Issues related to direct seeding of rice in rainfed cropping systems in northwest Bangladesh

Economic factors and developments in rice production technologies are the major drivers that have led to the adoption of direct seeding of rice in place of transplanting in Asia. The primary economic motives for a shift to direct seeding are the savings in labor cost and the possibility of crop intensification. A key development challenge in the drought-prone rainfed agriculture of the Barind Tract of northwest Bangladesh is to simultaneously improve the reliability and yield of monsoon rice while improving total system productivity by increasing the area planted to drought-tolerant postrice crops. Research trials and field-scale evaluation by farmers have demonstrated that dry direct seeding or wet seeding of pregerminated rice seed reduces labor for crop establishment, results in rice yields similar to or higher than those from conventional transplanting, and advances harvest by 7-10 days. Earlier harvest has the potential to reduce the risk of terminal drought in rice when the monsoon ends abruptly and increases the opportunity for establishing a postrice crop of chickpea on residual moisture. Herbicide use is essential with direct seeding and this further reduces rice production costs. This modified rice/legume system using direct seeding is knowledge-intensive. Widespread sustained adoption will depend on farmers undertaking timely tillage, adequate land leveling, and timely application of herbicides. Extension/farmer training supported by clear decision support frameworks will be needed to provide farmers with access to the knowledge needed to implement direct seeding effectively

Improved weed management for transplanted aman rice

Rainfed transplanted rice grown in the monsoon aman season accounts for more than 50% of the total area planted to rice in Bangladesh. Because of rising input costs, including labor, farmers are searching for ways to maintain income, by either increasing yields or reducing costs or both. On-farm trials in the High Barind Tract indicated that one-third of the farmers would be able to gain 0.5 t ha–1 or more additional grain by undertaking more intensive or timelier weeding than is usual under current management practices. Higher yields were observed on-farm from a preemergence application of butachlor(1.25 kg a.i. ha–1) compared with hand weeding twice. In Comilla District, trials of a range of weed management practices demonstrated that the yield advantage over the farmers’ practice, either one or two hand weedings, was on average 355 ± 18 kg ha–1 for Rifit (pretilachlor), 281 ± 39 kg ha–1 for Machete (butachlor), and 210 ± 34 kg ha–1 for Ronstar (oxadiazon), each followed by one hand weeding in aman 2003. Partial budgets calculated for inputs and returns showed that hand weeding was less profitable than herbicides in rainfed rice,incurring US$72 ha–1 lower return. Use of a push weeder plus one hand weeding was less profitable than herbicides, incurring$49 ha–1 lower return. To date, herbicides have been largely promoted for irrigated rice in Bangladesh. The trial results demonstrate that under rainfed conditions early in the aman season, water levels are adequate for herbicides to work effectively. The use of herbicides allows timely weed control when there is a shortage of labor and avoids transaction costs, such as the provision of meals and time needed to source laborers. Herbicides are likely to be adopted by growers experiencing labor shortages, particularly on large farms and for farmers seeking to reduce input costs. Sharecroppers and tenant farmers who pay rent are primarily concerned about obtaining a high aman yield, so innovations that raise aman yields (such as herbicides that will have a similar effect as a timely first weeding) are also likely to be adopted on sharecropped plots, even when costs are not shared between the landlord and tenant

Muddied waters: suspended sediment impacts on gill structure and aerobic scope in an endangered native and an invasive freshwater crayfish

Suspended sediment (SS) loadings in freshwater habitats have increased over the past century and SS is now a significant environmental stressor. Greater tolerance to environmental stressors has been proposed as a factor in the success of aquatic invasive species. Further, parasites may interact with environmental stressors to increase host susceptibility to loss of fitness and mortality. We compared the effects of SS exposure on the gill structure and aerobic scope of the endangered white-clawed crayfish (Austropotamobius pallipes), and the invasive signal crayfish (Pacifastacus leniusculus), and assessed impacts in relation to parasite burden. SS caused gill fouling and reduction in aerobic scope in both species, though A. pallipes was more susceptible than invasive P. leniusculus. The parasite Branchiobdella astaci, a crayfish worm that infests the gills, interacted with the sediment to affect gill structure whereas infection with the microsporidian parasite Thelohania contejeani had no effect on crayfish response to SS. Juvenile P. lenisuculus had a higher standard metabolic rate than A. pallipes, which may be linked to competitive advantages such as higher growth rate and behavioural dominance. Conservation of A. pallipes often involves relocation of threatened populations to isolated stillwaters; our findings suggest that SS levels should be assessed before relocation

Water chemistry and endangered white-clawed crayfish: A literature review and field study of water chemistry association in Austropotamobius pallipes

Populations of the endangered white-clawed crayfish (Austropotamobius pallipes) have rapidly declined in distribution and density in recent decades as a result of invasive crayfish, disease and habitat degradation. The species is thought to be particularly sensitive to water chemistry, and has been proposed as a bio-indicator of water quality. Here we detail the results of a systematic review of the literature regarding the chemistry of waterbodies inhabited by white-clawed crayfish, along with a wide-scale field study of the chemistry of crayfish-inhabited waterbodies in the UK. We use these data to examine potentially significant variables influencing crayfish distribution. Several variables appear to have thresholds that affect crayfish distribution; crayfish presence was associated with high dissolved oxygen, low conductivity, ammonium, sodium, and phosphate, and to a lesser extent low sulphate, nitrate, and total suspended solids. Some variables (magnesium, potassium, sodium, sulphate, nitrate, and total suspended solids) may be tolerated at moderate to high concentrations in isolation (indicated by the presence of some populations in high levels of these variables), but suites of chemical conditions may act synergistically in situ and must be considered together. Recent efforts to conserve white-clawed crayfish have included relocations to Ark Sites; novel protected habitats with reduced risk of the introduction of disease, invasive crayfish and habitat degradation. We use our findings to propose the first detailed guidelines for common water chemistry variables of potential Ark Sites for the conservation of the species throughout its European range

Promotion of integrated weed management for direct-seeded rice on the Gangetic Plains of India

Rice–wheat cropping is an effective use of land to maximise yields of vital cereal crops in India. However, the cropping system is facing constraints in part related to combining two crops with different growth habits and requirements. This project built on previous work to promote the adoption of direct-seeded rice, combined with appropriate weed management, to rice–wheat farmers on the Gangetic Plains of India. Field trials demonstrated that yields in direct-seeded rice can be comparable with those in transplanted systems. In the absence of weed control there is a significant reduction in yields under direct seeding, but this can be minimised with appropriate weed-management. The use of a herbicide followed by a single hand-weeding conferred a significant benefit in comparison with hand-weeding alone. The research has shown that changes in composition of the weed flora occurred under different direct-seeded crop establishment – information important to future weed-management strategies. Shortages of labour and water, coupled with the incentive for many farmers to reduce overall input costs, are likely to result in widespread adoption of direct seeding in many parts of the Gangetic Plains. The need to control weeds to protect yields will be paramount, and this project has laid a sound basis for the development and promotion of appropriate weed-management practice

Transfer to the continuum and Breakup reactions

Reaction theory is an essential ingredient when performing studies of nuclei far from stability. One approach for the calculation of breakup reactions of exotic nuclei into two fragments is to consider inelastic excitations into the single particle continuum of the projectile. Alternatively one can also consider the transfer to the continuum of a system composed of the light fragment and the target. In this work we make a comparative study of the two approaches, underline the different inputs, and identify the advantages and disadvantages of each approach. Our test cases consist of the breakup of $^{11}$Be on a proton target at intermediate energies, and the breakup of $^8$B on $^{58}$Ni at energies around the Coulomb barrier. We find that, in practice the results obtained in both schemes are in semiquantitative agreement. We suggest a simple condition that can select between the two approaches.Comment: 10 pages, 12 figures. Replaced by accepted version. To appear in Nucl. Phys.

Breakup reaction models for two- and three-cluster projectiles

Breakup reactions are one of the main tools for the study of exotic nuclei, and in particular of their continuum. In order to get valuable information from measurements, a precise reaction model coupled to a fair description of the projectile is needed. We assume that the projectile initially possesses a cluster structure, which is revealed by the dissociation process. This structure is described by a few-body Hamiltonian involving effective forces between the clusters. Within this assumption, we review various reaction models. In semiclassical models, the projectile-target relative motion is described by a classical trajectory and the reaction properties are deduced by solving a time-dependent Schroedinger equation. We then describe the principle and variants of the eikonal approximation: the dynamical eikonal approximation, the standard eikonal approximation, and a corrected version avoiding Coulomb divergence. Finally, we present the continuum-discretized coupled-channel method (CDCC), in which the Schroedinger equation is solved with the projectile continuum approximated by square-integrable states. These models are first illustrated by applications to two-cluster projectiles for studies of nuclei far from stability and of reactions useful in astrophysics. Recent extensions to three-cluster projectiles, like two-neutron halo nuclei, are then presented and discussed. We end this review with some views of the future in breakup-reaction theory.Comment: Will constitute a chapter of "Clusters in Nuclei - Vol.2." to be published as a volume of "Lecture Notes in Physics" (Springer

The EU societal awareness of landscape indicator: a review of its meaning, utility and performance across different scales

There is increasing recognition that agricultural landscapes meet multiple societal needs and demands beyond provision of economic and environmental goods and services. Accordingly, there have been significant calls for the inclusion of societal, amenity and cultural values in agri-environmental landscape indicators to assist policy makers in monitoring the wider impacts of land-based policies. However, capturing the amenity and cultural values that rural agrarian areas provide, by use of such indicators, presents significant challenges. The EU social awareness of landscape indicator represents a new class of generalized social indicator using a top-down methodology to capture the social dimensions of landscape without reference to the specific structural and cultural characteristics of individual landscapes. This paper reviews this indicator in the context of existing agri-environmental indicators and their differing design concepts. Using a stakeholder consultation approach in five case study regions, the potential and limitations of the indicator are evaluated, with a particular focus on its perceived meaning, utility and performance in the context of different user groups and at different geographical scales. This analysis supplements previous EU-wide assessments, through regional scale assessment of the limitations and potentialities of the indicator and the need for further data collection. The evaluation finds that the perceived meaning of the indicator does not vary with scale, but in common with all mapped indicators, the usefulness of the indicator, to different user groups, does change with scale of presentation. This indicator is viewed as most useful when presented at the scale of governance at which end users operate. The relevance of the different sub-components of the indicator are also found to vary across regions