In NW Europe, autumn-grown oilseed rape normally receives nitrogen (N) in autumn as seedbed N and in the spring as a split application at the beginning of growth and at stem elongation. In the growing seasons 1990/91 to 1992/93, the effects of slurry and mineral N fertilization on yield, N uptake by the seed and apparent N-use efficiency (NUE) by oilseed rape (Brassica napus) were investigated in a factorial field experiment at Hohenschulen Experimental Station near Kiel, NW Germany. The crop rotation was oilseed rape–winter wheat–winter barley, and soil tillage (conservation tillage without ploughing, conventional tillage), application of pig slurry (none, autumn, spring, autumn+spring) and mineral N fertilization (0 to 200 kg N ha−1) were all varied. Each year, the treatments were applied to all three crops of the rotation and were located on the same plots.

Between the years, average seed yield ranged from 3·04 to 3·78 t ha−1, while the corresponding N uptake by the seed varied from 107 to 131 kg N ha−1. Slurry application in spring increased the seed yield and N uptake by the seed in all years, whereas the effect of autumn slurry alone or in combination with spring slurry was negligible. Mineral N fertilizer increased seed yield and N uptake by the seeds except in 1991/92, when N amounts exceeded 160 kg N ha−1. No significant slurry×mineral N interaction occurred. Apparent NUE of mineral N was larger than that of slurry N, but decreased with increasing mineral fertilizer N rates. Only 5% of the autumn slurry N was apparently utilized by the seeds, compared with 24% of the spring slurry N.

Despite its ability to take up substantial quantities of N before the winter, oilseed rape utilized very little autumn slurry N for seed production. To minimize environmental impacts, slurry should be applied in the spring, when plants are more able to use N for yield formation, even if NUE of slurry N is lower than that of mineral N. However, since NUE changes with the amount of applied N, it is difficult to find the best combination of slurry and mineral N fertilization to avoid negative environmental effects.

A field experiment was established at the Institute of Grassland and Environmental Research (IGER), Aberystwyth, to compare the seasonal growth and annual yields of two white clovers when grown with each of five perennial ryegrasses. Swards were subjected to two contrasting defoliation managements, namely cutting only and continuous grazing with sheep. In addition to data recorded on dry matter yields of the swards, the effect of management on growth and development of white clover stolons and tillering of ryegrasses was also studied in the third harvest year. The management of the swards had a significant effect on ryegrass tiller number and on the ingress of weed grasses. Differences in persistency and tillering among the ryegrasses were significantly greater when continuously grazed by sheep than when swards were cut. It is argued that ingress of weed grasses under grazing could be used as an indicator of ryegrass persistency. Among those studied, only two of the ryegrasses were able to provide dense persistent swards under continuous sheep grazing. The white clovers included in this experiment differed in leaf size with Gwenda smaller than Ac 3785. Greater differences existed between white clover components when grazed than when under cutting management. Under continuous sheep grazing there were large differences between the clover varieties in stolon length, stolon weight, number of growing points and root weight.

The data indicate the importance of the persistence of mixture components under continuous sheep grazing and, since ryegrass is the main component of a clover/grass seed mixture, greater emphasis in breeding and evaluation programmes should be given to persistence, especially under grazing.

Twelve field experiments, carried out over 7 years, examined effects of shading and seed tuber spacing on plant growth, initiation and retention of tubers in four cultivars: Estima, Maris Piper, Maris Peer and Record. Ten of the experiments were carried out at Cambridge and two near Valencia, Spain. Other treatments included in some experiments were floating polythene mulch and planting date.

Shading by up to 75% did not affect the timing of onset or cessation of tuber initiation in Estima but shading by 50% or more delayed the completion of tuber initiation in Maris Piper compared with less severe shading. Except for intensely shaded treatments (50% or more), the majority of tubers were initiated in a very short period (4–7 days). Shading by 37% or more during the period of tuber initiation and increasing planting density, decreased number of tubers per stem initiated in all experiments, but number of tubers was not affected by shading at other stages of growth. At Cambridge, effects of shading on number of tubers >10 mm retained later in growth from normal planting dates (March to early May) were similar to effects on number of tubers initiated, but effects were much reduced or absent following later plantings at Cambridge and in both experiments in Valencia. The decreased effects of shading on number of tubers >10 mm at late plantings at Cambridge were associated with the initiation of fewer tubers at these plantings. Effects of shading, planting density and planting date on number of tubers were a consequence of changes in the frequency of occurrence and tuberization of different stolon types. Increasing shading and planting density and delaying planting reduced the number of lateral and branch stolons and the frequency of their tuberization but there were no effects on number of primary stolons or their tuberization. Consequently, at Cambridge a similar number of tubers was borne on primary stolons in shaded and unshaded crops. In Valencia a greater proportion of initiated tubers was retained at final harvest from shaded treatments than at Cambridge, which accounts for the absence of effects of shading on number of tubers >10 mm. The greater retention of tubers late in growth in Spain may have been associated with the higher peak growth rates achieved in higher radiation fluxes than at Cambridge.

Linear regressions of the data for normal planting dates at Cambridge and from Valencia indicated that the number of tubers >10 mm late in growth was dependent on the radiation environment during the period of tuber initiation. Radiation flux during the brightest period of the first few days of initiation appeared to be the most crucial aspect of radiation affecting number of tubers. As incident radiation can vary greatly over the short period of tuber initiation, it is potentially an important factor affecting number of tubers in field crops.

Between 1989 and 1993, 17 experiments tested the effect of cover crop species, sowing date and destruction date on cover crop dry matter (DM) yield, N uptake and on soil mineral nitrogen (SMN) content. All the experiments were carried out in Suffolk, Norfolk, Lincolnshire and Yorkshire on sandy-loam textured soils after crops of cereals or oilseed rape had been harvested. The largest DM yields were obtained with early sowings and averaged 1·6 t/ha. Cover crop N uptake was less dependent upon sowing date and averaged 35 kg N/ha. The average reduction in SMN was from 46 to 32 kg N/ha. Differences between cover crop species were small when compared with season/site variations.

Cereal cover crop DM yields were closely related to the thermal time accumulated from the first significant rainfall after sowing, whilst the yields of non-cereal cover crops were more affected by the moisture content of the soil at sowing. The amount of SMN in the soil at sowing had little or no effect on cover crop yield. The yields of cereal cover crops were much more predictable than those of non-cereal cover crops. Water usage by cover crops was estimated to be 20 mm/t DM and large cover crops delayed the onset of leaching and reduced the amount of water leached. However, even in dry autumns and winters, soils are likely to reach field capacity before the following beet crop is sown. Due to their large C[ratio ]N ratio (20[ratio ]1) little N would be mineralized after cover crop destruction. Cover crops comprising volunteer cereals and weeds often performed as well as the other cover crops and in most cases will be the most cost-effective cover crops.

The growth and development of cotton was studied on cotton plants grown in pots in growth rooms under constant day/night temperature (C) and varying temperature regimes throughout the day and/or night (V) The V-treatments had a common mean temperature of 22°C. The objectives were to determine the thermal requirements of three cultivars and to observe the extent of genotype×thermal environment interactions throughout the entire growth period.

Vegetative growth was found to be almost exclusively time and temperature dependent, varietal differences being largely insignificant. Plant material was found to accumulate four times faster under the warmest C-regime, which was 7°C warmer than the coolest. The C-treatments caused variation in the number and size of lateral shoots and leaves, causing leaf area to be larger at the squaring stage in cool environments but at maturity in warm regimes. Relatively cool nights lowered the position of the first floral or fruiting branch, whereas warm days shortened flowering intervals and thus promoted earliness. However, the effect of temperature in altering the position of the first floral branch seems to be less important than its effect on the shedding of early squares.

The effects of fluctuating temperature (V) on vegetative growth and earliness were similar to those from constant temperature environments. Growth and development rates were low in the low minimum V-regimes, especially when the maximum temperature was also low. Temperature variation affected vegetative growth to a greater extent in the early than in the later stages of development. At squaring, leaf area and dry weight were lowest under the regime with the highest minimum and maximum temperatures. Later on, only leaf area at flowering and total dry weight at maturity significantly differed between treatments. High maximum or minimum temperatures produced effects similar to a higher or lower mean temperature, respectively. The low minimum raised the node number of the first floral or fruiting branch, whereas in the case of boll dry weight it acted in the same way as a further drop in temperature, decreasing the weight, regardless of the maximum temperature. Boll period was affected mainly by the temperature variation itself rather by than the type of variation.

The inverse of time to a certain stage and the corresponding mean temperature were linearly related and allowed threshold temperatures (T0) and thermal time requirements to be estimated. T0=12°C, except for the initial stage, when it was lower. A cotton growing season cooler on average by only 1°C will considerably delay maturity.

Between 1989 and 1993, 17 experiments tested the effects of autumn-sown cover crops on the yield, processing quality and N nutrition of subsequent sugarbeet crops. Cover crops had no effect on sugarbeet plant population density or pesticide requirement. In nitrogen response experiments, the mean beet yield at the economic optimum was 83 t/ha. The mean N fertilizer requirement was 96 kg N/ha and the N uptake at maximum yield averaged 180 kg N/ha. Cover crops had no effect on yield, fertilizer requirement or N uptake. In addition, cover crops generally had no effect on the efficiency of N fertilizer use, the mineralization of N from the soil organic matter nor the amount of soil mineral nitrogen at sowing or at harvest of the beet crop. Processing quality was also not affected by cover crops. The cost of growing a cover crop ranged from 0 to 50 £/ha. Since these costs cannot be offset against increases in yields or reduced fertilizer application rates, cover crops need to be low cost, i.e. cheap seed and minimal cultivation. Cover crops using volunteer cereals and weeds or farm-saved grain that are established with a single stubble-cultivation should fulfil these criteria.

The effects of suppressing couch grass (Elytrigia repens L.), through integrated management, on soil biological quality and N and P nutrition of barley (Hordeum vulgare L.) were evaluated in a field experiment (1987–92) on a Dark Grey soil in Alberta, Canada. The management practices consisted of combinations of herbicide application, crop rotations and tillage treatments. The 3-year crop sequences consisted of continuous barley, canola (Brassica rapa L.)–barley–barley, fallow–barley–barley, and barley or canola undersown with red clover (Trifolium pratense L.)–red clover green manure–barley. In 1992, the sixth year of the experiment, soil and plant samples were analysed for nutrient content. Treatments that consisted of spring and autumn tillage only did not suppress couch grass and produced low barley yields and N and P uptake. More N was immobilized in couch grass shoots and rhizomes and soil microbial biomass with these treatments than with similar herbicide-treated crop rotations. Tillage-plus-herbicide treatments effectively suppressed couch grass and enabled the barley crop to compete for soil N, however, both spring and autumn tillage were required for weed control. The fallow treatment impaired soil quality by reducing soil and microbial C and N, but produced similar barley yields as continuous cropping with tillage-plus-chemical control. Red clover ploughed in for green manure enhanced soil quality indicators such as soil and microbial biomass C, total and mineralizable soil N, and microbial N, but did not increase barley yield compared to continuous grain cropping.

The occurrence of vesicular–arbuscular mycorrhizae (VAM) root colonization and spore number in soil was assessed for 18 fields under intensive lettuce (Lactuca sativa L.) production in California during July and August of 1995. Data on management practices and soil characteristics were compiled for each field, and included a wide range of conditions. The relationship between these factors and the occurrence of VAM in these fields was explored with multivariate statistical analysis. VAM colonization of lettuce tended to decrease with the use of chemical inputs, such as pesticides and high amounts of P and N fertilizers. Addition of soil organic matter amendments, the occurrence of other host crops in the rotation, and soil carbon[ratio ]phosphorus and carbon[ratio ]nitrogen ratios, were positively associated with VAM colonization of lettuce roots. The number of VAM spores in soil was strongly correlated with the number of other host crops in the rotation, the occurrence of weed hosts and sampling date, but was more affected by general soil conditions than by management inputs. Higher total soil N, C and P, as well as CEC, were inversely related to soil spore number. A glasshouse study of the two primary lettuce types sampled in the field showed no significant differences in the extent of root colonization under similar growing conditions. The results of this study are compared with other studies on the effects of management and soil conditions on mycorrhizal occurrence in agriculture.

Two aspects of yam storage practice were tested from 1994 to 1995 in central Côte d'Ivoire. The first experiment compared the storage environment in pits or sheds with that of the traditional yam open barn method. The pits allowed the daily range of variation in temperature to be reduced while maintaining a high relative humidity (RH), whereas the temperature and RH in the sheds were similar to those of the yam barns. Differences in temperature and RH between the storage systems had little effect on the fresh weight losses of the tubers. The more effective protection against solar radiation and rain afforded by the sheds and pits reduced fresh weight losses in D. cayenensis rotundata by 12% over 6·5 months in comparison with the barns. The second experiment tested the regular removal of the sprouts. Sprout removal reduced fresh weight losses equally over 5 and 6 months' storage. The reduction in fresh weight loss was 12% for cv. Gnan (D. cayenensis rotundata) during 6 months' storage. Monthly sprout removal gave an equal benefit in pits, in sheds and on yam barns. The monthly cutting of sprouts at the base should be encouraged in places where this is not already done. The total loss is mainly determined by the growth of the sprouts and the reduction in weight after onset of sprouting, which are highly dependent on species and cultivar. Bètè bètè yams had better keeping qualities than all the other cultivars tested.

Solid pig manure (240 g kg1 DM) and solid cattle manure (150-180 g kg1 DM) were stored in an open storage facility during spring-summer and autumn conditions for periods of 9-14 weeks during 1994 and 1995. Concentrations of C, N, P and K were determined prior to and after storage, corrected for dry matter losses and distance from the surface. Temperature and, in experiments with pig manure, gas phase composition inside the manure heap were monitored during storage. Nitrogen losses as ammonia volatilization, nitrous oxide emission and leaching were measured, while total denitrification was estimated from mass balance calculations. For both cattle and pig manure there was little difference between seasons with respect to the pattern of decomposition, as reflected in temperature dynamics and C/N turnover. In contrast, there was a distinct difference between manure types. Pig manure was characterized by maximum temperatures of 60-70°C, although the concentrations of oxygen and methane clearly demonstrated that anaerobic conditions dominated the interior parts of the heap for several weeks. Losses of C and N from pig manure both amounted to c. 50%. In contrast, the temperature of cattle manure remained close to the air temperature throughout the storage period and cattle manure had lower, not significant losses of C and N. Leaching losses of N constituted 1-4% with both manure types. Ammonia volatilization from cattle manure constituted 4-5% of total N, and from pig manure 23-24%. In pig manure a similar amount of N (23-33%) could not be accounted for after storage, a loss that was attributed to denitrification. Nitrous oxide emissions amounted to <2% of estimated denitrification losses.

Temperature effects on cotton yield and fibre properties of three cotton cultivars were determined. Plants were grown in pots maintained in growth rooms at varying day and night temperatures representing seasonally constant or varying (C) or daily varying (V) regimes.

Yield and fibre characters responded to variation of daily mean and amplitude of temperature. Mean temperature reduction improved yield components, but fibre length, uniformity, strength and micronaire were increased by high, particularly high day, temperatures. A large daily temperature amplitude produced an intermediate number of flowers and the lowest retention percentage.

Fruiting and yield were increased by reduction in temperature down to the threshold mean temperature of 22°C. However, V-regimes with a low minimum temperature acted as a further drop (below 22°C) of temperature and adversely affected these characters. An adverse effect of low minimum temperature combined with a moderate day temperature was observed also on lint percentage and fibre properties.

Varietal differences were more pronounced for highly heritable characters such as fibre properties, for which significant interactions between varieties and temperature also occurred. Differences in reproductive development were not sufficient to be of much practical importance.

Slurry was collected from two groups of finishing pigs fed either a standard commercial diet (containing 205 g/kg crude protein (CP)) or a specially formulated lower CP content diet (140 g/kg CP). The slurries were surface applied to grass/clover plots on a freely draining soil in SW England in mid-March 1995 at three application rates: 25, 50 and 70 m3/ha. Measurements were made from the 50 m3/ha plots of ammonia volatilization, denitrification, nitrous oxide and methane emissions and nitrate leaching. Measurements of herbage yield and apparent N recovery (ANR) were made from all plots. Decreasing the CP content of the pigs' diet reduced N excretion by the pigs and also changed other characteristics of the slurry. Slurry from pigs fed the lower CP diet (the slurry referred to hereafter as LS) had a higher dry matter (DM) content, lower pH, lower total ammoniacal N (TAN), total N and VFA content with a similar total C content compared with slurry from pigs fed the standard commercial diet (the slurry hereafter referred to as CS). From the 50 m3/ha treated plots, losses by ammonia volatilization represented 38 and 58% of the applied TAN and net losses through denitrification represented 5·3 and 12% of the applied TAN for LS and CS respectively. Nitrous oxide emission was similar from the two slurries, with net emissions of c. 0·5% of the applied TAN. Methane emission was significantly less from LS. No nitrate leaching was detected either in spring or in the following autumn. Yield and ANR increased with increasing slurry application rate up to 50 m3/ha. The best% N recovery was from the 50 m3/ha application rate with 58 and 47% of the applied TAN being recovered from LS- and CS-treated plots respectively. Changes in the slurry characteristics due to the lower CP diet resulted in lower losses to the environment and an improved utilization of the slurry N by the herbage.

Two experiments each with two rates of feeding (maintenance and twice maintenance) were conducted during summer 1993/94 (Expt 1) and summer 1994/95 (Expt 2), at Massey University, New Zealand. Four sambar and four red deer, including stags and hinds aged 10–14 months, were used in each year. Animals were fed a pelleted diet (total N 30 g/kg DM; NDF 247 g/kg DM). Digestibility and nitrogen (N) balances were determined using deer metabolism cages, whilst methane production and heat production were determined using open circuit respiration calorimetry, with measurements made on each deer at both rates of feeding. Digestibility and metabolizability of energy were greater for sambar than for red deer in Expt 1 but not in Expt 2. Nitrogen retention, expressed as a proportion of N intake, was similar for sambar and red deer. Metabolizable energy required for maintenance (MEm) was 474 kJ kg W−0·75 d−1 for sambar deer and 567 kJ kg W−0·75 d−1 for red deer, whilst the efficiency of utilization of ME above maintenance (kg) was similar for sambar deer and red deer. These studies indicated that the sambar deer had lower rates of maintenance heat production than the red deer, which may explain the sambar's superior feed conversion measured in previous experiments. However, the two species utilized nitrogen with similar efficiency, when fed a high quality ration.

Drought stress and virus yellows disease are two of the major problems of sugarbeet crop production in the UK. We have calculated the annual national drought losses from 1980 to 1995 by using long term data sets for two sites (IACR-Broom's Barn, Suffolk and ADAS Gleadthorpe, Nottinghamshire) to relate yield loss to cumulative potential summer moisture deficit, and combining these relationships with regional meteorological records, soil type and crop distribution data.

Experimentally measured relationships between yield losses and the timing of virus yellows infection were combined with annual survey data of the extent of the problem, and calculated infection dates from the UK aphid suction trap network, to calculate actual national annual losses to the disease. Potential losses in the absence of control measures were then calculated by use of data from trials and surveys of pesticide use.

The results showed a mean annual loss of production to drought stress of 141000 t/year of sugar, 10·5% of production, with a loss to the industry of £27·9 million. Losses in individual years varied from zero to 2·5 times the mean figure. Actual losses to virus yellows were much smaller, due to the efficacy of treatments, averaging 24700 t/year of sugar (1·8% of national yield, financial loss £5·5 million). Average potential virus yellows losses in the absence of control measures were approximately double this.

Control of virus yellows is a major, cost-effective contributor to rising and consistent sugarbeet production. Nationally, irrigation has made little impact on drought losses and, due to constraints in surface water supply, this situation appears likely to continue. Improved drought stress tolerance represents the largest single opportunity for yield and profitability improvement of the sugarbeet crop in the UK at present. Predicted climate change appears likely to increase the severity of both drought and disease stresses. Drought stress appears relatively less important in other NW European sugarbeet-growing areas.

The effects of dietary variations on microbial N turnover and recycling related to protozoal activities in the rumen were examined using a previously described model of rumen fermentation processes. Simulations were performed with diets containing variable proportions of concentrate (between 0 and 1 kg/kg diet dry matter) at a rate of daily dry matter intake (DMI) by cattle of between 5·3 and 21·0 kg/day. The roughages examined were hay, fresh grass and maize silage, and the concentrate supplements included molasses, barley, maize grain, untreated and formaldehyde-treated soyabean meal. The simulated fractional turnover rate of microbial N varied between 0·416 and 1·556/day, and simulated microbial N recycling ranged from 34·9 to 76·2% of gross microbial N synthesis. High turnover rates and recycling were observed particularly for diets containing maize silage as roughage and molasses and maize grain as concentrate supplements. Increased DMI generally resulted in reduced turnover rates with high-roughage diets, but increased turnover rates with high-concentrate diets. These responses of microbial N turnover and recycling were related to substrate availability and the substrate preferences of protozoa and, consequently, protozoal activities in the rumen. The large impact of recycling on the amount of organic matter required per unit of microbial protein washed out of the rumen was demonstrated. Thus, by quantification of the interactions between microbial populations in the rumen, the model can help to interpret the differences in microbial N recycling observed in the experiments and provide an improved understanding of the efficiency of microbial protein synthesis.

Studies of soil erosion in upland and marginal upland Britain are reviewed. Processes affecting soil erosion and runoff are described in marginal upland improved pastures of differing age in the Clwydian Hills, including one which was cultivated twice during the study period. A Gerlach-type trough was designed for trapping sediment and filtered runoff from bounded plots and for operating under grazing. Erosion and runoff amounts are interpreted in the light of ground cover, rainfall amounts and intensity, the action of grazing stock and other animals, and other influences. The chief erosion processes are the action of animals and surface wash by unconcentrated overland flow; no rilling occurred. The significance of particle size of eroded sediment is discussed.

The colonization of Lactobacillus spp., enterobacteria and facultatively anaerobic gram-positive cocci was monitored in intestinal samples of growing broiler chicks from 24 h to 28 days of age. Rapid bacterial growth occurred within the first week, followed by stabilization and decline of colony forming units (CFU). Xylanase supplementation led to significantly lower CFU per gram of wet weight for total presumptive enterobacteria and total gram-positive cocci in luminal and tissue samples in the first 3 weeks. Lactobacillus spp. colony counts from tissue samples were higher for animals with the xylanase-supplemented diet, but luminal CFU were not. The composition of dominant Lactobacillus spp. strains was different in duodenal and jejunal tissues, but distribution of Lactobacillus spp. colony forms was unaffected by xylanase treatment. Mucosa-associated Enterococcus spp. displaced the dominant gram-positive cocci in the jejunal samples. d- and l-lactic acid and acetic acid concentrations were significantly higher in ileal samples from the control group on days 7 and 14, while butyric acid concentrations were higher in the xylanase-treated group. It is concluded that the less viscous intestinal environment caused by the xylanase slowed proliferation of gram-positive cocci and presumptive enterobacteria in enzyme-supplemented animals in the first 3 weeks of life.

The effects on succeeding crops of nitrogen in residues returned to the soil of brassica vegetable crops (Brassica oleracea) were studied on a nitrogen-retentive silt loam soil at Horticulture Research International, Kirton, Lincolnshire, UK. A sequence of four crops was started in 1988 and again in 1989. In the first sequence, two successive cauliflower crops (Brassica oleracea cv. botrytis L.), crops 1 and 2 in the first year, were followed by Brussels sprouts (Brassica oleracea cv. Gemmifera D.C.), crop 3, in the second and spring barley (Hordeum vulgare), crop 4, in the third year. The second sequence, started in spring 1989, was on an area adjacent to the first, but with spring wheat (Triticum aestivum) as crop 4. The sites followed an unfertilized, 1-year grass ley (1987) or spring barley (1988) with 73 and 107 kg N/ha soil mineral nitrogen (SMN, NH4+NO3) in the 0–90 cm soil profile at the start of each sequence. The marketable yield of the first cauliflowers in both sequences increased with fertilizer nitrogen up to 240 or 300 kg/ha. The response of the second cauliflower crop to fresh N declined with increasing amounts of SMN (0–90 cm) at planting, with no response when SMN exceeded c. 270 kg N/ha. Crop 3 apparently responded to fresh N in sequence 1 but not in sequence 2 even though SMN at planting ranged up to c. 400 kg N/ha. This difference in response was largely explained by the amount and distribution of SMN in the 0–30 and 30–60 cm layers when the sprouts were planted. Soil mineral N to 90 cm when the cereals were sown was only c. 100 kg N/ha, which did not reflect the large amounts of N applied to the previous crops. In spite of this, barley yield without any fresh fertilizer N did vary with the amounts of N applied to the previous crops. The results showed that SMN was a useful predictor of fertilizer response in some, but not all, situations. To use SMN more generally requires interpretation using dynamic simulation models.

Brahman Shorthorn steers (213±4·6 kg initial weight) were grazed on a pangola (Digitaria eriantha cv. Steudel) pasture interplanted with leucaena (Leucaena leucocephala cv. Cunningham) in rows 1·8–2·7 m apart in the Ord River Irrigation Area (ORIA) in north-west Western Australia. The leucaena comprised a mean of 46% of the diet but ranged from 100% of the diet on day 1 to c. 18% on day 7 of a 7-day grazing period, within the rotational grazing system. It was suggested that the low herbage allowance of leucaena may have restricted the intake of the steers, reducing the quantity and quality of the herbage consumed.

The steers were also supplemented with maize during the dry and wet seasons (1992 and 1992/93). The maize supplement was offered at 0, 0·5, 1·0, 1·5 and 2·0 kg/head per day, over a 168-day period. Maize supplementation at 1·5 kg maize per head per day resulted in an increase in the liveweight gain of the steers grazing leucaena/pangola pastures in the dry season from 0·73±0·05 kg/day (mean±S.E.) for no supplementation to 1·1±0·05 kg/day for 1·5 kg/head per day of maize. Maize supplementation up to 2·0 kg/day did not further increase the liveweight gain. A high rate of substitution of leucaena and pangola intake for the maize supplement occurred.

There was a large seasonal difference in liveweight gain (mean 0·89 v. 0·63 kg/day for the dry and wet seasons respectively; P<0·001) irrespective of the level of maize supplementation. This seasonal difference in liveweight gain was not primarily a function of the herbage on offer, but was most probably a direct function of the effect of the seasonal temperature and humidity influencing the feed intake and growth rate of these Brahman crossbred cattle.

This system produced some of the higher liveweight gains recorded per hectare for a grazing system (1570–2110 kg/ha per year), as a result of the very good individual liveweight gains (250-340 kg/head per year) and high stocking rate (6·25 head/ha).

Sorghum grain was included in a basal diet of molasses (molasses 505, urea 21, sunflower meal 191, pangola grass hay 250, minerals 31 g/kg as fed) at rates of 0, 202, 391 and 707 g/kg, generating diets in which grain replaced 0 (diet A), 33 (diet B), 66 (diet C) and 100% (diet D) of the molasses and hay. The four diets were fed to groups of four Hereford steers (293–334 kg liveweight) over a 96-day period. One half of each treatment group was implanted with a growth promotant (zeranol), and all were slaughtered at a commercial abattoir at the end of the trial. The inclusion of 33% grain increased voluntary feed consumption, digestible dry matter (DM) intake (from 57·6 to 82·0 g digestible DM/kg0·75 per day and significantly increased liveweight gain from 592 to 900 g/day. Zeranol implantation also increased liveweight gain but not feed intake. Steers given only grain (diet D) had the highest liveweight gains (1127 g/day). The addition of grain to molasses diets decreased urinary N excretion and increased ammonia and volatile fatty acid (VFA) concentrations in rumen fluid. Molar proportions of propionic acid in total VFA increased from 0·15 to 0·20, and butyric acid decreased from 0·36 to 0·29 when 33% of the molasses was replaced by sorghum grain. The fat content (depth at sacral position) of the carcasses of steers given grain only (diet D) was significantly greater (14 mm) than that of steers given the basal diet of molasses (4 mm), and carcass fat contents were intermediate (10 and 11 mm) for steers given diets B and C respectively. It was concluded that the inclusion of small amounts of grain in molasses-based diets increased cattle growth principally by increasing digestible energy intake without decreasing molasses intake, thus improving the efficiency of utilization of molasses in molasses-based diets.