Experiments were conducted on sandy loam soils at Cambridge University Farm over the period 1989–99 to examine the effects of irrigation regime and variety on water uptake (WU) in potatoes. Unirrigated crops extracted water from considerable distances ahead of the rooting front but frequently watered crops took up water from depths shallower than the current depth of rooting. There was an increase in the extraction of soil water at depth if crops were irrigated less frequently at moderate (i.e. 40 mm) soil moisture deficits (SMD). The SMD measured at different positions across the ridge always differed and the relationship changed during the season. This is of concern since most reports on water use in potatoes are based on a single measurement position for the neutron probe in the centre of the ridge and this location over-estimates crop water use. Crops grown on the flat had a more uniform extraction of soil water across the row width than crops grown in ridges but there was no evidence that having one part of the rooting system drier than another affected overall crop water use. Once rooting systems were established to considerable depth, WU continued from deeper roots even though upper horizons were periodically re-wetted by irrigation. For this reason, it proved impossible to relate WU to rooting density in specific horizons over the course of the season. Only early in the season did the proportion of total WU correspond reasonably closely with the proportion of total root length in each horizon. It appeared that the pattern and extent of soil drying created by a crop changes the horizons where water is extracted at different growth stages and the relative rooting density in a particular horizon is not a good indicator of the potential to take up water from that depth. Although rooting density decreased rapidly with increasing depth, roots deeper in the profile contributed a considerable component of total crop water requirement irrespective of the water status of horizons closer to the soil surface.

A series of close relationships were established between the ratio of actual : potential evapotranspiration and SMD for different daily evaporative rates. These showed that there was a limiting deficit at which the ratio of actual : potential evapotranspiration decreased rapidly with increasing SMD and this limiting deficit was inversely related to daily evapotranspiration rate. However, even at small SMDs, as daily evapotranspiration rate increased there was a significant, slow decrease in actual : potential evapotranspiration ratio. In order to maintain potential evapotranspiration rates in conditions of extreme demand in the UK (e.g. 5–7 mm/day), crops need to be maintained at <25 mm deficit but allowable deficits can be increased as demand moderates.

Increasing crop competitiveness using higher seeding rates is a possible technique for weed management in low input and organic farming systems or when herbicide resistance develops in weeds. A range of wheat seeding rates were sown and resulted in crop densities between 50–400 plants/m2 (current recommendations are 100–150 plants/m2) in the presence and absence of annual ryegrass (Lolium rigidum Gaud.) in three wheat cultivars at nine experiments in southern Australia. Wheat densities of at least 200 plants/m2 were required to suppress L. rigidum and to a lesser extent increase crop yield across a wide range of environments (seasonal rainfall between 200–420 mm) and weed densities (50–450 L. rigidum plants/m2). Doubling crop density of all cultivars from 100 to 200 plants/m2 halved L. rigidum dry weight (averaged over all experiments) from 100 g/m2 to about 50 g/m2. Higher crop densities gave diminishing marginal reductions in weed biomass, while cultivar differences in weed suppression were small. Grain yields ranged from 0·5 t/ha to over 5 t/ha depending on site and season. Maximum yields in the weed-free plots (averaged over environments and cultivars) were at 200 crop plants/m2, and yield declined only slightly by 4–5% at densities up to 425 plants/m2. In the weedy plots grain yield continued to increase up to the highest density but at a slower rate. The percentage yield loss from weed competition was of a smaller magnitude than the suppression of L. rigidum by wheat. For example, 100 wheat plants/m2 led to an average 23% yield loss compared with 17% at 200 plants/m2, and the probability of reduced crop grain size and increased proportion of small seeds was negligible at these densities. Cultivar differences in yield loss from weed competition were small compared with differences due to crop density. Adoption of higher wheat seed rates as part of integrated weed management is now strongly promoted to farmers.

Seven genetically diverse pepper inbred lines were crossed in a half diallel to evaluate the performance of hybrids and determine heterosis over mid-parent, high-parent and standard control for various characteristics. The study was undertaken in the field and greenhouse using a randomized complete block design with three replications during 2001/02. Hybrids generally showed good overall performance for most of the characteristics compared with the inbred lines. Three of the 21 hybrids significantly out-yielded the standard control (Bakko Local). Five of the inbred lines and all the hybrids were earlier to flower and mature compared with the control. Substantial mid-parent (MPH), high-parent (HPH) and standard (SH) heterosis were observed for the majority of characteristics studied. Mean MPH and SH were high and positive for fruit yield, plant height, fruit diameter, fruit weight, pericarp thickness and fruit number per plant. High positive HPH was observed in fruit yield per plant and plant height. For days to flowering, days to maturity and fruit maturation period, the overall mean MPH, HPH and SH were negative. It was concluded that pepper hybrids of higher yield potential, good fruit characteristics and early maturation can be developed from appropriate parents.

The study reported examines the spectral specific responses of adult insect pests of mushroom (Agaricus bisporus (Lange) Imbach) cultivation to light traps and the potential for use of light trapping as a pest management tool within commercial mushroom production. Lycoriella ingenua (Dufour) (Diptera: Sciaridae) and Megaselia halterata (Wood) (Diptera: Phoridae) were the principal insect pests at the experimental site. Adult L. ingenua and M. halterata were positively phototactic and relatively high numbers were attracted to relatively low light emissions from light trap sources of differing wavelengths. Yellow sticky traps at a height of 1·7 m collected more flies of both species than traps located at crop height (0·6 m). Adult female L. ingenua were more numerous than males in all trap types suggesting that they were more active fliers than male counterparts. Numbers of females recorded in light traps greatly exceeded those in yellow sticky traps, indicating greater photo-responsiveness. Light wavelengths between 300–650 nm attracted greater numbers of adult L. ingenua than wavelengths exceeding 700 nm. This species was present throughout the year but was most abundant between May and December. Adult M. halterata were less numerous than adult L. ingenua in all trap types and particularly on yellow sticky traps at crop level. The lower disparity between numbers of adult M. halterata on light traps and yellow sticky traps suggests that adults of this species are not as photosensitive as adult L. ingenua. The observed response of adult M. halterata to light sources of different wavelengths was variable within the range 300–>700 nm. Adult M. halterata were most abundant between June and November.

Selection for specific adaptation in a breeding programme may be required when significant genotype×environment (G×E) interaction occurs within a target production region. Knowledge of the key stress factors underlying the G×E interaction permits delineating a production region into homogeneous zones for the purpose of recommending specific varieties. Twenty-eight cowpea genotypes were evaluated in 2002 and 2003 at four locations in the Guinea and Sudan savannah zones of Ghana, to assess grain yield stability and its relationship with intensity of stress in each production environment. Data were analysed in a year-location cross-classification, producing eight environments. Significant variations were observed between the genotypes for grain yield and grain yield components, biomass production, days to maturity, and resistance to Striga, pod-sucking bugs, and bacterial blight severity. Across environments, stress intensity (in terms of grain yield) was negatively correlated with the genotypic and error variances but positively correlated with the phenotypic, genotypic and experimental coefficients of variation. Stress intensity was also negatively correlated with heritability for grain yield. Genotypic correlations for grain yield between locations were moderate to high. The b-value as a measure of yield stability showed positive correlations with mean yield over all environments, and also with average yield in each of the three most favourable locations. In the least favourable location, the b-value showed a weak inverse relationship (P=0·10) with grain yield. Although direct selection for grain yield was considered superior in the target environments, simultaneous selection for grain yield and tolerance to stress in the less favourable environments will identify genotypes broadly adapted to the major cowpea growing regions.

North Carolina Design I (NCD I) progenies derived from Pool 16 DT, a white, dent, early maturing, drought-tolerant and streak resistant tropical maize (Zea mays L.) population, were evaluated in the 1995/96 and 1997/98 dry seasons, using two sites each season in Côte d'Ivoire. In all sites, the crop was irrigated from planting to about 2 weeks before anthesis; irrigation was discontinued thereafter for the rest of the season in one site (Soumis) in 1995 and both sites (Ferkessédougou and Sinematialli) in 1997. Irrigation was continued until maturity in the second site (Temoin) in 1995. In 1995, the additive component of genetic variance was much larger than the other components. The narrow-sense heritability estimate (h2) was 73% for grain yield and 43–71% for seven other traits. In 1997, only grain moisture at harvest, ear height, and days to anthesis and silking had positive additive genetic variances but the h2 were much lower (1·5–41%) than in 1995. Ears/plant, plant height and ear height had consistent positive correlation with grain yield; correlation of days to anthesis and silking date with yield were negative. Because of negative variances, additive genetic correlation could not be computed for most traits in 1997, but in 1995 grain moisture at harvest, plant height and ear height showed positive additive genetic correlation with yield. Other additive genetic correlation coefficients were low and/or not consistent. There is sufficient genetic variance to warrant continued selection for drought tolerance in Pool 16 DT. The induced stress, however, appears to be too severe to properly elicit the true differences among families and may, therefore, need to be modified.

A 3-year field study was conducted during 1998/99–2000/01 on the effect of tillage on crop growth, yield and nutrient use in wheat (Triticum aestivum L.) grown after different methods of rice (Oryza sativa L.) seeding. Treatments comprised three methods of rice seeding, viz. direct seeding (unpuddled), manual transplanting and mechanical transplanting by self-propelled rice transplanter as main plots and three tillage levels in wheat (conventional tillage (CT), reduced tillage (RT), zero tillage (ZT)) as subplots. Results indicated that tillage significantly decreased soil bulk density (1·59 Mg/m3) over the zero tillage system (1·69 Mg/m3). Greater root density in terms of root dry weight (7·50 Mg/20 cm row length) was recorded in CT and the lowest root dry weight (5·80 Mg/20 cm row length) was obtained in ZT during 2000/01. Significantly higher dry matter accumulation (254 g/m row) and leaf area index of wheat (3·04) were consistently recorded under direct seeding of rice, which was statistically different from the other methods of seeding adopted in the preceding rice crop. CT resulted in significantly higher dry matter (253 g/m row) and leaf area index of wheat (3·02) than RT and ZT respectively, during 2000/01. The highest mean yield of wheat (6·02 Mg/ha) was obtained in direct seeding of rice, followed by mechanical and manual transplanting. Among different tillage levels, CT recorded the highest mean yield of wheat (5·90 Mg/ha) followed by RT (5·82 Mg/ha) and ZT (5·40 Mg/ha). The yield reduction was in the order of 11·28 and 6·31% under ZT and RT, respectively. Soil chemical analysis showed that available soil N, P and K contents were affected significantly due to seeding method and tillage after each cycle of rice–wheat sequence. Significantly greater available soil N, P and K were recorded under direct seeding of rice followed by manual and mechanical transplanting. CT recorded significantly lower values of available soil N and higher values of soil P and K whereas ZT recorded higher values of available soil N and lower values of available soil P and K during the 3 years of study.

In Sweden, deposition of organic waste will be prohibited in the year 2005. Instead, the waste will be either incinerated or source separated, processed (composted or anaerobically digested) and recycled back to arable land. In order to evaluate the biologically processed waste products as fertilizers, a field experiment was initiated in Sweden in the autumn of 1998. The main focus of the experiment was to compare compost (C) from source-separated domestic waste with biogas residues (BR) from source-separated domestic waste. Each fertilizer was applied in two combinations: in treatments C50 and BR50, 50 kg N/ha/year originates from the waste and 50 kg N/ha/year from mineral nitrogen fertilizer, while in C100 and BR100, the organic wastes were the only plant nutrient sources (100 kg N/ha/year). Mineral fertilizer (NPS100) and unamended were used as controls. Generally pure mineral fertilizers resulted in the highest yield, while control without nitrogen generated the lowest yield. A combination of organic fertilizer and mineral fertilizer resulted in higher yield compared with applying sole organic fertilizer. Total mineral N in the fertilizer was generally the best overall predictor/regressor for grain yield, total nitrogen yield and apparent bioavailable nitrogen. Application of biogas residue resulted in higher yield and grain quality than compost. The higher concentration of nitrogen in oats suggested that oats is a better choice when using compost as a fertilizer. In conclusion, compost and anaerobic biogas residues should not be used as sole fertilizers. Compost should be complemented with mineral N and the biogas residues with P. If compensation for the low content of mineral N in compost is made by a higher application rate, large amounts of heavy metals might be applied along with the compost.

The proportions of alkanes in plant cuticular waxes are influenced by sampling date, site and grazing pressure. Alkanes in organs of major wild forage grasses in Japan were evaluated to estimate the intake and diet composition of grazing animals. Samples of four grasses from a fixed site in native grassland and three grass species from different sites were collected from June to November, to test the temporal and spatial effects on alkane concentrations. Most alkane concentrations in Miscanthus sinensis Anderss, Pleioblastus chino (Franch. Et Savat.) Makino, Sasa nipponica and Zoysia japonica increased from June to July, and then decreased to mid November. Alkane concentrations in the Z. japonica sward used to test the effects of grazing pressure decreased from May to September. Although the sampling dates affected the alkane concentrations, the species effects accounted for 70–93% of the observed variation. Grazing pressure affected only the C29 (n-Nonacosane) alkane concentrations in dead aboveground materials of Z. japonica, but altered the ratios of C29[ratio ]C31 (n-Hentriacontane) in both dead and live Z. japonica. There were positive correlations between C27 (n-Heptacosane), C29 and C35 (n-Pentatriacontane) alkane concentrations in live leaves of M. sinensis and of C31 in live leaves of P. chino with growing season temperature and radiation. The concentrations of C25, C27 and C29 in dead leaves of M. sinensis and of C33 (n-Tritriacontane) and C35 in live Z. japonica were significantly correlated only with radiation. Alkane concentrations differed between the sampling sites, and considerable differences were observed between samples from Iwate and Kumamoto. Both live leaf and dead leaf samples from M. sinensis contained substantial amounts of C27, C29, C31, C33 and C35, and showed that alkane concentrations in stems were much lower during the whole growing season. Although concentrations of C29 were highest in Sasa nipponica (Makino) makino et Shibata, concentrations of C31 or C33 were highest in the other three grass species. Grazing pressures had little effect on alkane patterns, in which alkanes with odd-numbered carbon chains were predominant and most alkanes were of chain length C25 (n-Pentacosane) to C35 (n-Pentatriacontane).

Reproductive performance has been reported to be declining within the UK dairy herd due to continued selection for increased milk production. The aim of the current work was to assess the influence of genetic merit for milk production (as described by PIN95, the index in use at the time), and level of herd performance on reproductive performance. Fertility records from seven commercial dairy farms over a two-and-a-half year period between August 1997 and January 2000, providing a total of 1003 cow records (with a mean genetic merit of 38·6 (±0·80) PIN95) were collected. The influence of genetic merit for milk production, herd mean 305-day milk yield and their interaction on the reproductive performance of individual dairy cattle was estimated. Additionally, 90-day milk yield, 90-day body condition score and deviation from herd mean 305-day milk yield were also investigated for their influence on fertility. A series of regression models using the Proc GLM procedure in SAS were run using data from those cows that conceived during the monitoring period (n=874) (PIN95=38·8±0·83). The models included the variables, year of calving, month of calving and parity. The results showed that days from calving to conception and services per conception increased significantly both with herd 305-day milk yield, and within herds with deviation from herd 305-day milk yield level. Calving to conception also increased with reduced body condition score of cows at 90 days postpartum. Genetic merit (PIN95) was not significantly related to these fertility measurements.

An experiment was conducted to investigate the effect of grazing legumes and ryegrass on the performance of Suffolk×Mule finishing lambs in terms of growth rate, days to finish and carcass characteristics. Replicate plots (n=2) of red clover (Trifolium pratense), lucerne (Medicago sativa), lotus (Lotus corniculatus) and perennial ryegrass (Lolium perenne) were established in May 1999 at the Institute of Grassland and Environmental Research (IGER), Aberystwyth, and maintained at a similar vegetative growth stage. From the beginning of September 1999 each forage was grazed by 10 wether lambs and 10 ewe lambs. The lambs grazed the experimental plots from weaning until they reached fat-class 3L. There was a significant decline in crude protein (CP) concentration in lucerne (−2·6 g/kg DM/day, P<0·05) and lotus (−2·5 g/kg DM/day, P<0·001) over the grazing period, while the CP concentration in red clover and ryegrass remained comparatively constant. Growth rates were highest for lambs grazing lotus compared with lambs grazing the other forages, and growth rates were significantly higher for lambs grazing red clover than for lambs grazing ryegrass. Growth rates of lambs grazing lucerne were significantly lower than lambs grazing lotus but similar to that of lambs grazing red clover and ryegrass. Lambs grazing the legume forages required significantly fewer days to finish compared with lambs grazing ryegrass. Cold carcass weight and killing out percentage were significantly higher for lambs grazing red clover compared with that for lambs grazing the other forages. Lambs grazing red clover and lucerne had significantly higher voluntary intakes, estimated using n-alkanes, than lambs grazing ryegrass, with intakes for lambs grazing lotus not significantly different. There were no treatment effects on in vivo digestibility. Levels of total protein and β-hydroxybutyrate in blood were unaffected by dietary treatment, although lambs grazing the forage legumes had significantly higher blood glucose and urea concentrations compared with lambs grazing ryegrass. Lambs grazing lotus had the highest plasma albumin. The results indicate that by grazing finishing lambs on forage legumes it is possible to increase growth rates and reduce time to finish without compromising carcass quality.