Showing papers in "The Journal of Agricultural Science in 2006"

Crop losses to pests

Abstract: Productivity of crops grown for human consumption is at risk due to the incidence of pests, especially weeds, pathogens and animal pests. Crop losses due to these harmful organisms can be substantial and may be prevented, or reduced, by crop protection measures. An overview is given on different types of crop losses as well as on various methods of pest control developed during the last century.Estimates on potential and actual losses despite the current crop protection practices are given for wheat, rice, maize, potatoes, soybeans, and cotton for the period 2001–03 on a regional basis (19 regions) as well as for the global total. Among crops, the total global potential loss due to pests varied from about 50% in wheat to more than 80% in cotton production. The responses are estimated as losses of 26–29% for soybean, wheat and cotton, and 31, 37 and 40% for maize, rice and potatoes, respectively. Overall, weeds produced the highest potential loss (34%), with animal pests and pathogens being less important (losses of 18 and 16%). The efficacy of crop protection was higher in cash crops than in food crops. Weed control can be managed mechanically or chemically, therefore worldwide efficacy was considerably higher than for the control of animal pests or diseases, which rely heavily on synthetic chemicals. Regional differences in efficacy are outlined. Despite a clear increase in pesticide use, crop losses have not significantly decreased during the last 40 years. However, pesticide use has enabled farmers to modify production systems and to increase crop productivity without sustaining the higher losses likely to occur from an increased susceptibility to the damaging effect of pests.The concept of integrated pest/crop management includes a threshold concept for the application of pest control measures and reduction in the amount/frequency of pesticides applied to an economically and ecologically acceptable level. Often minor crop losses are economically acceptable; however, an increase in crop productivity without adequate crop protection does not make sense, because an increase in attainable yields is often associated with an increased vulnerability to damage inflicted by pests.

Impacts of breeding on international collaborative wheat improvement

Abstract: For over 40 years a collaborative network of publicly funded international wheat scientists has made a significant contribution to food security in the developing world. Thousands of modern wheat varieties (MVs) have been released for use in both favourable and marginal environments on well over 50 million hectares. The yield increases associated with genetic improvement in yield potential and adaptation to biotic and abiotic stresses are well documented. Millions of small-scale farmers in the developing world have benefited. While this so-called 'Green Revolution' displaced landraces in favour of more productive MVs, these and other genetic resources, held in trust by international organizations, have been utilized to improve the inherent genetic diversity of modern varieties. Furthermore, the result of increased yields reduced the need to bring natural ecosystems under cultivation, by as much as a billion hectares. Although international wheat breeding has its origins in the 1940s, recognition of a common scientific basis of agricultural problems worldwide was highlighted by the creation of International Agricultural Research Centres (lARCs) which included the International Maize and Wheat Improvement Centre (CIMMYT) established in 1965. This grew into a larger network called the Consultative Group for International Agricultural Research (CGIAR) now comprising 15 IARCs, including the International Centre for Agricultural Research in the Dry Areas (ICARDA) established in Syria in 1977, another key player in the international wheat and barley breeding network. Two of the major coordination responsibilities of CIMMYT are maintaining the world collection of wheat genetic resources - a public good protected by international treaty - and the facilitation of the International Wheat Nurseries. After the initial impact of the Green Revolution in high production zones through exploitation of Rht-Bl and Rht-Dl dwarfing genes in conjunction with disease resistance, international breeding encompassed more challenging environments through, for example, international shuttle breeding between Brazil and Mexico to overcome problems associated with acid soils that restricted adoption of MVs. Another example is drought, which affects at least 30 million ha of wheat in the developing world. The approach focused initially on exploiting the inherent yield potential and disease resistance of MVs and later combined this with new stress-adaptive traits from wild wheat ancestors through wide crossing techniques. Adoption of modern varieties has increased substantially in drier areas between 1990 and 1997. In all environments, possibly the greatest threat to productivity is disease, especially those caused by fungal pathogens. International wheat breeding has placed great emphasis on genetic control of disease since resource-poor farmers generally lack the means to control diseases chemically.

A physiological analysis of oilseed rape yields: Past and future

Abstract: Oilseed rape yields on farms have not increased in several countries, including the UK, since the mid 1980s. This may be because the yield potential for the environment in these countries has been reached, or due to a lack of genetic improvement, or due to changes in the environment of the growing crop caused by crop management practices. The present paper investigates which of these factors may be causing the yield of farm crops in the UK to remain at 3 t/ha. The yield potential for the UK that would be possible by combining the best characteristics that have been observed with the best crop management is estimated to be significantly greater than average farm yields at 6·5 t/ha (90 g/kg moisture content). In order to achieve 6·5 t/ha, a crop would have a flower cover of less than 0·4 to facilitate the production of 130000 seeds/m2. Seed filling must last 46 days and have a solar radiation use efficiency of 0·75 g of seed/MJ. A tenth of the yield must come from stem reserves and the seed weight must be 5·0 mg. All of these characteristics have been achieved; therefore the challenge lies in combining these traits within the same crop. The ultimate yield potential for water retentive soils in the UK is estimated at 9·2 t/ha. This would require new characteristics to be bred into the crop and represents a long-term target. In the UK, new oilseed rape varieties are introduced each year and the yield of these varieties under optimum growing conditions is estimated to have increased by 62 kg/ha/year between 1978 and 2005. Lack of genetic improvement is therefore unlikely to explain the halt in farm yields. There have been trends for farm crops to be grown in shorter rotations, established using minimal cultivations rather than ploughing and to receive less nitrogen fertilizer. Sulphur applications have increased, but probably have not kept pace with the reduction in deposition from the atmosphere. Fungicide applications to farm crops are less than applied to the variety testing system and are unlikely to offer complete disease control. It is concluded that a combination of these crop management factors has caused the halt in yield improvement on UK farms.

The design and analysis of multi-phase plant breeding experiments

Abstract: Despite the importance of selection for quality characteristics in plant improvement programmes, literature on experimental design and statistical analysis for these traits is scarce. Most quality traits are obtained from multi-phase experiments in which plant varieties are first grown in a field trial then further processed in the laboratory. In the present paper a general mixed model approach for the analysis of multi-phase data is described, with particular emphasis on quality trait data that are often highly unbalanced and involve substantial sources of non-genetic variation and correlation. Also detailed is a new approach for experimental design that employs partial replication in all phases. The motivation for this was the high cost of obtaining quality trait data, thus the need to limit the total number of samples tested, but still allow use of the mixed model analysis. A simulation study is used to show that the combined use of the new designs and mixed model analysis has substantial benefits in terms of the genetic gain from selection.

Applying innovations and new technologies for international collaborative wheat improvement

Abstract: Despite the successes of the Green Revolution, about a billion people are still undernourished and food security in the developing world faces new challenges in terms of population growth, reduced water resources, climate change and decreased public sector investment. It is also becoming widely recognized that poverty is a cause of environmental degradation, conflict and civil unrest. Internationally coordinated agricultural research can play a significant role in improving food security by deploying promising new technologies as well as adapting those with well-established impact.In addition to the genetic challenges of crop improvement, agriculturalists must also embrace the problems associated with a highly heterogeneous and unpredictable environment. Not only are new genetic tools becoming more accessible, but a new generation of quantitative tools are available to enable better definition of agro-ecosystems, of cultivar by environment interactions, and of socio-economic issues, while satellite imagery can help predict crop yields on large scales. Identifying areas of low genetic diversity – for example as found in large tracts of South Asia – is an important aspect of reducing vulnerability to disease epidemics. Global strategies for incorporating durable disease resistance genes into a wider genetic background, as well as participatory approaches that deliver a fuller range of options to farmers, are being implemented to increase cultivar diversity.The unpredictable effects of environment on productivity can be buffered somewhat by crop management practices that maintain healthy soils, while reversing the consequences of rapid agricultural intensification on soil degradation. Conservation agriculture is an alternative strategy that is especially pertinent for resource-poor farmers.The potential synergy between genetic improvement and innovative crop management practices has been referred to as the Doubly Green Revolution. The unique benefits and efficiency of the international collaborative platform are indisputable when considering the duplications that otherwise would have been required to achieve the same impacts through unilateral or even bilateral programmes. Furthermore, while the West takes for granted public support for crucial economic and social issues, this is not the case in a number of less-developed countries where the activities of International Agricultural Research Centres (IARCs) and other development assistance organizations can provide continuity in agricultural research and infrastructure.

Recent progress in the ancient lentil

Abstract: Lentil (Lens culinaris Medikus subsp. culinaris) was among the first crops domesticated and has become an important food legume crop in the farming and food systems of many countries globally. Its seed is a rich source of protein, minerals, and vitamins for human nutrition, and the straw is a valued animal feed. Its ability in nitrogen and carbon sequestration improves soil nutrient status, which in turn provides sustainability in production systems. In the current paper, research progress achieved in lentil improvement at national and international levels is reviewed. Since the late 1970s there have been significant national and international lentil improvement programmes, with the main objectives being to develop phenologically adapted, stress resistant and high-yielding cultivars with improved production packages. Systematic research on lentil started recently, compared to other early-domesticated crops. During the last two and a half decades, research progress has been made in various aspects of the crop. Large numbers of germplasm have been collected, evaluated and preserved at national and international levels, with the International Center for Agricultural Research in the Dry Areas (ICARDA) holding the largest collection of cultivated and wild germplasm accessions. A major effort has been made to study the genetic variation in the world germplasm collection, in order to understand local adaptation and to develop specific research programmes. Genotypes with resistance to various biotic and abiotic stresses, particularly resistance to vascular wilt, rust and Ascochyta blight have been identified, and directly exploited or used in breeding programmes. New genotypes have been bred with good standing ability, suitable for mechanical harvest for West Asia and North Africa. Through introduction and hybridization, the genetic base of lentil has been broadened, most particularly in South Asia, by breaking an ancient genetic bottleneck. Agronomic practices, including seeding time, seed rate, tillage requirements, soil type, and weed control, are optimized locally and improved production packages have been developed to realize higher yield. To date, a total of 91 improved cultivars have been released globally, emanating from genetic material supplied by ICARDA. Due to adoption of improved varieties combined with production technologies, the average global productivity has increased from 611 kg/ha to 966 kg/ha, and total production from 1·3 million tonnes to 3·8 million tonnes in the last three decades. Research at the molecular level, including construction of a lentil genetic linkage map, identification of molecular markers, and genetic transformation, has progressed considerably.

Adoption and economic impact of improved wheat varieties in the developing world

Abstract: During the past century wheat breeders have produced a large number of genetically improved wheat lines and varieties. This activity has led to widespread adoption of improved varieties, a steady increase in average wheat yields during the past 4–5 decades and major contributions to food security and poverty reduction. The rate of generation and adoption of improved varieties, and therefore the time lag from varietal release to widespread use, varies across regions. The remarkable success of wheat improvement hinges on the decisions of millions of farmers to adopt, or replace older wheat varieties with superior material. The present paper summarizes studies on the determinants of adoption. Because adoption is a necessary but not sufficient condition for economic impact, the present paper synthesizes key assessments of impact from different farming systems in developing countries.

Temperate grassland : key developments in the last century and future perspectives

Abstract: In temperate regions, grassland provides most of the feed requirements for ruminants. Its management has implications for landscape and environmental quality as well as agricultural production. The present paper reviews the key developments in grassland management, production and utilization during the 20th century, focusing primarily on the UK but drawing on research and practice from other areas. Increased production from grassland has arisen from improved understanding of soil and plant nutrition, plant physiology and cultivar improvement, while improved understanding of feed evaluation, ruminant nutrition, grazing management and silage technology have contributed to increased utilization of grassland under grazing and cutting. Permanent and long-term swards occupied most of the total grassland area at both the beginning and end of the century, but inputs of nitrogen resulted in greatly increased herbage production, particularly from the 1960s; this, combined with reseeding and early cutting for silage, led to reduced botanical diversity with ryegrass dominance in lowland areas. Forage legumes were highly regarded at the beginning of the century, then decreased in many areas, but are again recognized as having a key role in low- and medium-input systems. Recognition of the environmental implications of grassland management has increased since the 1980s. This includes the need to reduce nutrient emissions in grassland agriculture, and also the role of grassland in biodiversity protection, carbon sequestration and landscape quality. Research is increasingly focused on addressing these issues and on integrating agricultural management with environmental protection. Improved nutrient management, legume-based systems and agri-environmental schemes, as well as interest in the food quality attributes of particular systems and grassland communities, are important in the medium term. In the longer term the effects of population increase, competition for other land uses and the impacts of climate change could impact on global food supplies and affect future grassland management in the temperate zones.

Ammonia volatilization from surface-applied livestock slurry as affected by slurry composition and slurry infiltration depth.

Abstract: Volatilization of ammonia (NH 3 ) from slurry applied in the field is considered a risk to the environment and reduces the fertilizer value of the slurry. To reduce volatilization a better understanding of the slurry-soil interaction is needed. Therefore, the present study focuses on measuring NH 3 volatilization as affected by differences in infiltration. Livestock slurries with different dry matter (DM) composition and viscosity were included in the experiments by using untreated cattle and pig slurry, pig slurry anaerobically digested in a biogas plant and pig slurry anaerobically digested and physically separated. NH 3 volatilization was measured using dynamic chambers and related to infiltration of the livestock slurries in the soil by measuring chloride (Cl - ) and Total Ammoniacal Nitrogen (TAN = ammonium (NH 4 + )+NH 3 ) concentrations in soil at different depths from 0·5 to 6·0 cm from the soil surface. The slurries were applied to sandy and sandy-loam soils packed in boxes within the chambers. There were no significant differences in relative volatilization of NH 3 from untreated cattle and pig slurries, but anaerobic digestion of pig slurry increased volatilization due to increases in pH. However, physical separation of the digested slurry reduced the volatilization compared with untreated slurry, due to increased infiltration. In general, the volatilization decreased significantly with increased infiltration. The present study shows that NH 3 volatilization from applied slurry can be related to infiltration and that infiltration is related to slurry composition (i.e. DM content and particle size distribution) and soil water content. The infiltration of liquid (measured by Cl - infiltration) was affected by soil water potential, therefore, Cl - infiltrated deeper into the sandy loam soil than the sandy soil at similar gravimetric soil water values. Dry matter (DM) and large particles (>1 mm) of the slurry reduced infiltration of liquid. A high proportion of small particles (<0·025 mm) facilitated infiltration of TAN.

Detection and quantification of the soil microbial biomass - Impacts on the management of agricultural soils

Abstract: Studies of single soil organisms, while useful in specialized cases, e.g. Rhizobia and mycohrrizae, do not yield information on the functioning of the soil ecosystem. This is because most important soil processes, e.g. carbon and nitrogen mineralization, depend upon interactions between entire suites of organisms, many of which still await identification and most of which remain unculturable. For many purposes, treating the soil microbial community as a single, undifferentiated unit, the soil microbial biomass (defined as all soil organisms <5000 μm 3 volume), has much to commend it. It is analogous to studying the forest rather than an individual tree and uniquely permits an understanding of the soil-plant-microbe system as a whole, rather than studying only a small part. The present paper reviews the development of methods to measure microbial dynamics over the last century, the evolution of biomass methodologies and how they have helped the study of crucial soil processes such as nutrient and carbon cycling. Possible future directions for this research are also discussed and an explanation set forth of why the manipulation of this huge population (easily comprising 10 tonnes per hectare of living microbial cells in UK arable soils) has, so far, proved elusive.

Estimated N leaching losses for organic and conventional farming in Denmark

Abstract: The impact of organic compared to conventional farming practices on N leaching loss was studied for Danish mixed dairy and arable farms using an N balance approach based on representative data. On mixed dairy farms a simple N balance method was used to estimate N surplus and N leaching loss. On arable farms the simple N balance method was unreliable due to changes in the soil N pool. Consequently, the FASSET simulation model was used to estimate N surplus, N leaching loss and the changes in the soil N pool. The study found a lower N leaching loss from organic than conventional mixed dairy farms, primarily due to lower N inputs. On organic arable farms the soil N pool was increasing over years but the N leaching loss was comparable to conventional arable farms. The soil N pool was primarily increased by organic farming practices and incorporation of straw. The highest increase in the soil N pool was seen on soils with a low level of soil organic matter. The level of N leaching loss was dependent on soil type, the use of catch crops and the level of soil organic matter, whereas incorporation of straw had a minor effect. N leaching was highest on sandy soils with a high level of soil organic matter and no catch crops. The study stresses the importance of using representative data of organic and conventional farming practices in comparative studies of N leaching loss.

Evaluation of management strategies for sustainable rice-wheat cropping system, using DSSAT seasonal analysis

Abstract: A simulation study using the Seasonal Analysis program of the Decision Support Systems for Agrotechnology Transfer (DSSAT 3.5) suite of models was conducted from 2001 to 2003 under a subhumid subtropical climate. The models CERES-Rice and CERES-Wheat in DSSAT 3.5 were calibrated and validated for transplanted rice, direct seeded rice and wheat crops using the soil and weather parameters of Kharagpur, West Bengal, India. The weather generator program, SIM-METEO, was used to generate future weather scenarios based on weather data from 9 consecutive years. These weather scenarios were used in the seasonal analysis program to run each treatment combination with 20 replications. The results of both biophysical and economic analyses of the Seasonal Analysis program predicted an application of 120 kg N/ha along with both rice and wheat crop residues at 4 t/ha for rice, whereas the economical analysis, specifically the Mean-Gini analysis, showed that application of 80 kg N/ha along with both rice and wheat crop residue incorporation at 4 t/ha as the most dominant management options for wheat. The present study revealed that the generated future weather data were reliable and DSSAT could successfully use it to predict the future crop yields under different management practices and select the best one for sustainable production of rice and wheat crops by DSSAT.

Agronomic regeneration of soil fertility in tropical Asian smallholder uplands for sustainable food production

Abstract: Smallholder cropping systems are a vital component in the agricultural sectors of tropical Asia, especially in the developing nations. These systems are important for producing food and providing a livelihood to a major proportion of the populations of Asia. While the rice systems, usually cultivated under puddled conditions are considered stable, the upland or highland units, which provide a range of food, fibre and feed commodities, are generally situated on marginal lands. Low soil fertility, erosion, sub-optimal crop management and subsistence farming conditions characterize these units. Hence, these units require improved but low cost strategies to reverse the trend of lower productivity, loss of sustainability and most importantly, the loss of livelihood for the farming populations. Among the many strategies available, the regeneration of soil fertility through agronomic measures would be a useful and easily adoptable method of enhancing productivity of tropical Asian upland small-holding farming units. The methods available include the revival of age-old traditions such as adding organic matter directly to soils, green manuring and mimicking forest ecosystems through agrofor-estry. Agronomic measures using plants to enrich the soil and regenerate its supporting capacity are presented in the present paper. Relevant examples are cited to highlight the potential of these methods for regenerating productivity of the upland smallholder farming units and more importantly the agro-based livelihood of a large majority of the populations of tropical Asia.

Accumulation pattern of toxin β-ODAP during lifespan and effect of nutrient elements on β-ODAP content in Lathyrus sativus seedlings

Abstract: In order to assess the influence of nutrient elements on the accumulation of β-N-oxalyl-L-a, β-diaminopropionic acid (β-ODAP; the probable cause of lathyrism) in Lathyrus sativus L. (grass pea), it was first examined under field conditions during the lifespan of a grass pea plant using high-performance liquid chromatography (HPLC). β-ODAP mainly accumulated in young seedlings, in developing and mature seeds and in young leaves, especially in young seedlings. In contrast, all mature leaves, roots, and stems showed a low level of β-ODAP. The β-ODAP accumulation pattern in seedlings grown in a nutrient-deficient solution was highest (3·57 mg/g) in shoots at 7 d growing in the nitrogen-deficient solution and higher compared to the control (2·31 mg/g) in zinc-, calcium-, phosphorus- and molybdenum-deficient shoots (P<0·05). The contents of β-ODAP in seedlings growing in other element-deficient solutions were similar to controls. When the content of β-ODAP in grass pea seedlings fertilized with different forms of organic nitrogen was assayed the results indicated that amino acids such as glutamine and serine, as well as nucleotide nitrogen, all significantly enhanced the accumulation of /3-ODAP in young seedlings relative to controls (P<0·05). Taken together, these data suggest that β-ODAP accumulation in grass pea might be related to the level of total free nitrogenous compounds and that nitrogen and phosphate may be the crucial nutrient factors influencing /3-ODAP content under field conditions. Thus, the application of appropriate nitrogen and phosphorus fertilizers to the soil could decrease the content of β-ODAP in the seeds and leaves of grass pea.

Effectiveness of vegetative filter strips in attenuating nutrient and sediment runoff from irrigated pastures

Abstract: Increasing concern about non-point source pollutants released from grazing livestock, a worldwide problem, motivated the present study on the effects of vegetative filter strips (VFS) for controlling pollutants (nutrients, micro-organisms and sediment loading) from grazed, irrigated pastures. Flood-irrigated pastures are an important source of forage for livestock during summer months in California, USA when the surrounding rangelands are dry and dormant. Significant amounts of runoff can be generated from these pastures during irrigation events. Nine plots on an irrigated pasture were assigned randomly to one of three treatments: Control (no VFS), Treatment VFS-1 (8-3 x 7 m. 0-0058 ha VFS) and Treatment VFS-2 (17·1 x 7 m, 0-012 ha VFS). In 2000, two grazing events (in April and June/July) occurred during the irrigation season prior to the experiment; further, the experimental plots were grazed between irrigations 2 and 3. Attenuation of runoff loads by VFS treatment was measured during four irrigation events (between 1 August and 3 October 2000) for total suspended solids (TSS), ortho-phosphate (Ortho-P), inorganic phosphate (Inorg-P), total phosphate (Total-P), organic phosphate (Org-P), polyphosphate (Poly-P), total Kjeldahl nitrogen (TKN), NH 3 , NO 3 and presumptive faecal coliforms (FC). On average, approximately 0-43 of the applied water left the plots as runoff. Treatment effects approached significance for TSS and TKN and were significant (P<0·05) for Poly-P and NH 3 . Irrigation number effects were significant for all but TSS, NO 3 and FC. The effects of VFS treatments were not consistent. Treatment VFS-2, although representing the largest buffer strip, did not always produce the lowest pollutant loads in runoff. Slope, relatively high runoff volumes and some channelled flow were probably responsible for the limited effectiveness of VFS in the present study. These results suggest that effectiveness of VFS for reducing sediment and nutrient transport from irrigated pastures may be questionable.

Variation in yield, N uptake and N use efficiency of medium and late duration rice varieties

Abstract: Field experiments were conducted at the village Kasiadihi, Dhenkanal district, Orissa, India during wet seasons 2001, 2002 and 2003 under non water-stressed conditions (0–25 cm standing water) to assess variability in N uptake and utilization by medium and late duration rice varieties. The N rates were 0, 40, 80 and 120 kg N/ha applied as urea in four equal splits at transplanting, active tiller initiation, panicle initiation and flowering stages. The grain yield response was up to 80 kg N/ha. The optimum grain yield attainable by the efficient medium duration varieties was 4·5 t/ha. The N efficient late duration varieties produced optimum grain yield of 5·8 t/ha. The relationship for total dry matter and grain yield production between N fertilized (40, 80 and 120 kg N/ha) and non-fertilized treatments were all significant, suggesting cultivar selection under optimum N fertilized conditions. The difference in optimum yield of the medium and late duration varieties was due to the differences in the amount of N uptake and its use efficiency by the plant for grain production. There was a curvilinear relationship between grain yield and N use efficiency for grain production. The relationship between N use efficiency for grain production and N contents of leaf, stem and grain at maturity was quadratic. The optimum plant N use efficiency of medium duration varieties was 49 kg grain/kg N uptake, achieved with leaf, stem and grain N contents of 10, 8 and 14 g/kg, respectively, at maturity. For late duration varieties, the optimum plant N use efficiency was 68 kg grain/kg N uptake and it was maintained with leaf and stem N content of 4·0 g/kg each and grain N content of 9·0 g/kg at maturity. The N content in plant organs could be the selection guide used to obtain efficient rice varieties.

Perennial grasses for turf, sport and amenity uses: evolution of form, function and fitness for human benefit

Abstract: The history of genetic modification and improvement of perennial grasses used for turf and sport can be traced back to the earliest events leading to the evolution of traits such as perenniality, asexual reproduction by rhizomes or stolons, apical dominance and hardening or acclimation responses to environmental stress. Human influences on perennial grasses likely began with the dawn of agriculture and the domestication of livestock about 8-10 000 years ago with the movement of grasses from forest margins and meadows to pastures and cropland. As agrarian cultures found more time for leisure and recreation, perennial grasses became multifunctional, taking on a greater role with the invention of ball games, sports and a sod industry. Early human selection of superior turf grasses was largely based on individual clones that were vegetatively propagated for commercial purposes, dating back as far as 12th century Japan. The science of turf breeding began in 1962 with the initiation of extensive efforts to collect superior clones from old turf sods in highly stressful environments, followed by numerous cycles of recurrent selection for turf traits in harsh environments and under realistic mowing regimes. These efforts spawned many public and commercial breeding ventures and thousands of cultivars that have spread throughout the world, improving the quality, persistence and functionality of turf for many uses.

Responses of developmental yield formation processes in oats to variety, nitrogen, seed rate and plant growth regulator and their relationship to quality

Abstract: Outcomes of developmental yield formation processes in oats, namely number of panicles/m 2 , number of grains/panicle, mean grain weight and incidences of aborted and tertiary grains, were measured in a series of experiments in Northern Ireland and the Republic of Ireland in 1997/98 and 1998/99. Seed rate (200 and 300 seeds/m 2 ), nitrogen (0-200 kg/ha) and plant growth regulator (chlormequat chloride) treatments were applied to the spring oat varieties Aberglen and Barra in one spring- and two autumn-sown experiments, and to the winter varieties Gerald and Image in one autumn-sown experiment. Large variation in number of panicles/m 2 and grains/panicle was observed between the experiments and varieties and in response to seed rate, with number of grains/panicle generally being inversely related to number of panicles/m 2 . At the higher rates of nitrogen rate both number of panicles/m 2 and grains per panicle increased. Mean grain weights were relatively constant and were largely determined by variety. Chlormequat chloride had relatively little effect on the yield components, the most consistent being small reductions in mean grain weight. Tertiary grains occurred rarely in the varieties and agronomic treatments used in the programme but were more frequent at higher rates of nitrogen in most of the experiments. Numbers of aborted grains were usually higher where grain numbers were higher although the effects of variety, seed rate and nitrogen on aborted grains were not consistent. Structure of the grain population, i.e. the relative proportions of primary and secondary grain, was stable despite the large differences in number of panicles/m 2 , spikelet numbers and mean grain weight. The greater yield and growth enhancing effects of nitrogen compared with seed rate and plant growth regulator were apparent in responses by developmental processes active later in the life cycle, namely production of tertiary grains and grain filling. Wide variation in number of panicles/m 2 (c. 200-450) and number of grains/panicle (c. 55-145) produced in the crops grown under a very full expression of agro-ecological conditions in this programme was accompanied by small variation in mean grain weight (c. 38-47 mg/primary grain and c. 22-29 mg/secondary grain) and in numbers of tertiary (<2/panicle) and aborted grains (<10/ panicle). Plasticity of development throughout the life cycle, manifested both as the established yield components and in numbers of tertiary and aborted grains, was largely effective in ensuring stability of mean grain weight and quality in oats.

Expression of Suaeda salsa glutathione S-transferase in transgenic rice resulted in a different level of abiotic stress resistance

Abstract: Glutathione S-transferases (EC 2.5.1.18, GSTs) are a family of multifunctional enzymes that play important roles in oxidative stress resistance. In the present study, it was investigated whether expressing Suaeda salsa GST in transgenic rice (Oryza sativa L. cv Zhonghua No.11) could confer resistance to abiotic stress. Several types of stress, including salt, paraquat and chilling were applied. It was shown that following paraquat applications, the activity of GST, catalase (CAT, EC 1.11.1.6) and superoxide dismutase (SOD, EC 1.15.1.1) increased significantly in the GST transgenic plants compared with non-transgenics. Following NaCl and chilling stresses, only SOD and CAT activities increased markedly in the transgenics and there were no significant differences in GST expression between transgenics and non-transgenics. Moreover, in stressed plants, the generation of H2O2 and Malon dialdehyde decreased more in the transgenics than in non-transgenics. These results imply that expression of the Suaeda salsa GST in transgenic rice could enhance abiotic stress tolerance and the antioxidant enzymes of the active oxygen-scavenging system might play integral roles in the protection of plants from oxidative stress.

Output and sustainability of organic ley/arable crop rotations at two sites in northern Scotland

Abstract: Trials at Tulloch, Aberdeen (sandy loam soil, 820 mm rainfall) and Woodside, Elgin (light sandy loam, 730 mm) compared organically managed crop rotations containing different proportions of spring oats, swedes, potatoes and grass/clover leys (0·50 and 0·67 of the rotation at Tulloch; 0·38 and 0·50 at Woodside). The trials simulated farm conditions through the use of grazing animals and the recycling of farmyard manure. The rotations at each site gave similar financial outputs. Yields of oats were higher where these were grown after the main ley phase of the rotation than where they were grown later in the rotation (more ears/m2 and grains/ear), but were not significantly higher after a 4-year ley than after a 3-year ley at Tulloch. It was concluded that all of the rotations were agronomically and financially sustainable. Cereal yields showed large year-to-year variations but little indication of a progressive decline. There were only small changes in soil organic matter, soil P and soil K. Increased early summer weed cover in the arable crops was not matched by increases in weed invasion in the grass/clover leys and did not appear to be affecting yields.

Development and resistance to Verticillium dahliae of olive plantlets inoculated with mycorrhizal fungi during the nursery period

Abstract: The current study, performed in Castilla-La Mancha (Spain) in 2003-04, reports the growth, nutrition, tolerance to transplanting stress, and resistance to Verticillium dahliae of olive plantlets (Olea europaea L.) inoculated with different arbuscular mycorrhizal (AM) fungi (Glomus mosseae, G. intraradices and G. claroideum). Inoculated plants tolerated the stress of transplanting better than non-inoculated plants. Compared with controls, plantlets inoculated with any of these three Glomus species grew taller, had more and longer shoots, and showed higher plant N, P and K concentrations. However, colonization seemed to have no influence on resistance to V. dahliae.

An evaluation of EPIC soil water and yield components in the gully region of Loess Plateau, China

Abstract: The Erosion and Productivity Impact Calculator (EPIC) has been used to determine the effect of different cropping systems and management practices on soil productivity in the Loess Plateau of China. However, its crop growth and soil water balance submodels have not been verified in this region. The objective of the present study was to evaluate the ability of EPIC to estimate soil water content (0 in m 3 /m 3 ), seasonal evapotranspiration (ET in mm/season) and crop yield (Y in t/ha) for winter wheat and maize. A 20-year field experiment was conducted at the Changwu Agro-ecological Experimental Station of the Loess Plateau, and divided into a calibration period and a validation period. Data from calibration (1984-94) were used to optimize the four most sensitive parameters of the EPIC crop yield submodel, whereas data from 1994 to 2004 were used for validation. For both crops, there were no significant differences between measured and estimated long-term means of the three variables (P=0·05) for either the calibration or validation periods. EPIC estimated all three variables with a small relative root mean square error (RRMSE), i.e. the ratio of root mean square error to the mean value. For wheat and maize, the calibration period resulted in respective RRMSE values of 0·112 and 0·100 for 0, 0·121 and 0·116 for ET, and 0·135 and 0·147 for Y. During the validation period, the RRMSE values obtained were 0·090 and 0·085 for 0, 0·129 and 0·135 for ET, and 0·169 and 0·149 for Y, for wheat and maize, respectively. The performance of EPIC in estimating annual values of 0, ET and Y was variable. For validation, EPIC explained 65, 79 and 64% of the measured variations of 0, ET and Y, respectively, for wheat, and 60, 70 and 67 % for maize. The EPIC-estimated long-term average values of the three variables were not significantly different from measured values for winter wheat and maize during the calibration and validation periods. It can therefore be used in the gully region of the Loess Plateau to define alternative cropping systems and management practices.

Phenological, agronomic and forage quality diversity among germplasm accessions of the tropical legume shrub Cratylia argentea

Abstract: Cratylia argentea (Desv.) O. Kuntze is a drought-tolerant tropical shrub legume that can help to ensure continuity of forage supply in smallholder systems either through direct grazing or as a cut-and-carry plant for fresh foliage or silage. A collection of 38 accessions was characterized agronomically and nutritionally. High diversity was detected between accessions. Time to flowering ranged from 217-329 days after transplanting seedlings to the field and from 129-202 days after cutting. Flowering is probably induced by reduction of day length. Seed production was high but variable. Dry matter production ranged from 190-382 g/plant in the rainy and from 124-262 g/plant in the dry season, content of in vitro digestible dry matter from 589-690 g/kg, crude protein content from 184-237 g/kg and fibre content from 403-528 g/kg (neutral detergent fibre, NDF), 240-335 g/kg (acid detergent fibre, ADF), and 9-13 g/kg (acid detergent fibre-bound nitrogen, N-ADF). Accessions CIAT 18674 and CIAT 22406 were identified as promising for further study. They were superior to the commercial cultivar in terms of dry matter (DM) production, particularly in the dry season. Further research is required to determine the prevailing reproduction strategy of C. argentea and to quantify outcrossing-rates. Multilocational trials with a selected set of accessions should be conducted under different environmental conditions.

The influence of 3,4-dimethylpyrazole phosphate and dicyandiamide on reducing nitrate accumulation in spinach under Mediterranean conditions

Abstract: The European Union has limited the maximum nitrate (NO 3 - ) content allowed for industrial processed spinach (Spinacia oleracea L.) to 2000 mg/kg fresh weight in order to avoid human pathologies associated with. uptake of high amounts of nitrate. Nitrification inhibitors (NIs) 3,4-dimethylpyrazole phosphate (DMPP) and dicyandiamide (DCD) allow changing of the molecular form (NH 4 + or NO - 3 ) in which soil mineral N is available for plants. Enhancing ammonium nutrition has successfully reduced the amount of nitrate accumulated in plants in hydroponic culture. Therefore, fertilizers containing NIs have been proposed to reduce nitrate accumulated by vegetables grown in field conditions. Basammon Stabil® (BS) and Entec 26®-(E26) are commercial fertilizers containing DCD and DMPP respectively. In the present paper, the effect of applying ammonium sulphate nitrate (ASN), BS and E26 at three rates (0, 150 and 250 kg N/ha) to spinach crops cultivated under Mediterranean growing conditions for industrial processing is analysed. During 1998 and 1999, eight field split-plot trials with four replicates were carried out in the Ebro Valley, northern Spain, during different seasons and with various soil types. The fertilizer effects were influenced by the season and the type of soil. In spring, fertilizers containing NIs increased the mineral N (Nmin) in the soil and greatly reduced nitrate accumulation in the crop. In autumn, with less solar radiation, the nitrate accumulation was more than 2000 mg/kg fresh weight on many occasions and the effect of NIs was smaller. The present paper concluded that, under Mediterranean growing conditions, DCD can reduce nitrate accumulation in spinach between 18 and 61% and DMPP between 33 and 84% without reducing yield or changing other quality characteristics. NIs are especially useful in the spring, when soil temperature is low and solar radiation interception by the crop is high.

Estimating nutrient contents of pig slurries rapidly by measurement of physical and chemical properties

Abstract: Livestock slurries contain organic matter, nitrogen, phosphorus and potassium, which can be recycled in arable systems; however, excess applications can cause pollution problems and therefore an estimation of the nutrients in slurries is necessary. The aim of the present experiment was to test methods of rapidly estimating nutrient contents of pig slurries based on physical and chemical analysis. A total of 216 samples with a dry matter content in the range 22·5 to 91·8 g/kg were collected in Beijing during 2003 and 2004. One part of each original sample was analysed for physical and chemical properties, such as electrical conductivity (EC), pH and specific gravity (SG). The other part of each original sample was analysed in the laboratory to measure organic matter (OM), total nitrogen (TN), ammonium nitrogen (AN), total phosphorus (TP) and total potassium (TK). Analytical results showed that OM could be estimated by a single property regression with SG (R2=0·92, P<0·001), TN could be estimated by a multiple property regression with SG and pH (R2=0·86, P<0·001), AN could be estimated by a single property regression with EC (R2=0·82, P<0·001), TP could be estimated by a single property regression with SG (R2=0·81, P<0·001), and TK could be estimated by a multiple property regression with EC and SG (R2=0·81, P<0·001).

Carbon sequestration potential and sustainable yield index for groundnut- and fallow-based cropping systems

Abstract: Soil organic carbon storage encompasses both soil productivity and environmental capabilities. The influence of fertilizer (nitrogen and phosphorus) levels (0 NP, 0·5 NP, 1·0 NP (recommended standard) or 1·5 NP) on total system productivity, sustainable yield index and soil organic carbon storage in Vertisols (Typic Haplustert) under groundnut and fallow-based cropping systems were examined in a field experiment over 6 years. The aim was to identify a system that provided an acceptable balance between total system productivity and soil organic carbon restoration. The experiment comprised two rainy season crops (groundnut or fallow) and five post-rainy season crops (wheat, mustard, chickpea, sunflower or summer groundnut), each post-rainy season crop with four levels of NP fertilizer. The total system productivity was 130% higher in the groundnut-based than in the fallow-based system and was in the order: groundnut–groundnut>groundnut–chickpea>groundnut–wheat>groundnut–mustard>groundnut–sunflower. The sustainable yield index was highest in the groundnut–groundnut system. The gross C input was relatively higher in the groundnut-based system but the C loss rate was greater. The amount of residue needed per ha per year to compensate for loss of soil organic carbon was estimated to be 4·3 t in the fallow-based and 7·6 t in the groundnut–based cropping system. Though the total system productivity was greater in groundnut–groundnut and groundnut–chickpea systems, soil organic carbon declined. The groundnut–wheat system contributed more C, particularly root biomass C, than other systems, improved the restoration of soil organic carbon and maintained total system productivity. It was concluded that current fertilizer recommendations are adequate for maintaining yields in groundnut-based systems but the addition of crop residues at regular intervals along with fertilizer is necessary to maintain restoration of soil organic carbon.

Genetic variation among Spanish pea landraces revealed by Inter Simple Sequence Repeat (ISSR) markers: its application to establish a core collection

Abstract: One hundred and twenty Spanish landraces of peas (Pisum sativum L.) collected in different micro-climatic areas, together with three commercial varieties and one breeding line, were subjected to molecular characterization using Inter Simple Sequence Repeat (ISSR) amplification. Landraces originated from 7 to 1427 m asl. Most accessions were collected in temperate areas with dry Mediterranean humidity regimes. ISSR markers detected high levels of variability between accessions and were useful for identification of individuals and clarification of genetic relationships between them. The 18 groups obtained with molecular data were not significantly related to 21 agro/climatic regions. Clustering based on climatic and ISSR characters differed because the data types present different aspects of genetic diversity. These results will be applied to establish a pea core collection at the Plant Genetic Resources Centre of the Spanish National Institute of Agriculture and Food Research and Technology (CRF-INIA).

Effects of incremental dietary chromium (Cr3+) on growth, hormone concentrations and glucose clearance in growing goats (Capra hircus)

Abstract: Castrated male black Bengal kids were supplemented daily with 0, 0·5, 1·0, 1·5 and 2·0 mg chromium (Cr 3+ as chromic chloride hexahydrate) for 150 days. Metabolic stresses such as a feeding challenge, an intravenous glucose tolerance test (IVGTT) and a short-term (72 h) feed deprivation were imposed on the animals to ascertain if supplemental Cr could alleviate these stresses and whether the stress-alleviating effect could provide an explanatory basis for the performance traits of the supplemented animals. The kids were fed with a concentrate diet containing 0·197 mg Cr/kg DM. DM intake (g/kgw 0·75 ) was lower (P=0·006) in the 0·5 and 1·5 mg groups. Feed efficiency tended (P=0.086) to improve in the Cr-supplemented kids, although a distinct dose response was absent. Basal serum T3 increased linearly (P=0·01) with increased dose of Cr although the post-prandial change did not follow any definite trend. Basal serum insulin increased (P=0·01) linearly while the post-prandial increment was higher (P=0·037) in the control group. The IVGTT indicated that the kids supplemented with 1·5 mg Cr had significantly (P 0·10) between the groups. Cr supplementation reduced (P<0·05) serum cortisol level in the supplemented animals consistently throughout the duration of the feed deprivation. Moreover, as the fast progressed serum cortisol tended to increase (P=0·059) in all the experimental groups irrespective of the level of Cr supplementation. It was concluded that inorganic Cr supplementation might appreciably increase serum T3 concentration and reduce the level of cortisol which might augment animal productivity. However, further research with a more sensitive design is required to establish the exact level of Cr supplementation for enhancing performance of livestock.

Estimation of economically optimum seed rates for winter wheat from series of trials

Abstract: The results of recent trials for winter wheat (Triticum aestivum L.) have influenced farming practice in the UK by encouraging the use of lower seed rates. Spink et al. (2000) have demonstrated that, particularly if sown early, wheat can compensate for reduced plant populations by increased tiller production. Results from seed-rate trials are usually analysed separately for each environment or each combination of environment and variety, and not combined into a single model. They therefore address the question of what the best seed rate would have been for each combination, rather than answer the more relevant question of what rate to choose for a future site. The current paper presents a Bayesian method for combining data from seed-rate trials and choosing optimum seed rates: this method can incorporate information on seed and treatment costs, crop value and covariates. More importantly. for use as an advisory tool, it allows incorporation of expert knowledge of the crop and of the target site. The method is illustrated using two series of trials: the first, carried out at two sites in 1997-99, investigated the effects of sowing date and variety in addition to seed rate. The second was conducted at seven sites in 2001-03 and included latitude and certain management factors. Recommended seed rates based on these series vary substantially with sowing date and latitude. Two non-linear dose-response functions are fitted to the data, the widely used exponential-plus-linear function and the inverse-quadratic function (Nelder 1966). The inverse-quadratic function is found to provide a better fit to the data than the exponential-plus-linear and the latter function gives estimated optimum rates which are as much as 40% lower. The economic consequences of using one function rather than the other are not great in these circumstances. The method is found to be robust to changes in the prior distribution and to other changes in the model used for dependence of yield on sowing date, latitude, variety and management factors.