In this paper we present the analysis of yield data from a broad cross-section of crop variety evaluation programmes (CVEP) conducted in Australia. The main sources of variety by environment interaction are ‘non-static’ interactions, namely those linked to seasonal influences. These contributed an average of 41·3% of the total variance. In contrast the static component accounts for only 5·3% of the total.

We develop methods for determining the relative accuracy of CVEP based on selection of newly promoted entries. The accuracy of the current testing regimes for the Australian CVEP under study is determined. The accuracy of alternative schemes, with different numbers of years of testing, numbers of locations per year and numbers of replicates per trial is also examined. Cost effective methods for improving the accuracy of CVEP are discussed.

The effect of different rates of potassium (K) fertilizer on the yield and quality of sugar beet was studied in a series of 26 trials on soils of different type and K index between 1992 and 1997. There were few yield responses even though the majority of trials were on soils of low K index, and large quantities of fertilizer were applied (0–600 kg K/ha). Potassium offtakes (kg/ha) in the harvested beet increased asymptotically, not linearly, with yield and were much larger for a given yield on high K index soils than on low index soils. Commercially acceptable concentrations of beet K for processing are in the range 700 to 1000 mg K/100 g sugar. Concentrations in excess of this decrease the amount of sugar crystallized from the extracted juice. They were not greatly affected by large applications of fertilizer K but were strongly influenced by long-established differences in soil exchangeable K (Kex) due to soil type, previous cropping or manuring history.

The asymptotic nature of the K offtake[ratio ]yield relationship was confirmed by factory tarehouse measurements relating to the national sugar beet crop delivered during the 1993–97 UK processing campaigns. Potassium offtakes generally increased linearly with yield up to 60–70 adjusted t of clean beet/ha, but increased little beyond that. The amount of K removed by a 60–70 t/ha crop of beet varied from 70 kg K/ha on low K index sandy loams to 120 kg K/ha on clay soils of K index 3 and above. Further increases in yield decreased the amount of K in fresh beet from 1·7 to 1·4 kg K/t on low K index soils, and from 3·6 to 2·5 kg K/t on high K index soils.

An analysis of data from individual fields of commercially grown sugar beet showed that much of the site and season variation in the K content of beet was due to differences in K uptake driven by Kex, and to differential effects of nitrogen (N) supply on K uptake and sugar yield. Regressions on Kex and total crop N (kg/ha) accounted for c. 30 and 50% of the variance in beet K content, respectively, and the two together for over 60%. Total N uptake by the crops ranged from 100 to 550 kg N/ha. The total K content of the crop and the amounts of K in the beet (kg/ha) both increased linearly with crop N over the whole of this range, whereas sugar yield increased asymptotically with total uptakes of N up to 250–300 kg N/ha. Consequently, low yielding crops grown on soils in which N and K were freely available produced beet of poor K quality. However, the asymptotic relationship between beet K (kg/ha) and yield implies that, in many situations, the processing quality of the beet could be improved by increasing yield through better agronomy.

Following germination, the ontogeny of white clover is characterized by two distinct morphological growth phases, a seminal taprooted stage followed by a clonal growth stage. Death of the seminal taproot and primary stolon initiates a process of fragmentation of the taprooted plant into a variable number of independent clonal fragments (plants) which comprise the initial population of the clonal growth stage. The objective of this study was to characterize the plant morphology of field-sown white clover populations from germination through to established clonal populations. Populations of eight white clover cultivars were assessed when sown with perennial ryegrass or tall fescue in pastures established under a common grazing regime for 16 months prior to imposition of continuous or rotational grazing treatments. One year from sowing, taprooted plants attained maximum size, with a mean plant branching order of 3·35, stolon DW of 460 mg and lateral spread of 250 mm, with some individuals having 6th order branching, 3·5 g stolon DW and 1m lateral spread. These taprooted plants were 4–5 times the size of plants in the subsequently formed clonal population. Nine months after sowing, the first individual taprooted plants fragmented into clonal plants. Twelve months from sowing, fragmentation processes were occurring at a linear rate, eliminating 6% of the original taprooted population each month. This resulted in a 12–15 month transition period when the white clover population comprised both taprooted and clonal plants. During this transition period, the initial clonal fragments produced from taprooted plants were large, and this maintained a larger mean plant size in the clonal plant proportion of the transition population than measured in the later fully clonal population. This process was also considered to act to prevent the development of the expected differences between grazing managements, as it was not until the third year when all taprooted plants had disappeared that the clonal populations developed characteristics reflecting the expected influence of grazing management. Variation due to white clover cultivar and companion grasses was minor. The substantial differences in plant size and branching structure between taprooted and clonal populations has significant implications for the evaluation of breeding lines.

Yields of arable crops are commonly lower on the crop margins or headlands, but the nature of the relationship between yield and distance from the crop edge has not been clearly defined, nor have the reasons for lower marginal yields. Surveys of 40 winter wheat headlands were carried out in 2 years to determine how yield changed with distance, and what factors might influence this relationship. Two field experiments were also conducted over 3 years in winter cereal headlands, in which the effect of distance was measured under conservation headland and conventional (fully sprayed) management.

Yields in the headland surveys varied from 0·8 to 10·2 t/ha. An inverse polynomial regression model was fitted to yield and weed data. Best fits were obtained by using separate parameters for each site. Adjusting yields to take account of weed dry matter improved the non-linear fit between yield and distance from crop edge. Field experiments provided similar results but the non-linear relationship was not as apparent.

There was a negative relationship between soil compaction, as measured by a cone penetrometer, and yield in one field experiment, where soil density values were relatively constant. No relationship was found between pattern of nitrogen fertilizer application and yield. Conservation headland management resulted in lower yield at one experimental site, especially in the third year, but not at the other site. Where yields were affected, weed dry matter was higher in conservation headland plots than in fully sprayed plots.

Although greater weed competition appears to account for at least part of the observed yield reductions on headlands, the role of other factors, particularly soil compaction, needs further study. Increased weed infestation may be an indirect result of reduced crop competition caused by other adverse conditions.

A spaced plant experiment and a sward experiment were conducted at INIA La Estanzuela, Uruguay in 1996 with six red clover (Trifolium pratense L.) populations, to study the efficacy of selecting genotypes for sward performance in a spaced plant nursery. This was examined through: (a) the ranking of the best linear unbiased predictors (BLUP) of populations and (b) the ratio of the correlated genetic advance in swards by selecting under spaced plant conditions to the direct genetic advance of selecting under sward conditions. From the eight characters analysed, only the rankings of BLUPs for leaf size and flowering were significantly the same between populations. The other six characters performed differently according to the level of competition imposed. Post-grazing leafiness and the difference between pre- and post-grazing leafiness (the two most important characters to measure preferential grazing) achieved greater genetic advance when selection was done as spaced plants: while for pre- and post-grazing height genetic advance was greatest by selecting under sward conditions. For other characters, the best conditions to select depended on the selection intensity achievable.

The performance potentials of six perennial ryegrass varieties for conservation or grazing use were compared between 1994 and 1996 in N. Ireland. They were maintained, either under constant lax defoliation (conservation) or constant severe defoliation (simulated grazing) management for 3 years, or annually alternated between these two managements with the changeover taking place either in autumn or at the first cut of the following year. Starting one set with lax defoliation in the first year and the other with severe defoliation created duplicates of these two alternating treatments. The results showed that variety yield differed depending on the season and the management imposed and there were differential responses to the various treatments. Conducting an alternating management system that implemented the management change in autumn provided a valid estimate of yield performance potential for both simulated grazing and conservation use, compared to constant management systems. Although significant differences in variety ranking between lax defoliation and severe defoliation management yields were only observed in the third year, the study showed that if the management change was implemented in autumn, the yield potential of varieties in the following year was not affected by the preceding year's management regime. Leaving a longer sward (6 cm) to over-winter increased the spring performance of the varieties in some years, compared to a shorter sward (3 cm), which may have implications for grazing management. There were also indications that imposing an alternating management system might alter the absolute magnitude of the sward density ratings relative to a constantly managed system, though variety rankings would remain unaffected.

It was concluded that the current alternating management testing system used to evaluate candidate varieties for UK National or regional recommended lists, does not cause any variety to be unfairly advantaged or disadvantaged.

Trials, reflecting the feed needs in dry Mediterranean environments of small-ruminant production systems based on barley, were established at two sites in Syria in 1982. They compared various 2-course rotations of barley with feed legumes, fallow or more barley. This paper summarizes a 14-year sequence of results from an incomplete factorial combination of four rotations (B-V, B-L, B-F, B-B) of barley with vetch (Vicia sativa), lathyrus (Lathyrus sativus), fallow, and barley, with two fertilizer regimes, zero control and biennial NP applied to the barley phase, in terms of long-term mean yields, production stability and yield trends over time.

On a 2-year rotational basis, most barley was produced by barley-only rotations, and differences between B-F and B-B were small; but, in terms of total biomass production, feed legume rotations (B-V and B-L) outyielded barley-only rotations by 29% at one site and 19% at the other. Responses to biennial fertilization were large but did not interact significantly with rotation treatment. The crude protein status (%N) of barley grain and straw was strongly determined by seasonal rainfall, but that of the grain could be enhanced, irrespective of rainfall, by a preceding feed-legume crop; and, altogether, the total mean crop nitrogen output of legume-based rotations exceeded that of barley-only rotations by 80% and 64% at the two sites. The inclusion of legumes thus enhances both quantity and quality of feed production.

Annual yield fluctuations, attributable mainly to rainfall difference, were greater at the drier site. No consistent effect from fertilizer was observed, but at the wetter site rotation differences were appreciable, with B-F rotation giving the most stable yields. A number of time trends in yield values were tentatively identified. On a relative basis, some widening over time of the gap between fertilized and unfertilized treatments was observed in feed-legume yields at both sites and barley yields at the wetter site; over 14 years, yields in unfertilized plots had apparently declined relative to those receiving biennial NP. But, apart from a probable decline in lathyrus productivity compared to that of common vetch, changes in relative yield performance between rotations were difficult to detect. Regression models developed to describe absolute yield trends indicated a real decline over time in barley grain yields in continuous barley (B-B) at both sites and in unfertilized plots of all four rotations at the wetter site.

The genetic control of pod dehiscence was studied through the production, field trial and subsequent analysis of a full diallel involving seven parents selected for high and low resistance to pod shattering. Additive gene effects were most significant among the measures of pod shattering resistance with only minor contributions from non-additive gene effects. Genetic variation in measures of the stiffness of the pod wall were, however, determined by dominant gene effects. Genes for increased pod shattering resistance acted recessively. All characters showed high levels of heritability. Correlations among pod shatter resistance characters and other pod, raceme and plant characters were low suggesting that resistance is likely to be independent of other important agronomic traits.

Leaves of 12 accessions of Brachiaria sp. (three accessions from each of four species) were subjected to tests of shearing strength using a Warner Bratzler meat shear. Morphological measurements of these leaves were also taken in an attempt to standardize shearing strength measurements per unit of leaf tissue. The technique was evaluated for its capacity to detect differences between accessions of the same species. All samples were also analysed for dry matter (DM), organic matter (OM), neutral detergent fibre (NDF), acid detergent fibre (ADF), lignin, crude protein, silica and digestibility in order to relate measures of physical strength to chemical components. Results demonstrated the presence of a clear relationship between shearing strength and structural (cell wall) components. Correlations between shearing strength and NDF, ADF and lignin were 0·74, 0·82 and 0·80 respectively. The technique identified clear differences between accessions of the same species (P < 0·05). These measurements can thus be used as a powerful tool for identifying forage plants of superior nutritional quality within selection programmes. Measurements of strength standardized for morphological characteristics illustrated that the ranking of the samples varied considerably depending on which morphological character was used.

Rotations of barley with feed legumes produce more biomass and crude protein than barley-fallow and continuous barley sequences, but scope remains to improve the potential value to farmers of feed legume-based systems. This paper summarizes 6-year results from two sites from 2-year rotations of barley with: narbon vetch (Vicia narbonensis) and lathyrus (Lathyrus sativus), each harvested mature; and common vetch (Vicia sativa), harvested by simulated green-grazing and mature, all in factorial combination with four NP fertilizer regimes applied biennially to the barley.

Mean yield differences between rotations were quite small, but at the drier site the narbon vetch rotation was significantly superior in both total biomass and crop total nitrogen. Other results implied yield compensation between barley and legume phases: barley performance was relatively depressed at the wetter site after high-yielding narbon vetch but was relatively enhanced at both sites after green-grazed common vetch. Evidence from year-round soil-water monitoring suggests that the benefit following green grazing may have arisen, in part, from a small carry-over of profile moisture between crops not much inferior to that residual from a fallow year. Both crop phases responded strongly to biennial P fertilizer; and barley responded strongly to three rates of N-fertilizer, but a sometimes significant curvilinear component to this response reflected a tendency for grain yields to be depressed by added nitrogen in the driest years. But interactions between N-rates and rotations were not significant.

It was concluded that narbon vetch may have greater potential than common vetch and lathyrus for mature harvest in drier areas, but its unsuitability for grazing green is a limitation. Flexibility of utilization is important, to accommodate the needs of different farmers and the exigencies of different seasons. The green-graze option has major potential where there is a demand for high-quality spring grazing; and indications that barley may be as productive after green-grazed vetch as after a year of fallow suggest an alternative approach for farmers who have previously avoided legumes in order to maximize barley production.

In the soyabean [Glycine max (L.) Merr.]–B. japonicum symbiosis, genistein has been identified as one of the major compounds in soyabean seed and root extracts responsible for inducing the expression of the B. japonicum nod genes. High combined nitrogen in the growth medium inhibits nodulation and nitrogen assimilation. Two experiments were conducted to test the possibility of overcoming this inhibition by adding genistein to the rooting medium and by incubation of B. japonicum cells with genistein. One soyabean cultivar was used in the first experiment, and two in the second experiment. The experiments were conducted in a glasshouse using a completely randomized design with three rooting medium nitrate concentrations (0, 5 and 10 mM) and four genistein treatments. The genistein treatments were 0 (control), incubation of B. japonicum cells with 5 μM genistein, and regular watering with 5 μM or 20 μM genistein. A two way interaction existed in the first experiment, and two and three way interactions existed in the second experiment. Root growth was inhibited by repeated watering with 20 μM genistein. Weight per nodule was greater at 5 mM than at 0 mM nitrate. At 10 mM nitrate watering with genistein resulted in significant increases in nodule dry weight per plant. Shoot nitrogen contents were significantly increased at 5 mM nitrate by genistein incubation and watering with 20 μM genistein. Watering with 5 μM genistein significantly increased nodule nitrogen concentrations at both 5 and 10 mM nitrate. The two soyabean cultivars responded differently to the genistein and nitrate treatments in terms of nodule number, nodule weight, leaf nitrogen concentration and nodule nitrogen content. Genistein could, at least partially, overcome the inhibition of soyabean nodulation and nitrogen assimilation by nitrate.

A comparison of the fibre and seed development in fibre flax and linseed types of Linum usitatissimum (L.) was carried out in replicated field plot experiments in 1993, 1994 and 1996 in Northern Ireland. Flax cultivar Ariane, and linseed cultivars Barbara (1993 and 1996) and Flanders (1994) were each grown at seed rates of 500, 1000 and 1500 seeds/m2 and sampled at 7-day intervals from the start of flowering until harvest. The number of buds, flowers and capsules per plant were counted and straw height and total, seed, straw, total fibre, long fibre and short fibre dry matter ( DM) yields determined for each sample date. Fibre yields were determined after water retting the straw for 7 days at 20°C and extracting the fibre by scutching and hackling.

The emergence dates were similar in all years, but site and season interactions resulted in later flower and capsule development in 1993. Although the total biomass of flax and linseed were similar at the start of flowering, flax maintained a more rapid straw growth rate and linseed a more rapid seed growth rate giving final fibre yields that were 1300 kg/ha higher in flax than linseed and seed yields that were 800 kg/ha greater in linseed than flax. The proportion of fibre in the straw was higher in flax than linseed and the proportion of long fibre within the total fibre fraction was also greater. Final seed yields were highest in 1993, and fibre yields from flax were higher in 1994 than in the other years. Seed rate had no effect on seed yield in either flax or linseed but at the lowest seed rate, which gave plant counts of about 400 plants/m2 , the total fibre yield was significantly reduced compared with the higher seed rates with plant counts of about 1200 plants/m2 . It is concluded that decreasing fibre flax seed rates from 1500 to 500 seeds/m2 will reduce potential fibre yields by 25% but have little effect on seed yield, whilst increasing linseed seed rates from 500 to 1500 seeds/m2 would only result in marginal increases in the potential yield of fibre.

Groundnut is an important crop of the semi-arid tropics where potential yields are frequently reduced by heat and water stress. Eight groundnut genotypes varying in heat tolerance were grown in controlled environments and exposed to either high (40/28°C) or near-optimum (30/24°C) temperature from 32 days after sowing (DAS) to maturity. There was significant variation among genotypes in mainstem leaf number and total flower number at 30/24 and 40/28°C and rates of appearance were faster at 40/28°C than at 30/24°C. Days from sowing to first flowering varied among genotypes from 28 to 41 days and therefore the time plants were exposed to high temperature relative to first flowering ranged from −4 to 9 days. Fruit number for seven out of eight genotypes at 40/28°C was linearly and negatively related to the time of first flowering relative to the onset of high temperature (r2 = 0·93; n = l7; P < 0·001), indicating that ‘escape’ was an important component of heat tolerance in this experiment. Further analysis showed that fruit number in all genotypes at 40/28 °C was closely associated with the cumulative number of flowers that had opened between first flowering and 3 days after the onset of the high temperature regime (r2 = 0·95; n = 8; P < 0·001). Variation in fruit number was therefore due both to the timing of flowering and the initial rate of flower production. These data also suggest that the most sensitive stage of development to high temperature in groundnut occurred around 3 days before flowers opened. Therefore, it was the timing of flowering, rather than heat tolerance or susceptibility, that was the dominant attribute determining fruit number.

The effect of sulphur (S) application on the efficiency of nitrogen (N) use was investigated using cut plot experiments on two contrasting soil types. Nitrogen was applied at 200 and 450 kg N/ha per year, with and without 38 kg SO3/ha (15·2 kg S/ha) per cut. Over three conventionally timed silage cuts for 2 years, measurements were made of herbage dry matter, the yield of N and S in herbage and losses of N and S by leaching, and N by denitrification.

Herbage dry matter and N yields were significantly increased by the application of S at the high N level at the sandy loam site (Halse). At the clay loam site (Great Close) the application of S had no significant effect on herbage dry matter or N yields. At Halse, the pattern of response through the year was not the same in the 2 years studied, although in both, the effect of S was significant at third cut at high N. Deficiency was suggested by the N[ratio ]S ratio of herbage on the plots without S, especially at first cut, and at later cuts at Halse. Nitrate leaching was reduced by S at Halse by 72% and 58% with high N in 1997 and 1998, respectively, and by 10% and 5% on the low N treatments in 1997 and 1998, respectively. Application of S at high N at Halse reduced the peak concentration of nitrate-N in leachate from 27·3 mg N/l to 9·3 mg N/l. At Great Close, application of S had no significant effect on the amount or peak concentration of nitrate-N leached. The improvement in efficiency reported at Halse suggests that on permeable soils receiving high levels of N, the application of S could have a large effect on nitrate leaching and its associated environmental impact.

The responses of Leucadendron ‘Safari sunset’, on its own roots and grafted on ‘Orot’ rootstock, to a range of fertilization regimes were studied. The experiment was conducted during the summer of 1994, at Bet Dagan, Israel, and included three levels of compound NPK, two levels of P, and two NH4[ratio ]NO3 ratios.

Ungrafted plants fed without P yielded fewest marketable branches and had the lowest fresh and dry weights. Increasing the P concentration in the irrigation water to 10 mg/dm3 improved the yield, whereas increasing the NPK level reduced the number of marketable branches and the fresh and dry weight yields. Lowering the NH4[ratio ]NO3 ratio in the irrigation water significantly reduced the yield.

The grafted plants were significantly better than the ungrafted plants under all the treatments examined. The superiority of the grafted plants was more evident under conditions of P deficiency and non-optimal pH.

Results from monocropped barley treatments in long-term rotation (RTN) and continuous barley (CB) trials at two sites were examined for fertilizer effects on yield means and long-term yield trends. In RTN trials, mean responses to fertilizer (N[ratio ]P2O5) applied annually at rates of 20[ratio ]60 at the drier and 40[ratio ]60 at the wetter site were almost double those from biennial application, confirming the need for annual fertilization in monocropped barley systems. In CB trials, with N and P applied annually in nine factorial combinations, at rates up to 120[ratio ]90, responses to each nutrient were curvilinear and dependent on the presence of the other nutrient. Trend analysis showed a decline in grain yields over time where NP fertilizer had not been applied or applied only at low annual rates (< 60[ratio ]45 or < 60[ratio ]90, according to site); but straw yields, at worst, remained approximately stable in the absence of fertilizer and generally increased strongly with higher NP rates. Uncertainties in the interpretation of trend-analysis results indicate the need for methodology improvements, to include (i) additional single-value parameters of the growth environment, to improve the model's ability to account for seasonal variability, and (ii) a more flexible, non-linear function for time.

It was concluded that barley monocropping is not necessarily non-sustainable in the medium term, provided adequate annual fertilization is maintained; but risks of pest or disease build-up, in addition to the superiority of legume-barley systems in biomass and crude protein output demonstrated in preceding papers, undoubtedly favour the introduction of some forage legumes into long-term barley sequences. The most practicable (and acceptable) systems may well be ones in which continuous barley is interrupted by a legume, or even a bare fallow, every third or fourth year. Above all, farmers should be helped to experiment with different forage legumes, barley–legume sequences, and modes of legume harvest, to optimize outputs in relation to their evolving and individual enterprise needs.

The effects of eight rates of nitrogen (N) application (0–245 kg/ha) on the performance of winter wheat over five seasons (1991–1995) on a long-term field experiment (established 1978) at Ropsley (UK) are described. In each of the five seasons, N was withdrawn from replicate plots in order to study the residual effect of fertilizer. N applications in excess of 140 kg/ha left significant residues as soil mineral N (SMN) in the autumn which, despite some loss over-winter, had a significant effect on the yield and N offtake of the subsequent crop. The amount of N carried over was equivalent to 8–20% of the fertilizer N and was observed at N applications up to 40 kg/ha lower than the optimum rate (c. 200 kg/ha). Part of the unrecovered N was also considered to contribute to the long-term build-up of fertility at the site. The results suggest that restrictions on N use to below the optimum will reduce leachable N, but may have an impact on soil fertility and future crop productivity. In addition, the rate of N applied to preceding crops should be taken into account when formulating fertilizer advice on retentive soils.

A field study was conducted on an experimental field of the Maize Research Institute Zemun Polje- Belgrade (latitude: 44° 49′ N), Yugoslavia over a 3 year period (1994–1996). The objective of this study was to find the optimal spatial arrangement of a maize–beans intercrop in irrigated and rainfed farming systems.

Plant arrangement patterns in an intercropping system did not significantly affect LAI values in maize compared with a sole crop, while irrigation had a greater positive influence on it. Leaf area values of beans were more sensitive to the same treatments. Microenvironmental conditions in maize–bean mixtures were more favourable for bean crop than for sole beans.

An intercropping system had a greater influence on yield components of maize. Component combination 1/2[ratio ]1/2 (maize[ratio ]bean) was most effective in all yield components of maize. Intraspecific competition appears to be more intense than interspecific competition in both crops. Yield component of bean was more sensitive to water regime of the site than to planting pattern in an intercrop. Irrigation increased all yield components of bean (especially pod number). The intercropping system decreased harvest index in both crops compared with monocrops. Maximum total grain yield was in 1994 in irrigated maize–bean intercrop 1/2[ratio ]1/2, with highest efficiency being in an intercrop in irrigation in 1995. The Land Equivalent Ratio (LER), based on grain yield, was consistently greater than 1·0 in an irrigation water regime in 1995. Proportion of maize[ratio ]bean = 1/2[ratio ]1/2 gave the highest increase of yield (LER = 1·54). Under conditions of chernozem soil type in Zemun Polje, with often-expressed dry periods, irrigation is a very important measure for increasing maize–beans intercrop productivity.

Thirty steers were used in two pen experiments (Expts 1 and 2), and 27 of these in a third (Expt 3), to quantify their responses of hay intake, rumen ammonia nitrogen (RAN) concentrations, and liveweight to inputs of rumen soluble nitrogen (urea) and rumen undegradable protein (formaldehyde-treated casein; F-casein) when added to a basal diet of low quality hays. The hays were made from unimproved native pastures typical of those grazed by cattle in the subtropics of Australia and contained 7·8 g N/kg dry matter (DM) with coefficient of organic matter digestibility of 0·503 in Expts 1 and 2, and 5·2 g N/kg DM with a digestibility range from 0·385 to 0·448 in Expt 3. The steers (15 months old) were either Brahman (B), Hereford (H) or the F1 Brahman×Hereford (BH) cross. Steers were offered supplementary minerals with the hays in each experiment. In Expt 1 (35 days) urea was sprayed on part of the hay, allowing for daily urea intakes (g/steer) of either 0, 5, 11, 16 or 26. In Expt 2 (42 days), F-casein was offered daily (g/steer) at either 0, 75, 150, 225 or 300 and in Expt 3 (56 days) discrete offerings were made of soluble casein (225 g/day), of urea (18 g/day)+F-casein (225 g/day) or of nil.

There were significant linear effects of urea intake upon hay intake and liveweight change of steers. However, B steers had smaller increases in intake and liveweight change than did H steers, and B steers did not have a linear increase in RAN concentrations with increasing urea intake as did H and BH steers. In Expt 2 there were significant linear effects of F-casein supplements on hay intake and liveweight change of steers and a significant improvement in their feed conversion ratio (i.e. DM intake: liveweight change). The B steers did not differ from H and BH steers in liveweight change but had significantly lower hay intakes and non-significantly smaller increases in RAN with increasing F-casein intake. In Expt 3, hay intake of the steers increased with soluble casein (by 16·8%) and with urea+F-casein (24·5%). Only steers given urea+F-casein had a high RAN concentration (94 mg/l) and a high liveweight gain. The B steers had a liveweight loss and a lower hay intake than H or BH steers in Expt 3 but a higher RAN concentration.

These studies have indicated the importance of the form and quantity of additional N required by cattle of differing breed types to optimize their feed intake and liveweight gain when offered low-N, low-digestible hays.

The possible impact of global rises in atmospheric CO2 concentration and temperature on the growth and development of French beans (Phaseolus vulgaris) was examined using growth cabinets. Five CO2 concentrations of 350, 450, 550, 650 and 750 vpm and five temperatures of 14·5, 15·5, 16·5, 17·5 and 18·5°C were tested using a fractional factorial design comprising nine treatment combinations of the two factors. Plants were grown under constant irradiance, common atmospheric humidities (vpd 0·5 kPa) and non-limiting supplies of water and mineral nutrients. The plant growth response was modelled by fitting polynomial response function curves to the times to first flower opening, first bean set, 50% maturity and the number and yield of beans. The effects of temperature were large and positive for most of the measured variables, whereas the effects of CO2 were small and negative or non-existent. Increased temperature substantially reduced the time to flowering and the time from bean set to 50% maturity and increased the number and yield of mature beans whereas increased CO2 concentration had little effect on plant growth except that bean yield was very slightly reduced. There was no significant evidence of interaction between the CO2 concentration effects and the temperature effects.

The time to maturity and yield of mature beans was simulated for the 2020s (2010 to 2039) and the 2050s (2040 to 2069) using the fitted polynomial models and four climate change scenarios suggested by the UK Climate Impacts Programme. These simulations showed that, depending upon the assumed scenario, the 2020s yields could rise by 39–84% and time to maturity reduce by between 6 and 15 days whereas the 2050s yields could rise by 51–118% and time to maturity reduce by between 9 and 25 days.