry weight during grain filling. The effects of shading on main stems and tillers were the same.
Two experiments were carried out to determine endogenous losses and the response of urinary purine derivatives to increased duodenal inputs of purine bases. Four ewes each fitted with a re-entrant cannula at the proximal duodenum, and conventionally fed, were subjected to full replacement of duodenal digesta followed by the administration of a solution either free of purines (Expt 1) or enriched with increasing amounts of purines, to supply 0.48-21.27 mmol/animal per day (Expt 2). Basal daily urinary excretions of allantoin, uric acid, hypoxanthine and xanthine were 11.5 +/- 0.94, 9.9 +/- 0.67, 6.9 +/- 0.46 and 1.2 +/- 0.16 mg/kg W0.75. Allantoin was the only purine derivative which increased in response to incremental inputs of duodenal purines. The relationship between allantoin excretion and infused purines showed a urinary recovery of 0.8 for purines infused at > 220-mu-mol/kg W0.75. Lower rates of infusion did not alter allantoin excretion. The results show urinary allantoin to be a useful index to estimate duodenal input of purines when animals are fed close to or above their energy maintenance requirements.
Simulation modelling was used to investigate interactions between forage degradation characteristics, rumen processes and body weight, and to predict the voluntary food intake and digestion of a range of forages. Predicted voluntary intake and digestion agreed well with empirical data, explaining 61 and 70%, respectively, of variance in observed values. Since the data covered a wide range of animal weights and forage qualities, these results suggest that the model is a useful means of integrating the effects of animal and forage variables. Interactions were examined between animal weight and diet quality, as defined by the proportion of potentially digestible cell contents and cell walls and their rates of digestion. Retention time of food in the digestive tract was shown by regression to scale with W0.27. The time taken to comminute large fibre particles also scaled with W0.27. Longer retention of digesta by large ruminants increases digestive efficiency compared with small animals and would permit them to survive on lower-quality foods. The model showed that maximum intake of metabolizable energy scales with c. W0.87, greater than the scaling of maintenance with W0.73.
In three experiments, carried out in 1985 and 1986 in the Netherlands, the effects of herbage maturation and rate of nitrogen fertilization on rumen degradability of organic matter (OM) and crude protein (CP) in fresh herbage (Lolium perenne) were studied using the nylon bag technique. Experimental farms at Lelystad and Swifterbant (clay soil) and Achterberg (sandy soil) provided the herbage samples. From the results, the content of digestible CP entering the small intestine (DPI) was estimated. Crude protein content and in sacco degradability of OM and CP decreased with increasing grass maturity and with decreasing rate of N application. With every 100 g/kg DM decrease in CP content. the estimated content of DPI decreased by 19 g/kg DM, no matter how the CP content was manipulated.
The Lolium-Festuca complex of related species provides a wide range of variation for the development of versatile grasses adapted to meet the changing requirements of livestock farming. Various approaches have been used in order to harness the full potential of this variation. Tetraploid hybrids between the two ryegrass species L. perenne and L. multiflorum have resulted in stable and successful commercial varieties. Hybrids between more distantly related ryegrass and fescue species have demonstrated useful combinations of traits from both parents. Chromosome doubling is necessary in these hybrids to restore fertility in synthetic amphiploids. However, genetic instability can still be a problem and research is in progress to obtain tighter control of chromosome pairing. An alternative approach is to introduce a few specific traits from fescues into ryegrasses, or vice versa, using introgressive breeding procedures. This review outlines the progress already achieved in exploiting the ryegrass-fescue complex by using these various approaches and assesses the potential of hybrid derivatives.
Components of the N cycle were studied at Hurley, UK, in 1985-87. In grass-clover (Lolium perenne and Trifolium repens) swards, grazed at three intensities, low total inputs of N were associated with low outputs and losses of N. Nevertheless, the flows (intake and excretion) of N through animals were substantial and gave rise, at the higher intensities of grazing, to an acceptably high agricultural output per hectare. This was considered evidence of a fast and efficient recycling of N between plants, animals and soil. The release of N to the environment (as nitrogenous gases and nitrate) was substantially less from the grass-clover swards than from a grass sward fertilized with 420 kg N/ha, and this was at the expense of only 20% loss in production. The mechanisms which might account for the high efficiency of utilization and recycling of N in grass-clover swards are discussed in the context of the balance of the supply of C and N to plant and soil biomasses under grazing. The results confirm that optimizing agricultural output in grass-clover swards has little adverse effect on the environment, but the importance to this end of sustaining a large proportion of N-deficient grass in grass-clover swards is emphasized.
The intake of temperate forages by herbivores can be determined using the C33 alkane naturally present in the forage and dosed C32 alkane. To determine whether the technique can be used with tropical forages, the concentrations of C33 alkane were determined in seven species. The leaves of Brachiaria decumbens, Digitaria decumbens, Pennisetum glaucum and Stylosanthes scabra contained sufficient C33 alkane (> 50 mg/kg DM) for the estimation of dry matter intake. Low concentrations of C33 alkane were found in the leaves of Setaria sphacelata, Sorghum sp. and Leucaena leucocephala. Setaria sphacelata was found to contain high concentrations of C27 alkane and therefore intake could be estimated by using C28 as the dosed alkane although the intake would possibly then be underestimated by c. 8%. Leaves of Sorghum sp. contained > 50 mg C31 alkane/kg DM and, with C32 as the dosed alkane, intake would possibly be underestimated by c. 5%. Leucaena leucocephala contained insufficient alkanes to estimate forage intake. The concentration of n-alkanes in Pennisetum glaucum and Sorghum sp. leaves decreased with age. It was concluded that some tropical forages contain insufficient C33 alkane for the measurement of intake by the double alkane technique. In these species, a shorter chain length alkane can sometimes be used, but only with a reduction in accuracy in estimating intake.
An experiment was carried out in Normandy between 1986 and 1988 over c. 6 months in each year, using a simplified rotational grazing technique (two paddocks in spring, four in autumn) with a total of 162 high-yielding cows (mean milk yield of 30.0 kg/day at turn-out). Three stocking rates, designated control (C: 2.3 cows/ha over the total area of the system), moderate (M: 2.6 cows/ha = 115% of C) and high (H: 3.0 cows/ha = 130% of C), were compared at two rates of concentrate supplement, 3.7 kg/cow per day and 0.5 kg/cow per day. Individual milk yield differed by a non-significant 5% between the extreme stocking rates (21.3 v. 20.3 kg fat-corrected milk (FCM) for treatments C and H, respectively). Milk production/ha was 23% greater in the H treatment (9816 v. 7970 kg FCM for H and C, respectively). Concentrate supplementation led, on average, to a 9% milk yield improvement (21.8 v. 20.0 kg FCM for high and low rates, respectively), i.e. a mean efficiency of 0.6 kg FCM/kg supplement. This response tended to be greater in the higher-yielding cows and for the high stocking rate. The sward measurements contributed to a better understanding of herbage utilization by the cows.
The objective of this study was to identify traits related to growth and yield response under drought stress in the field which would show less variation than yield itself. Experiments were conducted in 1987, at Durango, Mexico and at Michigan, USA. Twenty-six dry bean genotypes were sown under supplementary irrigation and terminal drought stress. Plant samples were taken at 50% flowering, mid-pod-filing and physiological maturity. At both sites, leaf expansion rate and crop growth rate at mid-pod-filling were greatly reduced by drought stress, resulting in significant reductions in total dry matter (DM) above ground and seed yield at physiological maturity. Because of differences in the timing and intensity of the drought stress, the yield components were affected differently at each location. Total DM content at physiological maturity, harvest index and number of pods/m2 were the only traits positively correlated with yield under stress at both locations. In order to evaluate a group of genotypes for adaptation to drought on the basis of seed yield, the genotypes should be grouped according to their phenological characteristics to stress them evenly.
Two experiments at Belclare, Co. Galway, in late autumn 1988, evaluated the use of herbage and dosed n-alkanes for estimating herbage intake by sheep. The first experiment examined faecal recoveries of dosed and herbage n-alkanes. The second experiment assessed the accuracy and precision of herbage intake estimates obtained using the n-alkane technique, and tested the effect of supplying n-alkanes to animals either in gelatine capsules (containing different ratios of n-alkane: cellulose fiber) or in pellets prepared from shredded paper onto which the n-alkanes had been adsorbed. Individually penned wether lambs were offered freshly cut herbage ad libitum (+ 10%) and actual dry matter intake was recorded daily. Intake was estimated using the C31:C32 and C33:C32 (natural: dosed) n-alkane ratios. There was no significant effect of n-alkane chain length on faecal recovery rate for either the dosed n-alkanes (C32 and C36), the herbage odd-chained n-alkanes (C29,C31,C33 and C35) or those used for the estimation of herbage intake (C31,C32 and C33). The accuracy and precision of the n-alkane technique for estimating herbage intake were unaffected by whether the dosed n-alkane was supplied in capsules or pellets or by the n-alkane: cellulose fibre ratio in the capsules. The bias in the estimated intake was -8% (+/- 1.1%) and + 3% (+/- 1.2%) for estimates based on C31:C32 and C33:C32 ratios, respectively. The estimates based on C31:C32 and C33:C32 exhibited similar precision in the estimation of herbage intake, with a R.S.D. of 6% in actual intake when adjusted for variation in estimated intake and a correlation of + 0.92 between actual and estimated herbage intake. The C.V. for acutal herbage intake was 17%. The repeatability of actual dry matter intake over three consecutive 6-day periods was 0.54 while those of estimated intake were 0.57 and 0.60 for estimates based on C31:C32 and C33:C32, respectively. The results show that the n-alkane technique can provide an accurate and precise estimate of herbage intake.
Prairie grass (Bromus catharticus) straw (13.7 g N/kg DM) was fed ad libitum to six goats and seven sheep kept in metabolism cages at Palmerston North, New Zealand in 1986 and 1987. Goats had greater voluntary feed intake (VFI) (56 v. 36 g DM/kg W0.75 per day), greater apparent DM digestibility (36.8 v. 32.6%) and a larger rumen pool of DM and liquid (W0.75) than sheep. Goats also had greater apparent digestibility of fibre, especially of lignin, and greater rumen fractional degradation rates (FDR) of cellulose, hemicellulose and lignin. Goats had a higher rumen ammonia concentration (115 v. 80 mg N/1), lower rumen pH (6.73 v. 6.90), a smaller proportion of large particles and greater proportion of small particles in rumen contents than sheep. Passage through a 1 mm sieve was established as the threshold particle size to have a high probability of leaving the rumen in both goats and sheep. Voluntary water intake/unit DM consumed was lower in goats than in sheep and, whilst rumen fractional outflow rate (FOR) of water and particulate matter also tended to be lower in goats, the difference was not significant. Irreversible loss rate of rumen NH3 and the amount of N calculated as recycled to the rumen, both expressed as mg N/kg W0.75 per day, were greater for goats than for sheep. It was concluded that the ability of goats to maintain a higher rumen NH3 concentration than sheep, their larger rumen pool and the higher proportion of small particles in rumen contents were all contributing factors to their greater VFI and fibre digestion of this low-quality roughage.
Results are reported from nine field trials carried out in 1985/86 and 1986/87 aimed at identifying plant traits which are associated with high yield in barley in low-rainfall Mediterranean areas. Thirty-seven two-rowed and 35 six-rowed genotypes, representing the known diversity in traits considered to be useful, were compared in trials at three sites differing in expected annual rainfall (212-328 mm) in northern Syria, and in droughted and irrigated trials at Cambridge, UK. Yield, its components and other morphological and developmental traits were measured and correlations calculated. Grain yields of the two- and six-rowed groups of genotypes were similar at all sites except in the irrigated trial in Cambridge, where the six-rowed genotypes gave the highest yield. Aside from the known difference in number of ears and number of grain/ear between two- and six-rowed genotypes, the simple correlations between grain yield and measured traits suggested that important traits for high yield in two- and six-rowed genotypes in dry environments were prostrate habit, vigorous seedling growth, good ground cover, early ear emergence, many ear/m2 and large grains. In the two-rowed genotypes, short stature and a short grain-filling period were also important, while in the six-rowed genotypes, tall stature, high straw yield, many grains/ear and long peduncles were important. Correlations of these characters with an index of drought susceptibility and with yield adjusted for yield potential and date of ear emergence supported the conclusions based on the simple correlations. The physiological basis of the correlated traits is discussed and the implications for breeding are considered.
Three rates of phosphate (0, 25, and 60 kg/ha P2O5) were applied phosphorus-deficient native grassland at Tel Hadya, in northern Syria, and biomass productivity, botanical composition and number of legume seeds in the soil were monitored for five seasons (1984/85-1988/89). The experiment was grazed at low (0.8 sheep/ha per year) and high (1.7 sheep/ha per year) stocking rates from the second to the fourth seasons of the experiment; in the fifth season, the low and high stocking rates were increased to 1.1 and 2.3 sheep/ha per year, respectively. The experimental site was typical of native grassland within the cereal zone of west Asia, where cropping is not possible because of shallow, stony soils and steep slopes. The results showed that annual applications of phosphorus, even as low as 25 kg P2O5/ha, alleviated the deficiency in soil P and resulted in improved pasture production, even in dry years. Legume production showed the greatest response to P, increasing by 0.3-3 times the production of the control treatments. By the fifth season, legume seed mass had increased threefold and number of seeds sixfold in the P-treated plots, compared with the first season, while in the control plots there was little change. Rain-use efficiency on the P-treated plots was more than double that of the controls by the fourth and fifth seasons. Practical application of the results depends on whether (i) legumes are as frequent in native grasslands, as a whole, as they are at Tel Hadya, (ii) the P deficiency observed at Tel Hadya is widespread, and (iii) grazing of communally owned grasslands can be controlled. It is suggested that all three criteria will often be fulfilled and, therefore, that grassland productivity in west Asia could be substantially increased. Furthermore, the results suggest that above-ground cover and soil organic matter will also increase after P application, both of which will help to reduce soil erosion and thereby increase the sustainability of livestock production in west Asia.
In 1989 three experiments with up to three different treatments each were carried out in North Germany to determine the ammonia flux densities after the application of liquid slurry using the micrometeorological mass balance method. In Expts 1 and 2, pig slurry was applied with a conventional surface spreader to wheat stubble. The results demonstrated the influence of meteorological conditions and that of incorporation on the extent of ammonia volatilization. In comparison to warm and windy conditions, NH3 losses decreased from 56% of the NH4-N applied to wheat stubble to 42% during a cool and rainy period. When slurry was incorporated immediately into the soil, ammonia losses were significantly reduced to 20 and 10%, respectively, of the applied NH4-N. The highest losses (67% NH4-N) were found when slurry was applied during warm weather on wheat stubble covered with chopped straw. Soil cultivation of the wheat stubble before the application of slurry diminished the ammonia emission from 42 to 28% of the NH4-N. In Expt 3, cattle slurry was applied to rape. It was found that compared with a conventional surface spreader the ammonia volatilization was reduced from 68 to 58% of the NH4-N when an alternative distribution system consisting of drag hoses was used for the application.
The minirhizotron technique was evaluated for estimating root length density in potatoes (Solanum tuberosum 'Record') by comparing observations in angled 45-degrees glass tubes with corresponding root length densities obtained by (a) destructive core sampling, and from (b) counts of root tips on the soil face of excavated trenches. Measurements were made in a field experiment in Bedfordshire, UK, in 1985, with shallow and deep cultivation as variables, and in a glasshouse trial. Only at depths below 0.3 m did root lengths observed with minirhizotrons reflect at all closely those estimated from core sampling and even then there was a tendency to overestimate root density. In the surface cultivated layers, where 80-90% of the total root length was present, results from minirhizotrons were unreliable, probably because of poor soil-tube contact and, in soils which shrink on drying, preferential root growth at the interface between the soil and the glass. Minirhizotrons can provide a realistic estimate of the rate of root growth of potatoes with depth over time when compared with maximum depths of water extraction, but appear to be unreliable for providing a quantitative measure of total root length density.
The effect on soil fertility and crop performance of different organic fertilizers; paddy straw (PS), farmyard manure (FYM), water hyacinth compost (WHC) and tank silt (TS), at different rates of application and in combination with N fertilizer, was studied in a rice-based cropping system on an acid lateritic soil at Kharagpur, India, during 1985/86. Organic manuring of wet-season rice (first crop) with 5 t PS/ha 10 days before transplanting and 10 t FYM or 10 t WHC/ha at transplanting increased grain yield as much as the application of 30 kg N/ha. Increasing the rates of FYM and WHC application up to 15 t/ha increased yield but increasing the rate of PS beyond 5 t/ha did not. Response to increasing amounts of N was not linear; there was a significant increase up to 90 kg N/ha and a decrease when N was applied in conjunction with organic fertilizers. There was a significant increase in the N uptake of the rice but a decrease in the recovery of applied fertilizer N with the application of increasing rates of organic and N fertilizer. The organic C content of the soil after the rice harvest increased significantly after PS application, whereas there was more available N after WHC and FYM. Increasing the rate of application of PS up to 15 t/ha increased organic C but not available N. Mineral N fertilizer had little effect on fertility build-up. Grain yields of wheat and gram (Cicer arietinum), grown after rice without any additional fertilizer, increased significantly. The residual N effect of the previous crop on wheat or gram yield was small and adding fertilizer directly is considered essential for higher productivity in these crops in a rice-based cropping system.
Feeding studies were conducted in 1986 with penned sheep and cattle fed legume (C3) and grass (C4) hays mixed in different proportions. Large fluctuations in diet delta-13C within or between days were associated with much smaller fluctuations in the delta-13C of faeces. When the overall daily legume percentage in the diet was held constant, there was little variation in the delta-13C of faeces irrespective of when during the day the legume, relative to the grass, was eaten. Cattle set stocked on Stylosanthes/grass pastures in Queensland showed only minor variations in faecal delta-13C within or between days in the short term. All animals within a group showed similar trends when the diet was changing. The changes in the delta-13C of faeces from day to day reflected small but real changes in diet selection. It was concluded that the delta-13C of a single faecal sample reliably reflects the integrated diet over the previous 3-4 days of a free-grazing ruminant so that the frequency and pattern of faecal sampling for estimating diet composition may be determined by considerations other than reliability.