The Rht-B1b, Rht-D1b and Rht-B1c alleles for reduced height in wheat (the Norin 10 and Tom Thumb dwarfing genes previously known as Rht1, Rht2 and Rht3) were exploited in combinations to generate a near-continuous range of plant heights, from 53 cm to 123 cm, amongst near-isogenic homozygotes and F1 hybrids. Pleiotropic yield effects of Rht genes were measured in both homozygous (intravarietal) and heterozygous (intervarietal) genetic backgrounds. Heterosis due to overdominance of Rht genes was detected among intravarietal hybrids. The effects of heterozygosity at other genetic loci (mean dominance) were determined, independently of Rht effects, from comparisons between intravarietal and intervarietal F1 hybrids.

Genotypes of intermediate plant heights gave maximum yields, in agreement with other trials of the homozygous lines, so that heterosis (hybrid exceeding best parent) for Rht yield effects was observed in crosses between tall and dwarf isogenic pairs. This heterosis combined additively with increased mean weight per grain in intervarietal crosses, generating the highest overall grain yields in hybrids with semi-dwarf stature in heterozygous genetic backgrounds. The Rht-B1c allele showed single-gene overdominance for grain yield, also the production of alpha-amylase in ripening grains of Maris Huntsman was effectively inhibited in the Rht-B1a/c intravarietal hybrid. The Rht-B1c allele thus offers advantages for both grain yield and grain quality in the heterozygous condition and should be considered as an alternative to the conventional semi-dwarfing genes Rht-B1b and Rht-D1b for F1 varieties in environments conductive to preharvest sprouting.

A model to predict wheat growth stage is briefly described. It is based on prediction of the number of emerged leaves and the final number of leaves on the main shoot, and the co-ordination between leaf emergence and apex development, including stem elongation. The input variables are daily maximum and minimum temperatures, date of sowing and site latitude, from which thermal time, vernalization and daylength are calculated.

Selected growth stages were predicted for six sites in each of three growing seasons. The differences between observations made by independent observers and predictions were mostly 7 days or less but in three site–season combinations the average difference was >10 days. Observer errors were implicated and examined, but it is concluded that the prediction scheme must also have been partly responsible for the discrepancies.

Functions which predict rate of leaf emergence and final number of leaves, used in a model to predict the date at which growth stages occur, were tested in an experiment on winter wheat cv. Mercia grown with standardized husbandry at six sites in 1992/93, 1993/94 and 1994/95. A study of the number of detectable nodes on the culm and leaf length was also made.

The predicted rate of leaf emergence was mostly within 5% of the observed value. The difference between observed and predicted final number of leaves was mostly less than half a leaf but suspected errors in leaf counts resulted in some differences of more than two leaves.

Variable extension of the basal internode impaired confidence in the detection of nodes. The mean number of detectable nodes differed significantly among sites and between seasons from 3·7 to 4·8 but could not be related to sowing date or final number of leaves. Further information on factors affecting extension of the basal internode is desirable to standardize node detection and improve prediction of culm leaf appearance.

Culm leaves showed successively longer laminae up to the penultimate leaf. There was a significant relationship between length of the flag leaf and the final number of leaves, but it was positive in 1993/94 and negative in 1994/95. This may have been due to greater water stress in 1994/95.

Wheat was grown in rotation with three different crops, namely wheat, chickpea and lentil, and with a fallow, in three consecutive seasons beginning in 1992 in NW Syria. Two rates of N fertilizer (0 and 30 kg N ha−1) were superimposed on these four rotations, giving eight treatments which were replicated three times in each season. 15N-labelled fertilizer was applied to microplots within the fertilized plots at sowing when unlabelled fertilizer was broadcast on the rest of the plot.

Yields of grain and dry matter were generally greatest when wheat followed a fallow, and least in the continuous wheat rotation; this was significant in 1993 and 1994. Applications of N fertilizer had no effect on productivity in 1992, but in the other two seasons grain yields were increased by 550 kg ha−1, on average. Depending on the season, between 8 and 26% of the 15N-labelled fertilizer was recovered in the shoot dry matter, while between 18 and 54% of the fertilizer remained as N in the soil at harvest, mostly in the 0–20 cm soil layer. More than half the fertilizer in the crop at harvest had been taken up by the end of March, although by March the plants were only c. 10% of their mass at harvest. Conversely, <35% of the soil-derived N in the crop at harvest had generally been taken up by March. This temporal difference in the pools of N utilized by the crop was attributed to the drying of the soil surface layers where most of the N fertilizer remained. Approximately 50% of the 15N-labelled fertilizer was unaccounted for in the crop and 0–40 cm soil layer at harvest.

The yield benefit of growing wheat in rotation with a fallow or either grain legume rather than continuously, ranged from nothing to the equivalent of a fertilizer application of at least 30 kg N ha−1 to continuous wheat, depending upon the season and the previous crop. Only in the season where the residual effect of the rotation on wheat yields was greatest (1993) did the preceding grain legume crop or fallow appear to contribute between 10 and 20 kg N ha−1 to the wheat crop. Otherwise they contributed no N at harvest. While a fallow may increase the availability of water to the succeeding wheat crop, the benefit from the preceding grain legumes may lie in their effect on the soil physical structure or on the increased availability of other limiting nutrients rather than additional N.

Field experiments were conducted at Cuttack, India during 1991–94 to study the effect of tillage, methods of crop establishment and weed control at varying levels of N fertilizer on the performance of rice under flood-prone lowland conditions (0·60 cm water depth). The loss in grain yield of direct-sown rice caused by unchecked weed growth ranged from 18·2 to 59·2% in the different years, and was greater when N fertilizer was applied and when the conventional practice of ploughing the fields just before sowing was followed. Increasing the number of tillage operations before sowing improved the crop stand, reduced weed infestation and, thereby, increased the yield significantly compared with that achieved by conventional tillage. Summer ploughing rather than conventional tillage decreased weed dry weight at harvest by 15·8–53·2% and increased grain yield by 47·4–56·3%. A pre-emergence application of thiobencarb at 2·0 kg/ha, hand weeding once at 20 days of growth and post-establishment inter-crop cultivation at 37–42 days provided effective weed control and increased yield by 32·7–34·7, 36·7 and 28·7–83·9%, respectively. The efficiency of weed control and the resulting increase in rice yield were comparatively greater under puddling than with inter-crop cultivation and herbicide application. The loss in yield due to weeds was negligible when the crop was transplanted due to the incorporation of weeds during puddling and a greater water depth in the later growth stages. Therefore, the grain yield of rice was highest with transplanting followed closely by the direct-sown crop with post-establishment inter-crop cultivation. The response of direct-sown rice to N fertilization up to 60 kg N/ha decreased with fewer ploughings when no weed control measures were adopted. However, the grain yield increased significantly with N application up to 40 kg N/ha when weeds were controlled by cultural or chemical methods. The results suggested that an integrated weed management strategy involving summer ploughing, thiobencarb application and inter-crop cultivation is essential for effective weed control in direct-sown, flood-prone, lowland rice, in order to ensure higher N-use efficiency and crop productivity.

Six plant species were compared in terms of their physical breakdown when eaten by sheep and when macerated: chickweed (Stellaria media (L.) Vill.), dandelion (Taraxacum officinale Weber), dock (Rumex obtusifolius L.), ribwort (Plantago lanceolata L.), spurrey (Spergula arvensis L.) and perennial ryegrass (Lolium perenne L.). In two experiments at Aberystwyth in 1985 and 1986, the species were artificially dried and fed to lambs as the total diet. In another experiment in 1987, they were fed fresh, in 1·5 min meals, to yearling sheep.

Perennial ryegrass was more difficult to break down than the dicotyledonous species, judging by the particle size distribution in macerated and in chewed material and in the rumen contents and from the rather long time the sheep spent eating and ruminating per 100 g dry matter (DM) intake and the rather high fibrosity index. The width of some of the smaller ryegrass particles in the rumen was such that they must have contained only a single vein. Spurrey was readily broken down by macerating and by chewing and a relatively short time was spent eating and ruminating per 100 g DM intake. The shape of spurrey particles in the rumen was quite similar to that of stemmy ryegrass particles and the fibrosity index of spurrey was high. The breakdown of chickweed was similar to that of spurrey, but the fibrosity index of chickweed was lower. Accumulation of DM in the caecum appeared particularly pronounced in sheep fed ribwort or dock. The dock particles in the rumen typically had a low ratio of length to width and it seemed that dock particles did not need to be reduced in size as much as ryegrass particles before passing out of the rumen.

The effectiveness of 20 strains of Rhizobium leguminosarum bv. trifolii was evaluated with Trifolium semipilosum and T. burchellianum grown in a Vertisol soil in the glasshouse at the International Livestock Research Institute (ILRI) in Addis Ababa. Several effective strains were identified for both species. In T. semipilosum, inoculation significantly increased nodule DM and root N yield over the uninoculated control; Ethiopian Rhizobium isolates outperformed isolates from other sources for shoot DM and N yield. In T. burchellianum, contrast analysis revealed that there was no significant response to inoculation, although one effective strain was identified. Inoculant strains failed to overcome the competitive dominance of indigenous strains as reflected in mean nodule occupancies by inoculant strains of 15 and 7% in T. semipilosum and T. burchellianum, respectively. The 20 strains showed variable persistence following a 5-week drought period; only two of eight (T. semipilosum) and six of eight (T. burchellianum) strains were recovered from nodules on seedlings planted in the soil following the drought period. Overcoming the constraints of low nodule occupancy and variable persistence will require further understanding of the competitive interaction and the factors affecting access to nodule infection sites if superior Rhizobium–clover combinations are to be identified and developed.

Glasshouse and field experiments were conducted in 1993 at the International Livestock Research Institute (ILRI) in Addis Ababa to identify effective combinations of Trifolium semipilosum genotypes and Rhizobium leguminosarum bv. trifolii strains and to investigate the effects of waterlogging of Vertisols on the response of clover to inoculation. In the glasshouse, the Rhizobium strain ILCA372str produced nearly ten times as much nodule DM, three times as much shoot DM, five times as much root DM, and twice as much plant N on cv. Safari as it did on accession ILCA7609 under normal watering conditions. This spontaneous streptomycin-resistant mutant strain performed better than its parent strain. Shoot DM and N yields of this combination were, however, only 55 and 71%, respectively, of the corresponding N-fertilizer (150 kg N ha−1) treatment. Waterlogging reduced nodule DM by 33%, shoot DM by 41%, root DM by 25% and N yield by 33%, and responses of both plant genotypes to inoculation and to N fertilizer were reduced. In the field, there were no significant differences in nodulation, plant DM and plant N between seed and soil inoculation methods. Dry matter and N yields of Safari inoculated with strain ILCA372str were at least twice as high as those produced by any other strain or N fertilizer supplied at 100 kg N ha−1. Waterlogging during early establishment in the field probably reduced the availability of N fertilizer to the plants. Further field testing of the Safari-ILCA372str combination is recommended, particularly in combination with broad-bed and furrow (BBF) technology to drain Vertisols.

Three glasshouse experiments were conducted between 14 September 1993 and 9 January 1996 at the Plant Growth Unit, Massey University, Palmerston North, New Zealand. Experiment 1 studied the effects of cutting height on the regrowth and biomass allocation of chicory (Cichorium intybus L. cv. Grasslands Puna), Expt 2 investigated the biomass allocation and root carbohydrate reserves of three chicory cultivars (Puna, PG90 and Orchies) in response to defoliation, and Expt 3 studied the morphological characteristics and persistence of Puna under extreme defoliation.

Cutting height had no significant effect on accumulated secondary leaf and stem masses in Expt 2, but affected secondary leaf mass in Expt 1. However, cutting height significantly reduced root size after two cuttings in both Expts 1 and 2. Three severe cuttings (removing all shoots including visible buds >5 mm on crown) killed 73% of plants, whereas 96% plants survived under lax cutting (100 mm) in Expt 3. Orchies had the highest total reducing sugar concentration in its taproot (56·6%), whereas PG90 had the lowest (32·1%). Therefore, Orchies was the most persistent but had the slowest growth rate, and PG90 the least persistent with the highest growth rate. The performance of Puna was intermediate.

It is concluded that the persistence of Puna would be more sensitive to cutting frequency than cutting intensity due to its medium level of root carbohydrate reserves. In contrast, PG90 could be defoliated frequently, but not closely. However, Orchies with its thick taproot was insensitive to cutting intensity and would also be insensitive to cutting frequency due to its larger root carbohydrate reserves. It is suggested that to improve the persistence and enhance the leaf production of Puna by plant breeding the emphasis should be on increasing taproot size without unduly prejudicing herbage production.

Results are reported from three experiments conducted at the Dairy Research Institute, Ellinbank, Australia during 1992/93 which examined the composition and kinetics of the gas in the rumen headspace of lactating dairy cows grazing white clover/perennial ryegrass pastures. Before grazing, rumen headspace gas was composed of carbon dioxide 65%, methane 31% and nitrogen 4% whereas, after one hour of active grazing, the headspace gas was composed of carbon dioxide 76%, methane 22% and nitrogen 2%. The composition of headspace gas was not affected by antibloat capsules (which release 250 mg/day of monensin). The headspace gas from bloated cows contained slightly less (P<0·01) carbon dioxide and slightly more nitrogen than that from non-bloated cows.

A novel technique which employs ethane as a tracer to measure rumen headspace volume and the kinetics of the rumen headspace gases is described. The tracer technique was used in two experiments in which the influence of grazing, antibloat capsules and bloat on the rumen headspace volume and the kinetics of the headspace gases were examined. It is concluded that our ethane tracer technique provides a simple and inexpensive way to estimate methane production by grazing ruminants.

The association between the rate of protein degradation and the components of the calpain system in lambs fed at sub-maintenance, maintenance and supra-maintenance levels of nutrition was investigated. Weights of the cold carcass, liver, kidney, pluck and m. semitendinosus increased with nutritional level (P<0·05). The rate of protein degradation in the hind-limb was determined using an in vivo arterio-venous method. Blood flow, protein gain and protein synthesis across the hind-limb increased with nutritional status (P<0·05). There was an increase in the amount of protein synthesised per unit of RNA (mg RNA/g protein) with improved nutritional status. The rate of protein degradation across the hind-limb increased between the sub-maintenance and maintenance treatments (P<0·05) but there was no further increase above maintenance (P>0·10). The activity of the components of the calpain system was determined after separation on a DEAE-Sepharose column with a stepwise gradient with increasing NaCl concentrations. Although there were no significant effects of nutritional status on the components of the calpain system, there was a negative association between the rate of protein degradation and the activity of μ-calpain (R2=0·61; P<0·005) and a weak positive association between calpastatin activity and protein gain (R2=0·44; P<0·05).

The effect of supplementation on the feeding and ruminating behaviour of sheep fed on low quality roughage was assessed at the Shimane University Animal Farm, Japan, in 1993. Four Japanese Corriedale wethers were used for four periods in a 4×4 Latin square design. The initial 10 days of each period were for adaptation by the sheep to their new environment and diets, followed by 5 and 7 days for rumination studies and digestibility trials, respectively. The four diets were: rice straw alone (RSA), rice straw+soyabean meal (RSS), barley straw+molasses meal (BSM) and barley straw+molasses meal+soyabean meal (BSS). Animals on the RSA and BSM diets spent less time eating (305 and 278 min/day respectively) and ate at a slower rate (1·8 g DM/min) than those on the RSS and BSS diets. Although there were no significant differences between treatments (P>0·01) in the number of rumination periods per day, animals on the RSA and BSM diets spent a longer time ruminating per 100 g NDF intake and exhibited slower chewing rates than those on the other diets. Cyclic rate and rumination indexes were both higher for RSA than for other treatment diets. The results show that sheep on the RSA and BSM diets spent less time eating and that those on RSA spent significantly (P<0·05) more time ruminating than those on supplemented diets. Animals on RSA and RSS generally regurgitated more boli but there was no significant difference (P>0·05) in chewing rates between the diets. However, generally, animals on RSA, in addition to regurgitating more boli, also had lower chewing rates, indicating more efficient rumination activity. The judicious use of small amounts of readily degradable nutrients, especially protein, will improve the rumination behaviour of sheep fed on low quality roughage diets, most probably through an improvement in microbial activity. This will result in a higher fibre digestion rate and an increase in the production of ruminal fermentation by-products, compensating for the loss in rumination efficiency.

Leaves from the tropical tree legume calliandra (Calliandra calothyrsus) were harvested and fed either fresh frozen (F) or dried (D) as a supplement (200 g dry matter (DM)) to sheep (n=4) given barley straw ad libitum in metabolism cages in a controlled-environment animal house. Sheep given these diets were intra-ruminally infused (0·5 litres/day) with either water or a solution containing 100 g/l polyethylene glycol (PEG). These treatments were administered in a randomized complete block design, and the results statistically analysed. Drying significantly increased the cell wall (cellulose, hemicellulose) and lignin contents, but decreased the condensed tannin (butanol-HCl method) content (F=35·7, D=21·7 g/kg DM). Both drying and PEG infusion significantly (P<0·05) increased straw organic matter (OM) intake, but the effects of drying plus PEG were not additive. Organic matter digestibility of the diets was significantly (P<0·05) increased by drying (F=433 g/kg, D=486 g/kg), but not by the infusion of PEG. Total nitrogen (N) digestibility was significantly (P<0·05) increased by drying (F=207 g/kg, D=316 g/kg) in the absence of PEG, and by PEG for both frozen (−PEG=207 g/kg, +PEG=392 g/kg) and dried (−PEG=316 g/kg, +PEG=434 g/kg) calliandra. PEG infusion significantly increased the proportion of feed N degraded in the rumen (−PEG=0·41, +PEG=0·52) and rumen ammonia concentrations (−PEG=63, +PEG=103 mgN/l), but had no significant effect on the rate or efficiency of microbial protein synthesis in the rumen. PEG infusions significantly increased the amount and proportion of N intake absorbed from the lower digestive tract, but had no significant effect on overall N balance. Drying decreased the tannin losses (as % intake) occurring in the rumen (F=37·3%, D=24·2%), and PEG infusion increased these losses for both frozen (−PEG=37·3%, +PEG=72·5%) and dried (−PEG=24·2%, +PEG=68·7%) calliandra supplements. It was concluded from these studies that the presence of tannins in fresh (frozen) calliandra depressed feed utilization, and that drying was an effective means of improving the nutritive value of calliandra when fed as a supplement to low quality straws.