Crops of winter wheat (Triticum aestivum L. cv. Hereward) were grown within temperature gradient tunnels at a range of temperatures at either c. 350 or 700 μmol mol−1 CO2 in 1991/92 and 1992/93 at Reading, UK. At terminal spikelet stage, leaf area was 45% greater at elevated CO2 in the first year due to more tillers, and was 30% greater in the second year due to larger leaf areas on the primary tillers. At harvest maturity, total crop biomass was negatively related to mean seasonal temperature within each year and CO2 treatment, due principally to shorter crop durations at the warmer temperatures. Biomass was 6–31% greater at elevated compared with normal CO2 and was also affected by a positive interaction between temperature and CO2 in the first year only. Seed yield per unit area was greater at cooler temperatures and at elevated CO2 concentrations. A 7–44% greater seed dry weight at elevated CO2 in the first year was due to more ears per unit area and heavier grains. In the following year, mean seed dry weight was increased by > 72% at elevated CO2, because grain numbers per ear did not decline with an increase in temperature at elevated CO2. Grain numbers were reduced by temperatures > 31 °C immediately before anthesis at normal atmospheric CO2 in 1992/93, and at both CO2 concentrations in 1991/92. To quantify the impact of future climates of elevated CO2 concentrations and warmer temperatures on wheat yields, consideration of both interactions between CO2 and mean seasonal temperature, and possible effects of instantaneous temperatures on yield components at different CO2 concentrations are required. Nevertheless, the results obtained suggest that the benefits to winter wheat grain yield from CO2 doubling are offset by an increase in mean seasonal temperature of only 1·0 °C to 1·8 °C in the UK.

Two grazing experiments were undertaken to evaluate the effects of sulla (Hedysarum coronarium) which contains condensed tannins (CT) and lucerne (Medicago sativa), which does not contain CT, on the performance of parasitized and non-parasitized lambs. The work was carried out near Palmerston North, New Zealand in 1992 and 1993.

Experiment 1 used lambs which were either genetically ‘conventional’ or ‘resistant’ to gastrointestinal nematodes and which had a naturally acquired heavy parasite burden (faecal egg count (FEC) 1300–2500 eggs per gram faeces (epg)). They were either drenched to remove all the parasites or remained undrenched when allocated to pure swards of either sulla or lucerne for the 28-day experimental period. Liveweight gains of drenched lambs were higher with sulla (mean 302 g/day) than with lucerne (mean 245 g/day; P < 0·02) and rates of gain were not reduced (P = 0·10) by genetic resistance to nematodes. Undrenched lambs had mean faecal egg counts of 1090–2220 epg after 28 days, with higher counts in lambs grazing lucerne than in those grazing sulla (P < 0·05). Lambs grazing lucerne also had a much lower average daily gain (ADG) (mean 50 g/day) than those grazing sulla (mean 206 g/day; P < 0·0001). Resistant lambs had reduced (P = 0·07) ADG in the sulla treatment only.

In Expt 2, lambs with a relatively low worm burden (average FEC 250 epg) were either drenched to remove all worms or dosed with 20 000 Trichostrongylus colubriformis infective larvae and grazed on pure sulla or lucerne swards for 42 days. Drenched lambs had a similar liveweight gain (mean 190 g/day) and wool growth when grazing either sulla or lucerne. Undrenched lambs grazing sulla had a greater ADG (mean 129 g/day) than those grazing lucerne (mean −39 g/day; P < 0·0001) and a higher rate of wool growth from mid-side patches (P < 0·009) and larger wool fibre diameter (P < 0·05) than those grazing lucerne. Undrenched lambs grazing sulla had lower FECs (P < 0·05) on days 14, 21, 35 and 42 than those grazing lucerne and lower (P < 0·05) Trichostrongylus colubriformis worm burdens at slaughter. Undrenched lambs had less perineal faecal contamination when grazing sulla rather than lucerne. Parasite-induced anorexia was evident in the lambs grazing lucerne but not in those grazing sulla.

These findings demonstrate that the performance of lambs infected with nematode parasites can vary substantially when given feeds of a similar chemical composition. The superior performance of lambs grazing sulla was probably caused by condensed tannins, which decrease protein degradation in the rumen and can increase post-ruminal protein availability.

The possible interacting effects of shading and N supply on number of grains of Triticum aestivum L. (cv. Buck Ñandú) were investigated at Balcarce, Argentina, during the 1988/89 and 1989/90 growing seasons. Shading was imposed from c. 13 days before anthesis to 6 days after, and four rates of N fertilization were supplied within each shading treatment around the date of terminal spikelet formation. Water and other nutrients were not limiting.

Total grain yield was strongly correlated with grain number/m2, regardless of shading or N supply. At the highest N rates, grain number and dry weight of spikes at anthesis were linearly related to a photothermal quotient, i.e. the ratio of intercepted photosynthetically active radiation (PAR) to mean temperature minus 4·5 °C, during the period from 20 days before anthesis to 10 days after. The response of grain number to the photothermal quotient was interpreted in terms of the supply of assimilates to the spike at anthesis, which determined flower survival. The response of dry weight of spikes to photothermal quotient was interpreted in terms of crop growth rate since there was a linear relationship between crop growth rate and intercepted radiation. The lowest N rates reduced the number of grains/m2, at any given photothermal quotient. Since the reduction in grain number also occurred at any given dry weight of spikes, it cannot be explained by a reduced supply of assimilates to the spikes. Grain number responded directly to the supply of N to the spike, probably through the survival of differentiated flowers. The relationship between spike growth rate and crop growth rate was not affected by N supply. Crop growth rate was reduced by reduced N supply, because less radiation was intercepted and because radiation-use efficiency was lowered. These results indicate that current models for determining yield and number of grains/m2, based on crop growth, are not adequate when N is deficient.

Near-infrared reflectance spectroscopy (NIRS) was used for the analysis of soil samples for silt, sand, clay, calcium (Ca), potassium (K), sodium (Na), magnesium (Mg), copper (Cu) and iron (Fe). A total of 332 samples of different soils from Uruguay (South America) were used. The samples were scanned in a NIRS 6500 (NIRSystems, Silver Spring, MD, USA) in reflectance. Cross validation was applied to avoid overfitting of the models. The coefficient of determination in calibration (R^2_{\rm cal}) and the standard errors in cross validation (SECV) were 0·80 (SECV: 6·8), 0·84 (SECV: 6·0), 0·90 (SECV: 3·6) in per cent for sand, silt and clay respectively. For both macro and microelements the R^2_{\rm cal} and SECV were 0·80 (SECV: 0·1), 0·95 (SECV: 2·9), 0·90 (SECV 0·8), for K, Ca, Mg in g/kg respectively, and 0·86 (SECV: 0·82) and 0·92 (SECV: 25·5) for Cu and Fe in mg/kg. It was concluded that NIRS has a great potential as an analytical method for soil routine analysis due to the speed and low cost of analysis.

Forty-eight 4-month-old lambs, reared worm-free from birth, were allocated to six groups and offered ad libitum a complete diet containing 139 g crude protein/kg D.M. One group was killed at the outset as initial control (CI). Further groups, ALC, 1, 2, 3 and 4 were dosed daily for 84 days with zero, 1000, 3000, 5000 and 5000 larvae of Ostertagia circumcincta, respectively. Lambs in group 4 also received anthelmintic (fenbendazole, 5 mg/kg) on days 21, 42, 63 and 84. Lambs were killed after 98 days and their carcasses and those of the initial controls analysed for fat, protein and mineral contents.

The effect of sowing date on root growth of high-yielding crops (8–1 It grain/ha, 85% D.M.) of winter wheat (Triticum aestivum L. cv. Hustler) was measured at Rothamsted and Woburn in 1980 and 1981. Roots were sampled by coring on five occasions and changes in root dry weight and length were determined. The average growth rate between March and June was about 1 g/m2/day (200 m/m2/day), over 5 times that measured between December and March. Increases in root weight or length with time were generally exponential to anthesis when the crops had 101–172 g root/m2 (20–32 km/m2). September-sown wheat had more root than October-sown wheat at all times, but whereas early differences in length were maintained throughout the season, root weights converged between March and June. Overall, there was no significant difference in root dry-matter production between sites at anthesis, but there was a substantial difference between years. Differences in root growth between crops were reduced by plotting the amount of root against either the number of days from sowing or accumulated thermal time. Using che latter, root growth between December and June was reasonably linear although there was some indication of a lag below 500 °C days. Regression equations obtained for the relationships between root growth and accumulated thermal time also fitted previously published data and may provide general descriptions of root growth with time.

Roots of September-sown crops reached 1 m depth by December but those of October-sown crops were not detectable at this depth until April. For most crops the distribution of roots with depth was reasonably described by an exponential decay function, with over 50% of the roots in the top 20 cm of soil at all times. At Woburn in 1981, a plough-pan restricted roots to the upper soil horizons for most of the season but apparently had little effect on the total amount of root produced. For one of the experimental crops an empirical mathematical function describing the distribution of roots with depth and time is presented.

Using the data from this and previously published studies, the relationship between grain yield and the amount of root at anthesis was investigated. Total root length was positively correlated with grain yield but nonetheless similarly yielding crops could have different-sized root systems. Total root dry weight was poorly correlated with grain yield.

A stepwise adaptation was carried out on eight sheep through diets containing 10, 24, 44, 60 to a final diet containing 71% maize meal and molasses. The numbers of protozoa in the rumen increased in proportion to amount of readily fermentable carbohydrate fed, up to and including the 60% grain and molasses diet, while the numbers of total culturable bacteria remained essentially constant. However, the proportions of amylolytic and lactate-utilizing bacteria increased, and there was an orderly shift from acid-sensitive to more acid-tolerant species, particularly amongst the lactate-utilizers in response to the gradual decrease in the ruminal pH. Up to this stage the protozoa probably controlled the rate of fermentation by engulfing starch grains and bacteria and were thus able to maintain the pH of the rumen above 5·5. Lactic acid appeared only transiently and the peak values tended to diminish as adptation progressed.

The first day the final diet was fed the ruminal pH decreased to 5·4 or below for several hours. Within 7 days the number of protozoa had decreased by 50–80% and the number of total culturable bacteria increased sharply. Conditions in the rumen became unstable: peak values of D- and L- laotic acid increased by ca. 0·5 HIM, the acetate/propionate ratio decreased to ca. 2 and peak glucose concentration increased t o 3·2–9·5 mM. One animal refused all food for 1 day. Acid-tolerant species of lactate-utilizing bacteria multiplied rapidly in response to the increased production of ruminal lactic acid and the ratio of amylolytics to lactate-utilizers decreased from a mean of 10·7 to 3·6. This controlled the increase in lactic acid and the decrease in ruminal pH, allowing the ciliate protozoa to proliferate and regain control of the fermentation.

The types of cellulolytic bacteria did not change during the experiment. Despite their acid sensitivity, the number of cellulolytic bacteria per gram of ingesta was of the same order after 54 days on the 71% grain and molasses diet (0·5–13·3 × 107) as on the initial high roughage diet (3·2–7·6 × 107).

Three sheep which bloated showed no marked chemical or microbiological differences from the non-bloating animals.

Brazil is one of the most important soybean producers in the world. Soybean is a very important crop for the country as it is used for several purposes, from food to biodiesel production. The levels of soybean yield in the different growing regions of the country vary substantially, which results in yield gaps of considerable magnitude. The present study aimed to investigate the soybean yield gaps in Brazil, their magnitude and causes, as well as possible solutions for a more sustainable production. The concepts of yield gaps were reviewed and their values for the soybean crop determined in 15 locations across Brazil. Yield gaps were determined using potential and attainable yields, estimated by a crop simulation model for the main maturity groups of each region, as well as the average actual famers’ yield, obtained from national surveys provided by the Brazilian Government for a period of 32 years (1980–2011). The results showed that the main part of the yield gap was caused by water deficit, followed by sub-optimal crop management. The highest yield gaps caused by water deficit were observed mainly in the south of Brazil, with gaps higher than 1600 kg/ha, whereas the lowest were observed in Tapurah, Jataí, Santana do Araguaia and Uberaba, between 500 and 1050 kg/ha. The yield gaps caused by crop management were mainly concentrated in South-central Brazil. In the soybean locations in the mid-west, north and north-east regions, the yield gap caused by crop management was <500 kg/ha. When evaluating the integrated effects of water deficit and crop management on soybean yield gaps, special attention should be given to Southern Brazil, which has total yield gaps >2000 kg/ha. For reducing the present soybean yield gaps observed in Brazil, several solutions should be adopted by growers, which can be summarized as irrigation, crop rotation and precision agriculture. Improved dissemination of agricultural knowledge and the use of crop simulation models as a tool for improving crop management could further contribute to reduce the Brazilian soybean yield gap.

1. By establishing the relationship between linear carcass measurements and the quantitative composition of the carcass in terms of bone, muscle and fat, we have provided a scientific basis for the use of many measurements hitherto only presumed to provide an index to carcass quality.

2. External carcass measurements are correlated with weight of the skeleton. The most useful for this purpose are length of tibia + tarsus and length of the fore-cannon.

3. As indices of muscle, external measures are only of indirect value. Thus, both F – T and G/F × 100 are strongly correlated with weight of muscle as a percentage of skeletal weight.

4. Similarly, F provides an index of fat, being negatively correlated with fat as a percentage of bone.

5. For muscle and fat internal measures permit a more precise estimate to be made. A + B is the best index of the former while C + J + Y provide the most accurate estimate of the weight of fat.

6. Still better indices for muscle and fat are provided by suitable combinations of external and internal measurements. Thus L/10 + A + B is very highly correlated with the weight of muscle, and L/10 × (C + J + Y) is the best index of fat in the hoggets. For bone, a most efficient single index is shown to be the weight of the fore-cannon bone.

7. The weight of the skeleton can be estimated with a high degree of accuracy from the weight of the bones in either one leg or loin. Both these joints combined, however, provide a still better estimate.

8. The muscle in one leg or loin + leg provides an excellent index of the weight of muscle in the whole carcass.

9. The fat in one leg, loin, or both these joints combined provides a good index of the weight of the total fat in the carcass. Both joints combined give the most precise measure.

10. The value of certain measurements which are not necessarily associated with the quantity of the major tissues of the carcass, but which nevertheless have important qualitative significance, is emphasized.

Linear relationships between both total and tuber dry-matter yields and the amount of radiation intercepted by potato crops are demonstrated. Their existence suggests that, in the absenceof disease and drought, the essential objective in the production of this crop is to maximize radiation interception. This paper critically assesses the influence of factors which the grower can control on light interception and estimates potential yields for specific environments. The implications of this analysis for growers, breeders, research and the whole industry are discussed.

Field experiments were conducted to test the seed yield responses of winter oilseed rape (Brassica napus L., cvs Libravo or Falcon) to the addition of different rates of S fertilizer, at three N application rates, on a sandy loam at Woburn, Bedfordshire, in 1990/91, 1991/92 and 1993/94. Large increases in seed yields, ranging from 0·7 to 1·6 t/ha, or 42–267% on a relative scale, were obtained in response to the application of 40 kg S/ha with 180 and 230 kg N/ha treatments. The effects of S were highly significant in 1991/92 (P < 0·01) and 1993/94 (P < 0·001) and close to significant (P = 0·053) in 1990/91. The yield benefits were obtained mainly from the application of the first 10 kg S/ha and further yield increases were unlikely above 40 kg S/ha. Increasing N application from 180 to 230 kg/ha decreased seed yield in 1990/91 and 1993/94, when no S was applied. In contrast, seed yield was not increased by S at zero or low (50 or 100 kg/ha) N rates. The interactions between N and S on seed yield were significant (P < 0·05) in 1990/91 but not in the other two seasons. Application of S also increased seed oil content in 1993/94, when the degree of S deficiency was particularly severe. With an application of 230 kg N/ha, the crops took up 5–22 kg S/ha at maturity when no S was applied and 26–51 kg S/ha when 40 kg S/ha was applied. The utilization efficiency of the fertilizer S ranged from 50 to 73% in the three seasons. Although the concentrations of total N in plants were largely unaffected by S treatments, large amounts of NO3-N accumulated in the leaves of S-deficient plants in 1993/94. This indicates that N metabolism was disrupted by S deficiency. The concentrations of S and the N: S ratios in different tissues and the whole plant changed considerably with time. The concentration of S in leaves at early flowering was found to be the best index in predicting S deficiency in terms of seed yield, and a critical value of 3·8 mg/g was obtained. In comparison, the N: S ratio in leaves at early flowering was a much poorer predictor of S deficiency.

Rice plants (Oryza saliva L., cv. IR30) were grown in paddy culture in outdoor, naturally sunlit, controlled-environment, plant growth chambers at Gainesville, Florida, USA, in 1987. The rice plants were exposed throughout the season to subambient (160 and 250), ambient (330) or superambient (500, 660, 900 μmol CO2/mol air) CO2 concentrations. Total shoot biomass, root biomass, tillering, and final grain yield increased with increasing CO2 concentration, thegreatest increase occurring between the 160 and 500 μmol CO2/mol air treatments. Early in the growing season, root:shoot biomass ratio increased with increasing CO2 concentration; although the ratio decreased during the growing season, net assimilation rate increased with increasingCO2 concentration and decreased during the growing season. Differences in biomass and lamina area among CO2 treatments were largely due to corresponding differences in tillering response. The number of panicles/plant was almost entirely responsible for differences in final grain yield among CO2 treatments. Doubling the CO2 concentration from 330 to 660 μmol CO2/mol air resulted in a 32 % increase in grain yield. These results suggest that important changes in the growth and yield of rice may be expected in the future as the CO2 concentration of the earth's atmosphere continues to rise.

The risk of drought is high in the Sudan savannah zone of West and Central Africa because rainfall in this area is unpredictable in quantity and distribution. Thus, improved maize genotypes tolerant to drought could stabilize maize grain yield in this zone, where recurrent drought threatens grain production. Six maize genotypes, two each of hybrids, open-pollinated varieties (OPVs) and landraces, were evaluated for tolerance to terminal water deficit before flowering. Water deficit significantly reduced growth, grain yield and yield components of the maize genotypes. Significant differences were observed among genotypes for all the traits measured. One hybrid, 9011-30, and two improved OPVs, STR-EV-IWD and IYFD-C0, that showed tolerance to water stress recorded higher grain yield, and accumulated and partitioned more assimilates to the grain than the drought-susceptible genotypes. Also the drought-tolerant genotypes, 9011-30, STR-EV-IWD and IYFD-C0 had more ears/plant and greater numbers of kernels/ear. These genotypes could serve as sources of drought tolerance for the development and improvement of new drought-tolerant maize genotypes.

(1) The expression of mechanical composition by means of continuous curves is discussed. It is suggested that a convenient representation will be obtained by showing summation percentage as a function of the logarithm of settling velocity.

(2) The effect of a gel coating on the settling velocity of a particle is examined and it is shown that a reduction in velocity takes place which is a simple function of the thickness of the gel coating.

(3) A method is outlined by which the mechanical composition of a soil or clay is derived from determinations of the concentration of a settling suspension for different values of depth/time.

(4) A shortened method for mechanical analysis is described which gives results in good agreement with results obtained by the present standard method.

(5) The effect of various modifications in conditions of working is discussed.

(6) The nature of the concentration gradients in a settling column of a suspension is examined. It is shown that below the first few centimetres the change in concentration with depth is very gradual.

1. Six diets in which the percentage of hay varied from 0 to 100% and the percentage of flaked maize varied conversely from 100 to 0% were each given to three sheep and three steers in a series of 72 calorimetric experiments. In addition the fasting metabolism of each animal was determined on two occasions.

2. The loss of energy in the faeces increased linearly with the percentage of flaked maize in the diet, but the loss of N in the faeces did not, the loss being proportionately smaller for diets containing more than 60 % maize.

The theory of the capillary behaviour of moist soil has been further amplified for the ideal case and its relationship to various soil properties considered. Over part of the moisture range which has been dealt with by other authors it is found that there are alternative forms for the water distribution. This appears to explain why some differences of opinion have been expressed regarding some of the main points presented in a previous paper.

The theory is considered in relation to capillary rise in soils as well as to the problem of cohesion previously dealt with. It is shown that the moisture distribution attained by capillary rise can be inferred from simple direct measurement of the suction pressure. Various other experimental illustrations of the theoretical conclusions are introduced.

Sowing winter oil-seed rape cv. Victor late in autumn (late September or October) in seven seasons from 1970 to 1977 gave enormously variable seed yields, from 120 to 450 g/m2. All crops made little growth before winter, and yield was related to the size of the crop at flowering, a function of the length of time for radiation interception and growth between the ‘beginning of spring’, when mean temperatures rose consistently above 5 °C, and full flower in late May. A late spring in 1970 gave the poorest growth and lowest yield, whereas in 1977 an early spring coincided with late flowering to give exceptional growth, and yields higher than from any early sowing.

Crops sown in early autumn (before mid-September) produced more consistent seed yields, 280–360 g/m2, except in the dry year of 1976. All grew well in autumn, overwintered with a large leaf area, and once temperatures rose in spring, rapidly reached peak area and full flower in early May. They were all large at flowering, and yield was apparently limited more by post-flowering events.

With all sowings numbers of pods and seeds were largely determined during a 3-week phase in late May and early June, extending from full flower until most pod hulls had finished growing. Late sowings produced 3000–6000 pods/m2, and the number of seeds retained per pod varied widely, from 7 on a poorly grown crop to 22 on a well grown crop, thus expressing the yield potential determined by crop size at flowering. Early sowings, however, produced apparently excessive numbers of pods (6000–12000/m2) and few seeds per pod (6–10), so that yield varied little, regardless of crop size. Early in the phase, when the number of seeds was determined, the mass of yellow flowers at the top of the crop reflected or absorbed up to 60 % of incoming radiation, and then the large number of pods increasingly shaded each other and competed for assimilate, resulting in heavy seed losses. A high-yielding crop type may therefore need to incorporate the restricted pod production and good seed retention of some well-grown latesown crops with the reliability and desirable agronomic features of early-sown crops.

Final seed weight varied more between seasons (3·7–5·3 nag) than between sowings. Seed growth mainly took place after the number of seeds had been determined, the duration depending on temperature, but rate of growth apparently more on assimilate supply, a function of environmental factors and the number of competing seeds.

The voluntary intake by sheep of seventy silages was measured in experiments in several years. Linear and multiple regression analyses were made between these voluntary intakes and the contents of dry matter, various acids and nitrogen and the digestibility value determined in vivo. There were some differences in these relationships for silages made from different groups of species, particularly those made from legumes. Voluntary intake was positively correlated with the contents of dry matter, nitrogen, lactic acid as a percentage of total acids and with the Flieg index. Voluntary intake was negatively correlated with the contents of acetic acid and ammonia as a percentage of total N. Although pH alone did not account for a significant part of the variation in intake, multiple regressions in which pH and one of the measurements of fermentation quality were included were significant, with pH positively related to intake. When all silages were considered, the correlation between voluntary intake and the apparent digestibility of dry matter was not significant. However, for legumes this correlation was significant and positive and for grasses other than ryegrass the correlation was significant and negative.

The magnitude of experimental error attaching to one or more field plots is a question of extreme importance in Agricultural Science, because upon its proper recognition depends the degree of confidence which may be attached to the results obtained in field work. A very cursory examination of the results of any set of field trials will serve to show that a pair of plots similarly treated may be expected to yield considerably different results, even when the soil appears to be uniform and the conditions under which the experiment is conducted are carefully designed to reduce errors in weighing and measurement.

Fourteen young wether sheep were fed freshly cut Lotus pedunculatus as a sole diet to examine the effects of condensed tannins (CT; 55 g/kg lotus DM) on nitrogenous aspects of digestion. The experiment was carried out indoors at Palmerston North, New Zealand over 32 days with one group of sheep receiving an intraruminal infusion of polyethylene glycol (PEG; 100 g/day) to preferentially bind CT (PEG group) so that the lotus was essentially ‘CT-free'. The other sheep, not given PEG, were termed the ‘Tannin’ group.

The principal effects of CT were to increase the flow of feed nitrogen (N) to the abomasum despite a 12% reduction in DM intake of the Tannin sheep. Rumen microbial N turnover rate was slower in Tannin animals than in those receiving PEG (1·86 v. 2·63/day) but microbial N flux to the abomasum was similar in both treatments. The proportion of N intake disappearing from the rumen was lower in Tannin (0·13) than in PEG sheep (0·26) and the N digestibility was 0·67 and 0·81 for the respective treatments (P < 0·001).

The beneficial effects of CT in reducing rumen degradation of feed protein were negated in part by a reduction in fractional absorption of amino acids (AA) from the small intestine. Fractional absorption of essential AA was 0·66 in Tannin and 0·79 in PEG sheep; values for non-essential AA were 0'59 in Tannin and 0·73 in PEG groups. Amino acid concentrations in blood were similar for both groups, but Tannin sheep had lower plasma urea concentrations, a more rapid plasma urea turnover rate and a higher irreversible loss than those receiving PEG. Growth hormone concentrations in plasma were similar for both treatments.