A bivariate normal model is proposed for the joint distribution of potato tuber size and weight. Parameters in the model are estimated from the yields and numbers of tubers in a range of riddle-size categories. The method is illustrated using data from a field experiment; parameters are estimated for each plot, and subjected to analysis of variance. The result is a more succinct summary of treatment effects than that produced in the traditional analysis, where data from each riddle size are analysed separately.

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 67·6;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.

A decline in supplies of organic manures and the increased use of chemical fertilizers has led to a decrease in the micronutrient content of the soil, with attendant effects on yield.

Field studies were conducted in 1986 and 1987 at the Giza Agricultural Research Centre, Egypt, to determine the effect of Cu-EDTA and Mn-EDTA foliar sprays on growth, mineral content, yield components and fibre properties of the Egyptian cotton cultivar Giza 75 (Gossypium barbadense L.).

All combinations used significantly increased the uptake of Cu and Mn and the dry matter yield. The earliness of harvest and the value of yield components were all increased by the application of Cu or Mn; 25 mg/1 of both Cu and Mn gave the highest values. Lint percentage and fibre properties were not significantly affected.

This study indicated that the yield of cotton, grown under otherwise standard conditions, may be increased by foliar sprays of Cu-EDTA and Mn-EDTA combined.

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® (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®, peat and foil were small.

The concentration of N in samples of urine from dairy cattle fed on grass herbage, or grass or maize silage, sometimes with additional concentrate feeds, ranged from 6·0 to 13·8 mg N/l with 67–91% of the total N being present as urea. The concentration of N in 11 samples of dung was 0·32–0·52% on a fresh weight basis (2·74–3·82% N in dry weight). About 18% of the dung N was contained in particulate material of > 0·2 mm diameter, c. 72% in fine particulate plus colloidal material, and c. 10% was soluble in the presence of A12(SO4)3.

When urine was stored for 3 weeks, the urea component was hydrolysed with the formation of ammonium. The rate at which hydrolysis occurred was greatly influenced by temperature. Hydrolysis of urea was complete within 2 days at 35 °C, within 7 days at 20 °C and within 21 days at 10 °C, but was only c. 90% complete after 21 days at 5 °C. The rate of hydrolysis of urinary urea-N at 20 °C was increased slightly by inoculation with slurry, dung or soil, and was also increased slightly by the greater aeration resulting from a continuous stream of bubbled air. No nitrification was detected, even in urine that was aerated for 6 weeks, probably because the process was inhibited under the conditions of high pH (9–10) and high concentrations of ammoniacal N.

When dung was stored for 3 weeks at 5 or 10 °C, there was little change in the amount of organic matter or in the form of N. However, at higher temperatures, some mineralization occurred and the amount of organic matter declined by 8% at 20 °C and by 17% at 35 °C. About 10% of the organic N was converted to ammonium during 3 weeks at 20 °C, and c. 18% at 35 °C.

With a slurry prepared from approximately equal amounts of urine, dung and water, more of the dung material was mineralized than with the dung stored alone: c. 15% of the organic matter was lost during 3 weeks at 5 °C and c. 34% at 35 °C. Despite this loss of organic matter, there was net immobilization of soluble N during the 3-week period by the solid fractions of the slurry, at all four temperatures.

Erect type groundnut germplasm belonging to the Valencia and Spanish botanical groups was examined in the field for five consecutive cropping seasons (wet 1988, 1989 and 1990 and dry 1989 and 1990) at Junagadh, India, in order to identify groundnut genotypes with the ability to grow in calcareous soil and tolerate iron deficiency (lime-induced iron chlorosis). On the basis of the visual chlorotic rating scores of their leaves, 17 and 19 genotypes of the Valencia and Spanish groups, respectively, which showed the least or no chlorosis were classified as tolerant (iron-efficient) to iron chlorosis. These genotypes may now be used as donor parents in groundnut breeding programmes for the development of iron chlorosis-tolerant varieties.

Almost all the iron-efficient groundnut genotypes had higher pod and seed (kernel) yields and Harvest Index (HI) than the susceptible types. The seed yield of 12 iron-efficient groundnut genotypes was either equal to or higher than a commercial cultivar which showed tolerance to iron chlorosis and, hence, these genotypes could profitably be grown in those areas where chlorosis due to iron deficiency is a major problem.

Three field experiments in Eastern England, in which 15N-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 2·2% 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.

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.

Between 1980 and 1986, six field experiments were conducted to investigate the relations between planting density, total dry matter and pod yield of groundnut (Arachis hypogaea L. cv. TMV2) grown at different levels of irrigation and rainfall at two sites in central India. In general, the relationship between total dry matter and planting density for most treatments was well described by the function:

where W is the crop dry weight per unit ground area, wm is the maximum weight per plant, Wm is the maximum crop weight per unit ground area and P is the plant population. Because the harvest index, h, was constant for each treatment irrespective of plant population, a similar equation described the relationship between pod yield and planting density. When nine of the eleven treatments planted in a square (i.e. 1:1) arrangement were compared, the asymptotic value Wm varied between treatments depending on available soil water and atmospheric demand. To quantify the effects of plant and environmental factors on crop productivity, a ‘transpiration equivalent’ (ωw; (g/kg)/kPa), i.e. the product of the dry matter/water ratio and mean seasonal saturation deficit D, was used as a crop constant to calculate productivity at each site or season from a knowledge of seasonal rainfall and/or irrigation and soil water-holding capacity. Thus, total crop productivity, W'8, was calculated using the equation W'8 = ωwS/D where S (mm) is a soil supply term dependent on soil water-holding capacity and monthly values of rainfall and/or irrigation. When values for Wm and W'8 were plotted against each other, a linear regression was obtained with a slope = 1·02 (R2 = 0·78). The mean harvest index of 0·38 was used to predict pod yield from a knowledge of W'8. It was concluded that of all the climatic, soil and management factors that influence crop growth in semi-arid situations, it is the interaction between the supply of and demand for water that ultimately determines total productivity, pod yield and optimum plant population.

The fate of 35S-labelled sheep urine sulphate in the soil and its plant uptake were measured in field experiments over a 12 month period in 1990/91 in Canterbury, New Zealand. Urine was applied in either summer or winter. After the summer application, there was a marked increase in pasture growth and S uptake which lasted for a period of c. 90 days. Plant uptake of applied 35S was very rapid and c. 11% was recovered in the pasture herbage within 65 days of application. By the end of the experiment, c. 80% had been recovered in the herbage. A portion of applied 35S was incorporated into soil organic forms mainly as C-bonded S. After 86 days, 30% of the applied 35S was in the C-bonded form but during the rest of the experiment this declined to 17% as the 35S was remineralized and absorbed by the growing pasture plants.

Following the winter urine application, the increase in pasture dry matter production and 32S uptake was much less marked than that for the summer application. Twenty five percent of the applied 35S was recovered in pasture herbage within 65 days and this increased to 70% by the end of the experiment. Some of the applied S was incorporated into soil organic forms and, by 83 days, 20% of the applied 35S was present in C-bonded form. Through mineralization this declined to 7% by the end of the experiment. Over the initial 41 days of the experiment, c. 25% of the 35S was lost due to leaching.

Copper deficiency in cattle is a world-wide problem. A deterministic digital computer simulation of copper metabolism was applied to cattle and especially to their response to dietary copper. This simulation was verified by comparison with published data on copper metabolism of cattle. Copper loss under conditions of dietary deficiency was governed largely by the rate of hepatic loss of copper. Copper stores were replenished gradually when the animal was returned to a normal diet. The increased copper consumption associated with increased total digestible nutrients (TDN) during lactation compensated for loss of copper in milk. Cattle have a very efficient mechanism for extrahepatic copper homeostasis by storage of excess copper in the liver, which can then be withdrawn in future deficiencies.

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 (Nmin i.e. NH4-N and N03-N). Amounts of Nmin varied widely between sites, indicating the difficulty in estimating soil supply following ploughing grass or manure application although type of manure and Nmin 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, Nmin was greater in the second year after application than the first. The relationship between Nmin 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 Nmin 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 Nmin. Nmin 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.

Red deer stags in New Zealand were given a series of immunizations against GnRH at 9–12 months of age (spring/early summer) in 1989 and 1990 and the effects upon plasma concentrations of luteinizing hormone (LH) and testosterone during the rut (15–17 months; autumn) and upon body growth to slaughter at 22 months (spring) were studied in two experiments. Control animals showed a sharp peak in plasma LH and testosterone concentration during late summer/early autumn, just preceding the rut, with scrotal circumference increasing to a maximum during the rut; body growth stopped during the rut in Expt 1 but not in Expt 2. Immunization caused the development of significant antibodies against GnRH during late spring and summer, and reduced but did not eliminate the increase in plasma LH and testosterone and scrotal enlargement leading up to the rut. Immunization did not affect body growth or voluntary feed intake during the rut in either experiment, but in Expt 1 early immunization significantly increased growth during both the pre-rut and post-rut periods. Immunization did not effect dressing out percentage, slightly increased carcass fatness in Expt 1 but not Expt 2, and reduced velvet antler growth by 12 months of age.

The lactation curve may be represented mathematically by the general equation Y = Aϕ1(t)ϕ2(t), where A is a positive scalar, ϕ1,(t) is a positive monotonically increasing function with an asymptote at ϕ1 = 1, and ϕ2 is a monotonically decreasing function with an initial value of unity and an asymptote at ϕ2 = 0. Functions considered as candidates for ϕ1 were: (Mitscherlich), (Michaelis-Menten), (generalized saturation kinetic), 1/(1 + b0 (logistic), b0 exp (Gompertz) and [1+ tanh(b0 + b1t)]/2 (hyperbolic tangent). Candidates for ϕ2 were e–ct (exponential) and 1/(1 + ct) (inverse straight line). The 12 models thus obtained and Y = Atb 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 × 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.

The production of biomass and its partitioning into stem, leaf, ear and dead material were monitored weekly in crops of wheat and oats from 16 May 1990, which corresponded approximately to ear emergence in the wheat, until ensilage on 29 June, 7 July and 19 July 1990 using the Ag-Bag system. An enzyme/inoculant additive was used on both crops on each ensilage date, although a portion of oats was ensiled without additive on the first two cutting dates, giving a total of eight silages. Changes in rumen degradability of dry matter were assessed for both crops throughout the monitoring period using the synthetic fibre bag technique. The digestibilities of gross energy, modified acid detergent fibre, organic matter and crude protein were determined in vivo using sheep.

Over the total period of monitoring, the daily rates of increase in dry matter (DM) yield were 15·1 (± 1·6) and 16·5 (±1·9) g DM/m2 for wheat and oats respectively. From 29 June to 19 July the rates of increase were 11·3 (± 3·1) and 23·1 (±6·0) g DM/m2. The increase in weight of the ears accounted for almost all of this increase and, by the end of the monitoring period, the ears contributed approximately half of the dry matter of each crop. In both crops the portion of dead material was small until 19 July, when there was a rapid increase in the amount of dead stem. The DM content of both crops remained < 30% up to day 33 (18 June) but increased from c. 33% to c. 52% between days 53 and 65 (8–20 July). Rumen degradability of both crops decreased rapidly from c. 66% on 16 May until 16 June, when it was c. 56% for wheat and 55% for oats; it remained constant at these values thereafter.

For silages made on the three successive ensilage dates, there was an increase in DM and starch contents but decreases in digestible energy, digestible fibre and digestible crude protein contents. Digestible organic matter was similar for the first two ensilage dates but lower in silage made on the third date.

The use of an additive with the oat crop resulted in decreases in the digestible energy, digestible organic matter and digestible crude protein contents of the silages compared with untreated oats.

Maximum yield of DM from wheat (18·6 t/ha) was obtained with the third cutting date, but optimum yield of energy (170 GJ/ha) and digestible crude protein (746 kg/ha) were found at the second cutting date. For oats, maximum yield of DM (17·3 t/ha) was again found with the third cut and maximum yield of energy (159 GJ/ha, untreated; 140 GJ/ha with additive) with the second cut. Digestible crude protein yield was greatest with the second cut of oats when no additive was used (708 kg/ha) but with additive it was greatest with the first cut (661 kg/ha).

It was concluded that, under these conditions, the optimum date for ensilage of wheat or oats was 7 July and that the use of the additive was detrimental to the quality of the oat silage.

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 41·0 ml/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 35 ml/kg, min respectively. HAF was 11·2% of total hepatic blood flow.

Beef cows in the 14 weeks before calving and during the first 12 weeks after calving were fed one of three diets based on 15, 30 and 45 % broilers poultry litter (PL), 20 % maize grain (MG) and 65, 50 and 35% wheat straw (WS) on a DM basis, respectively. They were housed from June to November in individual open pens. Four weeks before and 9 weeks after calving, in vivo digestibility, fibre and fluid mean retention time (MRT) were measured. The intake of all diets before calving was low. Nine weeks after calving the intake of DM increased 2·1 times on the 15% PL diet, and 1·6 times on the two other diets. The in vivo digestibility of the 15% PL diets was lower than that of the two other diets before calving, and increased after calving, in spite of the doubling of its intake, while that of the 45% PL diet decreased. The mean retention time of fibre in the digestive tract was not affected by the increase in DM intake after calving on the 15 % PL diet and was shortened on the two other diets. It seems that the combination of the volume taken up by the gravid uterus and the bulkiness of the 15% PL diets (65% WS) reduced the intake and impaired the digestibility of that diet before calving. After calving, the fibre pool increased considerably and consequently both intake and digestibility were increased.

Ten young crossbred Finnish Landrace sheep and eleven young crossbred Damascus goats with liveweights ranging from 14 to 50 kg and of different ages and body condition, were used to develop equations to predict the body composition (chemical) in the intact body and dressed carcass of young sheep and goats. After injection with tritiated water, the animals were slaughtered and their carcasses partitioned into anatomical body components which were each analysed for chemical composition (water, fat, protein, ash) and energy content. From these components, the energy content and chemical composition of the intact bodies were calculated by summation. Apart from organ and gut fat, the two species had a similar body component composition. Goat intact bodies were more hydrated and had less fat, but were similar to sheep in protein and ash content. The energy concentration in their body components was also similar, but goats had a lower energy concentration in their intact bodies. Total body water, energy content and dressed carcass were predicted accurately by the derived equations, but fat, protein and ash were predicted with less precision.

Monensin, an ionophore, and Aspergillus oryzae fermentation extract (AO), a fungal feed additive, are growth promoters which modify rumen fermentation. The effects of combining these additives were determined in the rumen simulation technique (Rusitec). Sixteen vessels received 20 g/day of a diet of hay, barley, molasses, fishmeal and a mineral/vitamin mixture (500, 299·5, 100, 91 and 9·5 g/kg DM respectively). AO, monensin (M) and AO + monensin (AO/M) were each added to four vessels at 500, 10 and (500 + 10) mg/day respectively. Both M and AO/M increased propionate (14·5 and 138 v. 91 mmol/day in controls; P < 0·001) and reduced butyrate production (6·6, 5·2 and 9·1 mmol/day respectively; P < 0·01), whereas AO had no effect. AO increased bacterial numbers by 70% (P < 0·055), while M had no effect, and in the presence of M, AO also had no effect. Proteolytic activity in samples from the vessels decreased (P < 0·05) in all treatments (1·06, 0·71, 0·60 and 0·47 mg 14C-casein/mg protein/h for control, AO, M and AO/M respectively). In contrast, deamination of amino acids increased (P < 0·001) with AO and AO/M but decreased slightly with M alone (482, 646, 434 and 644 nmol NH3/mg protein/h). Ammonia output was unchanged (47·4, 57·2, 42·7 and 44·8 mg/day). Thus each additive was dominant over the other for different activities, with monensin generally suppressing the effects of AO rather than vice-versa.

Research into the mechanisms that control the initiation and development of wool follicles has been severely hampered by the inaccessibility of fetal skin in utero. The aims of this study were to determine whether ovine fetal skin, when grafted onto the athymic nude mouse (nu/nu), could be maintained outside the uterine environment and, if so, whether it would retain its ability to initiate and develop wool follicles capable of producing wool fibres.

Skin was removed from the mid-side region of ovine fetuses on days 45, 55, 65, 75, 85 and 95 of gestation, and transferred to graft beds prepared on anaesthetized nude mice. After developing for 20 days on the recipients, the grafts were excised for histological examination. Control ovine fetal skin was also obtained at the above times and from fetuses on days 105 and 115, and similarly processed for histological examination.

Fetal skin at all ages was successfully grafted onto nude mice; 90% of all grafts were accepted and maintained by the recipients. Follicle initiation and/or development occurred in all grafts, including those formed from day 45 fetal skin, collected and grafted prior to follicle initiation in vivo. The number of follicles in grafted skin was reduced compared to that in control fetal skin of equivalent age; however, follicle development was generally accelerated. Follicle initiation and development occurred predominantly in the peripheral zone of the grafts. Some of the follicles present in the skin at grafting were lost due to the grafting procedure, while others continued to develop and produce wool fibres. Follicle development varied considerably between grafts. All grafted skin exhibited premature loss of the periderm layer and cornification of the epidermis, probably in response to the exposure of the skin surface to the atmosphere. There was a notable absence of both arrector pili muscles and sweat glands associated with graft follicles, and a retardation of sebaceous gland development.

The grafting technique developed in this study has enabled ovine fetal skin to be maintained outside the uterine environment for extended periods of time and may provide an improved means for future investigation of wool follicle initiation and development.