Ten daylit, controlled-environment cabinets were used to investigate the possible impacts of global rises in atmospheric CO2 concentration and temperature on beetroot (Beta vulgaris L.), carrot (Daucus carota L.) and bulb onion (Allium cepa L.) plants. Their responses to CO2 concentrations of 350, 450, 550, 650 and 750 vpm and temperatures of 12, 13·5, 15, 16·5 and 18°C were examined by using a fractional factorial design for the two treatment factors. Use of the daylit cabinets allowed the plants to be grown in natural light, common atmospheric humidities (vpd 0·7 kPa) and non-limiting supplies of water and mineral nutrients.

Polynomial models were used to summarize the whole plant dry weight and fresh weight yield responses and to indicate the potential impact of climate change. Additionally, the models were used to generate predictions of the percentage change in whole plant dry weight and plant fresh weight yield for the years 2025 and 2050 relative to 1992. Baseline values of 350 vpm for CO2 and a mean temperature of 13·5°C for 1992 together with forecast CO2 values of 407 and 442 vpm and temperature increases of 0·7 and 1·1 C for 2025 and 2050 respectively were used. For 2025, fresh weight yield changes of +19%, +9% and +13% were obtained for beetroot, carrot and onion crops respectively, while for 2050 the respective changes were +32%, +13% and +21%.

Measurements of the ratio of the maximum diameter of the bulb to the minimum diameter of the neck for onions showed that there was little or no influence of CO2, whereas the effect of temperature was substantial. Bulbing was accelerated by high temperature and was greatly delayed at low temperature. At temperatures <15°C, the delays to bulbing resulted in the development of undesirable, thick-necked onions which tended to remain green with erect leaves. These results suggest, therefore, that a warmer climate will be advantageous for the commercial production of bulb onions in Britain.

Chicory (Cichorium intybus) is perhaps best known for the extract of its roots used as an ingredient in ‘coffee substitute’ beverages. It is less well known as a grazed forage for ruminants. Thomas et al. (1952) reported the high content of some major and minor trace minerals in chicory grown in the UK, and commented on its use in pasture mixtures as a source of these minerals. Chicory was first mentioned in New Zealand (NZ) literature as an animal forage by Cockayne (1915), but a long period then elapsed before Lancashire (1978) reported its excellent value for forage production under rotational grazing in dry summer conditions. Plant selection then followed and the cultivar ‘Grasslands Puna’ was approved for commercial release as a grazed forage plant in 1985 (Rumball 1986). The use of Puna chicory has now spread throughout NZ and the variety is also being used commercially in Australia, North America and South America and is being evaluated in parts of Europe and Asia (W. Green, personal communication). Chicory is a herb, whereas other temperate forages used for ruminant production are either grasses or legumes. This paper reviews work on the chemical composition, nutritive value and feeding value of chicory relative to perennial ryegrass (Lolium perenne) and to red clover (Trifolium pratense), a legume that, like chicory, is used as a forage for dry summer conditions. Throughout this paper, feeding value is defined as the animal production response to grazing a forage under unrestricted conditions (Ulyatt 1973), with its components being voluntary feed intake (VFI), the digestive process and the efficiency of utilization of digested nutrients; the latter two comprise nutritive value/dry matter (DM) eaten.

Increasing the efficiency with which crops use supplied nitrogen (N) can minimize the impact on the environment. In the growing seasons 1990/91 to 1992/93, the effects of different cropping systems on yield, N uptake by the grain and apparent N-use efficiency (NUE) of the grain of winter wheat and winter barley were investigated in a factorial field experiment at Hohenschulen Experimental Station near Kiel in NW Germany. The crop rotation was oilseed rape–winter wheat–winter barley, and soil tillage (conservation tillage without ploughing, conventional tillage), application of pig slurry (none, autumn, spring, autumn+spring), mineral N fertilization (0–240 kg N ha−1) and application of fungicides (none, applications against pathogens of the stems, leaves and ears) were all varied. Each year, the treatments were applied to all three crops of the rotation and were located on the same plots.

Averaged over all factors, wheat yield was >7 t ha−1 dry matter in all years and N uptake of the harvested grain varied between 140 and 168 kg N ha−1. Pig slurry application in autumn increased grain yield and N uptake more than spring slurry in two out of three years. Mineral N unfertilized wheat yielded only 5·3–6·3 t ha−1 depending on the year, mineral N fertilization increased wheat yield up to 8 t ha−1. Barley yield was lower than wheat yield, ranging from 4·5 t ha−1 in 1993 to 6·3 t ha−1 in 1992. Unlike wheat, spring slurry N affected barley yield and N uptake more than autumn slurry.

Wheat apparently utilized 12–21% and barley up to 13% of the applied slurry N for its grain development. In 1991, the highest apparent slurry N-use efficiency (SNUE) of wheat and barley occurred after the late spring slurry application. However, in the following years, autumn SNUE of wheat was similar to (1992) or higher than (1993) spring SNUE, presumably because of vigorous tiller growth before winter. Additionally applied mineral fertilizer N decreased SNUE.

Apparent mineral fertilizer N-use efficiency (FNUE) was higher than SNUE and ranged in wheat from 40 to 59% and in barley between 19 and 37% of the applied mineral fertilizer N. FNUE decreased with increasing N fertilization.

To improve the N-use efficiency of both slurry N and mineral fertilizer N, more information is needed about the combined use of both N sources, with special emphasis on split applications of slurry as is common practice for mineral N fertilizer.

Much of the error in field experiments comes from environmental differences, which traditional methods (e.g. blocks or rows and columns) sometimes fail to control, especially if the fertility pattern is complex or unexpected. In 1937 Papadakis proposed an alternative approach in which the performance of each plot was judged by that of its neighbours. If a plot was situated in an area of generally high cropping, its own high crop was partly discounted but if surrounding plots were yielding poorly, it was given special weight. Adjustment was by the analysis of covariance. The method has not been much used, partly because it still lacks a mathematical basis and partly because it is suspected of bias in the estimation of contrasts between treatments.

It has been studied here by simulation, i.e. bodies of data have been generated on the computer with known characteristics and then analysed by Papadakis's method to see if a correct answer was returned. Also, an improvement in the covariate is suggested and an iterative procedure developed to ensure more consistent results.

It emerges that the suspicion of bias was unjustified. Also, the method can be extremely effective in reducing experimental error. In all its variant forms it has difficulty with outside plots, and for that reason is more effective on compact areas than on strips. Also, interference between plots is especially serious, because the neighbours affected are those needed to form the adjusting covariate. Discontinuities arising from past use of the land can cause problems but a method is suggested for minimizing their effect.

Field experiments, conducted during 1992/93 and 1993/94 at the Indian Agricultural Research Institute, New Delhi, indicated that dicyandiamide (DCD) blended with urea produced taller wheat plants with more grains ear−1 and thus higher grain and straw yields than following urea alone. The economic optimum dose (EOD) of nitrogen was estimated to be 73 kg N ha−1 for DCD-blended urea (8[ratio ]2) and 84 kg N ha−1 for urea alone, and the grain kg−1 N of the crop at the EOD was calculated to be 23 kg grain kg−1 N with DCD-blended urea and 18·6 kg grain kg−1 N with urea alone. Thus DCD-blended urea produced more grain using less nitrogen than urea alone. The nitrogen requirement for a targeted yield of 4 t ha−1 was also less when using DCD-blended urea (29 kg N ha−1) than when using urea alone (38 kg N ha−1). The DCD-blended urea resulted in higher N, P and K uptakes, agronomic efficiency and apparent recovery of nitrogen than urea alone.

Latin square and near-Latin square designs are valuable row-and-column designs for crop research but the practical size range of such designs is severely limited. Semi-Latin square designs extend this range but not all semi-Latin squares are suitable for experimental designs. Trojan square designs are a special class of optimal semi-Latin squares that generalizes the class of Latin square designs. The construction of Trojan squares both for unstructured and for factorial treatment sets is discussed and the utility of Trojan square designs for practical crop research is demonstrated. The corpus of available designs is further extended by a discussion of incomplete Trojan square designs obtained by omitting one main row or one main column from a complete Trojan square design. Some advantages of Trojan square and incomplete Trojan square designs for crop research are discussed and some suggestions for further design research are made.

Root branching and architecture play a significant role in water and nutrient uptake, but description of these parameters has not been easy due to the difficulty of observing roots in their natural arrangement. Fractal geometry offers a novel method for studying the branching patterns of roots. Plants of ten diverse sorghum (Sorghum bicolor (L.) Moench) genotypes (five of African origin, three of US origin and two hybrids composed of African×US lines) were grown in root boxes containing 80% sand and 20% fine-textured Sharpsburg silty clay loam topsoil. The root fractal dimension (D) and abundance (log K) were determined at nine regions within the profile. Roots were washed free of growth media and photographic slides were taken of each region. Values of D and log K were determined by projecting photographs onto grids of progressively increasing sizes. The number of intersects was regressed on log grid size. Differences in D were found among genotypes (1·44[les ]D[les ]1·89) suggesting that these sorghum genotypes may be associated with greater root branching patterns. Greater fractal dimension (branching) and abundance values occurred in the 0–35 and 35–70 cm depths of the soil profile within the root box, indicating a greater root distribution in that part of the profile. Significant differences were also noted in branching patterns for sorghum genotypes derived from different sources. In general, the African sorghums were more branched and deeper rooted than the US-derived genotypes. Results indicated that fractal dimension can be used for the description of sorghum root system morphology and provides a good measure of branching patterns which can be distinguished.

The results of field experiments in 1983/84 and 1984/85 were used to test the hypotheses (i) that cultivars and management systems which result in high biomass of winter barley will also produce high grain yield and (ii) that greater uniformity of tiller and ear size is associated with greater yield. In a set of cultivars, grain yield per plant was significantly correlated with biomass per plant despite no correlation with any individual yield component. Biomass per shoot was significantly correlated with grain yield per shoot. Treatments to increase shoot uniformity (the mass of individual tillers relative to that of the main stem) generally increased biomass per shoot and grain yield per shoot. The re-examination of data in the literature where yield and biomass were available confirmed the association of biomass and grain yield both on a per plant and per shoot basis. It is argued that harvest index is not a character which can be easily targeted for manipulation by growers, whereas crop management systems to increase biomass should be easier to specify.

Three white clover cultivars of differing geographical origin, namely AberHerald, Grasslands Huia and Sandra, were grown in binary mixtures with perennial ryegrass (cv. Preference) for a period of 3 years at Uppsala (59° 49′ N, 17° 39′ E) where the length of the main growing season is c. 200 days. Changes in growing point numbers, stolon length and stolon weight from autumn until late spring were followed by four to six destructive harvests each season. Changes in carbohydrate content (starch and water-soluble carbohydrates) were also determined on six or seven occasions during the same time. Cold hardening and dehardening were followed by artificial freezing tests on stolons removed from the plots on seven occasions during the last study season. The rate of node production was followed in the last spring. Temperatures in the stolon environment were recorded during the last two study seasons.

All cultivars suffered a loss of stolon length during the winters, with Huia being most affected. The extent of recovery during spring varied between years. Late spring frosts checked the growth of both AberHerald and Huia more than that of Sandra. The accumulation of starch appeared to depend on autumn temperatures and there was a decline in starch content during the winter. Sandra maintained a higher content of water-soluble carbohydrates during the winter and the spring than the other cultivars. Sandra also achieved a higher degree of freezing tolerance and dehardened later than both AberHerald and Huia. However, temperatures in the stolon environment always exceeded the degree of freezing tolerance attained irrespective of cultivar.

It is concluded that the accumulation and utilization of non-structural carbohydrates are important in determining the extent to which a white clover cultivar survives the winter and spring in a harsh climate. Freezing tolerance per se does not seem to be the most limiting trait, but in a climate where frequent spring frosts occur, a late dehardening seems to be valuable.

Amounts of spring nitrogen (N) fertilizer (0–240 kg/ha), combined with three timing treatments (single, divided early or divided late), were tested at 14 sites in England and Wales between 1984 and 1988 to determine the optimum fertilizer N requirement for winter oats. The trials were superimposed on commercial crops of the cultivars Pennal (9 sites) or Peniarth (5 sites). Optimum amounts of N ranged from nil to 202 kg/ha (mean 119) and optimum yields varied between 5·8 and 9·9 t/ha (mean 7·3). Much (c. 60%) of the inter-site variation in N optimum was explained by differences in soil N supply, as indicated by N offtake in the grain at nil applied N. Mean yield differences between single and early (+0·08 t/ha) or late (−0·04 t/ha) divided dressings were slight, although significant (P<0·05) but inconsistent yield effects were obtained from early N at two sites and late N at three sites.

Lodging occurred at 11 of the 12 sites where lodging scores were recorded and always increased significantly (P<0·05) with applied N. The amount of crop lodging at N optimum was, on an area basis, <50% at nine of the sites. The overall extent of site lodging was also influenced by soil N fertility and hence inversely related to N optimum. However, multiple regression, using site lodging as well as soil N supply, only accounted for slightly more (65%) of the variation in N optimum, which suggests that lodging was not a major limiting factor. Lodging was unexpectedly less from early N (mean 43%), but more from late N (53%) divided dressings, compared with a single N dressing (49%). Early N reduced lodging significantly (P<0·05) at four sites, although the actual reduction was only large at one site where early N also increased yield significantly (+0·57 t/ha).

Grain N concentrations increased significantly (P<0·05) with applied N, on average by 0·12% per 40 kg/ha N increment. Timing effects on grain N concentration were very small, with mean values of 1·94, 1·91 and 1·96%N respectively from single, early and late divided dressings. Apparent recovery in grain of fertilizer N at the optimum amount ranged from 13 to 57% (mean 37), with better N recovery at the more yield-responsive sites. Changes in mean grain weight due to the amount and timing of fertilizer N were small, with an average reduction of 0·6 mg/grain per 40 kg/ha N applied. The adverse effects of N fertilizer on grain quality were slight and unlikely to have commercial significance. The agronomic implications of these results on the N fertilization of winter oats are discussed.

Nitrate leaching losses from intensively managed monoculture grass and grass–clover pastures were measured during 1994–96 at a long-term experimental farm in south-west Scotland. Field-size lysimeter plots were established in 1993 on the existing pastures on a silty clay loam non-calcareous gley. No fertilizer-N was applied to the grass–clover, while the monoculture grass was fertilized with c. 240 kg N ha−1 year−1, but both swards received 2–3 cattle slurry applications annually (120–390 kg total N ha−1 year−1). The pastures supported 2–3 cuts for silage conservation, and were grazed by dairy cattle and stocked with sheep during the winter months.

Initially, leachate nitrate concentrations from the fertilized grass were considerably larger than those from the clover-based pasture, but became similar with time. The annual nitrate leaching losses from the grass–clover (24–38 kg NO3-N ha−1) were less than that from the monoculture grass (30–45 kg NO3-N ha−1), but the differences were not large considering the additional fertilizer-N applied to the latter treatment. Results also suggested that greater leaching losses occur during a warmer, drier year, compared to a cooler, wetter year, regardless of the source of N-input.

To date, little molecular genetic research has been conducted in Lolium and the current study is the first investigation of diversity in ribosomal DNA (rDNA) among perennial ryegrass cultivars. Ribosomal DNA probes derived from the intergenic spacer (IGS–M) and transcribed (COD–M) regions of mustard (Sinapis alba) were used to examine 35 perennial ryegrass (L. perenne L.) cultivars for genetic diversity using RFLP methodology. Analysis of digested genomic DNA on Southern blots revealed only 10 cultivars with unique RFLP patterns. Genetic diversity was exclusively associated with the IGS–M probe, as the cultivars were all indistinguishable when examined with the COD–M probe. This low incidence of distinctions was not expected, given that the 35 cultivars were known genetically distinct entities, representing the very wide range of the major phenotypic and physiological characteristics present in commercial stocks. Furthermore, the forage cultivars were proportionately less polymorphic in comparison to the amenity cultivars. This was also unexpected as amenity cultivars are recognized as a more closely clustered group than the forage cultivars, based on morphological characteristics. The potential use of rDNA for assessing cultivar diversity and breeding histories in perennial ryegrass is considered.

In a trial over three successive seasons, the yields of winter barley crops were mapped on a 6 ha field, the soils of which had been mapped according to a system of simple units corresponding to soil series as defined by the Soil Survey of England and Wales. Significant yield variation was explained by differences between soil map units, and the interaction with differences between seasons. The physical properties of the soil series and the potential soil moisture deficits in the three seasons suggested that moisture differences between the soils accounted for much of the observed differences in yield. The implications of these results for crop management in response to within-field variability are discussed.

A series of experiments investigating the interactive effects of light and temperature on vegetative growth, earliness, fruiting, yield and fibre properties in three cultivars of cotton, was undertaken in growth rooms. Two constant day/night temperature regimes with a difference of 4 °C (30/20 and 26/16·5 °C) were used throughout the growing season in combination with two light intensities (75 and 52·5 W m−2).

The results showed that significant interactions occurred for most of the characters studied. Although the development of leaf area was mainly temperature-dependent, plants at harvest had a larger leaf area when high temperature was combined with low rather than with high light intensity. Leaf area was least in the low temperature–low light regime. However, the plants grown under the high temperature–low light combination weighed the least.

Variations in the number of nodes and internode length were largely dependent on temperature rather than light. Light did, however, affect the numbers of branches, sympodia and monopodia. The first two of these were highest in the high light–high temperature regime and the third in the low light–low temperature regime.

All other characters, except time to certain developmental stages and fibre length, were reduced at the lower light intensity. Variation in temperature modified the light effect and vice versa, in a character-dependent manner. More specifically, square and boll dry weights, as well as seed cotton yield per plant, were highest in high light combined with low temperature, where the most and heaviest bolls were produced. But flower production was favoured by high light and high temperature, suggesting increased boll retention at low temperature, especially when combined with low light. Low temperature and high light also maximized lint percentage.

Fibres were shortest in the high temperature–high light regime, where fibre strength, micronaire index and maturity ratio were at a maximum. However, the finest and the most uniform fibres were produced when high light was combined with low temperature.

Cultivar differences were significant mainly in leaf area and dry matter production at flowering.

The consequences of sowing seed of burr medic (Medicago polymorpha) cultivars Circle Valley and Serena that was either free of or infected to different extents with alfalfa mosaic virus (AMV) was studied in mixed species pasture swards that regenerated annually. The swards were grazed by sheep and the predominant plant species in them were burr medic and capeweed (Arctotheca calendula). Serena matured earlier and was more tolerant of AMV infection than Circle Valley. Each year, seed-infected medic plants were the source for virus spread by aphids to healthy medic plants. When the extent of infection was determined in the fourth to sixth growing seasons, the amount of virus spread in the medic component of the swards varied between seasons. Final infection in plots originally sown with infected seed ranged from 47 to 93% for Serena and from 25 to 79% for Circle Valley. Viral seed transmission rates in medic seed produced each year by these plots ranged from 19 to 31% with Serena and from 3 to 7% with Circle Valley. Final percentage infection within swards originally sown with healthy seed (control plots) was smaller regardless of cultivar (0·1–7%) as were transmission rates in their harvested seed (0–0·6%).

AMV infection of the burr medic in regenerated plots originally sown with Circle Valley seed diminished medic seed yields, thereby decreasing the proportion of medic in the seed bank. This decreased germination of medic but increased germination of capeweed. In control plots, plant densities were up to 36% greater in the medic and 52% smaller in the capeweed components than in plots originally sown with infected Circle Valley seed. In plots containing Serena there was a smaller decrease in medic seed yields due to AMV infection, so the impact on germination was less. In the fourth to sixth years from sowing, when yields were determined at different times after grazing ceased, there was either a small decrease (up to 8%) or no significant decrease in overall herbage yields due to infection with AMV. However, in plots originally sown with infected Circle Valley seed, the balance of medic to capeweed was altered in favour of capeweed, sometimes dramatically so (e.g. capeweed content increased from 19 to 45% in the fourth year from sowing). In contrast, by the end of the growing season the balance of medic to capeweed was little altered by the presence of the virus in plots containing Serena. Thus, infection with this insidious virus disease substantially diminished the ability of Circle Valley but not Serena medic to compete with other species such as capeweed in self-regenerated, mixed species pasture swards. It did this both directly by decreasing the competitive ability of the medic plants that became infected during the growing season, and indirectly via seed production and the seed bank, by altering the proportions in which the species germinated.

Guinea grass (Andropogon gayanus Kunth cv. Bisquamulatus) and Buffel grass (Cenchrus ciliaris L. cv. Biloela) are grown as temporary fodder crops in the Sahelo-Sudanese region of Africa. Differences in their responses to drought conditions may be important in optimizing cattle feeding programmes in integrated farming systems. An experiment conducted in a wind tunnel equipped with a tank forming a weighable lysimeter compared net photosynthesis (A), stomatal conductance (gs) and leaf water potential (Ψ leaf) of both species in a mixed sward during three simulated environmental conditions: (1) rainy season, (2) drought period within the rainy season and (3) dry season.

With a soil water reserve (SWR in % volume) of 8% during the drought period and the dry season, the Ψ leaf and A parameters were significantly lower (P<0·001) when compared to those recorded with a SWR of 32% in the rainy season. Mean gs values were significantly different during each environmental condition (P<0·001). No significant difference (P>0·05) was found in gs and A between the two species during the rainy and the dry season or during a diurnal cycle, although a significant difference (P<0·05) in Ψ leaf existed between the species during the dry season. During this season, Guinea grass was dormant while Buffel grass was growing slowly.

When the drought period was imposed during the rainy season (SWR declined from 25 to 5%), A was reduced from 19·8 to 7·7 μmol m−2 s−1 for Guinea grass and from 16·8 to 3·7 for Buffel grass. Ψ leaf in both species dropped below −2 MPa while gs declined slowly from 0·70–0·80 to 0·55–0·60 cm s−1. A was significantly higher (P<0·05) in Guinea grass during the last days of the drying cycle, but declined rapidly when drought was extended up to the wilting point. Two days after rewatering, all the parameters of both plants were restored to previous levels.

It is concluded that Guinea grass was as drought-resistant as Buffel grass and that no competition for water existed between the species in the mixed sward. The study also gives relationships between the physiological parameters of both species and the soil water content during a drying cycle.

The commercial future of Linum usitatissimum is intrinsically linked to its cultivation as a dual-purpose crop for producing increased seed and fibre yields. The present study evaluates 36 F1 crosses derived from nine linseed/flax accessions for their potential as dual-purpose cultivars and/or their suitability for extracting new recombinants producing high seed yield as well as increased fibre output. The quantitative analysis indicated that variation between the F1 families is largely but not exclusively due to the additive and non-additive (dominance) effects of genes. Dominance is high for plant height (H1), height at maturity (HMT), number of branches (NBr) and seed weight (SdWt) while 100 seed weight (Wt100) displays no dominance at all. The repeatability estimates representing the heritability of each trait, vary from low (0·20) for number of branches (NBr) to high (0·71) for height at flowering time (HFT). The dual-purpose traits such as seed weight (SdWt) and straw weight (StWt) were only moderately inherited while flowering time (FT) and various heights were rather highly heritable. A moderate and positive correlation (r=0·57) between StWt and SdWt, and a completely independent inheritance of Wt100 suggested that there are good chances of combining these traits into a single genotype. The phenotypic performance of the crosses also confirmed this trend and at least four crosses showed superior performance for both SdWt and StWt compared to their parental lines. All these crosses involved a linseed line (B3) as a common parent and the second parent was either another linseed line (A1 and A3) or a flax accession (K3 and L2); none of the flax×flax crosses showed good potential for seed yield. While all four crosses possess the potential to become highly productive, dual-purpose, hybrid varieties, the extraction of desirable inbred lines from them, however, may prove difficult because the superior performance of the hybrids seems largely due to strong unidirectional dominance and high SCA effects.

In parts of peninsular India, sorghum (Sorghum bicolor L.) is grown during the dry season using water stored in the root zone. The optimum application of nitrogen is difficult to assess because no comprehensive model exists for the interaction of water and N. To explore this system as a basis for modelling in the first instance and ultimately for better management, sorghum (cv. SPH–280) was grown in the post-rainy season at ICRISAT (Andhra Pradesh, India) with and without irrigation and at six rates of nitrogen from zero to 150 kg/ha applied before sowing. The biomass of top components was measured weekly and of roots every 2 weeks. Interception of solar radiation was monitored continuously in all treatments.

Leaf expansion was strongly influenced both by water and by N, whereas specific leaf area was almost independent of treatment. In the irrigated treatment, the Biomass Radiation Coefficient (e) for the main growth period was almost independent of N application at 1·3–1·4 g/MJ and was also independent of leaf N. In consequence, the main source of differences in yield was a decrease in radiation interception with decreasing N. In contrast, without irrigation, biomass, yield, e and leaf N were all maximal at 60 kg/ha N.

At 33 days after emergence (DAE), root mass was almost independent of N whether water had been applied or not, but was somewhat smaller with irrigation. Later, root, leaf, and panicle mass all responded to N and to water, but stem mass was unresponsive to N with irrigation. There was evidence of translocation from stem to grain in most treatments. With irrigation, a maximum grain yield of 4·8 t/ha was obtained at 150 kg/ha N and without irrigation the maximum was 3·2 t/ha at 90 kg/ha.

Nitrate leaching was measured over a 3-year period from rotationally grazed perennial ryegrass (Lolium perenne L.) pasture receiving 200 kg fertilizer-N/ha and from similarly grazed ryegrass/white clover (Trifolium repens L.) pasture that received no N fertilizer. The results are discussed together with those from the same plots in the preceding 3 years when they were stocked continuously. Under both managements, the numbers of grazing sheep were adjusted on the basis of the quantity of herbage available on the plots. During the whole 6 years, mean nitrate concentrations in soil water collected by porous cup samplers remained below the European Union limit of 11·3 mg N/l except for the fertilized grass plots in year 5 of the study. Quantities of nitrate leached ranged from 6 to 34 kg/ha per year from the grass/clover plots and 2·46 kg/ha from the fertilized plots. Leaching losses from both types of pasture were positively correlated with the numbers of lamb grazing days in the later part of the grazing season. This relationship and the high spatial variability associated with the measurements indicated that N derived from excreta was the main source of leached nitrate. It was concluded that, where pastures of equal productivity are compared, similar quantities of N are likely to be leached from grass/clover swards as from grass swards receiving N fertilizer.

In the context of EEC agricultural policy, the efficient production of sunflower (Helianthus annuus L.) requires the development of a wider range of crop management schemes than were used previously. Five different management options were applied to sunflower over a period of 10 years (1984–94) on a deep silty clay soil at Auzeville, near Toulouse, south-western France, combining different levels of crop density, N fertilization and supplementary irrigation. The effectiveness of these practices was evaluated on the basis of grain yield, oil production, amount of disease infection, N leaching, soil water deficit and economic return, using both experimental values and simulations with the epic-phase model.

Grain yield ranged from 1 t/ha (with severe disease incidence) to 4 t/ha (no diseases, full irrigation). There was no evidence of higher yield variability between years for low-input cropping systems managed without irrigation.

In the deep soils of Auzeville, c.100 mm of irrigation, split into two or three applications around flowering, appeared to be a good strategy for maximizing irrigation efficiency. Limiting leaf area expansion under rainfed management, by reducing crop density and N fertilization, limited stem infection frequency by Phomopsis helianthi and delayed soil water depletion, thus maximizing grain yield. Oil concentration was generally higher under full irrigation, but high values were also observed under rainfed conditions provided that a suitable genotype was used. The annual amount of N leaching, simulated by epic-phase, ranged from 17 to 40 kg/ha depending on N amount and irrigation volume. Under the current conditions of the Common Agricultural Policy, low-input and rainfed management appeared to be the most profitable strategy for the deep soils of south-western France.