A field experiment was carried out on soyabean (Glycine max (L.) Merr.) to measure the effect of planting date (soil temperature) on seedling emergence. Seeds were sown at weekly intervals on seven planting dates from April until the end of May in SE England in 1997. Planting date had no significant effect on final percentage emergence but had a highly significant effect on time to emergence. The coefficients of variation (c.v.) for the number of days to emergence (calendar days) were high (43–45%), and therefore not a reliable method for predicting emergence. Three accumulated heat unit (AHU) methods based on air and soil temperatures were compared with the calendar day method to determine the most reliable system for predicting seedling emergence. Accumulated soil temperatures above a base of 9·0 °C had the lowest c.v.s (8–15%) and were shown to be the most reliable predictor of emergence.

The re-introduction of forages into the farming systems of central and southern Italy has been advocated by EU policies in order to reduce high inputs and favour more sustainable agricultural systems. Since legumes could certainly play a major role, landraces and natural populations of Trifolium alexandrinum (2), T. incarnatum (5) and T. squarrosum (3) were investigated. Two experiments were conducted during the 1991/92, 1992/93 and 1993/94 seasons in Perugia, central Italy. The objective of the first was to obtain the morphological and physiological characteristics of the entries, while the second assessed the biomass production, forage quality (stem: leaf: inflorescence ratio, protein, fibre, O.M. digestibility, milk and meat Forage Units) and seed yields. In T. incarnatum, flowering time, leaf area, stem length and diameter were important characteristics for discriminating between populations. Norcia and Rocca di Corno, two natural populations of T. incarnatum, flowered early, produced the most biomass and had high forage quality. Their potential as forage/pasture crops and/or cover crops in Mediterranean farming systems is discussed.

The effects of residual phosphate (P) fertilizer were monitored for six seasons on Mediterranean grassland. The phosphate fertilizer was originally applied annually at three rates (0, 25 and 60 kg P2O5/ha) for 7 years (1984–1990) to phosphate-deficient grassland at Tel Hadya, northern Syria. The herbage biomass productivity, botanical composition and the seed bank in the soil were monitored for six seasons (1991/92–1996/97). The experiment was grazed at two annual stocking rates (1·1 sheep/ha (low) and 2·3 sheep/ha (high)). The experimental site was typical of native grassland within the cereal zone of west Asia, where cropping is not possible because of shallow, stony soils and steep slopes.

Available soil phosphorus in May 1991 was 6·5, 20·8 and 40·1 mg P/kg under the 0, 25 and 60 kg P2O5/ha treatments and 6·6, 13·4 and 14·8 mg P/kg respectively, in May 1997. Yields of both legumes and total herbage (legume+grass+other species) were significantly influenced by the residual phosphate. Legume yields were between 6- and 7-times the control yield in the first two years of the study. This decreased with time but was still in the range of 1·5 to 1·9 times the yield of the control in 1997, six years later. Total herbage yield was consistently higher on the plots previously fertilized with P, which ranged between 1·5- and 2·5-times the control. Both legume seed and grass seeds were significantly larger with residual P, which ranged between 5·4- and 2·0-times the control for the legume and 2·5- and 1·4-times for the grasses. All these factors have practical implications for the use of P fertilizer on grassland which could help control soil erosion and improve livestock production on marginal lands on which farming communities largely depend.

The response of spring field beans (Vicia faba) (cv. Victor) to irrigation applied before, during and after flowering and in combinations was studied on sandy soils, overlying sand, in Nottinghamshire, England in three years, 1993, 1994 and 1995. Irrigation was only needed pre-flowering in 1995, thus the opportunity to evaluate the effect at this timing was limited. Seasonal rainfall was higher than the long-term 30-year mean in 1993, but lower in 1994 and much lower in 1995.

Irrigation increased spring field bean yield in all three years, even in 1993 when a period of drought post-flowering caused a yield depression of 2 t/ha on unirrigated plots. The yield response for fully irrigated, compared with unirrigated field beans per 25 mm water was 0·34, 0·28 and 0·36 t/ha in 1993, 1994 and 1995 respectively. Irrigation applied during or post-flowering gave statistically significant yield increases and there were indications of greater efficiency of water use from post-flowering applications.

The response of two cultivars of dry harvest field peas (Pisum sativum), Solara and Bohatyr, to irrigation at different growth stages was studied on light soils overlying sand in Nottinghamshire, England in 1990, when the spring was particularly dry, in 1991 which had a dry spring and summer and in contrast, 1992, when rainfall was greater compared with the long-term (40 year) mean.

Solara, short haulmed and semi-leafless was more sensitive to drought than the tall conventional-leaved cultivar Bohatyr and gave a greater yield response to irrigation, particularly at the vegetative growth stage in the first two dry years 1990 and 1991, of 108% and 55% respectively, compared with unirrigated plots. Bohatyr was less sensitive to the timing of single applications.

In all years, peas irrigated throughout on several occasions produced the highest yields, but this was the least efficient use of water.

Inverse yield–density relationships were used to evaluate how competitive balances in mixed plant species associations may influence productivity, as measured by three indices : Relative Yield Total (RYT), Relative Land Output (RLO), and Total Land Output (TLO). Parameters of the inverse relationships, which express competitive influences and plant growth potential in the absence of competition, were incorporated into expressions used to predict RYT, RLO and TLO. Initial parameter values were derived from 25 experiments on binary species mixtures, and parameter values were systematically varied over a 100-fold range. Response to parameter manipulation was also investigated in five specific binary associations representing a broad range of relative mixture productivity. As indicated by RLO or RYT, and in accord with ecological concepts of niche differentiation, high productivity of mixtures relative to monocultures occurred if between-species competition was low. As indicated by TLO, the total combined productivity of the mixed species was enhanced by higher potential growth per plant in the absence of competition. Lower within- and between-species competition also increased TLO. There was a significant positive correlation between RYT and RLO. Relative and total measures of mixture productivity, however, showed different responses to parameter manipulation, and were not correlated.

The combined effect of two rapid multiplication techniques (sprout and top-shoot cutting) was assessed using four Dutch potato cultivars during 1991/92–1993/1994 at the Tuber Crops Research Centre (TCRC), Bangladesh Agricultural Research Institute (BARI), Gazipur-1701, Bangladesh. On average, a 70–80 g tuber produced 29 sprout cuttings which were subsequently used for taking top-shoot cuttings. Top-shoot cuttings were taken at a number of dates from 25 November and continued at 10 day intervals, thereafter, until 15 January. The number of top-shoot cuttings produced by 29 sprout cutting-derived plants varied (P<0·01) from 761 to 663 across the cultivars. Cardinal gave the greatest yield. Most of the characters studied varied (P<0·01) between cultivars but not over years while the interaction between cultivars and years was significant (P<0·01).

Early planted top-shoot cuttings produced more tubers per plant (4·0) with a greater mean tuber weight (>22 g) than from the late planting (1 tuber and 5·5 g). On average, about 2·8 tubers per plant were produced with a mean tuber weight of 15·8 g. Cardinal and Patrones produced the most tubers per plant (2·9) and Diamant the greatest mean tuber weight (16·8 g). Cardinal gave the greatest yield (P<0·01) of tubers (268) followed by Patrones (241). The 29 sprout cutting plants derived from a 70±5 g tuber produced 160 tubers while the 771 top-shoot plants derived from 29 sprout cutting-derived plants produced 1420 tubers. The rate of multiplication of the combined two RM techniques was 1580[ratio ]1 against 11[ratio ]1 for the conventional method.

Potted 1·5-year-old apricot plants (Prunus armeniaca L.), growing under polycarbonate glasshouse conditions with a cooling system, were subjected to two successive water stress/recovery periods until pre-dawn leaf water potential (Ψpd) reached values between −2·0 and −2·5 MPa, during summer 1996. Control plants were irrigated daily to maintain the soil matric potential at c. −20 kPa. Water stress limited plant growth and induced a significant reduction in leaf area, caused by mature leaf abscission. The parallel behaviour of leaf turgor potential and epinasty in stressed plants indicated that these movements are turgor-dependent. Osmotic adjustments of 0·27 and 0·60 MPa were observed at the end of the first and second stress period, respectively. Relative apoplastic water content (RWCa) values were high, ranging from 27 to 42%, and were not affected by water stress. The rapid decrease in leaf conductance (gl) from the beginning of the stress periods, together with the delay in stomatal reopening after rewatering the plants, indicated that stomatal behaviour was not a simple passive response to water deficits. Net photosynthesis decreased only at the end of both stress periods and recovered quickly. These observations indicate that leaf productivity may be affected only slightly by short-term water stress. The results indicate that drought resistance in apricot is based mainly on avoidance mechanisms, such as stomatal control, epinasty and limitation of transpiration by reducing leaf area. However, some tolerance characteristics, including osmotic adjustment, high RWC a and low leaf osmotic potential at turgor loss point (Ψtlp) values were observed.

The effect of environmental conditions immediately before anthesis on potential grain weight was investigated in wheat at the experimental field of the Faculty of Agronomy (University of Buenos Aires, Argentina) during 1995 and 1996. Plants of two cultivars of wheat were grown in two environments (two contrasting sowing dates) to provide different background temperature conditions. In these environments, transparent boxes were installed covering the spikes in order to increase spike temperature for a short period (c. 6 days) immediately before anthesis, i.e. between ear emergence and anthesis. In both environments, transparent boxes increased mean temperatures by at least 3·8 °C. These increases were almost entirely due to the changes in maximum temperatures because minimum temperatures were little affected. Final grain weight was significantly reduced by higher temperature during the ear emergence–anthesis period. It is possible that this reduction could be mediated by the effect of the heat treatment on carpel weight at anthesis because a curvilinear association between final grain weight and carpel weight at anthesis was found. This curvilinear association may also indicate a threshold carpel weight for maximizing grain weight.

Field experiments were conducted during the wet seasons of 1995 and 1996 at the Central Rice Research Institute, Cuttack, Orissa, India using two rice cultivars, Matangini (improved) and Champaisali (local) to study the advantages of organic manuring in conjunction with inorganic fertilizer with the objective of enhancing rice productivity under semi-deep (0–65 cm) lowland conditions. In 1995, application of 10 t FYM/ha increased grain yield compared with no FYM. The yield produced with FYM alone was similar to the yield following the application of N fertilizer at 20 and 40 kg/ha. There was no significant difference in grain yield due to the application of 20 and 40 kg N/ha in plots treated with FYM. Nitrogen fertilization was effective only when FYM was not applied. In 1996, FYM application alone or in combination with N fertilizer had a beneficial effect on crop growth and grain yield. This was contrary to the results obtained in 1995 when N fertilization at 20–40 kg/ha did not prove beneficial in plots where FYM was applied. The yield due to application of FYM alone was similar to that from the application of 40 kg N/ha as urea. However, the maximum yield was produced when FYM application was supplemented with 40 kg N/ha. There was a significant interaction between N application rate and cultivar. Cultivar Matangini outyielded Champaisali in both years.

Twenty-eight high genetic merit and 32 medium genetic merit Holstein/Friesian dairy cows with Predicted Transmitting Abilities for milk fat plus protein yield, calculated using 1995 as the base year (PTA95 fat plus protein) of 43·3 and 1·0 kg respectively, were used in a continuous design, 2 (cow genotypes)×4 (concentrate proportion in diet) factorial experiment consisting of eight treatments. Concentrate proportions in the diet were 0·37, 0·48, 0·59 and 0·70 of total dry matter (DM), while the forage component of the diet was grass silage. Diets were offered ad libitum in the form of a complete diet. Animals remained on these concentrate regimes for a mean of 84·7 days before completing a standard 98-day grazing period. At pasture, cows received either 5·0 or 6·0 kg concentrate daily according to turnout date. There were no significant genotype×nutrition interactions for any of the variables examined during either the indoor feeding or post-turnout grazing periods (P<0·05). Outputs of milk, fat, protein and fat + protein were greater for high merit cows than for medium merit animals (P<0·001). Milk output and milk protein output responses to increasing concentrate proportion were linear for both cow genotypes (P<0·001), while high merit animals showed a linear response in terms of milk fat plus protein output (P<0·01) with these responses being statistically parallel for both merits. High merit cows had a significantly higher DM intake than medium merit animals (P<0·01). With high merit animals, concentrate proportion had little effect on body tissue reserves, while medium merit animals showed a tendency for increased condition score and backfat thickness with increasing concentrate inclusions (P<0·05). In terms of the output of milk and milk constituents during the grazing period, there were no significant residual effects from winter concentrate feed rate (P>0·05), while high merit cows continued to have higher outputs of milk and milk constituents (P<0·001). Body tissue reserves of both genotypes changed little during the grazing period. It is likely that the higher milk yields of the high merit cows can be attributed both to their higher DM intakes and their ability to partition a greater proportion of the nutrients consumed into milk rather than body tissue reserves. Although statistically both high and medium merit cows responded in a similar manner to an increasing proportion of concentrate in the diet, high merit cows did exhibit a 49% greater fat plus protein yield response during the indoor period, compared to animals of medium genetic merit, perhaps hinting at the existence of a genotype×nutrition interaction.

Sixty Holstein/Friesian dairy cows, 28 of high genetic merit and 32 of medium genetic merit, were used in a continuous design, 2 (cow genotypes)×4 (concentrate proportion in diet) factorial experiment. High and medium merit animals had Predicted Transmitting Abilities for milk fat plus protein yield, calculated using 1995 as the base year (PTA95 fat plus protein), of 43·3 kg and 1·0 kg respectively. Concentrate proportions in the diet were 0·37, 0·48, 0·59 and 0·70 of total dry matter (DM), with the remainder of the diet being grass silage. During this milk production trial, 24 of these animals, 12 from each genetic merit, representing three animals from each concentrate treatment, were subject to ration digestibility, and nitrogen and energy utilization studies. In addition, the efficiency of energy utilization during the milk production trial was calculated.

There were no genotype×concentrate level interactions for any of the variables measured (P>0·05). Neither genetic merit nor concentrate proportion in the diet influenced the digestibility of either the DM or energy components of the ration (P>0·05). When expressed as a proportion of nitrogen intake, medium merit cows exhibited a higher urinary nitrogen output and a lower milk nitrogen output than the high merit cows. Methane energy output, when expressed as a proportion of gross energy intake, was higher for the medium than high merit cows (P<0·05), while urinary energy output tended to decrease with increasing proportion of concentrate in the diet (P<0·05). In the calorimetric studies, neither heat energy production, milk energy output and energy retained, when expressed as a proportion of metabolizable energy intake, nor the efficiency of lactation (kl), were affected by either cow genotype or concentrate proportion in the diet (P>0·05). However when kl was calculated using the production data from the milk production trial the high merit cows were found to have significantly higher kl values than the medium merit cows (0·64 v. 0·59, P<0·05) while k l tended to fall with increasing proportion of concentrate in the ration (P<0·05). However in view of the many assumptions which were used in these latter calculations, a cautious interpretation is required.

In order to learn more about the digestibility, breakdown when eaten and physical structure of stovers and straws, seven diets were compared in one experiment and eight in another. The diets in the first experiment were: the upper and lower parts of lucerne (Medicago sativa) hay, the leaves, upper stem and lower stem of maize (Zea mays) stover and the leaves and stem of sorghum (Sorghum vulgare) stover. The diets in the second experiment were: the upper and lower parts of lucerne hay, the leaves, stems and whole stover of millet (Setaria italica), wheat (Triticum aestivum) straw, rice (Oryza sativa) straw and sweet potato (Ipomoea batatas) haulm. The diets were examined for in vitro digestibility in three forms: milled, chopped (1 cm lengths) and chewed (by cattle). The lengths and widths of the chewed particles were recorded in both experiments. Aspects of the morphology and vascular structure of plant parts of the diets and of chewed particles were recorded in the second experiment.

The in vitro digestibility of chopped or chewed plant material was lower (by 11 and 12 percentage units, respectively, on average) than that of milled material. The difference between chewed and milled material in in vitro digestibility was smaller with leaves (5 percentage units, on average) than with stems (18 percentage units, on average) in maize, sorghum and millet. Digestibility of chewed material was similar to or lower than that of chopped material, except with the leaves of maize, sorghum and millet. Millet stover had higher in vitro digestibility than wheat straw or rice straw, whether the diet was milled, chopped or chewed.

The thinnest stem internode vascular bundles recorded (0·14 mm) were in wheat. The percentage of stem internode cross-sectional area occupied by vascular bundles was in the range 6–8 for lucerne, millet, wheat and rice. The mean numbers of veins or vascular bundles per chewed particle were in the range 6–23. The mean length of the chewed particles varied from 10 mm with the upper stem of maize to 18 mm with sorghum stem and maize leaves. The mean width of the chewed particles varied from 1·8 mm with rice straw to 5·4 mm with maize leaves.

It is suggested that the low digestibility of mature plant tissue such as stovers and straws is not particularly due to thick vascular strands or to a high proportion of vascular tissue, but rather to a high proportion of cell wall and incomplete and delayed access by rumen microorganisms to much of the cell wall.