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 Lire 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% ill cotton production. The responses Lire 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 IS and 16%). The efficacy of crop protection was higher in cash crops than in food crops. Weed control call 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. all increase ill 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.
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 (IARCs) 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-B1 and Rht-D1 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.
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/m(2). 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.
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.
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.
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 mu m(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.
Volatilization of ammonia (NH3) 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 NH3 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. NH3 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 (NH4+)+ NH3) 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 NH3 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 NH3 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.
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 Lit 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, Lind 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 Lind 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 Lind 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 9 total production from 1(.)3 million tonnes to 3(.)8 million tonnes in the]List three decades. Research Lit the molecular level. including construction of a lentil genetic linkage map, identification of molecular markers, and genetic transformation, has progressed considerably.
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 socioeconomic 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.
The impact of organic, compared with 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 Farm ASSEssment Tool (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 increased over time but the N leaching loss was comparable with conventional arable farms. The soil N pool was increased primarily by organic farming practices and incorporation of straw. The highest increase in the soil N pool was seen on soils with a low initial level of organic matter. The 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 present results stress the importance of using representative data from organic and conventional farming practices in comparative studies of N leaching loss. Lack of representative data has been a major weakness of previous comparisons on N leaching losses on organic and conventional farms.
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.
Potted 1.5-year-old apricot plants (Prunus armeniaca L.), growing under polycarbonate glasshouse conditions with a cooling system, were subjected to two successive water stress/recovery periods until pre-dawn leaf water potential (Psi(pd)) reached values between -2.0 and -2.5 MPa, during summer 1996. Control plants were irrigated daily to maintain the: soil matric potential at c. -20 kPa. Water stress limited plant growth and induced a significant reduction in leaf area, caused by mature leaf abscission. The parallel behaviour of leaf turgor potential and epinasty in stressed plants indicated that these movements are turgor-dependent. Osmotic adjustments of 0.27 and 0.60 MPa were observed at the end of the first and second stress period, respectively. Relative apoplastic water content (RWCa) values were high, ranging from 27 to 42 %, and were not affected by water stress. The rapid decrease in leaf conductance (g(1)) from the beginning of the stress periods, together with the delay in stomatal reopening after rewatering the plants, indicated that stomatal behaviour was not a simple passive response to water deficits. Net photosynthesis decreased only at the end of both stress periods and recovered quickly. These observations indicate that leaf productivity may be affected only slightly by short-term water stress. The results indicate that drought resistance in apricot is based mainly on avoidance mechanisms, such as stomatal control, epinasty and limitation of transpiration by reducing leaf area. However, some tolerance characteristics, including osmotic adjustment, high RWCa and low leaf osmotic potential at turgor loss point (Psi(tlp)) values were observed.
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 (chlomequat 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. Chlorincquat 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', 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.
Glutathione S-transferases (EC 126.96.36.199, 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 188.8.131.52) and superoxide dismutase (SOD, EC 184.108.40.206) 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 dialdchyde 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.
In order to assess the influence of nutrient elements on the accumulation of beta-N-oxalyl-L-alpha, beta-diaminopropionic acid W-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). beta-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 beta-ODAP. The beta-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 P-ODAP in seedlings growing in other element-deficient solutions were similar to controls. When the content of P-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 beta-ODAP in young seedlings relative to controls (P < 0(.)05). Taken together, these data suggest that P-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 P-ODAP content under field conditions. Thus, the application of appropriate nitrogen and phosphorus fertilizers to the soil could decrease the content of P-ODAP in the seeds and leaves of grass pea.
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 8-10000 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.
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, SIMMETEO, 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.
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 smallholding 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 agroforestry. 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.
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/m' 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.
The European Union has limited the maximum nitrate (NO3) 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 (NH4+ or NO3-) 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 (R) (BS) and Entec 26 (R)-(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 characteristies. Nis are especially useful in the spring, when soil temperature is low and solar radiation interception by the crop is high.