A computer model is presented that describes the flow of nitrogen between crop and soil on the field scale. The model has a compartmental structure and runs on a weekly time-step. Nitrogen enters via atmospheric deposition and by application of fertilizer or organic manures, and is lost through denitrification, leaching, volatilization and removal in the crop at harvest. Organic nitrogen is contained within three of the model compartments - crop residues (including plant material dying off through the growing season), soil microbial biomass and humus. Inorganic nitrogen is held in two pools as NH4+ or NO3-. Nitrogen flows in and out of these inorganic pools as a result of mineralization, immobilization, nitrification, leaching, denitrification and plant uptake. The model requires a description of the soil and the meteorological records for the site - mean weekly air temperature, weekly rainfall and weekly evapotranspiration. The model is designed to be used in a 'carry forward' mode - one year's run providing the input for the next, and so on. The model also allows the addition of N-15 as labelled fertilizer, and follows its progress through crop and soil. Data from a Rothamsted held experiment in which the fate of a single pulse of labelled N was followed over several years were used to set the model parameters. The model, thus tuned, was then tested against other data from this and two contrasting sites in south-east England. Over a period of 4 years, the root mean square (R.M.S.) difference between modelled and measured quantities of labelled N remaining in the soil of all three sites was c. 7.5 kg N/ha, on average. The root mean square error in the measurements was c. 2.5 kg/ha. Similarly, the R.M.S. difference between modelled and measured recovery of labelled N by the crop was 0.6, compared with 0.3 kg/ha in the measurements themselves.
The effects of two diets, formulated to be either synchronous or asynchronous with respect to the hourly supply of energy and nitrogen, on rumen fermentation and microbial protein synthesis were studied in sheep. In Expt 1, the in situ degradation characteristics of nitrogen (N), organic matter (OM) and carbohydrate (CHO) fractions were deter-mined in winter wheat straw, winter barley, malt distillers dark grains, rapeseed meal and fishmeal. The feeds exhibited a large range in degradability characteristics of the nitrogen and energy-yielding fractions. A computer program was developed, based upon the raw material degradation characteristics obtained from the above studies. The program was used to formulate two diets with similar metabolizable energy (9.5 MJ/kg DM) and rumen degradable protein contents (96 g/kg DM) but to be either synchronous (diet A) or asynchronous (diet B) with respect to the hourly rate of release of N and energy. The program was used to predict the hourly release of N, OM and CHO and the molar production of volatile fatty acids (VFA). In Expt 2, the two diets were fed to four cannulated sheep at the rate of 1 kg/day in four equal portions, in two periods, using a change-over design. Rumen ammonia concentrations followed the predicted rate of N degradation. A maximum concentration of 10.5 and 7 mm for diets A and B respectively was achieved within the first hour of feeding which then fell to 7 and 3 mm respectively. Rumen VFA proportions were more stable for the synchronous diet (A) than the asynchronous diet (B) and were more stable than predicted for both diets. True ruminal degradation of OM and CHO was similar for both diets and close to that predicted, although fibre degradability in diet A was 30 % lower than predicted due to a reduction in both cellulose and hemicellulose digested. Microbial protein production was estimated simultaneously with L-[4,5-H-3]leucine and a technique based on cytosine. Estimates varied with marker but mean values indicated a 27 % greater production of microbial N (g N/kg DMI) with the synchronous diet (A) and an average improvement in microbial protein efficiency (g N/kg OM truly degraded or CHO apparently degraded) of 13 %, although neither difference was significant. There was evidence of a greater recycling of N in the animals and a significantly lower content of rumen degradable protein when the sheep were fed the asynchronous diet (B). The results are consistent with the view that synchronizing the rate of supply of N and energy-yielding substrates to the rumen micro-organisms based upon ingredient in situ degradation data can improve microbial protein flow at the duodenum and the efficiency of microbial protein synthesis.
Gaseous NH3 losses from pig and cattle slurry stored in eight storage tanks were measured simultaneously using wind-tunnels. The slurry was either stirred weekly (uncovered), or-was allowed to develop a natural surface crust. Oil, peat, chopped cereal straw, PVC foil, leca(R) (pebbles of burned montmorillonitic clay) and a lid were tested as additional covers. Convective transport of ammonium to the surface layers caused NH3 volatilization losses of 3-5 g NH3-N/m2 per day from the stirred, uncovered tanks. The loss of NH3 from the stirred slurry was related to air temperature. The development of a natural surface crust reduced NH3 losses to 20 % of those from stirred slurry. NH3 losses from slurry not developing a natural surface crust layer and left undisturbed were similar to the losses from stirred slurry. A 15 cm layer of straw was as effective as a surface crust layer in reducing NH3 losses. In one experiment, cracks developed in the oil cover and losses were therefore only reduced to 50 % of those of uncovered slurry. Apart from this experiment, NH3 losses from slurry covered with oil, leca(R), peat and foil were small.
Winter wheat cultivars Apollo, Hornet, Longbow and Norman were each sown at 50, 100, 200, 400, 800 and 1600 seeds/m2 in a field experiment conducted in Northern Ireland over the 1989/90 crop year. No growth regulators were applied and the wheat received 178 kg N/ha top-dressing in the spring. Hourly rainfall, windspeed and wind direction data were recorded and lodging was visually assessed from the end of May to harvest. Lodging first occurred in the 1600 seed-rate plots as the ears were emerging in early June and then progressively increased in the 800, 400 and 200 plots during June, July and August. Lodging did not occur suddenly but took several hours, with the stems first lying at an angle before lodging completely. Stem buckling or breakage did not appear to be the principal form of structural failure. The longest strawed cultivar, Longbow, lodged most severely. The shorter-strawed Norman also lodged badly in contrast with Hornet which had a similar straw length. Apollo, which was taller than Norman and Hornet and produced more ears per square metre than the other cultivars, lodged least but tended to lean at c. 30-degrees from the vertical. Lodging occurred during or within 24 h of periods of rainfall which, in many cases, coincided with windspeeds at crop height averaging > 25 km/h and occasionally > 50 km/h. Lodging also occurred following rainfall when the windspeed did not exceed 16 km/h. The grain yield was negatively correlated with the average lodging from ear emergence to harvest, there being a 1 t/ha decline in yield for each 10% increase in average area lodged. The 50 and 100 seed-rate plots yielded 10 t/ha and had little or no lodging. The decline in yield with increased lodging and seed rate was attributed to the effect of lodging rather than to seed rate and was associated with a fall in the number of grains/ear and 1000-grain weight from 56 and 53.5 g at the lowest seed rate to 15 and 42.7 g at the highest, respectively. A comparison of the plants from lodged and unlodged plots of the 1600 and 800 seed rates, and subsequently of the 800 and 400 seed rates, indicated that at the higher seed rate, lodged plots had less fresh weight per unit area, basal internodes with smaller diameters, fewer support roots per stem, and a lower root dry weight per stem.
The lactation curve may be represented mathematically by the general equation Y = Aphi1(t)phi2(t) where A is a positive scalar, phi1(t) is a positive monotonically increasing function with an asymptote at phi1 = 1, and phi2 is a monotonically decreasing function with an initial value of unity and an asymptote at phi2 = 0. Functions considered as candidates for phi1 were: 1 - b0e-b1t (Mitscherlich), 1/[1 + b0/(b1 + t)] (Michaelis-Menten), 1/[1 + b0/(b1 + t(b2))] (generalized saturation kinetic), 1/(1 + b0 e(-b1t))(logistic),b0 exp[(-ln b0)(1-e(-b1t))](Gompertz) and [1 + tanh(b0 + b1t)]/2 (hyperbolic tangent). Candidates for phi2 were e(-ct) (exponential) and 1/(1 + ct) (inverse straight line). The 12 models thus obtained and Y = At(b) e(-ct) (Wood's model) were fitted to whole-lactation data from 23 animals. Mitscherlich x exponential, Michaelis-Menten x exponential. logistic x exponential, logistic x inverse straight line and Wood's model all fitted well. For these models, expressions for time to peak, maximum yield, total yield over a finite lactation and relative decline at the midway point of the declining phase were obtained. The Mitscherlich x exponential model generally fitted better than Wood's model and, unlike Wood's model, gives simple algebraic formulae for all these summary statistics.
A 2-year study conducted in Salinas, California in 1989-91 showed that soil nitrate (NO3-N) concentrations were reduced by cover crops during a short winter fallow period and that this practice can be compatible with year-round vegetable crop production schedules by planting and incorporating cover crops directly on the beds into which the lettuce crop will be direct seeded in the early spring. Cover crops grown the first year were oilseed radish (Raphanus sativus cv. Renova), white senf mustard (Brassica hirta cv. Martigena), white mustard (Brassica alba), phacelia (Phacelia tanacetifolia cv. Phaci), rye (Secale cereale cv. Merced) and annual ryegrass (Lolium multiflorum). Only phacelia and Merced rye were included in the second year. In both years, all of the cover crops depleted soil NO3-N and soil moisture relative to the fallow control. Estimates of cover crop root length, based on core sampling to 60 cm soil depth, averaged 18 800 m/m2 after 17 weeks of growth the first year and 12 500 m/m2 after 13 weeks of growth the second year. Above-ground dry matter production averaged 449 g/m2 (12.8 g N/M2) the first year and 161 g/m2 (6-1 g N/m2) during a shorter growing period and under the more adverse growing conditions of the second year. Following cover crop incorporation with a rotary tiller, soil ammonium (NH4-N), NO3-N and net mineralizable N (anaerobic incubation) peaked after c. 1 week, then gradually declined for 1 month. Cover-cropped plots sustained higher net mineralizable N levels than the fallow control after incorporation. Nitrate concentrations after spring rains were lower in soils left fallow during winter. The subsequent lettuce crop was not affected by cover crop treatment.
The rumen degradation and gas production characteristics (methane, carbon dioxide) of leaves of 20 accessions of multipurpose trees (MPTs) from six genera: Acacia, Cajanus, Chamaecytisus (L. fil.) Link, Erythrina, Leucaena and Sesbania and some poisonous plants were investigated in vitro and in sacco in rumen fistulated cows fed on a diet of grass hay ad libitum supplemented with cotton seed cake. The degradation constants (i.e. the soluble fraction (a), the slowly degradable fraction (b) and the rate of degradation (c) and the potential degradability (a + b) (PD)) were calculated. The gas production constants were estimated following the equation: Volume = b(g)(1 - e(-c)g(t)) where b(g) is gas production and c(g) is the rate of gas production. Between and within genus comparisons of degradability and gas production constants were done. The soluble fraction (a) was significantly higher for Sesbania (59) (P < 0.05) than the other genera, which had values between 45.18 and 40.38 units. There were no significant differences in the slowly degradable fraction (b) between genera. Sesbania was degraded significantly faster (P < 0.05) than either Acacia, Leucaena or Cajanus. Similarly, the potential degradability was significantly higher (P < 0.05) for Sesbania (92.7) than for the other genera. Acacia was the least degradable genus. Degradation characteristics were similar between species within the genera Acacia, Erythrina and Leucaena. However, within the Leucaena genus, L. revoluta had the highest soluble fraction (50.02) and the cross L. leucocephala x L. diversifolia had the lowest (29.24). L. leucocephala had the highest slowly degradable fraction (57.32) and L. revoluta had the lowest (42.37). L. leucocephala x L. pallida had the highest rate of degradability (0.0626) and L. pallida had the lowest (0.0221). L. leucocephala had the highest potential degradability (92.23) and the cross L. pallida x L. diversifolia the lowest (84.81). Between the genera, more gas was produced from Sesbania than from any other genus. The effect of genus was significant (P < 0.003). On the other hand, the rate of gas production (c(g)) was higher with the genus Chamaecytisus than with any other genera (P < 0.0001). Although the two methods used agree in the position of a forage of a high degradability like Sesbania, they fail to agree on the relative positions of the forages of lower degradabilities. For some genera, drying of the tree foliage reduced the volume of gas produced, but increased the rate of gas production.
The effects of plane of nutrition on blood flow in the portal vein (PBF) and on the rate of clearance of progesterone from the circulation (MCR) were measured for 14 or 24 h in six ovariectomized gilts given 1 or 3 kg of food per day. On a body weight basis, PBF was significantly increased by the increase in food intake from a mean for all gilts of 14.9 ml/kg.min (1.34 litres/min) on 1 kg to 21.6 ml/kg.min (1.96 litres/min)on 3 kg, a mean increase of 45%. Metabolic clearance of progesterone was increased by a similar percentage, 47.1%, from 4.10ml/kg.min (3.70 litres/min) to 60.3 ml/kg.min (5.67 litres/min) by the increase in food intake. Both MCR and PBF were lowest between 04.00 and 06.00 h, increasing after each feed except that when 3 kg/day was fed the MCR remained high throughout the period between meals. In two gilts, blood flow in both the portal vein and hepatic artery (HAF) was measured. The mean PBF and HAF for each pig were 40.6 and 5.8, and 32.4 and 3.5 ml/kg.min respectively. HAF was 11.2% of total hepatic blood flow.
Three field experiments in Eastern England, in which N-15-labelled fertilizer had been applied to winter wheat, were used to measure the persistence of the labelled N remaining in soil and stubble at harvest and the availability of this N to up to four subsequent wheat crops. A portion of the labelled fertilizer N quickly became stabilized in the soil, with only small and ever-decreasing amounts recovered by subsequent crops. Combining all sites, all years and all applications of fertilizer, 6.6 +/- 1.92 (S.D.) % of the labelled fertilizer remaining in soil (0-70 cm) plus stubble in the year of application was taken up by the next wheat crop, i.e. by the first 'residual year' crop. A further 3.5 +/- 0.39 % was taken up in the second residual year, 2.2 +/- 0.43 % in the third and 22 % in the fourth. Loss of residual labelled N was more rapid from a sandy soil than from two heavier-textured soils, particularly in the first residual year. After four residual crops on one of the heavier soils (at Rothamsted), 16 % of the labelled N remaining in soil (0-70 cm) and stubble in the year of application had been taken up by the crops, c. 29 % had been lost from the soil/crop system and 55 % remained in the soil.
The response of low glucosinolate, low erucic acid (double low) cultivars of oilseed rape to spring nitrogen application was examined at Cockle Park, Northumberland in three successive seasons (1987-90). Seed yield and protein content increased in response to increasing nitrogen application. In each season over 85 % of the maximum recorded yield was obtained with an application of 150 kg N/ha. In the absence of spring nitrogen, seed yield varied considerably over the three seasons. The variation in seed yield and protein content between 1987/88 and 1988/89 can partly be explained by differences in the availability of soil nitrogen in the different seasons. Seed glucosinolate concentration was significantly increased with nitrogen applications between 0 and 150 kg/ha. Increasing nitrogen beyond 150 kg/ha had little or no effect on seed glucosinolate concentration. The results are examined with reference to the varying effects of increasing nitrogen application rates on seed glucosinolate concentrations reported previously.
Lentil (Lens culinaris Medikus) is a rain-fed crop in North Africa and West Asia whose yields are limited by the amount and distribution of rainfall and winter cold. This study aimed to quantify the effects of climatic variables on lentil seed yields through the fitting of simple empirical models to trial data of two cultivars sown at six sites, 1983-89, representing 31 environments in Syria. The ranges over environments were 152-527 mm for total season rainfall and 1-52 for the number of frost nights. Overall, the total seasonal rainfall accounted for 40.8% of the variance in mean seed yield (1.27 t/ha, S.D. 0.82) with a response of 5.68 kg/ha/mm. A multiple regression model with monthly rainfall from November to May explained 67.0% of the variance in mean seed yield. From November to February the response of seed yield to rain was < 10 kg/ha/mm; rain in March, the period of late vegetative growth, made the most important contribution to seed yield. The response to April rain was negative. At Tel Hadya (the most frequently used site), the total seasonal rainfall accounted for 79.8% of the variance in mean seed yield, and the addition of the number of frost nights to the model improved the fit to 92.7%. Winter cold had a smaller effect on yield than rainfall, with no consistent overall effect, but differences over regions. The cultivars contrasted in their responses to drought (78S26002 was superior to ILL4400 at seasonal rainfall levels down to 134 mm) and the number of frost nights at Breda and Tel Hadya (78S26002 was more susceptible to cold than ILL4400). Thus, despite the predominant influence of rainfall on yield, the genetic variability in response to moisture and cold shows the scope for selection under rainfed Mediterranean environments.
In the autumns of 1985, 1986 and 1987, a total of 84 fields in England and Wales, which had received a recent dressing of organic manure or had recently been ploughed out of grass, was sampled to 90 cm depth to measure soil mineral nitrogen (N(min) i.e. NH4-N and NO3-N). Amounts of N(min) varied widely between sites, indicating the difficulty in estimating soil supply following ploughing grass or manure application although type of manure and N(min) were related. Soils contained much inorganic nitrogen where manures containing a large proportion of readily available N (pig slurry or poultry manure) had been applied. Where manures containing straw were applied, N(min) was greater in the second year after application than the first. The relationship between N(min) and response of winter wheat to fertilizer was measured on 62 of the 84 sites sampled; there was no simple relationship between N(min) and response to N. For fields just ploughed out of grass, the relationship was particularly poor. However, for fields with a history of arable cropping, there was no response to N fertilizer when N(min) was > 300 kg/ha N in either autumn or spring. Below this amount, response to fertilizer N varied considerably even for sites with similar amounts of N(min). N(min) measurements are of value in identifying soils containing sufficiently large N residues to allow fertilizer applications to be reduced, or even omitted, with confidence. Where residues are smaller, models need to be developed which take into account other factors, such as mineralization of organic nitrogen reserves, which modify nitrogen supply.
Fifteen grassland species were grown in a heated glasshouse in February-April 1985. The harvested herbage was separated into leaf and 'stem' and analysed for neutral detergent fibre, digestibility, physical breakdown when macerated, fibrosity, water soluble carbohydrate and N, P, K, Ca, Mg and Na. Lolium perenne was digestible, but rather high in neutral detergent fibre and not readily broken down by maceration. The other grasses tested, Holcus lanatus, Poa annua and Glyceria fluitans, tended to be less digestible and higher in neutral detergent fibre than L. perenne. The leaves of all 11 dicotyledonous species were much lower in neutral detergent fibre than the leaves of the grasses, and most broke down readily when macerated. The stems of Medicago sativa and of two shrub species (Lonicera periclymenum and Prunus spinosa) were the highest in neutral detergent fibre. Rumex obtusifolius, Spergula arvensis and Stellaria media were high in Mg; Plantago lanceolata, S. arvensis and S. media were high in Na; and S. arvensis was high in P. Three perennial and two annual herbaceous, dicotyledonous non-legumes were selected as being of sufficient promise and interest to be compared with Lolium perenne in feeding experiments: Plantago lanceolata, Taraxacum officinale, Rumex obtusifolius. Spergula arvensis and Stellaria media.
Fungal spoilage of animal feed silage occurs frequently. In spoiled silage of sugarbeet press pulp sampled in The Netherlands during the period 1986-90, 40% of the samples were infested by Penicillium roquefortii. Other fungi of health significance included Aspergillus fumigatus (8% of all samples) and Byssochlamys spp. (4% of all samples). P. roquefortii is also the dominant spoilage mould in maize silage. However, no PR-toxin could be detected in 25 lumps of P. roquefortii-infested maize silage, although one lump contained a fluorescent substance, with an R(f)-value close to that of PR-toxin. This silage sample was not mutagenic, but had a cytotoxic effect towards Salmonella typhimurium in the Ames test. All P. roquefortii-infested lumps contained fluorescent fungal metabolites which were absent in samples taken at 5 cm distance from the corresponding lumps in the silage heaps. It is recommended that lumps of fungal-infested silage are removed before feeding the silage to cattle.
Wheat, barley and two morphologically contrasting cultivars of peas (leafy and semi-leafless) were grown in pure stands, at standard agricultural densities, and in additive mixtures of cereals with peas. The stands were grown in boxes in the field, and partitions were used to separate the effects of root and shoot interactions. The cereals and peas were either planted at the same time, or one species was planted 10 days before the other. The origin of the N present in each species was determined by applying N fertilizer labelled with N-15. Both cultivars of peas had greater shoot and root competitive abilities than wheat or barley, probably because of their larger seed size; leafy peas had greater shoot and root competitive abilities than semi-leafless peas. Sowing peas after cereals reduced their competitive ability. The relative yield total (RYT) of cereal-pea mixtures, based on total biomass, averaged 1.6 when only the root systems interacted, and 1.4 when only the shoot systems interacted, but did not differ significantly from 1.0 when both root and shoot systems interacted. RYT values were greater when peas were grown with wheat, rather than with barley, and when peas were sown at the same time as the cereals. Shoot competition from peas increased the N % of cereals, but substantially reduced their total N content, because biomass yield was reduced. Shoot competition from cereals had no effect on the N % of peas, and only slightly reduced their total N content. Shoot competition between cereals and peas had no significant effect upon the proportion of N derived from various sources by either cereals or peas. Root competition from peas significantly reduced both the N % and total N content of cereals. Root competition from cereals had little effect on the N % of peas, but significantly reduced their total N content and increased the proportion of N derived from rhizobial fixation from 76 to 94 %. Since cereals and peas largely used different sources of N, resource complementarity for N was probably an important component of intercropping advantage, when the roots of cereals and peas shared soil resources.
Two experiments were conducted at the Massey University Deer Unit, New Zealand in 1990 and 1991 to evaluate the' performance of lactating red deer hinds and their calves grazing conventional perennial ryegrass-based pastures, red clover or chicory. In both experiments, hind and calf performance was evaluated from 1 month post-parturition over a 2 1/2 month summer period to weaning at 3 1/2 months of age. In Expt 1, hinds and calves were grazed on low (5.4 kg dry matter (DM)/hd/day), medium (10.8) or high (16.4) allowances of red clover, or on a medium allowance of a conventional ryegrass/white clover sward (9-9 DM/hd/day). In Expt 2, hinds and calves grazed equal DM allowances (12 kg DM/hd/day) of perennial ryegrass/white clover, chicory or red clover. Red clover generally had higher organic matter digestibility (OMD) and higher total N than ryegrass/white clover, and when grazed at equal DM allowances, promoted higher voluntary food intake in the hinds, increased calf growth (430 v. 330 g/day) and increased hind liveweight change. Although decreasing the red clover allowance in Expt 1 slightly but non-significantly decreased hind voluntary food intake and decreased both calf and hind liveweight change, all low red clover values were still consistently higher than all ryegrass/white clover values (P < 0.05). In Expt 2, chicory was of higher OMD and ash content than red clover but N content was lower and similar to ryegrass/white clover. Chicory promoted lower levels of calf liveweight change than red clover but higher than ryegrass/white clover. Hind liveweight change on chicory was lower than on red clover and was similar to ryegrass/white clover. It was concluded that red clover offers potential as a special purpose forage for deer production and that further experimental work is needed with chicory.
Grain yield of barley (Hordeum vulgare L.) in northern Syria is limited by water stress and extremes of temperature. The present study compared the grain yield of two barley cultivars, Harmal (spring type, cold-sensitive, early heading) and Arabi Aswad (winter type, cold-tolerant, medium early heading), under varying rainfall and temperature. Grain yield was obtained from three sites in northern Syria for seven seasons (1984/85 to 1990/91), resulting in 18 site x season combinations, here called environments. Multiple regression models, containing one rainfall and one temperature variable, were used to quantify yield responses to environmental fluctuations. Total seasonal rainfall was the variable most strongly correlated with the grain yield of Harmal, accounting for 62.8% of the variance. For Arabi Aswad, rainfall from November to January gave the best fit, accounting for 61.8% of the variance. December and January rainfall had the highest contribution to the yield of both cultivars; the contribution of March rainfall tended to be negative. The overall yield response to seasonal rainfall was 11.89 kg/ha/mm for Harmal and 8.57 kg/ha/mm for Arabi Aswad; the expected grain yield at the driest site was c. 1270 kg/ha for both cultivars. The addition of a temperature variable gave a better fit, accounting for c. 80% of the variance in grain yield for both cultivars if winter rainfall was combined with number of night frosts in spring. It reduced the expected yields at the driest site to c. 986 kg/ha. Arabi Aswad had a lesser response to both rainfall and frost than Harmal. In environments where low yields are due to both water and temperature stress, farmers are advised to grow Arabi Aswad because its lesser sensitivity to environmental fluctuations will ensure a better yield stability.