Field experiments to determine the optimum fertilizer treatment and ratio of wheat to chickpea in late-sown irrigated intercropped populations were done during the winter seasons of 1983–85 on sandy loam soils at the research station of the Directorate of Pulses Research, Kanpur, India. Of the three populations tested (2:2, 2:1 and 3:1 row ratios of wheat: chickpea), the 2:2 row ratio allowed more light interception and transmission to the lower canopy and gave significantly higher yield (4155 kg/ha wheat equivalent) and land equivalent ratio (LER) than the other treatments. Chickpea yields were reduced more than those of wheat under all intercropping systems and the reduction was largest at the 3:1 row ratio. Wheat (cv. Sonalika) was more productive than chickpea (cv. BG261). Application of the normally recommended rate of fertilizer to the wheat only was as effective as applying fertilizers, at the appropriate rates, to both the component crops; indicating that fertilizers applied only to wheat were adequate to meet the requirements of the associated chickpea also.

Multifactorial experiments at Rothamsted Experimental Station in two contrasting seasons, 1985/86 and 1986/87, tested the effects of treatment combinations that varied the supply of nitrogen at important stages of crop development in autumn and spring on the grain yield and nitrogen content of September- and October-sown winter wheat. Treatments that altered the nitrogen supply in autumn were an application of winter fertilizer N and sowing the wheat after rape or oats, which left different amounts of residual N. These were combined with treatments which tested the effects of 200 kg N/ha in spring applied as early or late dressings and as single or divided dressings. The effect of applying an additional 50 kg N/ha in summer was also tested in 1985/86.

In both experiments, larger yields were obtained from sowing in September than in October. The September-sown wheat grew better over winter in 1986/87 than in 1985/86 but the early advantage in size and N uptake resulted in enhanced production of straw rather than grain. Residues of N from previous crops were smaller after oats than rape in both years. This difference in soil N did not affect the over-winter growth and N uptake of the October-sown wheats. Neither this difference in residual N nor an application of fertilizer N in winter affected the yield of the following September-sown wheat in 1985/86 because autumn growth and N uptake were restricted by adverse weather. In 1986/87, however, wheat that followed oats yielded 0·42 t/ha less grain than wheat that followed rape, and the deficit in yield was removed by an application of fertilizer N equivalent to the deficit in soil N.

Yields were decreased when the spring N was applied as a delayed, single dressing in April especially if the wheat was sown in September after oats, or was not given winter N. Yields were not affected by any of the other combinations of single v. divided dressings or early v. late applications of spring N, despite these being given at very different stages of apical development.

The percentage of N in the harvested grain was greatly increased by winter applications of fertilizer N, especially to wheat grown after oats, by applying the spring N as a late, single dressing and, in 1986, by applying N in summer.

The phenotypic stability of seven Finnish and Nordic oat cultivars and 12 breeding lines developed at the Hankkija Plant Breeding Institute, Finland, was studied using the Finlay–Wilkinson regression method, Eberhart–Russell stability analysis, principal component analysis (PCA) with biplot presentation, canonical variate analysis (CVA) and Procrustes analysis. Comparison of stability analyses was based on four dissimilar growing seasons. In addition to the measurement of phenotypic stability of grain yield, the performance of 12 morpho-physiological traits was evaluated, including maturity class and structure of canopy and plant stand.

The different stability analyses examined produced uniform results and ranked the cultivars and breeding lines without major disagreements. Lines with exceptionally stable yield performance over the different growing seasons were identified. In general, there was an association of high yielding ability with poor stability. However, some cultivars deviated from this tendency and showed high grain yield production and average stability of yield performance.

Winter wheat cultivars Apollo, Hornet, Longbow and Norman were each sown at 50, 100, 200, 400, 800 and 1600 seeds/m2 in a field experiment conducted in Northern Ireland over the 1989/90 crop year. No growth regulators were applied and the wheat received 178 kgN/ha top-dressing in the spring. Hourly rainfall, windspeed and wind direction data were recorded and lodging was visually assessed from the end of May to harvest. Lodging first occurred in the 1600 seed-rate plots as the ears were emerging in early June and then progressively increased in the 800, 400 and 200 plots during June, July and August. Lodging did not occur suddenly but took several hours, with the stems first lying at an angle before lodging completely. Stem buckling or breakage did not appear to be the principal form of structural failure. The longest strawed cultivar, Longbow, lodged most severely. The shorter-strawed Norman also lodged badly in contrast with Hornet which had a similar straw length. Apollo, which was taller than Norman and Hornet and produced more ears per square metre than the other cultivars, lodged least but tended to lean at c. 30° from the vertical. Lodging occurred during or within 24 h of periods of rainfall which, in many cases, coincided with windspeeds at crop height averaging > 25 km/h and occasionally > 50 km/h. Lodging also occurred following rainfall when the windspeed did not exceed 16 km/h. The grain yield was negatively correlated with the average lodging from ear emergence to harvest, there being a 1 t/ha decline in yield for each 10% increase in average area lodged. The 50 and 100 seed-rate plots yielded 10 t/ha and had little or no lodging. The decline in yield with increased lodging and seed rate was attributed to the effect of lodging rather than to seed rate and was associated with a fall in the number of grains/ear and 1000-grain weight from 56 and 53·5 g at the lowest seed rate to 15 and 42·7 g at the highest, respectively. A comparison of the plants from lodged and unlodged plots of the 1600 and 800 seed rates, and subsequently of the 800 and 400 seed rates, indicated that at the higher seed rate, lodged plots had less fresh weight per unit area, basal internodes with smaller diameters, fewer support roots per stem, and a lower root dry weight per stem.

Grain yield of barley (Hordeum vulgare L.) in northern Syria is limited by water stress and extremes of temperature. The present study compared the grain yield of two barley cultivars, Harmal (spring type, cold-sensitive, early heading) and Arabi Aswad (winter type, cold-tolerant, medium early heading), under varying rainfall and temperature. Grain yield was obtained from three sites in northern Syria for seven seasons (1984/85 to 1990/91), resulting in 18 site × season combinations, here called environments. Multiple regression models, containing one rainfall and one temperature variable, were used to quantify yield responses to environmental fluctuations.

Total seasonal rainfall was the variable most strongly correlated with the grain yield of Harmal, accounting for 62·8% of the variance. For Arabi Aswad, rainfall from November to January gave the best fit, accounting for 61·8% of the variance. December and January rainfall had the highest contribution to the yield of both cultivars; the contribution of March rainfall tended to be negative. The overall yield response to seasonal rainfall was 11·89 kg/ha/mm for Harmal and 8·57 kg/ha/mm for Arabi Aswad; the expected grain yield at the driest site was c. 1270 kg/ha for both cultivars. The addition of a temperature variable gave a better fit, accounting for c. 80% of the variance in grain yield for both cultivars if winter rainfall was combined with number of night frosts in spring. It reduced the expected yields at the driest site to c. 986 kg/ha. Arabi Aswad had a lesser response to both rainfall and frost than Harmal.

In environments where low yields are due to both water and temperature stress, farmers are advised to grow Arabi Aswad because its lesser sensitivity to environmental fluctuations will ensure a better yield stability.

A series of 240 thin-layer drying runs carried out in 1988 and 1989 at the Scottish Centre of Agricultural Engineering were analysed to find out which factors influenced the rate of drying of grass mixtures. The grass used in the experiments was cut by hand, by a mower without conditioner or by a mower with conditioner. The experiments covered a range of air conditions from 16·0 to 40·4 °C temperature and 24·4 to 82·8% relative humidity. By fitting curves to the experimental data it was shown that the drying curves could be simulated by a two-parameter, exponential equation. Analysis of the data showed that the experimental results could be adequately represented by holding one of the parameters fixed and fitting the curves with only one parameter varying. The variable parameter, called the drying coefficient, was dependent on harvesting method and related to drying air temperature, initial moisture content and ratio of leaf area to stem area. A regression equation relating the drying coefficient to these variables for conditioned and unconditioned grass is presented.

Predictions from the regression equations indicated that the temperature of the drying air had a major effect on the drying coefficient. Both the initial moisture content of the samples and ratio of leaf to stem had a smaller influence on the coefficient over their likely range.

White clover (Trifolium repens L.) is well adapted to the cool moist climate of Atlantic Canada, where it improves digestibility and protein content in pastures, but little is known about its role in pasture stockpiled for autumn grazing in this region. The objectives of this study were to determine the effect of autumn harvest dates on dry matter yield and clover content in herbage mixtures. Two experiments conducted in Nova Scotia between 1985 and 1991 on two different soil types showed that the effects of autumn harvest dates were inconsistent from year to year. Herbage growth rates ranged from 11 to 41 kg/ha per day between early September and mid-October. Clover content was generally lower in August–early September than in November harvests and declined in subsequent years irrespective of harvest date or forage species. Kersey White and Sonja white clovers were the highest yielding cultivars. Crude protein declined in late autumn harvests whereas acid detergent fibre tended to increase, and there were differences between years. Forage quality was significantly better in tall fescue (Festuca arundinacea Schreb.) than orchardgrass (Dactylis glomerata L.)/white clover mixtures.

A long-term field experiment on permanent grass at Rothamsted (UK) was studied between 1988 and 1991 to determine the relationship between soil and plant K and to identify critical soil and plant concentrations for grass yield. Maximum dry matter yield was obtained at a soil exchangeable K concentration (Kex) of 114 mg/kg dry soil (45 μм-K in the soil solution). Grass well-supplied with K maintained an average concentration of c. 200 m м-K in the tissue water of whole shoots in spring, although individual measurements varied in the range 140–320 mм, depending largely on the soil water availability. These tissue concentrations were not exceeded in soils with Kex values up to 800 mg/kg. Yield was reduced by 60% on plots low in K (Kex in the range 60–90 mg/kg). The yield reductions were probably due to low turgor because tissue osmotic pressures were low and potassium concentrations in tissue water (which averaged 64 mм) were probably too high to disrupt the biochemical functions of K. The results suggest that there is no universal critical tissue water concentration for K in the biophysical role of turgor maintenance, as other cations and solutes are able to substitute for it. The ultimate determinant of turgor-dependent yield loss is tissue osmotic pressure. The critical tissue osmotic pressure in grass shoots in a typical season at Rothamsted was c. 400 mosm/kg. No universal critical osmotic pressure can be expected however, as this will depend on the availability of water and therefore on growing conditions.

Fungal spoilage of animal feed silage occurs frequently. In spoiled silage of sugarbeet press pulp sampled in The Netherlands during the period 1986–90, 40% of the samples were infested by Penicillium roquefortii. Other fungi of health significance included Aspergillus fumigatus (8% of all samples) and Byssochlamys spp. (4 % of all samples). P. roquefortii is also the dominant spoilage mould in maize silage. However, no PR-toxin could be detected in 25 lumps of P. roquefortii-intested maize silage, although one lump contained a fluorescent substance, with an Rff-value close to that of PR-toxin. This silage sample was not mutagenic, but had a cytotoxic effect towards Salmonella typhimurium in the Ames test. All P. roquefortii-infested lumps contained fluorescent fungal metabolites which were absent in samples taken at 5 cm distance from the corresponding lumps in the silage heaps. It is recommended that lumps of fungal-infested silage are removed before feeding the silage to cattle.

All combinations of five cutting heights (2, 4, 6, 8 and 10 cm), two rates of P application (0 and 100 kg P/ha per year) and two irrigation treatments (0 and maximum soil water deficit 35 mm) were compared on field plots sown with a mixture of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) in Wales. The cutting and P treatments were applied for 4½ years (1986–90) and the irrigation treatments for 2 years (1987 and 1988). The plots were cut at 4-week intervals from April to October each year.

Applied P and irrigation had only a small effect on the productivity and composition of the swards. The proportion of white clover in the sward was inversely related to the height of cutting, so that clover was almost eliminated by 3 years of 10 cm cutting. This reduction in clover content led to a 50% reduction in herbage yield. Close cutting increased the tiller density of ryegrass in May and June of the first harvest year, but this effect was subsequently reversed as clover competed more strongly with ryegrass under close cutting. The proportion of unsown species, predominantly Agrostis tenuis, was much higher in the third and fourth than in the first and second harvest years and was positively related to the height of cutting. Close cutting depleted soil K and soil water.

Fifteen cultivars of orchardgrass (Dactylis glomerata L.) were grown in the field at Hiroshima University, Japan, to investigate seasonal changes in leaf water relations and cell membrane stability (CMS) measured by the polyethylene glycol (PEG) test. Leaf water potential and osmotic potential were measured from August 1988 to August 1989. Solute concentration in leaf cell sap was also estimated.

Cell membrane stability increased, leaf water potential and osmotic potential decreased and turgor potential increased with decreasing environmental temperatures during autumn and winter. The significant increases observed in CMS may enable plants to tolerate freezing temperatures during winter. Decrease in leaf water potential may be a result of water-deficit effects due to soil freezing at low temperatures and the decrease in osmotic potential may help plants to maintain turgor and tolerate freezing conditions. Plants maintained higher turgor as the osmotic potential decreased to values as low as – 3·98 MPa during winter; the maintenance of turgor helps to maintain water uptake under water deficit conditions at low temperatures.

Sugar and K were the major osmotic contributors in orchardgrass leaves. Sugar and Ca concentrations increased and Mg and P concentrations decreased at cold temperatures. K concentration increased in six cultivars and decreased in nine others at cold temperatures. Sugar concentration in cell sap was negatively correlated with osmotic potential. It was concluded that seasonal changes in CMS may be mainly associated with the osmotic potential of the leaf tissues.

All combinations of five cutting heights (2, 4, 6, 8 and 10 cm) were compared, for 3 years (1986–88), on field plots sown with a mixture of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) in Wales. The plots were cut at 4-week intervals from April to October each year.

A reduction in cutting height reduced the length, width and weight of clover leaflets, petiole length, stolon diameter, the length of stolon internodes and the height of stolons above ground level, but increased the length of clover stolon/m2, the number of stolon nodes/m2 and the proportion of stolon nodes which produced branches. The latter factors out-weighed the former, leading to the inverse relationship between cutting height and the proportion of clover in the sward previously reported (Acuñia & Wilman 1993).

A reduction in cutting height reduced the following attributes of ryegrass: the height of the shoot apex, the length and width of leaf blades, sheath length, leaf extension rate, the death rate of leaves and the net gain in blade length.

Cutting height had little effect on either the thickness of clover leaflets or the rates of leaf emergence in clover and ryegrass.

The seed yields and maturity dates of an indeterminate cultivar (Lunoble) and a determinate line (CH304/70) of Lupinus albus L. were measured at three locations in France (Lusignan, Dijon and Gotheron) and at Rothamsted, UK, in 1989/90 and 1990/91. Different combinations of sowing dates, plant densities and irrigation treatments were tested at some sites.

Averaged over all sites, CH304/70 yielded more than Lunoble (3·26 v. 2·98 t/ha) but there were significant genotype × location interactions for yield and date of maturity. Both genotypes gave similar yields at the three locations in France (3·13 and 3·06 t/ha, respectively). But under the cool and wet conditions at Rothamsted, CH304/70 yielded 4·26 t/ha compared with only 202 t/ha for Lunoble. Yields of CH304/70 were more stable than those of Lunoble across locations and years; the coefficients of variation about the overall means were 14 and 22%, respectively. CH304/70 ripened up to 16 days sooner than Lunoble in France, and 6 weeks earlier than Lunoble in the cooler conditions of the UK.

In wet growing conditions (Lusignan 1989/90, Rothamsted 1990/91) Lunoble had increased vegetative growth which decreased the proportion of yield produced by mainstem pods and correspondingly increased the proportion borne on second-order branches. This continued branching also delayed harvest, especially in the UK where the crop was not harvestable until early November. In these conditions, CH304/70 outyielded Lunoble at Lusignan (3·4 v. 2·7 t/ha) and at Rothamsted (4·3 v. 2·0 t/ha) and was harvested acceptably early in mid-September. However, under warm, dry conditions, Lunoble produced only one order of branches at Gotheron and two orders at Lusignan in 1990/91. At Gotheron, both genotypes matured at the same time but CH304/70 yielded slightly better (3·1 v. 2·8 t/ha) because it produced a higher proportion of its yield on the mainstem, whereas at Lusignan, Lunoble yielded better than CH304/70 (4·1 v. 3·4 t/ha) because of extra yield from pods on second-order branches.

CH304/70 produced seeds of larger mean size and had greater stability of seed size across years and locations than Lunoble did. This was apparently the result of CH304/70's determinate structure, in which c. 75–100% of the yield was from pods on the mainstem and first-order branches, whose seeds were larger and less variable in size than those from pods on higher-order branches of indeterminates.

The development of autumn-sown genotypes with a determinate structure that combine adequate yield and early harvest under cool conditions offers the prospect of extending the geographical range of lupins, grown for grain, both to the cool regions of northern Europe and to hotter and drier regions in southern Europe where summer drought limits the yield of conventional indeterminate types.

A half-diallel design, with parents, involving a random sample of nine partially inbred (S1) lines was used to examine the genetic control of bolting in a broad-based North-West European sugarbeet breeding population. The diallel was analysed using the Hayman (1954a) and Jinks & Hayman (1953) analyses. Additive genetic effects were shown to be highly important and significant dominance effects were found. A general trend for bolting resistance to be dominant was detected but there was also evidence that the control was ambidirectional. Furthermore, the dominance effects seemed only partially effective. Some indication of epistatic effects was found, although the possibility that this was spurious, caused by failures in the genetic assumptions required by the analyses, is discussed. The genetic control of bolting in the breeding population appeared complex.

Field experiments with the potato variety Desiree at Cambridge, UK, in 1988–90 examined the effects of windrowing on the development of blemishing diseases during storage on tubers from crops grown with differing irrigation regimes and dates of defoliation and harvest. Irrigation reduced levels of silver scurf (Helminthosporium solani) at harvest in all three years and increased black dot (Colletotrichum coccodes) in one year. Early crop defoliation slightly increased silver scurf at harvest in one year only. Silver scurf developed less during storage at 3 °C than at 7 °C and disease levels on tubers after storage were related to levels present at harvest. The effects of leaving tubers for up to 6 h in a windrow at harvest on silver scurf after storage were small and inconsistent between years despite similar drying conditions. The results suggest that windrowing may be of little practical use in controlling silver scurf during storage.

An advancing and devernalizing treatment for sugarbeet seed has been developed which, in England, allows sowing to be brought forward safely by c. 10 days to around 10 March. Experiments done each year from 1988 to 1991 were used to assess the value of this change. They showed that sugar yield increased by 0·048 t/ha/day because seed advancement resulted in more rapid emergence, and by 0·042 t/ha/day as a result of earlier sowing. As an average of all appropriate data from experiments in England since the 1950s, the advantage of sowing in March is 0·035 t/ha/day. However, the actual change in sowing date which the farmer might achieve will depend on soil type and rainfall. Daily rainfall and evaporation data for eastern England in March and April were used to predict the number and distribution of available machinery work days. On this basis, the average sowing date was predicted to advance by 9 days. Thus the sugar yield improvement which could be produced by advancing and devernalizing beet seed is equivalent to 9 days at 0·035 t/ha/day, plus 0·19 t/ha, or c. 0·5 t/ha. In practice, this should translate into an increase of 0·35 t/ha, or c. 5% of the average yield.

The population dynamics of the potato tuber moth (PTM) Phthorimaea operculella (Zeller) and the influence of potato cultivar, planting date, planting depth, hilling-up, irrigation intervals and mulching on insect infestation and on the greening of tubers in the field were studied at Shambat, Khartoum North, Sudan in the 1987/88 and 1988/89 winter seasons.

The insect population initially increased slowly, then more rapidly after crop establishment and throughout the harvest period, after which it declined sharply. Tuber shape and skin characteristics had no effect on the degree of PTM infestation. Planting in the second week of November resulted in less insect damage and a significantly greater total yield compared with crops planted 3 weeks later. Greater depth of planting and more frequent hilling-up significantly lowered infestation levels and reduced the greening of tubers; for example, insect damage in early planted crops ranged from 3·3% (planting 10 cm deep and hilling-up thrice) to 16% (planting at 5 cm depth and hilling-up once).

Irrigation and mulching both significantly reduced PTM damage and the greening of tubers.

Light irrigation every 4 days and mulching with neem (Azadirachta indica) leaves during the last 4 weeks before harvest were the most effective treatments.

Significant reductions in losses inflicted by PTM and by the greening of tubers were therefore achieved by the manipulation of crop husbandry practices.

A 2-year study conducted in Salinas, California in 1989–91 showed that soil nitrate (NO3–N) concentrations were reduced by cover crops during a short winter fallow period and that this practice can be compatible with year-round vegetable crop production schedules by planting and incorporating cover crops directly on the beds into which the lettuce crop will be direct seeded in the early spring. Cover crops grown the first year were oilseed radish (Raphanus sativus cv. Renova), white senf mustard (Brassica hirta cv. Martigena), white mustard (Brassica alba), Phacelia (Phacelia tanacetifolia cv. Phaci), rye (Secale cereale cv. Merced) and annual ryegrass (Lolium multiflorum). Only phacelia and Merced rye were included in the second year. In both years, all of the cover crops depleted soil NO3-N and soil moisture relative to the fallow control. Estimates of cover crop root length, based on core sampling to 60 cm soil depth, averaged 18800 m/m2 after 17 weeks of growth the first year and 12500 m/m2 after 13 weeks of growth the second year. Above-ground dry matter production averaged 449 g/m2 (12·8 g N/m2) the first year and 161 g/m2 (61 g N/m2) during a shorter growing period and under the more adverse growing conditions of the second year. Following cover crop incorporation with a rotary tiller, soil ammonium (NH4-N), N03-N and net mineralizable N (anaerobic incubation) peaked after c. 1 week, then gradually declined for 1 month. Cover-cropped plots sustained higher net mineralizable N levels than the fallow control after incorporation. Nitrate concentrations after spring rains were lower in soils left fallow during winter. The subsequent lettuce crop was not affected by cover crop treatment.

The response of groundnut to different amounts of irrigation water and the effect of irrigation on the occurrence of chlorosis during the establishment period of the crop were studied in south-west Cyprus in 1984–88. The irrigation requirement of groundnut for the entire growing season was found to be 480 mm. Under-irrigation resulted in a soil water deficit and reduced production. Application of water in excess of requirement also reduced yield. Daily evapotranspiration under optimum soil moisture conditions increased from 1·5–2·0 mm at the beginning of the growing season to 7·0–7·5 mm at full crop development; it then decreased to 2·0–3·0 mm by the end of the season. In soils of low CaCO3 content, neither frequent water application nor over-irrigation during the crop establishment period caused any chlorotic symptoms or affected yield.