There is a strong correlation between the digestibility of the organic matter and the percentage crude fibre, percentage lignin, and percentage cellulose plus lignin in the foodstuffs examined.

There is evidence that the holocellulose and xylan in grasses are different from those in legumes in the extent to which they are digested. It is suggested that this is due mainly to the xylans or hemicellulose fraction in the forages, and may be a reflexion of a different molecular structure for the xylans in either group.

Within each group of plants both the holocellulose and xylan percentages are strongly correlated to the percentage digestible organic matter.

Excessive heating of hay led to a marked rise in the percentage lignin. This is probably due to the xylans becoming horny and insoluble, therefore being determined as lignin. This also offers an explanation for the decrease in digestibility of the organic matter.

This paper gives measurements of soil physical conditions and root growth made in the experiment described in the previous paper. The effect of methods of tillage on soil properties (strength, bulk density, nutrient distribution and fauna) and the effects on root development and the absorption of nutrients from different depths in the soil were investigated. The procedures used for these measurements are described.

Greater soil compaction occurred in all years after direct drilling. The growth of seminal roots of young plants was reduced by direct drilling in each year but only in the first year were there significant differences in root development between treatments at later stages of growth. Similarly, in each year early shoot growth was reduced by direct drilling but, with the exception of the first year, the plants were subsequently able to compensate adequately. Direct drilling resulted in more earthworms being present in the soil, and caused the surface soil to be more friable and contain a higher concentration of available phosphorus and potassium.

A dynamic model of rumen processes is constructed. The nine state variables considered are: rumen metabolic volume, non-rumen-degradable β-hexose, rumen-degradable β-hexose, α-hexose, water-soluble carbohydrates, non-protein nitrogen, rumendegradable protein and non-rumen-degradable protein. The dietary and salivary inputs to the rumen may be continuous, or pulsed. Rumen outflow given by the model is compared with data on sheep fed with different diets. Reasonable agreement is obtained when the model is run in the continuous mode, but there are considerable discrepancies between the experimental data and the pulsed model.

Based on the knowledge that alpaca (Lama pacos) have a lower fractional outflow rate of feed particles (particulate FOR) from their forestomach than sheep (San Martin 1987), the current study measured methane (CH4) production and other digestion parameters in these species in three successive experiments (1, 2 and 3): Experiment 1, lucerne hay fed indoors; Experiment 2, grazed on perennial ryegrass/white clover pasture (PRG/WC); and Experiment 3, grazed on birdsfoot trefoil (Lotus corniculatus) pasture (Lotus). Six male alpaca and six castrated Romney sheep were simultaneously and successively fed on the forages either ad libitum or at generous herbage allowances (grazing). CH4 production (g/day) (using the sulphur hexafluoride tracer technique), voluntary feed intake (VFI), diet quality, and protozoa counts and volatile fatty acid concentrations in samples of forestomach contents were determined. In addition, feed digestibility, energy and nitrogen (N) balances and microbial N supply from the forestomach (using purine derivatives excretion) were measured in Experiment 1.

Diets selected by alpaca were of lower quality than those selected by sheep, and the voluntary gross energy intakes (GEI, MJ) per kg of liveweight0·75 were consistently lower (P<0·001) for the alpaca than for the sheep (0·74 v. 1·36, 0·61 v. 1·32 and 0·77 v. 2·53 on lucerne hay, PRG/WC and Lotus, respectively). Alpaca and sheep did not differ (P>0·05) in their CH4 yields (% GEI) when fed on lucerne hay (5·1 v. 4·7), but alpaca had a higher CH4 yield when fed on PRG/WC (9·4 v. 7·5, P<0·05) and Lotus (6·4 v. 2·7, P<0·001). When grazing on Lotus, the sheep had very high protozoa counts in their forestomach contents, compared with those with the other forages and those in the alpaca. On lucerne hay and Lotus, but not on PRG/WC, the alpaca had higher (P<0·01) acetate/propionate ratio in their forestomach fluid than sheep. When fed on lucerne hay, alpaca and sheep did not differ (P>0·05) in diet N partition or microbial N yield, but alpaca had higher (P<0·05) neutral detergent fibre digestibility (0·478 v. 0·461) and lower (P<0·01) urinary energy losses (5·2 v. 5·8 % GEI) than sheep. It is suggested that differences between these species in forestomach particulate FOR might have been the underlying physiological mechanism responsible for the differences in CH4 yield, although the between-species differences in VFI and diet quality also had a major effect on it.

The development of stable suckling order, the incidence of fighting when suckling, weight gain during the suckling period, and the severity of facial wounding were studied with litters of piglets in which the canine and lateral incisor teeth were either clipped at birth or left intact. Facial wounding was largely confined to litters with unclipped teeth. Severity of wounding correlated with the observed incidence of fighting on the udder (P<0·01); and both wounding and fighting were more common among litters comprising a large number of piglets (P<0·05). When the effect of litter size was taken into account, there were no substantial differences in weight gain to 3 weeks between piglets with high and low scores for facial wounding, nor between clipped and unclipped litters. Piglets which habitually occupied the most anterior or most posterior teats had less facial wounding than middle-suckling piglets, and showed greater consistency in teat choice. No gross differences between clipped and unclipped litters were observed in the development of stable suckling order during the first week of life. It is concluded that the ‘eye’ teeth, although used in disputes over teat choice, have little influence on the frequency of such disputes or on the original development of stable suckling order.

1. Data are presented indicating that both the total yield of potatoes and the proportions of the yield in size grades were a function (independent of set size) of the number of main stems per unit area for the maincrop varieties Majestic and King Edward.

The growth and water use of sugar beet affected by early (ED) and late (LD) drought was compared with that of irrigated (I) and unirrigated (NI) controls. Mobile shelters were used to exclude rain from ED plots during June and July, and LD plots during August and September, respectively, whereas outside these periods the ED and LD plots were irrigated as necessary.

The ED treatment affected the fibrous roots severely. Many of the roots in the top 60 cm of soil died and development of the root system below this depth was slow. Expansion of the leaf canopy slowed, radiation interception was reduced and the rate of water use fell from about 1·2 times to 0·6 times Penman potential transpiration rate. The LD treatment, which was imposed when the fibrous root system was already extensive, had little effect on the fibrous roots except in the top soil. The accessible soil water was quickly depleted and the resulting stress was accompanied by earlier senescence of leaves. The rate of converting intercepted light to crop dry matter was reduced in both treatments. However, the ED treatment was the most detrimental because the amount of light intercepted in the months of highest radiation was greatly reduced owing to the restricted leaf cover. The relative effects on growth are reflected in the final sugar yields which were 8·7, 10·5, 9·9 and 12·0 (±0·30) t/ha in the ED, LD, NI and I treatments respectively.

More of the deep soil water was used in the drought-affected plots (particularly LD) than in the irrigated controls. Maximum depths of water extraction were 140–150 cm in ED and I plots and > 170 cm in LD plots. The highest uptake rates per unit length of root (20–40 μl/cm per day) were measured in the deepest part of the root system. At all depths, uptake rates declined as the soil dried. After correcting for overestimated water use where necessary, the ratios of final dry matter and sugar yields respectively to season-long water use (June–October) were close to 1·4 and 0·8 t/ha per 25 mm for all four treatments.

The feeding behaviour of Mamber dairy goats grazing on Mediterranean woodland in the Upper Galilee mountains of Israel was studied throughout a year (1991/92). The percentages of crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL) and condensed tannins (CT) were determined in samples collected by hand to simulate the plant parts selected by the goats. Total feed intake was evaluated by using Cr-sesquioxide as an external marker to determine the amount of faeces excreted, and 48 h in sacco degradability to assess the digestibility of samples. Overall, more time was spent by goats in feeding on ligneous material (tree and shrub foliage) than herbaceous vegetation (60 and 40% of total feeding time, respectively, P<0·05). The main ligneous species consumed by the goats were Quercus calliprinos, Sarcopoterium spinosum and Calicotome villosa (20, 13 and 7% of total grazing time, respectively). There was considerable variability in the 48 h dry matter (DM) in sacco degradability, and in the concentration of CP, NDF, ADF, ADL and CT, within and between seasons and plant species. Although requirements for nutrients varied according to the physiological stage of the goats, 48 h in sacco DM degradability and the concentration of non-ADF linked (available) CP, NDF, ADF, ADL and CT in the diet did not vary greatly: respective ranges were 45·0–49·4; 9–12·5; 44–53; 33–39; 12–17 and 3·5–4·7%. It is concluded that Mamber goats (i) may not select the best quality diet available, but may avoid wide variations in nutrient content of their diets throughout the year; and (ii) may not select a diet consistent with maximization of milk yield, but rather with optimization of body condition at the onset of the mating season.

Digestibility trials were carried out using wether sheep, to determine the organicmatter digestibility of several forages. Acid detergent fibre (ADF) was isolated from samples of feed and faeces, incubated in buffered cellulase solution, and the ash-free residue remaining (IADF) was used as an internal marker to estimate the organicmatter digestibility (OMD) of the feeds. Estimates of the OMD value of the samples were also made using the standard in vitro digestibility technique.

IADF had reached a constant value after incubation for 4–5·5 days and predicted OMD more precisely than the in vitro digestibility technique.

It is concluded that IADF is a suitable internal marker and predicts OMD well. However, more work is required to test this technique over a wider range of herbage species and digestibilities.

Growth and yield components of a semi-dwarf spring wheat (Triticum aestivum L., cv. GWO 1809) were determined under three different atmospheric CO2a concentrations (350, 675 and 1000 μ1/1) in controlled environment chambers of the Duke University Phytotron. CO2 enrichment enhanced tiller and head emergence and increased the number of head-producing tillers and the total dry weight of the plants. Total leaf area, stem height and root/shoot ratio of the plants were greater at high CO2 concentrations than at low. Net assimilation rate (NAR) increased with increasing CO2 concentration and decreased with plant size. There was little effect of CO2 enrichment on leaf weight ratio (LWR) and leaf area ratio (LAR) and no significant effect on specific leaf area (SLA). The weight and number of seeds were significantly higher with increasing CO2 concentration. The results of this study provide evidence that important changes in plant growth and development may occur during the next century if global CO2 enrichment continues. Some of these changes would have important ecological impact in natural and managed ecosystems in the future.

1. An analysis has been made of milk records from 13,000 cows bred by artificial insemination in Denmark.

2. The herds were divided into three equal groups on the basis of their average production. The variance of yield within herds increased as the average yield increased, but the coefficient of variation declined slightly. The genetic variance was more than five times as large in the high-yielding herds than in the low, and correspondingly the heritabilities in low, medium and high herds were 0·05, 0·15 and 0·22 respectively. These were estimated from the variation observed between progeny groups of the same 152 bulls at each production level.

3. No evidence was obtained of any sire-herd interaction for yield, either within or between management levels. The true ranking of bulls for breeding value was apparently the same at all levels.

4. The heritability of fat content in the three groups was 0·27, 0·47 and 0·49 respectively, and no evidence of sire-herd interaction was found.

5. The contemporary comparison method of assessing A.I. bulls for yield was found to have the accuracy expected in theory.

6. These results are discussed in relation to those of other workers with which there are some discrepancies. On our results, a policy of choosing bulls on the basis of their daughters' performance in high-yielding herds should be the most satisfactory way of progeny-testing bulls used in artificial insemination.

Dilute formalin was used to sample earthworm populations after the second (1969) and sixth (1973) harvests from a continuous barley experiment in which the cultivation treatments include deep (30 cm), normal ploughing (20 cm) and tined (three passes to 20 cm) cultivations and no tillage (direct drilling), at four nitrogen rates: 0, 50, 100 and 150 kgN/ha. Eight species of Lumbricidae were found, with Allolobophora chlorotica and A. longa co-dominant in both years, joined by A. caliginosa in 1973.

In 1969, Lumbricus spp., particularly large Lumbricus terreslris, tended to be more numerous in the untilled plots.

In 1973, the total populations had increased by 170%, with 50–100% more earthworms in untilled than ploughed plots, one third more with 50 and 100 kg N/ha fertilizer than with no nitrogen, and one-third more in the slightly heavier sandy clay loam soil than the lighter loam.

Most earthworm species reacted in the same way, and the reasons for any unusual reactions are discussed.

Winter oilseed rape (Brassica napus) is an important crop for human consumption and biofuel production and its production is increasing worldwide. It is generally assumed that cross-pollination by insects increases oilseed rape yield but testing of this has been restricted to a few rapeseed varieties and produced varying results. The present study determines whether cross-pollination benefits a number of oilseed rape varieties by comparing yield in the presence and absence of insects. Four rapeseed varieties (Sherlock, Traviata, Treffer and Visby) were used with ten individuals each in four pollination treatments: (1) supplementary hand-pollination, (2) open pollination with insects able to access the flowers, (3) wind pollination and (4) autonomous self-pollination. Across all four varieties, open and supplementary hand-pollination treatments resulted in higher fruit set, numbers of seeds per pod and seed yield compared with wind and self-pollination. The cross-pollination benefits, however, differed among rapeseed varieties: Treffer and Visby had a higher dependence on open (insects) and supplementary cross-pollination than Sherlock and Traviata. Across all four varieties, seed weight compensated for reduced fruit set and was highest when plants were self-pollinated. The present results highlight the importance of considering varietal differences in crop pollination research. Information on the pollination requirements of crop varieties is required by farmers to optimize management decisions in a world of increasing agropollination deficits.

1. A method of determining fixed ammonium in soil based on estimation of the difference in the amounts of ammonium released on treatment with N-HF:N-HC1 and with N-KCI has been investigated and compared with the hydrofluoric acid method of Rodrigues and the alkaline distillation method of Barshad.

2. Results obtained by the N-HF:N-HCl procedure with profile samples of various soils indicated that 3–8% (average, 5·6%) of the nitrogen in the surface soils and 9–44% (average, 21·5%) of the nitrogen in the subsoils examined was in the form of fixed ammonium. Rodrigues's method gave much higher values and Barshad's method gave much lower values.

3. Studies on the forms of nitrogen in soil profiles showed that the proportion of soil nitrogen released by acid hydrolysis as total-N and α-amino-N decreased with depth in the profile, whereas the proportion liberated as ammonium by acid hydrolysis increased with depth. They also showed that a considerable amount of the ammonium released by acid hydrolysis was derived from fixed ammonium in clay minerals.

4. It was found that the proportion of soil nitrogen dissolved by N-HF:N-HCl increased with depth in the profile, whereas the proportion dissolved by neutral and alkaline reagents used to extract soil organic matter decreased with depth. On the average, 23·2% of the nitrogen in the surface soils and 47·4% of the nitrogen in the subsoils was dissolved by a single treatment with N-HF:N-HCl at room temperature for 24 hr.

5. The reliability and significance of the results obtained by the N-HF:N-HCl method are discussed.

This paper provides estimates of varieties × environments and plot error variances based on more than 1000 trials of varieties of oats, barley, wheat, perennial and Italian ryegrass, timothy, cocksfoot, potato, sugar beet, swedes, autumn kale, forage maize and field beans. Tables of critical differences and acceptance probabilities are presented to guide in planning future series of trials.

The mixed buffer salts of artificial saliva were incorporated at three rates: 0 (diet 1), 5·7 (diet 2) and 11·4% (diet 3) (w/w) in pelleted diets prepared from60% ground flaked maize and 40% dried ground grass. The control and mineral-supplemented diets were fed to sheep hourly (Expt 1) or twice daily (Expt 2).

When the sheep were fed hourly or twice daily the pattern of fermentation in the rumen was altered from a predominantly propionate to mainly acetate fermentation. Dilution rate in the rumen increased from 0·036 to 0·053 to 0·064 when diets 1, 2 and 3 were fed hourly, and dilution rate was negatively related to the molar proportion of propionic acid (P < 0·05) and positively related (P < 0·05) to the molar proportion of acetic acid in rumen fluid, but these relationships were not apparent in Expt 2.

Nitrogen retention was higher for lambs fed diet 2 than for those fed diets 1 and 3 (P < 0·05) in Expt 1.

In sheep fed hourly, selenomonads and bacteroides were the predominant rumen bacteria associated with the control diet but the inclusion of mineral salts resulted in the bacteroides being replaced by large number of chain-forming cocci. Numbers of protozoa were variable. The relationship of these changes to the fermentation pattern is discussed. In sheep fed twice daily there was much variation between animals.

1. During the period May 1948 to May 1952, a study was made of the influence of seasonal fluctuations in the nutritive value of the natural pastures in the Bankenveld region of the Transvaal, on the growth, reproduction and production of cattle. The paired method of investigation was adopted, each heifer maintained on grazing alone having a related counterpart of the same age which received supplementary feeding during the winter months. The former treatment was termed ‘Low plane’, and the latter referred to as the ‘High plane’. Four breeds were included in the investigation, viz. Friesians and Jerseys, and Shorthorns and Afrikaners, thus representative of both dairy and beef types. The latter breed also represented the stock indigenous to South Africa. Initially five pairs per breed were studied, but deaths and other causes depleted the numbers to twenty-eight head after 4 years of investigation.

2. Since the investigation formed part of a series of studies which have been in progress at the University of Pretoria and Agricultural Research Institute during the past two decades, the results of which hitherto remained unpublished, a review is provided in the early chapters. To furnish some indication of the natural conditions ruling in the Bankenveld region, the agro-ecological background is discussed, particular attention being paid to physical and nutritional factors. It is shown that for at least 6 months of the year the climate tends to be subtropical, whilst the results of digestion trials on pasture samples, indicated serious nutritional depressions in the natural grazing during winter.

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 18800 m/m2 after 17 weeks of growth the first year and 12500 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 (61 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), N03-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 relationship has been investigated between the yield of oil-seed rape (Brassica napus L.) plants and (a) the proportion of podless stalks, (b) the proportion of pods infested by seed weevil larvae and (c) the effect of removing a proportion of buds and pods. Plants compensated for damage and, although late removal of buds or pods sometimes caused greater yield loss than early removal, only plants with more than 60% podless stalks or buds removed had diminished yields. The numbers of podless stalks per plant increased with plant size. Removal of 60 % of a plant's pods caused no yield loss; in the field a maximum infestation of only 25% of the plant's pods with seed weevil larvae occurred. The results are discussed in relation to damage by pollen beetles (Meligethes aeneus Fab.) and seed weevils (Ceutorhynch.ua ossimilis Payk.)

In continuation of earlier work, a study has been made of the factors controlling the competition between spring-sown cereals and annual weeds. During the years 1934 and 1935 some eighteen replicated trials were carried out in widely different localities. In six experiments, observations involving some 20,000 counts were made on the cereal development. Competition between Brassica arvensis (yellow charlock) and spring barley primarily reduced the number of tillers and fertile shoots; competition on the other hand with Raphanus raphanistrum (white charlock) diminished in addition ear size. The presence of R. raphanistrum in spring oats may decrease panicle size to the same extent as shoot number. In four out of six experiments the addition of nitrogen to both the weedy and clean crop had similar effects, greatly increasing tiller production in barley and both panicle size and shoot number in oats.

In six experiments nitrogenous manuring raised the yield of the weedy crop (containing either B. arvensis, R. raphanistrum or Chrysanthemum segetum (corn marigold)) to or above the level of the clean crop; n i four the yield increases were greater in the weedy than in the weed-free crop. In one experiment doubling the amount of nitrogen applied to the weedy crop did not increase the yield of oats more than the single rate, although the final yield level was considerably below that of the weed-free oats. In four other experiments additional nitrogen did not raise the yield of the weedy crop; but in only one was the yield of the clean crop increased by nitrogenous manuring.