Twenty slurries, 20 farmyard manures (FYM) and 10 poultry manures were chemically analysed to characterize their nitrogen (N) fractions and to assess their potential organic N supply. The organic N fraction varied between manure types and represented from 14% to 99% of the total N content. The readily mineralizable N fraction, measured by refluxing with KCl, was largest in the pig FYMs and broiler litters, but on average only represented 7–8% of the total N content. A pot experiment was undertaken to measure N mineralization from the organic N fraction of 17 of these manures. The ammonium-N content of the manures was removed and the remaining organic N mixed with a low mineral N status sandy soil, which was sown with perennial ryegrass (Lolium perenne L.). N offtake was used as a measure of mineralization throughout the 199 day experiment. The greatest N mineralization was measured from a layer manure and a pig slurry, where N offtake represented 56% and 37% of the organic N added, respectively. Lowest (%) N mineralization was measured from a dairy cow slurry (< 2%) and a beef FYM (6%). The mineralization rate was negatively related to the C[ratio ]organic N ratio of the ammonium-N stripped manures (P < 0·01, r = −0·63).

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 determined 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-[4,5–3H]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 DM I) 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 energyyielding 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.

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 15N as labelled fertilizer, and follows its progress through crop and soil. Data from a Rothamsted field 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.

Further genetic gains in wheat yield are required to match expected increases in demand. This may require the identification of physiological attributes able to produce such improvement, as well as the genetic bases controlling those traits in order to facilitate their manipulation. In the present paper, a theoretical framework of source and sink limitation to wheat yield is presented and the fine-tuning of crop development as an alternative for increasing yield potential is discussed. Following a top-down approach, most crop physiologists have agreed that the main attribute explaining past genetic gains in yield was harvest index (HI). By virtue of previous success, no further gains may be expected in HI and an alternative must be found. Using a bottom-up approach, the present paper firstly provides evidence on the generalized sink-limited condition of grain growth, determining that for further increases in yield potential, sink strength during grain filling has to be increased. The focus should be on further increasing grain number per m2, through fine-tuning pre-anthesis developmental patterns. The phase of rapid spike growth period (RSGP) is critical for grain number determination and increasing spike growth during pre-anthesis would result in an increased number of grains. This might be achieved by lengthening the duration of the phase (though without altering flowering time), as there is genotypic variation in the proportion of pre-anthesis time elapsed either before or after the onset of the stem elongation phase. Photoperiod sensitivity during RSGP could be then used as a genetic tool to further increase grain number, since slower development results in smoother floret development and more floret primordia achieve the fertile floret stage, able to produce a grain. Far less progress has been achieved on the genetic control of this attribute. None of the well-known major Ppd alleles seems to be consistently responsible for RSGP sensitivity. Alternatives for identifying the genetic factors responsible for this sensitivity (e.g. quantitative trait locus (QTL) identification in mapping populations) are being considered.

A hyperbolic model relating crop yield to weed density is extended to include crop density as a further variable. Other models were obtained from published sources, eight being originally applied to yield of above-ground biomass and six to marketable yield. Data were obtained from a field experiment in which spring wheat and spring barley were planted either in monoculture or together and at a range of densities. Further data were obtained from a published experiment on Sinapis alba and barley grown in containers. The models were fitted to data using maximum likelihood estimation. Comparisons of residual sums of squares showed that for the wheat and barley field experiment biomass yield and marketable yield were sufficiently described by a three-parameter model. The Baeumer & de Wit (1968) equation proposed for replacement series experimental designs is considered reasonable for the analysis of field additive designs provided the parameters are interpreted in agronomic terms. For the Sinapis alba and barley experiment more complex models could be justified.

Using the conception of the “ideal soil” a calculation has been made of the cohesion due to the capillary attraction between the particles when wetted. Experimental verification of this theory is afforded by cohesion tests on the ignited silt fraction separated from soil.

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-/CO32- 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.

Field experiments comparing 13 winter wheat varieties representing very old, old, intermediate and modern groups were carried out over three seasons. The experimental sites were on soils of high fertility and weeds, diseases and pests were controlled by applications of proprietary agrochemicals. Lodging was prevented by supporting the plants with coarse-mesh netting.

The average yield of all varieties over the three harvest years 1984, 1985 and 1986 was 7·7 t/ha (at 15% moisture content). Compared with the very old varieties which were grown by farmers during the 19th century, the modern varieties gave 59% more grain, had 14% more ears/m2 and 30% more grains per ear, but a similar mean grain mass. The modern varieties yielded slightly more biomass (total above-ground dry matter at harvest), were much shorter and reached anthesis about 6 days earlier than the older ones. In 1984, when the yields were greater than in 1985 and 1986, the yield advantage of the modern varieties was more in percentage and absolute terms than in the other years. Also, in 1984, the differences between the very old and the modern varieties in biomass was the greatest.

The genetic gain in yield measured in these experiments is compared with those estimated for other countries and reasons for the variation are discussed.

1. The chemical changes which take place in a urine patch have been studied using urine from wethers and to a small extent from cows.

2. The sizes of individual urine patches vary considerably, depending mainly on the volume of the urination. The average from wethers is about 45 sq.in.

3. The volume of urine per wether per day averages 2880 ml. with a nitrogen content of 0·92%, of which about 75% was in the form of urea; 4·1% as allantoin; 2·6% as hippuric acid; 1·5% as creatine-creatinine; and 12·4% as amino-nitrogen.

4. Improved herbage growth results in twice the area actually wetted with urine. The total area affected averaged 100 sq.in.

5. The probable area wetted with urine from cow urinations was about 650 sq.in. with a further 200 sq.in. affected indirectly.

6. With wethers the average rate of nitrogen application on a urine patch amounts to 432 lb. of nitrogen per acre.

7. The rate of hydrolysis of urea in laboratory experiments is affected by temperature and is increased by small amounts of hippuric acid but not by the other urinary constituents tried. The hydrolysis rate is greater at soil moisture content of 24% than at higher moisture levels.

8. Urea hydrolysis in soil (both in laboratory and in the field) is accompanied by pronounced increase in pH (up to pH 9·2 with urea equivalent to that applied to a urine patch).

9. The rate of nitrification is greatly affected by the pH changes. At pH values in excess of 8 nitrites accumulate and nitrate formation is retarded.

10. Heteroauxin and allantoin were both found to stimulate nitrification in laboratory experiments when used at levels found in urine. Other urinary constituents were without effect.

11. The hold up of urine on leaf surfaces of pastures was shown to amount to as much as 12·5% of the green weight of herbage.

12. Ammonia in considerable amounts may be lost to the air both from herbage and from soil.

13. Field experiments are in complete agreement with laboratory experiments and no essential difference of wether and cow urine was noticed.

14. The fate of the nitrogenous constituents is briefly considered and shown schematically.

1. Methods of investigating denitrification in soil are critically discussed with special reference to methods based on total-N analysis.

2. A modified Kjeldahl method of determining nitrogen which includes nitrate and nitrite and is applicable to waterlogged soil is described and the use of this method in studies on denitrification in soil is illustrated and discussed.

3. It is shown that rapid denitrification of nitrate in soil can be induced by incubating the soil under waterlogged conditions with organic materials such as glucose and that denitrification can be followed by total-N analyses if the organic material used to induce denitrification is not added in such excess that it also promotes significant fixation of atmospheric nitrogen.

4. The percentage of added nitrate-N lost by denitrification on incubation of waterlogged soils with different amounts of nitrate and sufficient glucose for denitrification was found to be the same whatever the level of application of nitrate.

5. Denitrification of nitrate in waterlogged soil containing glucose was found to be accompanied by a rapid but temporary accumulation of large quantities of nitrite and by the formation of smaller amounts of ammonia. Hydroxylamine could not be detected during denitrification, but it was found that this compound was rapidly decomposed in the soils examined by a process which appeared to be purely chemical.

6. It is shown that denitrification of nitrate in soil is a microbiological process and that the viability of the micro-organisms responsible for denitrification is not affected by air-drying and storage of the soil.

1. Three methods, based on treatment with neutral detergent or acid detergent, or involving ultrasonic disintegration, are described and compared for the direct estimation of undigested dietary nitrogen in individual samples of sheep faeces. Estimates of the true digestibility of the nitrogen in several sheep diets derived from analyses performed with these methods agreed well with each other, and were in accord with published estimates, derived by extrapolation techniques. Two other methods, based on treatment with phenol–acetic acid–water, and lysozyme–trypsin, respectively, were found to be unsuitable for such estimates.

2. The quantitative distribution of nitrogen between undigested dietary residues, bacterial residues, endogenous debris residues and the water soluble fraction was determined chemically. It was concluded that 57–81% of the non-dietary faecal nitrogen was associated with bacterial material.

3. Indirect evidence suggested that most of the bacterial nitrogen in faeces originated in the rumen.

Methane, in addition to being a significant source of energy loss to the animal that can range from 0·02 to 0·12 of gross energy intake, is one of the major greenhouse gases being targeted for reduction by the Kyoto protocol. Thus, one of the focuses of recent research in animal science has been to develop or improve existing methane prediction models in order to increase overall understanding of the system and to evaluate mitigation strategies for methane reduction. Several dynamic mechanistic models of rumen function have been developed which contain hydrogen gas balance sub-models from which methane production can be predicted. These models predict methane production with varying levels of success and in many cases could benefit from further development. Central to methane prediction is accurate volatile fatty acid prediction, representation of the competition for substrate usage within the rumen, as well as descriptions of protozoal dynamics and pH. Most methane models could also largely benefit from an expanded description of lipid metabolism and hindgut fermentation. The purpose of the current review is to identify key aspects of rumen microbiology that could be incorporated into, or have improved representation within, a model of ruminant digestion and environmental emissions.

The current paper briefly summarizes the available evidence regarding the potential of urban agriculture to respond to a number of key urban challenges and reviews the perspectives on urban agriculture applied by local and national authorities. The last section of the paper briefly presents the authors’ views on the development of urban agriculture as an integral part of sustainable city development.

A growing trend for nutraceutical and gluten-free cereal-based products highlights the need for development of new products. Buckwheat is one of the potential candidates for such products and the present paper reviews the functional and nutraceutical compounds present in common buckwheat (Fagopyrum esculentum) and tartary buckwheat (Fagopyrum tataricum). The vital functional substances in buckwheat are flavonoids, phytosterols, fagopyrins, fagopyritols, phenolic compounds, resistant starch, dietary fibre, lignans, vitamins, minerals and antioxidants, which make it a highly active biological pseudocereal. Cholesterol-lowering effects that lessen the problems of constipation and obesity are important health benefits that can be achieved through the functional substances of buckwheat.

In a field experiment with 47 wheat genotypes, plant samples were taken at anthesis and maturity and analysed for nitrogen. Taking means over all genotypes, the plants contained at anthesis 83 % of the total present at maturity, while at maturity 68 % of the plant nitrogen was present in the grain.

There was significant genetic variation in most of the component attributes determining nitrogen uptake. At anthesis, the heaviest plants contained most nitrogen. Because the nitrogen concentration in the leaves (average 2·8%) was much greater than in the stems and ears (average O8 %) and the leaves comprised, on average, 37 % of the plant weight at anthesis, variation in leanness was the main cause of variation in the nitrogen content of plants of a given weight. During grain filling, plants which lost the most dry weight from their stems and leaves took up the least nitrogen.

It is suggested that the strong positive correlation between the accumulation of dry matter and of nitrogen, both until anthesis and during grain filling, occurred because both carbon assimilation and nitrate reduction depend on energy made available from chloroplasts. In addition, assimilate is required to sustain the growth of roots which is necessary for continued nitrate uptake.

The results show that it should be easier for breeders to select for high nitrogen uptake from among heavy than from among light genotypes. However, although dwarf genotypes tended to be light, none of the correlations found was strong enough to render it impossible to produce dwarf genotypes capable of giving high yields of high-protein grain.

Several models have been proposed in the literature relating gain per animal (Ya) and stocking rate (x) from grazing experiments. Results from an experiment in which tropical pasture species were grazed continuously by beef cattle at a number of stocking rates (Jones, 1974) were used to examine this relation. A simple linear model of the form y = a − bxfitted the data well. Production per hectare (Yh) was related to stocking rate by yh = ax − bx2.

Stocking rate for maximum gain per hectare (the optimum stocking rate) on each pasture could be calculated from the linear regression by a/2b.

Data from a number of stocking rate experiments in tropical and temperate environments were examined to see if this relation held for a wider range of stocking rates and pasture types. Results were expressed on a common basis by calculating the optimum stocking rate and relating ratios of gain to ratios of stocking rate relative to that at the optimum.

For gain per animal, the overall relation obtained: Ya = l·999–0·999x (r = –0·992; P < 0·001; n = 114) did not differ significantly from the expected linear relation: y = 2−x. Linearity was established over the range 0·18–2·0 times the optimum stocking rate. At rates greater than twice the optimum, animal gain was negative. When expressed as gain per hectare (Yh) the quadratic equation Yh = 2x − x2 gave a good fit to the data over this range.

It is suggested that, since the relation between production per animal and stocking rate (animals/ha) remains linear over a wide range of stocking rates, two rates of stocking (with replication) may be adequate for grazing experiments and these would not have to span the optimum stocking rate in order to predict gain at the optimum stocking rate.

A new method of arranging variety trials involving large numbers of varieties is described. This type of arrangement, for which the name pseudo-factorial arrangement is proposed, enables the block size to be kept small without the use of controls.

Various possible types of pseudo-factorial arrangement are discussed in detail and the necessary formulae developed. The appropriate methods of computation are illustrated by numerical examples based on the results of a uniformity trial on orange trees. It is shown that pseudofactorial arrangements are likely to be more efficient than arrangements involving the use of controls. In cases where there is considerable soil heterogeneity they are also markedly more efficient than randomized blocks containing all the varieties. In the chosen example gains in efficiency ranging from 26 to 57 per cent, were obtained.

The effects of an altered rumen dilution rate (D) upon the molar proportions of volatile fatty acids (VFA) in rumen liquor, VFA production rate, microbial protein synthesis and carbohydrate digestion within the rumen were studied using adult wether sheep.

Dilution rate and VFA proportions were unaltered by the infusion of up to 121 water/day into the rumen of sheep fed dried grass and concentrate (9:1). There was a small but significant (P < 0·05) increase in the rumen volume when the infusion rate was increased from 8 to 12 1/day.

The intraruminal infusion of artificial saliva (41/day), or artificial saliva containing 4% or 8% w/v polyethylene glycol (PEG) caused a significant increase in D with an associated decline in the molar proportion of propionate (Pr) in the rumen liquor. A similar effect was obtained with the intraruminal infusion of 2·5% w/v sodium bicarbonate. The overall regression of Pr on D was highly significant: Pr = 32·5–82·1D; r = –0·99, P < 0·001.

A diet of flaked maize: dried grass (6:4) was offered to three sheep each fitted with a rumen cannula and with a re-entrant cannula at the proximal duodenum. The intraruminal infusion (4 1/day) of artificial saliva containing 4% w/v PEG caused a significant (P < 0·01) increase in D and a significant (P < 0·01) depression in Pr in two animals. The dilution rate and Pr in the third animal were virtually unaltered by infusion. The regression of Pr on D for the three animals was highly significant: Pr = 34·8–136·8D; r = –0·98, P < 0·001. Each increase in D was associated with an increased flow of α-linked glucose polymer, total amino acids and total microbial amino acids into the small intestine and with an increased efficiency of microbial protein synthesis within the rumen.

An area of plant science that is still uncertain is precisely what determines plants' demand for nitrogen (N), that is the amount of N they need to take up from the soil to meet their requirements for potential growth and synthesis of new tissue. A robust and unequivocal physiological basis from which to determine N demand is lacking. Yet N dominates plant nutrition. No nutrient is needed in larger quantities and, in most environments, no nutrient is in such limiting supply. Knowledge of the factors governing N demand is essential to predict the needs of crops under a wide range of field situations, so that growers can be given more reliable fertilizer recommendations (Greenwood 1982; van Keulen et al. 1989). This is important, not just for economic reasons, but because of the risks to the environment that can arise from the over-application of N fertilizers, in particular the problem of nitrate leaching (Addiscott et al. 1991).

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.