The rate of growth of individual seeds of soybean (Glycine max L. Merrill) is determined, in part, by the concentration of sucrose in the seed. Water stress during seed filling reduces photosynthesis, but the effect on seed sucrose concentration is not well understood. Soybean plants (cultivars Elgin 87 and Asgrow 232HS) were exposed to water stress from early in the seed-filling period until maturity in field and greenhouse experiments. Stress reduced yield (5–38%) and seed size (11–35%) but it did not affect the number of seeds. Stress accelerated leaf senescence as shown by a more rapid decline in leaf photosynthesis in both experiments. Seed-growth rate and cotyledon sucrose concentrations (expressed on a mM basis using the bulk water content of the cotyledons) during the linear phase of seed growth were not affected by stress in either experiment. Thus, water stress during seed filling had no direct effect on seed growth; its only effect was to accelerate leaf senescence, which shortened the seed-filling period and resulted in smaller seeds. Strategies to reduce yield loss from water stress during seed filling should focus on leaf senescence instead of seed growth.

In 1998/99 and 1999/2000, field trials were conducted to try to explain why grain legume yields and harvest index are more variable than many other crops. Treatments involved varying plant populations and sowing depths and were selected to maximize plant variability. Both yields and harvest index were variable. Total dry matter (TDM) production generally increased as plant population increased up to twice the optimum population. Increases ranged from 80 to 130% with lupins producing the highest yields of 878 and 972 g/m2 of TDM in 1998/99 and 1999/2000 respectively. While plants sown at 10 cm depth produced more TDM than did plants sown at 2 cm, the difference was only 3%. Seed yields followed similar trends to TDM, with maximum yields (mean of 403 g seed/m2) produced at twice the optimum population. Crop harvest index (CHI) was quite variable and ranged from 0·31 to 0·66. Crop HI was lowest (0·43) at the lowest population and increased to 0·55 at twice the optimum plant population. In both seasons, lentil had the highest CHI and lupin the lowest. While CHI was variable there were very close relationships between seed yield and TDM which suggested that maximum seed yield depends on maximizing TDM production. The results also suggest that growers should increase population by a factor of two to obtain maximum seed yields.

The effects of plant population (one-tenth of the optimum to four times the optimum populations in 1998/99 and 10–400 plants/m2 in 1999/2000) and sowing depth (2, 5 and 10 cm) on yield and yield components of four grain-legumes (Cicer arietinum, Lens culinaris, Lupinus angustifolius and Pisum sativum) were studied. Seed yields were strongly positively correlated with the number of pods and seeds/m2 in both years in all species. The mean seed weight and number of branches/plant were inversely related to plant population. There was a nearly six-fold reduction in the number of branches/plant as plant population increased, which was due to restricted branching, and not to branch senescence. Generally, the variation in yield components was species dependent. However, for all species the number of pods/m2 and seeds/m2 could be used as primary criteria for selection in a breeding programme.

Seeds of oilseed rape (Brassica napus L.) can persist in the soil over several years by becoming secondarily dormant and can then germinate to create volunteer plants in following crops. As well as agricultural impacts caused by volunteers, gene dispersal in time – particularly from genetically modified cultivars – can be another undesirable consequence. Conventionally bred and transgenic seeds were tested in 2001 and 2002 in laboratory experiments, and in a field experiment, by burying seeds in the soil to determine the variation in dormancy and persistence capacity.

In the conventional group of cultivars tested in the laboratory, the level of dormancy was 13–76% in 2001, and 3–76% with an extended group in 2002. The transgenic group of cultivars was 1–31% dormant. In the burial experiments the number of viable seeds recovered in the conventionally bred cultivars ranged from 34–90% in 2001, and 7–68% in 2002. In the same studies the transgenic cultivars developed persistence levels from 12–79% in 2001, and 46–67% in 2002. Since dormancy levels of conventionally bred cultivars from 2 harvest years in the laboratory tests correlated significantly (r=0·71), it appears that there is a genetic background to secondary dormancy. There was also a significant correlation (r=0·61 in 2001 and 0·80 in 2002) between the results from laboratory and burial experiments. This indicates that the laboratory approach can simulate the situation in the field. Ageing over 6 months decreased the capacity for seed persistence to about a fifth of the level shown when freshly harvested. As a consequence of ageing and environmental impacts on persistence, only seeds from the same location and harvest year should be used for testing genetic variability. The high genetic variability among currently available rape seed cultivars gives breeding strategies a good chance of ideotyping low persistence genotypes and minimizing the risk of gene dispersal in time.

Under rainfed Mediterranean conditions the dominant crops are cereals and legumes, with the most common crops being barley (Hordeum vulgare) and vetch (Vicia sativa). These two species are grown in rotation, where the cycle length depends on the productivity and the value of the products in the market. In order to study the productivity of cereals and legumes growing in various rotation combinations, an experiment was conducted during the 1982–2000 period, at Athalassa. The experimental site had a calcareous soil and is located in the central plane of Cyprus. The average rainfall is 250 mm per year. The rotation treatments tested were: (a) continuous barley, (b) continuous vetch, (c) vetch–barley, (d) vetch–barley–barley, (e) vetch–vetch–barley–barley and (f) vetch–vetch–vetch–barley–barley. Barley plots were equally divided to accommodate two rates of N fertilizer (0 and 60 kg N/ha) which were applied at seeding. Production of both vetch and barley was lower in monocultures than when the two species were grown in rotation. Vetch yield was similar in all rotations, irrespective of the position in the cycle. Productivity of barley was increased by nitrogen application only when grown as a second barley after vetch. However, in years with low productivity due to the rainfall amount and distribution, barley did not respond to nitrogen application. The first crop of barley after vetch gave maximum production without any nitrogen fertilizer application. Nitrogen fertilizer had a decreasing effect on the size and weight of barley grains. These results enable the farmers to select any of the rotation systems studied, based on the economics of the two species, without risking productivity. Nitrogen fertilizer should be applied only to the second crop after vetch in years with high rainfall.

Experiments to evaluate the optimum sowing date for okra (Abelmoschus esculentus) sown in monoculture or in mixed stands with cassava (Manihot esculenta) were sited on free-draining sandy loam soils in southwestern Nigeria. Okra was sown at the end of July, in mid-August and early September as a late-season crop in 1999 and at the end of May, in early June and at the end of June as an early-season crop in 2000. It was sown at seed rates sufficient to achieve final population densities of 33000 and 40000 plants/ha in late-season crops (1999) and early-season crops (2000), respectively. The late-season crops had shorter growth duration, received less rainfall, and experienced cooler temperatures during establishment and the early vegetative stage, and warmer temperatures during the reproductive phase than the early-season crops. Intercropping had no significant effect on the growth and tuber yields of cassava, or on phenology (i.e. time to vegetative growth, flowering and fruiting) and pod yield of okra in both seasons. However, it reduced weed growth by 35–57%, and kept both the soil and canopy environments of cassava cooler by 2·3–5·8 °C and more moist by 15–30 g/kg, compared with monoculture. The phenology and pod yields of the early- and late-season okra in both cropping systems were dependent on sowing date, indicating that okra production is only suitable at particular sowing dates in both seasons. July-sown okra in the 1999 late-season and May-sown crop in the 2000 early-season took progressively the longest time (i.e. 3–10 and 2–5 days, respectively) to flower and fruit, but these crops controlled weeds and modified the cassava environment better than the rest, and gave the highest fresh pod yields and economic returns. It took okra pods longer to reach marketable size in the late season than early season (i.e. 5–9 v. 2–6 days). It is concluded that the optimal sowing date to attain maximum pod yield and economic returns from late-season okra is July or August and from early-season crop is May or early June. Bearing in mind financial constraints and production costs, the optimal season target for maximum edible pods is the early season and for maximum economic returns is the late season.

A methodology was developed for large area yield forecast using a crop simulation model and a discrete technology trend, and was applied to the coherent wheat yield variability zones of Eastern Uttar Pradesh, India. The approach consisted of three major steps: (a) prediction of technology trend yield using historical yield series of the region; (b) prediction of weather-induced deviation in wheat yield using CERES-Wheat simulation model and relating weather-induced deviation in simulated yield to deviation in observed yield deviations from technology trend; and (c) final yield forecast by incorporating predicted yield deviation in trend predicted yield. The regression coefficients for step (b) were generated using 10 years' data (1984/85–1994/95) and the reliability of the approach was tested on a data set of 5 years' independent data (1995/96–1999/2000). The results showed that this approach could capture year-to-year variability in large area wheat yield with reasonable accuracy. The Root Mean Square Error (RMSE) between observed and predicted yield was reported as 0·098 t/ha for the mean yield of 2·072 t/ha (4·72%). However, the RMSE was slightly higher in the forecasting period in comparison to the calibration period. The use of this methodology for issuing the pre-harvest forecast and the effect of upgrading the technology trend were also studied. The pre-harvest forecasts were made using in-season weather data up to the end of February and climatic-normal for the rest of the wheat-growing season, which showed good agreement with observed wheat yields. The forecasts of wheat yield for the season 1999/2000 were made using the technology trend up to 1994/95 and the updated technology trend up to 1998/99, which showed that the RMSE fell in the latter case, from 4·10 to 2·50%.

Previous investigations have shown that the long-chain fatty alcohols and long-chain fatty acids of plant waxes have potential as diet composition markers. This study was conducted to measure faecal recoveries of long-chain fatty alcohols (C20–C30) and long-chain fatty acids (C20–C32) in sheep fed mixed diets. Methodology for quantitative analysis of these compounds in feed and faeces is also presented. The method was an extension of the original n-alkane method of Mayes et al. (1986) in which separate hydrocarbon (n-alkanes, n-alkenes and branched-chain alkanes), alcohol (free+esterified) and acid (free+esterified) fractions could be obtained from a single sample. A fraction containing alcohols and sterols was eluted from the silica gel column after removal of the hydrocarbons. Sterols were removed from alcohols using aminopropyl solid-phase extraction columns. Alcohols were converted to their trimethylsilyl (TMS) ethers and run on a gas chromatograph (GC). Acids were extracted from the aqueous phase of saponification products after removal of hydrocarbons, alcohols and sterols, purified through silica gel columns and were converted into their methyl esters (FAMES) prior to analysis on a GC. Tests were carried out to evaluate the reproducibility of the results obtained from the analytical method developed for quantifying alcohols and acids. Twelve sheep, in metabolism crates, were offered (0·8 kg DM/animal/day) four different mixtures of hill grass (Agrostis capillaris), birch (Betula pendula) leaves and current season's growth of heather (Calluna vulgaris) and bilberry (Vaccinium myrtillus) for 17 days. Total daily faeces and feed refusals collections were carried out over the last 7 days. Faeces collections were bulked for each animal. Representative samples of feed, refusals and faeces were analysed for alcohols and acids using the described method. Faecal recoveries of alcohols and acids were calculated from the ratio of output and input of each marker. The results showed high, though incomplete, faecal recoveries for both alcohols and acids. Alcohols had consistently higher faecal recoveries compared with acids. Mean (±S.E.) faecal recovery values for alcohols C20, C22, C24, C26, C28 and C30 were 0·58±0·04, 0·67±0·01, 0·72±0·008, 0·80±0·007, 0·94±0·005 and 1·01±0·02, respectively, whereas those of acids C20, C22, C24, C26, C28, C30and C32 were 0·47±0·02, 0·57±0·02, 0·61±0·02, 0·77±0·017, 0·84±0·01, 0·79±0·015 and 0·84±0·013, respectively. Increasing chain-length had a significant effect (P<0·05) on the recoveries of both alcohols and acids (R2=0·808, 0·741, respectively). Different dietary plant mixtures had no effect (P>0·05) on the recoveries of alcohols and acids in faeces.

To assess the effect of grassland management on the ruminal digestion of silages, four lactating dairy cows, fitted with a rumen cannula, were fed diets consisting of concentrates and different grass silages. The grass silages consisted of intensively managed grass (IM) in variable proportions replaced by silages harvested from a ‘species-poor’ grassland managed to stimulate nesting of birds (SPP) or from a grassland managed to increase plant species diversity (SPR). The roughage part of the diets was composed completely of IM (100IM), or 200 g/kg (in dry matter) of IM replaced by SPP (20SPP) or 600 g/kg of IM replaced by SPP (60SPP), or SPR (60SPR). The pH in the rumen was highest on 60SPR and lowest on 100IM and 20SPP (P<0·05), whereas volatile fatty acids (VFA) concentrations were lowest on 60SPP and 60SPR and highest on 100IM (P<0·05). No differences in the ratio non-glucogenic: glucogenic volatile fatty acids were observed among the diets. The NH3 concentration was highest on 100IM and 20SPP and lowest on 60SPR (P<0·05), reflecting differences in CP intake. The concentration of uric acid in the urine (mg per kg metabolic body weight) was highest on 100IM (P<0·05). Rumen pool size of OM and DM did not differ among treatments, but pool size of NDF and IADF were highest on 60SPR (P<0·05). Passage rate was high on 100IM and 60SPR, but no significant differences with the other treatments were established. Also, no significant differences were observed in rates of degradation. Clearance rate of large particles was highest on 60SPP and differed significantly from 60SPR (P<0·05) only. No differences were observed in clearance rate of small particles. In conclusion, for most rumen fermentation characteristics measured in the study, no noticeably aberrant behaviour of the silages from semi-natural grassland was observed.

The effects of acetic, propionic, butyric and lactic acids (short-chain acids), and of glycerol, on the in vitro dry matter digestibility (IVDMD) of oat hay, and on cellulolysis by a protein extract of rumen fluid were studied. The objective was to gain information on the impact of increasing the concentrations of those compounds in the medium on degradative activities carried out by rumen microorganisms. Short-chain acids were assayed as sodium salts and, for all compounds, the concentrations were 50, 100, 200 and 300 mM. The volatile fatty acids (VFA: acetic, propionic and butyric acids) were tested separately or in two mixtures A and B that contained different proportions of each VFA. The IVDMD was assayed according to a modified Tilley & Terry (1963) technique while cellulolysis was assessed by the hydrolysis of carboxymethylcellulose (CMC) in 1-h incubations at 39 °C. Parallel incubations with NaCl were utilized as controls for ionic strength and osmolarity changes in the incubation medium. Increases of 100–300 mM of short-chain acids decreased IVDMD between 7 and 39%. The inhibitions produced by increases of 200 and 300 mM of acetic acid were smaller than those caused by the same concentrations of either butyric or lactic acids. Increases of 100, 200 and 300 mM of glycerol reduced by 8–15% the IVDMD, and the inhibitions produced by increments of 200 and 300 mM of this compound were smaller than the ones elicited by the short-chain acids, with the exception of 200 mM of acetic acid that did not differ. The IVDMD was inhibited by NaCl only when concentrations were increased by 200 (12%) and 300 mM (26%). The degradation of CMC was reduced by 7–20% by 200 and 300 mM increases of the short-chain acids or glycerol, the exception being lactic acid that had no effect. One hundred mM increases of acetic and butyric acids inhibited the CMC degradation by 7 and 9%, respectively, whereas only butyric acid was inhibitory (7%) at 50 mM. Greater concentration increases of both VFA mixtures A and B than of the individual VFA were necessary to inhibit the hydrolysis of CMC. Cellulolytic activity was decreased 6 and 9% by increases of 200 and 300 mM of NaCl, respectively, and these drops of activity were smaller than those obtained with increases in any of the other compounds. Since osmolarity and/or ionic strength changes in the medium cannot completely account for the observed inhibitions of IVDMD and cellulolysis, it is suggested that glycerol and the anions of short-chain acids produce changes in the reaction media polarity that contribute to the inhibitory effects observed. Alterations in the media could also bring about conformational changes in the degradative enzymes leading to reduced rates of reaction and subsequent decreases in IVDMD and cellulolysis. Since most of the effects were observed with concentration increases that were larger than the physiological concentrations in the rumen, it is suggested that the compounds tested have little impact in vivo on the ruminal degradative activities that were evaluated.

Spring grazing managements which allowed some early inflorescence development, followed by hard grazing in order to remove the reproductive stems (designated ‘late control’), were compared with a conventional close grazing strategy (‘early control’) in three paddock-scale complete randomized block studies with dairy cows grazing perennial ryegrass/white clover pastures during consecutive years (1990–1993) in Palmerston North, New Zealand. Experiment 1 was designed to evaluate the timing of late control, Expt 2 to investigate the most suitable intensity of control, and Expt 3 tested different practical approaches to carrying out the late control management.

Late control generated an average herbage production increase of 24% (750 kg DM/ha) in October and November (spring) and 22% (950 kg DM/ha) from January to April (summer–autumn) compared with the conventional management. The increase in herbage accumulation during spring was a consequence of greater perennial ryegrass reproductive development. Increased summer–autumn herbage accumulation after late control management was attributed to enhanced tillering activity and accumulation of perennial ryegrass. Effects on white clover production were inconsistent. Experiment 3 compared the effects of two practical late control strategies, involving either a short period of rapid rotational grazing or a simulation of increased stocking rate normally associated with forage conservation, on the milk production and forage intake of groups of cows in self-contained farmlet systems. During the control period, the reproductive state of the sward caused a small decrease in herbage digestibility. However, the extra herbage produced subsequently did not differ in digestibility from that produced on the conventionally managed sward and resulted in an increase of around 11·5% in total milk solids yield (fat, protein and lactose) per cow, particularly towards the end of the season (March and April).

The late control spring grazing management strategy is a viable option for dairy farmers. It should coincide with the time of anthesis of ryegrass plants (late November–early December), and is more effectively achieved when forage conservation practices are used to augment grazing pressure in the grazed area of the farm.

The effect of sward bulk density on bite mass and bite dimensions was examined in two experiments using oesphageally fisulated cows to graze microswards under field conditions. In Experiment 1 microswards of uniform sward height were hand thinned to create differences in sward bulk density. In Experiment 2 plots were sown with monocultures of a range of ryegrass cultivars selected on the basis of their contrasting sward structures to provide a range of sward bulk densities and grazed down in two consecutive strata. Both methods were successful in providing a range of microswards of different sward bulk densities. In Experiment 1 bite mass increased significantly as sward bulk density increased. In Experiment 2 bites taken from the first stratum did not differ significantly in mass due to bites being deeper in swards with low bulk density, compensating for the lower bite bulk density. However, mass of bites taken mainly from the second stratum were lower in some swards due to lower bite bulk density which was related to tiller density rather than sward bulk density. The results emphasize the importance of sward bulk density in determining bite mass and dimensions, especially for the first stratum, and of tiller density in the bulk density of bites in the lower stratum in sward depletion, the latter requiring to be studied further.