Plant characters that determine stem and root lodging were measured on 15 winter wheat cultivars at three UK sites between 2000 and 2002. A model of lodging was used to estimate stem failure wind speeds (resistance to stem lodging) and anchorage failure wind speeds (resistance to root lodging). The degree and type of natural lodging was also recorded in the plots and this correlated well with the stem and anchorage failure wind speeds. Only a weak correlation (R2=0·33) was observed between the stem and anchorage failure wind speeds for the 15 cultivars. This can be explained by the absence of genetic correlation between the plant characters that determine the stem and anchorage strength. There was a significant interaction between type of lodging (stem or root) and cultivar for failure wind speed (P<0·001). This showed that the difference between the resistances for root and stem lodging was not the same for all cultivars. Separate classifications for the stem and root lodging resistance of cultivars are developed that would allow the most appropriate crop management to reduce the risk of both types of lodging. Significant differences were found between cultivars for all lodging-related plant characters (P<0·05). These resulted in the cultivar range of the anchorage failure moment to be 110% of the overall mean. Stem failure moment, shoot and plant base bending moments had ranges of 37–49% of their overall means. Breeders should select for wide, deep root plates and wide stems with a high stem wall failure yield stress for the greatest improvement in lodging resistance.

Compared with growth at 20/15°C (day/night), exposure of wheat (Triticum aestivum L.) plants to moderately high temperature (30/25°C) significantly decreased grain weight through shortening the duration of grain filling, combined with small (or no) positive increases in the rate of grain filling. Several mathematical models of grain filling were assessed for their suitability as means of analysing these effects of temperature. The ordinary logistic model was found to be the most appropriate model and was used for the analysis of grain filling responses in four cultivars differing in their responses. Genotypic variation in response to temperature was observed for both rate and duration of grain filling, but the variation for the duration of grain filling among cultivars was small at the higher temperature. Significant correlation was found between single grain weight with the rate, but not with the duration, of grain filling at high temperature, which indicated an important role for synthetic processes involved in grain filling in the temperature sensitivity of wheat cultivars. As they are independent traits, both rate and duration are required selection criteria for the improvement of heat tolerance. Responses of one attribute estimated from the logistic model, the inflection point of the course of grain filling, may give insight into a temperature response that is distinguishable from that associated with the duration of grain filling. The inflection point appears to be worth including as a criterion in selecting for high temperature tolerance in wheat.

Sprouted potato tubers lose nutritional value, and their increased content of reducing sugar renders them unsuitable for the french fry and chipping industries. Thus, tuber sprouting in storage is a primary concern of the potato industry, and is currently controlled by application of chemical sprout suppressants. Such suppressants are subject to widespread regulation by governmental agencies. The present study was initiated to investigate the role of the plant hormone ethylene in potato (Solanum tuberosum L.) tuber dormancy release. To this end, potato cv. ‘Russet Burbank’ was transformed with ETR1, an ethylene receptor gene from Arabidopsis. The resulting clones were genetically characterized to verify integration and expression of the ETR1 mRNA and protein. Transgenic clones showed developmental and morphologic changes in plant and tuber, and differing responses to environmental stress and pathogen attack relative to untransformed controls. Lengthening of dormancy was also observed in ETR1 antisense clones stored at 4 °C. Transgenic potato clones treated with solutions of silver thiosulfate (STS), an ethylene action inhibitor, showed restoration of normal plant morphology, while controls were unaffected. These results demonstrate the pleiotrophic effects of ethylene in potato, and identify a need for additional studies on the relationship between ethylene and tuber dormancy.

The influence of dairy cattle feed composition on the manure composition and on the dynamics and plant availability of cattle slurry N was studied. Dairy cows were fed seven different forages either with or without supplemental concentrates. The concentration of N in faeces dry matter varied from 18 to 38 g/kg dry matter and increased with increasing digestibility of the feed. Cattle slurries consisting of a mixture of 0·5 faecal N and 0·5 urinary N were stored according to common agricultural practice in Northern Europe. The mineralization of faecal N during slurry storage was very variable (0·09–0·50). The plant availability of N in the slurries originating from cattle fed with known diets was tested in small, framed field plots with spring barley, under conditions with minimal N losses. The nitrogen uptake in barley was determined and the mineral fertilizer equivalent (MFE) of slurry N was calculated. The net release of mineral N and CO2 from the slurries in soil was also measured in a parallel incubation study. The MFE of cattle slurry N varied from 53 to 75%. After correcting for the measured urine-N/faeces-N ratio and expected ammonia emission, the MFE varied from 51 to 78%. The plant availability and net release of cattle slurry N were influenced by forage type and feeding level. The MFE was negatively correlated with the concentration of crude fibre and neutral detergent fibre (NDF) in the diet, and positively correlated with the dietary protein content. The net release of CO2 from the slurries after 12 weeks in soil was significantly influenced by the concentration of crude fibre in the diet. The plant availability of slurry N was significantly correlated with the ammonium content (R2=0·53) and negatively correlated with the slurry C[ratio ]N ratio (R2=0·67) and the dry matter[ratio ]N ratio (R2=0·58). Residual slurry N left in the soil after harvest of the first crop varied from 0·25 to 0·47 of total slurry N. It is concluded that the fibre and the protein content of cattle diets have a significant influence on the plant availability of cattle slurry N and on the amount of residual slurry N remaining in the soil after the first growing season.

Management of semi-domesticated reindeer (Rangifer tarandus tarandus) in the northern regions have historically focused on reindeer–vegetation interactions, while few data on the food intake of these animals exist. Dry matter intake (DMI) was therefore estimated successively during winter in reindeer calves fed (i) ad libitum pelleted reindeer feed (RF-80; n=6), (ii) fed ad libitum mixed lichens (n=6) and (iii) in free-ranging reindeer calves (n=3) on natural winter pasture (March/April; 69 °N). Faecal output, determined with faeces collection bags, was 24±4, 6±3 and 22±3 g DM/day/kg BM0·75 in reindeer fed RF-80, mixed lichens and on winter pasture, respectively. Actual DMI of reindeer in captivity fed RF-80 and mixed lichens was 70±10 g DM/day/kg BM0·75 and 27±8 g DM/day/kg BM0·75, respectively. The DMI of the captive reindeer calves was accurately estimated on both diets on the basis of the digestibility of their diet and their faecal output. Using the same method, the DMI of free-ranging reindeer calves on natural winter pastures in northern Norway was estimated to be 34–61 g DM/day/kg BM0·75. The present study discusses factors that influence the food intake of reindeer in winter with emphasis on the seasonal regulation of appetite and DMI in these Arctic ruminants.

Prediction of micronutrient deficiency normally involves soil extraction tests and correlations between soil extractable micronutrients and their concentration in plant tissues. The present study reports that the inclusion of soil properties in addition to soil extraction data represents a powerful tool for improving models for a simple determination of phytoavailable Zn and Cu. Soil and plant samples were collected in spring 2000 from 19 cereal fields in Central and Southeast Norway at sites with known micronutrient deficiency. Based on the sample information, the model approach used stepwise regression, applying actual plant Zn and Cu concentration as the response, and soil extractable Zn/Cu and physico-chemical properties of the soil as model predictors. A model involving citric acid extractable Zn coupled with selected soil properties could predict the concentration of Zn in plant tissues of barley and oats grown under field conditions with a significantly high precision (R2=0·96, P<0·001). The soil parameters included in the model, and their importance for phytoavailability of Zn, were in the order: citric acid extractable Zn>clay content>total Zn>pH>total C>total N. Inclusion of DTPA extractable Zn in the model, rather than citric acid, resulted in a slightly lower precision in the prediction of phytoavailable Zn (R2=0·86, P<0·001). A corresponding model for phytoavailable Cu, determined by DTPA and soil parameters, gave less precise prediction (R2=0·59, P<0·01). DTPA was more suitable for predicting phytoavailable Cu than citric acid. Plant Mn concentration could not be correlated to any of the extracting agents.

In high productivity zones of the Indo–Gangetic Plain Region (IGPR) of India, the rice–wheat cropping system (RWCS) is exhibiting a decline in factor productivity, low N use-efficiency and deterioration in soil health. Inclusion of legumes in RWCS is advocated as one of the promising agro-techniques to sustain productivity. A field experiment was conducted during 1996/97 and 1997/98 on sandy loam (Typic Ustrochrept) soil of Modipuram, India (29°4′N, 77°46′E, 237 m above sea level) to explore the possibilities of inclusion of cowpea as a break crop in RWCS. The effect of rice or cowpea was measured on the yield, fertilizer N requirement and N use-efficiency in wheat, and also on the soil organic carbon and available N content. The yields of wheat following cowpea were significantly (P<0·05) greater by 19–20%, compared with those following rice. In a cowpea–wheat rotation economic optimum dose of fertilizer N for wheat was smaller than that in a rice–wheat rotation due to increased N availability, better growing environment and greater N use-efficiency (measured as agronomic efficiency, apparent recovery and partial factor productivity) in the former case. On termination of the experiment, soil organic carbon and available N content increased over initial content with increasing rates of fertilizer N under both rotations, but the magnitude of increase was greater in treatments where cowpea preceded wheat.

A comparative slaughter experiment was carried out to examine the effects of feeding either grass silage alone or a mixed diet of silage and concentrate on animal performance and the partitioning of nutrients between lean and fat deposition in steers. Eighteen Hereford×Friesian steers were randomly assigned to two dietary treatments; grass silage only (S) or a mixture of grass silage and a barley/soya bean meal concentrate (80[ratio ]20 on fresh basis) in the ratio of 60[ratio ]40 (on a metabolizable energy basis; SC), and to one of three target slaughter liveweights, 250, 350 or 500 kg. Metabolizable energy (ME) intake was maintained at 800 kJ ME per kg metabolic liveweight (kg0·75) per day. The relationships between chemical composition and empty body weight (EBW) at slaughter were assessed using allometric equations (logey=logea+blogeEBW). When assessed across the slaughter weights, supplementing silage with concentrates resulted in higher rates of liveweight (P<0·001), carcass fat (P<0·05) and protein (P<0·01) gains and a reduction in time taken to reach the average slaughter weight by 57 days (P<0·001). Carcass protein deposition was relatively linear across the slaughter weights (250–500 kg) and the relationship with EBW was Y=0·2372X0·8831 across treatments and did not differ between the diets. The rate at which carcass fat was deposited in relation to weight across all steers was Y=0·0004X1·9648 and was not different between the two diets. Hence, ratios of carcass fat[ratio ]protein and carcass fat[ratio ]protein gain ratios were not different. The results suggest that the main effect of feeding grass silage compared with grass silage-concentrate at similar levels of ME intake was to increase the rate of tissue accretion, but nutrient partitioning between fat and protein deposition was unchanged. There was no evidence of increased carcass fat[ratio ]protein deposition in silage-fed animals, which suggests that there is no problem of greater fat and reduced protein deposition in animals fed higher quality grass silage.

The field experiments were carried out at the Indian Agricultural Research Institute, New Delhi during 1996–97 to 1998–99 to study the effect of phosphate solubilizing bacteria (PSB) and incorporation of wheat and rice residue on the relative efficiency of diammonium phosphate (DAP) and Mussoorie rock phosphate (MRP) in three cycles of rice–wheat cropping system. Application of MRP had no significant effect on grain and straw yield and P uptake by rice and wheat; however, when it was inoculated with PSB, it increased grain and straw yields as well as P uptake of both rice and wheat. Efficiency of MRP+PSB was further increased when rice and wheat residues were incorporated and this practice made MRP on a par with DAP. Available P in soil after three cycles of rice–wheat cropping was more after MRP+PSB and incorporation of rice and wheat residues than after DAP. The results of the present study, therefore, indicate that low grade rock phosphate such as MRP can be advantageously utilized in rice–wheat cropping system when applied with PSB inoculation and incorporation of rice and wheat residues.

Eighteen S1 lines of maize (Zea mays L.) derived from a low nitrogen tolerant pool and two inbred lines were evaluated for agronomic performance under moderate N conditions in the southern Guinea savannah of Nigeria. Generally, the breeding lines differed in yield, growth, vertical root-pulling resistance, N-uptake and N-use efficiency. Breeding lines with high vertical root-pulling resistance took up more N and utilized it more efficiently. They also showed better agronomic performance and recorded higher yields. Principal component and cluster analyses classified the breeding lines into six groups. The results of principal components analyses (PCA) suggest that the most important variables for the classification of the S1 lines were grain yield, plant height, total dry matter during the grain-filling period and at maturity, N-accumulation, N-uptake and N-use efficiency. Other important traits were days to silking, anthesis-silking interval, ears per plant, harvest index and vertical root-pulling resistance. Two groups containing a total of 14 S1 lines that had higher agronomic performance than others are recommended for further evaluation under severe N stress to ascertain their tolerance of low N stress before recombination to form a new population for the next cycle of selection.

The present paper reports on three sets of experiments exploring the persistence of seeds of oilseed rape (Brassica napus). The first, where known numbers of seeds were buried in September 1991 in two field experiments, demonstrated substantial initial losses of seeds, such that only 0·2 and 3·8% of seeds were still present after 4 months. In these experiments, which were not disturbed by mechanical cultivation, there was little evidence of further decline over the following 13 months. In the second of the two experiments, seeds were then left undisturbed for a further 136 months. A mean of 1·8% of seeds were still present after this period, providing further confirmation of the lack of decline in seed numbers in these undisturbed conditions. In the second pair of experiments, known numbers of seeds of three rape cultivars were broadcast onto plots and then either ploughed into the soil immediately after the start of the experiments, or were exposed to weekly shallow tine cultivation followed by ploughing after 4 weeks. The former created a larger seedbank than the latter. The experiments were then ploughed, annually (Expt 1) or at less frequent intervals (Expt 2); appreciable numbers of seeds survived for 65 months in both. Calculations based on exponential decline curves indicated that 95% seed loss would take 15–39 months, depending on the site, cultivar and initial post-harvest stubble treatment. The third part of the paper is based on more detailed studies of persistence of seeds of six cultivars in Petri dishes and buried in 25 cm pots. This work confirmed that cultivars differed in their persistence, as Apex was confirmed as highly persistent, whereas Rebel was short-lived. There were inconsistencies in the response of cultivar Synergy between the Petri-dish and pot experiment, which need further study. This experiment also reinforced the conclusion of the initial field experiments that little seed loss occurs in the absence of cultivations. Appreciable numbers of rape seeds will persist up to 4 years, in normal cropping conditions and in the absence of cultivation one experiment has confirmed persistence for over 11 years.

Calliandra calothyrsus is a tree legume native to Mexico and Central America. The species has attracted considerable attention for its capacity to produce both fuelwood and foliage for either green manure or fodder. Its high content of proanthocyanidins (condensed tannins) and associated low digestibility has, however, limited its use as a feed for ruminants, and there is also a widespread perception that wilting the leaves further reduces their nutritive value. Nevertheless, there has been increasing uptake of calliandra as fodder in certain regions, notably the Central Highlands of Kenya. The present study, conducted in Embu, Kenya, investigated effects of provenance, wilting, cutting frequency and seasonal variation both in the laboratory (in vitro digestibility, crude protein, neutral detergent fibre, extractable and bound proanthocyanidins) and in on-station animal production trials with growing lambs and lactating goats. The local Kenyan landrace of calliandra (Embu) and a closely-related Guatemalan provenance (Patulul) were found to be significantly different, and superior, to a provenance from Nicaragua (San Ramón) in most of the laboratory traits measured, as well as in animal production and feed efficiency. Cutting frequency had no important effect on quality; and although all quality traits displayed seasonal variation there was little discernible pattern to this variation. Wilting had a much less negative effect than expected, and for lambs fed calliandra as a supplement to a low quality basal feed (maize stover), wilting was actually found to give higher live-weight gain and feed efficiency. Conversely, with a high quality basal diet (Napier grass) wilting enhanced intake but not live-weight gain, so feed efficiency was greater for fresh material. The difference between fresh and wilted leaves was not great enough to justify the current widespread recommendation that calliandra should always be fed fresh.

Most current biological problems in agriculture occur at the higher levels of organization: populations, communities and ecosystems. These are the levels addressed by the science of ecology rather than other biological sciences. Therefore ecology will by necessity become the central science of agriculture. Agricultural production will be seen as a form of applied ecology or ecological engineering. This change in perspective has major implications for agricultural research. It brings the discussion of the assumptions of a research programme into the open and forces researchers to prioritize among potentially conflicting objectives. It sees agricultural strategies in terms of trade-offs, rather than improvements, and it suggests that agricultural research needs to be more bold and ambitious if it is to solve the most important problems facing us in the new century.

Perennial ryegrass (Lolium perenne L.) is often subject to transient waterlogging during winter under dryland conditions and summer when flood-irrigated. Despite this, little is known about the physiological responses of perennial ryegrass genotypes to waterlogging. In a pot experiment, four perennial ryegrass genotypes with contrasting root growth characteristics were subjected to waterlogging for 0, 3, 7, 14, 21 or 28 days. The masses of roots and shoots of the genotype Aurora6 were not significantly (P>0·05) reduced by waterlogging, throughout the experiment. All other genotypes exhibited reductions in root and shoot biomass between 14 and 21 days after waterlogging was imposed. The masses of laminae and roots of susceptible genotypes were reduced by up to 70% after 28 days of waterlogging. Aurora6 was also able to maintain photosynthesis for longer into the waterlogging period. However, after 28 days of waterlogging, photosynthesis of all genotypes was reduced by 30–50%. The waterlogging tolerance of Aurora6 was not due to its relatively poor root growth, as its progeny (2178), which also had poor root growth under control conditions, was susceptible to waterlogging. These findings show that there is variation in physiological processes and herbage yield of perennial ryegrass under waterlogged conditions. The implications of these findings for the genetic improvement of waterlogging tolerance of perennial ryegrass are discussed.