Field experiments explored the relationship between canopy apparent photosynthesis (CAP) and grain yield and examined the effect of plant population density on CAP. Two cultivars of wheat were grown at five plant population densities in 1986 and 1987 in Taian, China. Measurements of CAP were made at intervals during the growth period by placing a large plastic-covered chamber over a 0·7 m2 segment of the canopy and measuring CO2 depletion with infra-red gas analysers for 1–2 min at c. 25 °C around noon when solar radiation was > 1100 umol/m2/s. Canopy respiration (CR) rates were measured by covering the whole chamber with a black screen in the daytime. Calculations of CAP and CR were made using the chamber volume, air temperature and changes in CO2 concentration over time and expressed on a land area basis.

Maximum values of CAP and CR were 4–6 g and 2–3 g CO2/m2/h, respectively, at the anthesis stage, decreasing with age during grain filling. The decrease was more rapid at the high than at the low population density. The difference in CAP between plant densities before booting and after anthesis could be attributed to reductions in leaf area index (LAI) and photosynthetic rate.

Grain yield also differed between plant population densities, the range being from 5250 to 7500 kg/ha in both years. Grain yield and 1000-grain weight were positively correlated with CAP during grain filling (r = 0·78 and 0·99, P < 0·01, 8 D.F.). Effects of plant density on CR were highly significant, but CR was not related to yield (r = 0·50).

Changes in leaf area index (LAI) of wheat are predicted by using information on daily heat units, atmospheric evaporative demand, water supply and nitrogen. The results of experiments on two different soils at Punjab Agricultural University Farm, Ludhiana, India from 1987 to 1990 showed that the rate and extent of leaf area development and its decline were dependent on the amount and pattern of water supply. Maximum leaf area index (LAImax) during the three years was found to depend on a combined effect of NO3-N in the 180 cm soil profile at sowing plus fertilizer N added. A relative growth factor (RGF) to scale cumulative water supply commensurate with crop growth was computed, which takes into account the combined effect of crop demand and supply of water and nitrogen from the soil. For adequately irrigated wheat, leaf area senescence could be predicted from cumulative potential evapotranspiration (PET). However, under droughted conditions, water supply, along with PET, also affected leaf area senescence. The dependence of wheat grain yield on LAImax in conjunction with water supply subsequent to attainment of LAImax was almost linear. It is concluded that, for adequately irrigated wheat, N availability at sowing and cumulative PET determines LAImax and the pattern of leaf development. Wheat grain yield is determined by LAImax and cumulative water supply from LAImax to maturity.

Leaf emergence, apex development stage, internode length and Zadoks principal growth stage 3 were measured over 3 years at several sites.

Internode elongation and Zadoks score were strongly related to the number of emerged culm leaves. The final length of the most basal internode was very variable and contributed to variation in the relationship between Zadoks stage 30 and the number of emerged culm leaves. Variation in the length of the basal internode was related to the final number of culm leaves. Most plants had six culm leaves but the number of leaves was affected by sowing date. In an experiment where sowings were made from September to March, stem elongation and Zadoks stage 30 started at a later stage of apex development in later sowings.

Recognition and prediction of culm elongation and number of emerged culm leaves is important for the application of growth regulator and fungicides. Combined with functions to predict the rate of leaf emergence and final number of leaves, the relationships described in this paper may enable Zadoks principal growth stage 3 and number of emerged culm leaves to be predicted.

Pot and field experiments were conducted at the Faculty of Agriculture Arable Crops Farm, Kumasi, Ghana during the major rainy season to compare the agronomic efficiency of potassium in cocoa pod ash with that of muriate of potash and to determine the optimum rate of application of cocoa pod ash to maize (Zea mays L. cv. La Posta). Results from the two experiments indicated that the application of 90 kg N/ha and 67 kg P2 O5/ha did not increase shoot dry matter (DM) yield over the control. However, significant increases in DM yield over the control were obtained when N and P were applied together with 56 kg K2O/ha, demonstrating the complementarity of the major nutrient elements N, P and K. Shoot and root DM increased with increasing application of cocoa pod ash. Application of 140 kg/ha cocoa pod as (equivalent to 56 kg K2O/ha) produced the same DM and shoot potassium yields as 56 kg K2O/ha as muriate of potash. The optimum rate of application of cocoa pod ash was 280 kg/ha (112 kg K2O/ha).

In 1990 and 1991, four rice cultivars – Utkalprabha, Panidhan, CN573–321–7–1 and Jaladhi–1 were sown in dry soil at the end of May and grown thereafter under semi-deepwater conditions (0–80 cm) at Cuttack, India. These crops were subjected to foliage cutting at the collar of the uppermost leaf on 1 September and/or on 1 October. The amount of foliage cut was greater in 1990 than in 1991 due to a relatively slower rise in water level in the initial stages of the experiments, which resulted in a more vigorous growth of the plants. The tall, rapidly elongating and floating deepwater cultivar Jaladhi–1 yielded the most foliage, followed by the relatively shorter cultivars CN573–321–7–1, Panidhan and Utkalprabha. However, the grain yield of CN573–321–7–1 was greatest and the effect of foliage cutting was least pronounced; whereas Jaladhi–1 gave the lowest grain yield which further decreased significantly when foliage was removed. Cutting in September had no effect on the yield of CN573–321–7–1, Panidhan and Utkalprabha, but the later cut in October had a detrimental effect, particularly when cutting was done a second time. Nevertheless, a single late cutting in October was not found to be harmful to the yield of the tall cultivar CN573–321–7–1 and the long-duration semitall Panidhan. Decrease in grain yield with two cuts of foliage was due to a reduction in the weight and number of grains/panicle as panicles/m2 and 1000-grain weight remained unaffected. The results suggest that foliage could be harvested for feeding cattle from the long-duration, tall and photosensitive rice cultivars without any adverse effect on grain yield under semi-deep lowland conditions.

Field experiments were conducted for three consecutive years during 1988–90 at a research farm near the Indian Institute of Technology, Kharagpur, West Bengal, India to study the influence of organic and inorganic fertilizers on the performance of rice and fish in a dual culture system. Under waterlogged conditions the grain yield and dry matter of the rice variety CR1018 was increased both when inorganic N fertilizer (50 kg N/ha) was supplied or when a combination of organic (lOt FYM/ha) and inorganic N fertilizer (25 kg N/ha) were applied as compared with an organic fertilizer alone (20 t FYM/ha). The recovery of N as well as grain yield response per kg of N applied was also greater when inorganic N was applied. On the other hand, the growth of the fish species Java punti (Puntius javanicus) when grown alone (monoculture) and Catla (Catla catla), Mrigal (Cirrhinus mrigala) and Java punti (Puntius javanicus) grown together (polyculture) in the rice field was found to be superior when organic fertilizer was applied either alone or in combination with an inorganic fertilizer. The total number of phytoplankton species as food for the fish under organic manuring was more than under inorganic fertilization. In low-lying waterlogged situations (15–45 cm water depth), the total productivity could be increased by supplying the appropriate nutrition to both rice and fish in such dual culture systems.

Field experiments with the South American grain crop, quinoa, were carried out at two sites in Denmark in 1988–90 in order to study the effects of varying the nitrogen fertilization rate, seed rate, row spacing, harvesting method and harvest date. Although there was a significant yield increase when the amount of nitrogen fertilizer was increased from 40 to 160 kg N/ha, quinoa seems to be well adapted to poor soils. Yield decreased by 24–1% when the nitrogen supply was reduced from 160 to 40 kg N/ha, while the yield decrease was 120 and 2–7% when the nitrogen supply was reduced to 80 and 120 kg/ha, respectively.

A model expressing yield as a function of plant density, for three experiments analysed as one, showed an optimal plant density with respect to yield of 327 ± 220 plants/m2. This plant density was the top point of the curve relating yield to plant density. However, the large standard deviation indicates that apparently a rather wide range of plant densities would provide similar yields. When the row spacing was varied, it was shown that plots with a row spacing of 50 cm, which were hoed, gave a higher yield than plots with 25 or 12·5 cm row spacing, which were unhoed. There was an overall increase in yield when changing from combined harvesting to swathing; however, when comparing the yields from the optimal harvest dates for the two methods, no yield differences could be detected. The optimal harvest date for swathing was found to be the stage when the inflorescences start to turn brown, whereas for combining, the optimal harvest date was the stage when most of the inflorescences are already brown.

Two commercial bacterial inoculants (Lacto-flora and Ecosyl) were added to kikuyu grass (Pennisetum clandestinum) at ensiling, in 1985 and 1988 respectively, at Cedara, South Africa, using laboratory silos. In 1985 (Expt 1), Lacto-flora was added on its own and in combination with the enzymes Celluclast or SP249. In 1988 (Expt 2), Ecosyl was added on its own and in combination with molasses, at two levels of addition.

The addition of Lacto-flora alone did not significantly increase the lactic acid bacteria or the lactic acid content of the treated silage. However, treated silage contained 53·6% less iso-butyric acid and 53·7% less ammonia than the control silage. Kikuyu silage supplemented with a combination of Lacto-flora and Celluclast or SP249 had higher numbers of lactic acid bacteria at ensiling (0·231 × 108/ml) than the control silage or silage receiving Lacto-flora alone. However, only silage supplemented with the combination of Lacto-flora and Celluclast had a significantly higher lactic acid content (2·23 compared with 0·04, 0·18 and 0·13% DM for the control silage, silages with Lactoflora and with a combination of Lacto-flora +SP249, respectively). Nevertheless, this silage contained 19·78% more acetic than lactic acid.

Silage supplemented with Ecosyl on its own did not differ significantly in digestibility, loss of dry matter, ammonia, total non-structural carbohydrates, lactic acid and crude protein, from the untreated silage. A significant decrease in silage pH (from 5·08 to 4·70) was observed when Ecosyl was added together with molasses at the higher level of addition only. However, no other benefit was obtained by the addition of Ecosyl in combination with molasses.

The influence of weight of stakes planted on subsequent cassava yields and the stability of yields was investigated in a 4-year study (1986–90) in Nigeria using two cultivars (TMS30572 and TMS91934). Harvest yields were dependent on the weight of stakes planted and an optimum weight of 875 kg/ha for both cultivars was established; which corresponds to an average stake weight of 88 g. Cultivar TMS30572 consistently outyielded TMS91934 (P <0·05). Tissue analysis of 25 cm long stakes from the mainstem and from the primary and secondary branches of both cassava cultivars showed differences in the amounts of food reserves stored in the stakes. More carbohydrate was found in each of the three stakes of the mainstem than in the stakes from the primary and secondary branches of both cultivars. The yields of each cultivar for the three growing seasons did not vary significantly, which suggests that sustainable high root yield appears to be achievable and is greatly aided by the appropriate management of the stakes.

The effects of periods of drought occurring during different phases of reproductive growth of faba bean (Vicia faba L.) cv. Xichang Dabai on dry matter production, seed yield, photosynthetic rate and stomatal size were investigated in pot experiments in 1987/88 and 1988/89 at Xichang Agricultural College, China. Six treatments were imposed: no drought (control), and drought from floral initiation to first flowering (D1), from first flowering to full bloom (D2), from full bloom to initiation of podset (D3), from initiation of pod-set to full pod-set (D4), and from full pod-set to maturity (D5).

Photosynthetic rate, chlorophyll content, leaf area, stomatal pore breadth, biomass and seed yield were decreased by all drought treatments, but stomatal frequency and respiratory rate were increased. The light saturation point for photosynthesis was decreased from 950 µmol/m2/s (PAR) to 570 µmol/m2/s (PAR) in leaves from drought-stressed plants, which also showed maximum stomatal opening between 08.00 and 11.00 h followed by progressive stomatal closure.

The response of faba bean to drought varied during the different reproductive growth stages. Plants subjected to drought at stage D1 were less affected than those at other stages, while plants at stage D4 were most sensitive to drought, which reduced seed yield by c. 45% in 1987/88 and by c. 43% in 1988/89 relative to the control plants, suggesting that stage D4 is the stage of reproductive development most sensitive to soil drought in the faba bean.

The largest yields of wheat and potatoes came from the combination of longer ley plus optimum fertilizer N but yields of winter beans were decreased where N had been given to the previous crops. Without fertilizer N, two year old leys significantly increased yields compared to one year leys and the effect of longer leys was small except for the first wheat, when grain yields were large and plateaued after the three year ley.

Exponential response curves were fitted to the wheat yields and an exponential plus linear trend to the potato yields after each of the leys. Maximum yields and maximum economic yields and their associated N dressings were then estimated. Maximum economic yields of wheat in 1987 ranged from 811 to 914 t/ha grain and the fertilizer N needed declined from 174 kg/ha after the one year ley to 48 kg/ha after the six year ley. For potatoes in 1988, yields ranged from 63 to 71 t/ha tubers but the N required (137–150 kg/ha) varied little with ley age. For winter wheat, in 1989 yields ranged from only 5·51 to 6·99 t/ha grain, because of drought but, as with the potatoes, the N required (203–218 kg/ha) varied little. For each crop the six individual N response curves could be shifted to bring them into coincidence, and the benefits of the ley estimated in terms of a quantity of fertilizer N applied in spring (horizontal shift) and effects other than spring N (vertical shift). The spring N effects relative to the one year ley varied with ley age; for the first wheat the range was from 6 to 126 kg N/ha for the two to six year leys respectively. Spring N effects were negligible, however, for potatoes (average 6 kg/ha) and also for wheat in the third year (6 kg/ha). Benefits other than those which could be ascribed to spring N increased yield of the first wheat, on average, by 0·94 t/ha grain for the two to five year leys; for potatoes they ranged from 3·5 to 8·1 t/ha tubers for the three to six year leys; for the third crop wheat they ranged from 0·86 to 1·49 t/ha grain for the three to six year leys.

On average, the first wheat recovered only 34% of the applied fertilizer N whilst potatoes and the following wheat recovered 55 and 56% respectively. There was a benefit from the longer leys which affected the efficiency with which fertilizer N was used.

Increasing ley age up to five years increased total soil carbon by a maximum of 0·17%C; 18% of the carbon content of the soil in the one year ley plots. This small increase in soil organic matter provided up to 230 kg/ha mineral N in the first autumn after ploughing. Between 17 October 1986 and 27 April 1987 the average loss of NO3-N from soils following three to six year leys was equivalent to 202 kg N/ha, whilst the average uptake of N by 11 May in the above-ground wheat was only 88 kg/ha; the net loss was 114 kg N/ha. A computer simulation, which included mineralization of organic N during this period together with N uptake and nitrate leaching losses, computed a loss of 250 kg N/ha following the six year ley, and this would have given 400 mg NO3/1 in the 275 mm through drainage that winter.

A field plot experiment of 271 days duration was conducted on New Zealand irrigated pastures, commencing in the summer (January) 1988, on a Templeton silt loam soil (Udic Ustochrept) by applying 35sulphur (35S)-labelled urine (250 μCi/g S with 1300 μg S/ml) to field plots (600 × 600 mm) at a rate equivalent to that normally occurring in sheep urine patches (150 ml/0·03 m2) to investigate the distribution, transformations and recovery of urinary S in pasture soil–plant systems and sources of plant-available soil S as influenced by the available soil moisture at the time of urine application and varying amounts of applied irrigation water. Results obtained showed that c. 55–90% of 35S-labelled urine was incorporated into soil sulphate (SO42−), ester SO42− and carbon (C)-bonded S fractions within the major plant rooting zone (0–300 mm), as early as 27 days after urine application. Hydriodic acid (Hl)-reducible and C-bonded soil S fractions showed no consistent trend of incorporation. On day 271, labelled-S was found in soil SO42−, Hl-reducible S and C-bonded S fractions to a soil depth of 500 mm, indicating that not only SO42− but also organic S fractions from soils and 35S-labelled urine were leached beyond the major rooting zone. A large proportion (c. 59–75%) of 35S-labelled urine was not recovered in pasture soil–plant systems over a 271-day period, presumably due to leaching losses beyond the 0–300 mm soil depth. This estimated leaching loss was comparable to that (75%) predicted using the S model developed by the New Zealand Ministry of Agriculture. The recovery of urinary S in soil–plant systems over a 271-day period was not affected by different amounts of irrigation water applied 7 days after urine application to soil at either 50 or 75% available water holding capacity (AWHC). However, significantly lower S recovery occurred when urinary S was applied to the soil at 25% AWHC than at field capacity, suggesting that urinary S applied at field capacity might not have sufficient time to be adsorbed by soil particles, enter soil micropores or be immobilized by soil micro-organisms. Both soil ester SO42− and calcium phosphate-extractable soil S in urine-treated soils were found to be major S sources for pasture S uptake. Labelled S from 35S-labelled urine accounted for c. 12–47% of total S in pasture herbage.

The effects of green manuring with Sesbania aculeata, or with Leucaena leucocephala leaves and of weed incorporation on the physical properties of a clay loam soil under a rice–wheat rotation were compared at New Delhi, India, in 1986–87. Under puddled conditions, the volumetric moisture content of the saturated topsoils varied from 0·400 cm3/cm3 in the Sesbania-treated plots to 0·425 cm3/cm3 in plots receiving no green manure, but in the unsaturated soils at rice harvest the corresponding values were 0·317 and 0·271 cm3/cm3. The effects of the green manures on the water content of the soils were still evident after a subsequent wheat crop. Other soil physical properties affected by the treatments were the following (data refer to topsoils measured after the rice harvest): settling index (cm/cm), an estimate of structural instability, which ranged from 25·5% (Sesbania-treated plots), to 28·6% (weed incorporation), 29·7% (Leucaena-treated plots) and to 33·5% (NPK-fertilizer only). Soil dispersion increased from 6·0 to 10·0 g/100g through the same treatment sequence. Hydraulic conductivity in the NPK-fertilizer only plots was 31 cm/day, but increased to 4·8 cm/day in the Sesbania-trealed plots. Sesbania was superior to the other green manures for improving soil physical properties after its incorporation.

Red clover (RC) and perennial ryegrass (PRG)-based forages were cut fresh during late spring/early summer and fed at similar levels of dry matter (DM) intake to rumen fistulated castrated red deer kept indoors in metabolism pens. RC contained higher concentrations of total N and non-protein cell contents than PRG and lower concentrations of fibre. Rumen pool size and fractional outflow rates of liquid (13·3 ν. 15·1%/h) and of paniculate matter (2·5 ν. 3·9%/h) were lower for deer fed RC than PRG. Apparent digestibility of energy and fibre, rumen fibre fractional degradation rate and rumen fractional disappearance rate of non-protein cell contents were all higher for RC than for PRG deer. Nitrogen retention was similar for deer fed both forages. However, the concentration, pool size and outflow of ammonia from the rumen, together with urinary N excretion, were all much greater for deer fed RC than those fed PRG. The acetate: propionate ratio in rumen volatile fatty acids (VFA) was lower for the RC than the PRG group. It was concluded that the greater fibre digestion in deer fed RC was due to a faster rumen fractional degradation rate and a longer particulate mean retention time in the rumen, and that the very rapid outflow of water from the rumen relative to particulate matter in deer fed RC (5·5:1 ν. 3·8:1) may explain why deer are not susceptible to rumen frothy bloat when grazing RC. One reason for the greater voluntary feed intake (VFI) of deer grazing RC than those grazing PRG may be due to its greater concentration of protein and non-protein cell contents and their more rapid degradation and removal from the rumen.

Hereford (H × H), Brahman × Hereford (B × H), Simmental × Hereford (S × H) and Friesian × Hereford (F × H) females born over a 5-year period (1973–77) were placed on pastures of high, medium or low nutritive value at Grafton, New South Wales, Australia, at weaning (7–8 months of age). The first mating of heifers on high pasture was at 15 months (1974) while that on medium and low pastures was delayed until 27 months of age (1975). This paper reports the reproductive performance of these cows up to 5 years of age and the preweaning growth of their calves which were sired by Hereford bulls at Grafton, Australia. In total, 1222 calving records were analysed.

Most traits were subject to interaction between genotype and other main effects (pasture, year of birth of cow, cow age and sex of calf). Eyelid pigmentation was an exception, with calves from B × H cows having more than calves of other genotypes (73 v. 43%). There were significant genotype differences in calving difficulty among 2-year-old heifers only, with H × H (33%) requiring more assistance than F × H (15%) and SxH (10%) heifers, while B × H heifers did not require any assistance. Genotype differences in percentage of calves born and weaned were observed on low pastures only, where B × H (66% born, 65% weaned) exceeded H × H (48%, 39%) and S × H (39%, 38%) cows, with F × H (58%, 50%) cows being intermediate. Calves by H × H cows were the slowest-growing and were the lightest at weaning on all pastures, with mean gains of 759, 604 and 340 g/day, and mean weaning weights of 212, 188 and 110 kg, on high, medium and low quality pastures, respectively. F × H and S × H cows produced the fastest-growing calves on high quality pasture (966 and 936 g/day, respectively) while B × H cows produced the fastest-growing calves on medium (823 g/day) and low (679 g/day) quality pastures. F × H cows weaned the heaviest calves on high quality pasture (274 kg) while F × H and B × H weaned the heaviest calves on medium (230 and 229 kg, respectively) and low (162 and 169 kg, respectively) quality pastures. Differences in body measurements followed a pattern similar to weaning weight.

The preweaning growth of the progeny of mature cows grazing high, medium or low quality pasture was evaluated. The cows were 5–9 years of age at the beginning of the study and were either purebred Hereford (H x H), first-cross Brahman x Hereford (B x H), Simmental x Hereford (S x H) or Friesian x Hereford (F x H). Hereford and Brahman bulls were mated to these cows for three mating seasons commencing in 1982, at Grafton, New South Wales, Australia. Records on 634 calves born over three consecutive years were used.

Most traits were subject to significant sire breed or dam breed effects or their interactions with one or more of the other main effects (pasture, year of birth of calf, cow age and sex of calf). The incidences of calving difficulty and stillbirths were exceptions. Stillbirths (mean of 3·8%) were not affected by any of the effects studied, while calving difficulty was affected only by sex of calf effect (males, 3·9%; females, 0·8%). The mean calving date of Brahman-sired calves was 11·4 days later (P < 0·05) than that of Hereford-sired calves. Differences between Brahman-sired and Hereford-sired calves for weaning weight were not significant for S x H (Brahman, 237 kg; Hereford, 232 kg) and FxH (Brahman, 238kg; Hereford, 238kg) dams. For HxH dams however, calves sired by Brahman were heavier at weaning (205 kg) than those sired by Hereford (193 kg) bulls, while for B x H dams the reverse was true (Brahman, 222 kg; Hereford, 231 kg). For calves with B x H dams average daily gain (ADG) was the same (957 g/day) for each sire breed, while for the other dam breeds, Brahman-sired calves had a higher ADG than Hereford-sired calves (862 v. 779, 1014 v. 946 and 1022 v. 950 g/day for H x H, S x H and FxH, respectively). Calves sired by Brahman bulls had > 90% eyelid pigmentation while Hereford-sired calves had 44–74%. On high quality pasture, the weaning weights and ADG of calves of F x H and S x H dams were higher than those of B x H and HxH dams. On medium quality pasture, weaning weight of calves of crossbred dams (B x H, S x H and FxH) were similar but higher than those of H x H dams. On low quality pasture, mean weaning weight of calves of B x H was higher than those of S x H and F x H dams, which in turn, were higher than that of H x H dams.

The quantity of imbibed water that bypassed the rumen directly or rapidly effluxed from the rumen was investigated in four steers offered water marked with CrEDTA. Water was offered for short periods designed to simulate the drinking patterns that occur under extensive grazing conditions. Animals were fed either low quality pangola hay in the long form or a concentrate diet. Bypass of imbibed water was calculated by difference from marker imbibed and that present in the rumen on emptying after water had been imbibed. It thus represents the passage of marked water directly to the omasum/abomasum and that which rapidly effluxed from the rumen before emptying. Bypass of imbibed marked water was 19·0 and 25·3% for animals consuming pangola and concentrate respectively (significantly different from zero but no significant diet effect). Imbibed water entering the rumen mixed rapidly so that liquid from a posterior site in the rumen had a similar concentration of Cr to that from an anterior site in the proximity of the reticulum and cranial sac by about 1 h after drinking. There was no effect of rumen sampling site on the fractional outflow rate of CrEDTA (from imbibed marked water) from the rumen. It was concluded that most water which is drunk after a period of water deprivation will enter the rumen, mix rapidly and have a fractional outflow rate similar to other fluid in the rumen. The values derived may be used to calculate the amounts of supplement needed in drinking water if the target site is the rumen or intestines of cattle with intermittent access to water under extensive grazing conditions.

In each of two experiments, eight silages supplemented with concentrates containing a high proportion of either starch or digestible fibre were given to rumen-cannulated sheep. The silages constituted c. 65% of the total dry matter and differed widely in chemical composition, reflecting differences in the extent of fermentation in the silo.

Rumen pH was lower (P < 0·01 and P < 0·001 for Expts 1 and 2 respectively) and the concentration of total volatile fatty acids (VFA) in the rumen was higher (P < 0·001 for Expt 2) for the starchy concentrate. Silages differed in their effects on ruminal proportions of acetate (P < 0·001 and P < 0·01 for Expts 1 and 2 respectively) and, inversely, of propionate (P < 0·001 for Expt 1). There was evidence of a strong relationship between the molar proportion of propionate in the rumen and the concentration of lactic acid in the silage. The results indicate that the production of propionate during the metabolism of silage lactic acid by the rumen microbial population was the predominant influence on rumen fermentation pattern.

It is suggested that this relationship is the basis of some of the differences in milk production reported for silages showing restricted as opposed to extensive fermentation.

In the first two of four experiments, sheep were fed, ad libitum, sorghum stover supplemented with graded levels of foliage of the shrub leucaena (Leucaena leucocephald) or mulga (Acacia aneura), which provided between 0 and 0·34 or between 0 and 0·43 of the dietary dry matter (DM) respectively. A second treatment (with or without urea) was superimposed in a factorial design. The effect of treatments on liveweight (LW) was explainable by their effects on voluntary intake of apparently digestible organic matter (DOMI). D0M1 was increased by mulga, largely due to an increase in the total voluntary intake of organic matter (OM). Leucaena increased DOMI by increasing the ration OM digestibility and, at low levels of inclusion, intake of the basal diet. Roughage intake was greatest when leucaena provided 0·15–0·20 of the dietary DM. Leucaena increased rumen ammonia, and whenever roughage intake was increased by urea, leucaena also increased it.

In the third experiment, when diets were made isonitrogenous with urea, roughage intake was slightly greater when leucaena, rather than its ash or a mineral mixture, was supplemented. Total OM intake and DOMI were greatest when leucaena was fed.

In the final experiment, sheep were fed one of ten treatments: three basal diets (two of sorghum stover and the third of native pasture hay) each supplemented with legumes (leucaena to the hay and one stover diet and cowpea straw to the second stover diet), ash of the respective legume and formaldehyde-treated casein. The tenth treatment was sorghum stover plus urea. For sorghum stover diets with leucaena-based or cowpea straw-based supplements, DOMI responded linearly to the nonurea nitrogen concentration of the diet. On the other hand, for native hay with leucaena-based supplements, the response of DOMI to non-urea N was negligible. It was noted that the native hay (predominantly Flinders grass, Iseilema vaginiflorum), contained lower concentrations of polyphenols than sorghum stover.

It was concluded that browse foliage can increase the voluntary DOMI of sheep consuming low quality roughages by providing nitrogen and sometimes minerals and OM of greater digestibility. The slowly-degradable proteins in leucaena, cowpea straw or formaldehyde-treated casein are more effective with polyphenol-rich sorghum stover than with native hay of otherwise similar composition.