Farm Size and the Share of Irrigated Land in total Landholding: the case of Water-Harvesting Irrigation in Ethiopia

Rain-fall shortage constrains production in small-holder agriculture in developing countries and with ongoing climate change these shortages may increase. Rain-water harvesting are interesting technologies that decrease this risk. Therefore, one would expect an increasing use of these technologies in drought-prone areas. However, data collected in Ethiopia shows that the share of irrigated land in total landholding declines with farm size. This study investigates why the share declines with farm size using panel data collected in 2005 and in 2010. A random-effect tobit model is estimated for the share of irrigated land as a function of variables affecting returns, market prices, source of finance and expectation formation. The findings show farm-specific factors such as credit per hectare, distance to market, ease of selling output, landholding, regional differences, aridity and distance of plots from natural water sources significantly affect the share. Thus, encouraging investment has to consider farm-size, and also geographical, environmental and regional diversity.Land Economics/Use, Resource /Energy Economics and Policy,

Harnessing entropy to enhance toughness in reversibly crosslinked polymer networks

Reversible crosslinking is a design paradigm for polymeric materials, wherein they are microscopically reinforced with chemical species that form transient crosslinks between the polymer chains. Besides the potential for self-healing, recent experimental work suggests that freely diffusing reversible crosslinks in polymer networks, such as gels, can enhance the toughness of the material without substantial change in elasticity. This presents the opportunity for making highly elastic materials that can be strained to a large extent before rupturing. Here, we employ Gaussian chain theory, molecular simulation, and polymer self-consistent field theory for networks to construct an equilibrium picture for how reversible crosslinks can toughen a polymer network without affecting its linear elasticity. Maximisation of polymer entropy drives the reversible crosslinks to bind preferentially near the permanent crosslinks in the network, leading to local molecular reinforcement without significant alteration of the network topology. In equilibrium conditions, permanent crosslinks share effectively the load with neighbouring reversible crosslinks, forming multi-functional crosslink points. The network is thereby globally toughened, while the linear elasticity is left largely unaltered. Practical guidelines are proposed to optimise this design in experiment, along with a discussion of key kinetic and timescale considerations

Prokaryotic respiration and production in the meso- and bathypelagic realm of the eastern and western North Atlantic basin

We measured prokaryotic production and respiration in the major water masses of the North Atlantic down to a depth of,4,000 m by following the progression of the two branches of North Atlantic Deep Water (NADW) in the oceanic conveyor belt. Prokaryotic abundance decreased exponentially with depth from 3 to 0.4 3 105 cells mL21 in the eastern basin and from 3.6 to 0.3 3 105 cells mL21 in the western basin. Prokaryotic production measured via 3H-leucine incorporation showed a similar pattern to that of prokaryotic abundance and decreased with depth from 9.2 to 1.1 mmol C m23 d21 in the eastern and from 20.6 to 1.2 mmol C m23 d21 in the western basin. Prokaryotic respiration, measured via oxygen consumption, ranged from about 300 to 60 mmol C m23 d21 from,100 m depth to the NADW. Prokaryotic growth efficiencies of,2 % in the deep waters (depth range 1,200–4,000 m) indicate that the prokaryotic carbon demand exceeds dissolved organic matter input and surface primary production by 2 orders of magnitude. Cell-specific prokaryotic production was rather constant throughout the water column, ranging from 15 to 32 3 1023 fmol C cell21 d21 in the eastern and from 35 to 58

Tracing the origin of dissolved silicon transferred from various soil-plant systems towards rivers: a review

Silicon (Si) released as H4SiO4 by weathering of Si-containing solid phases is partly recycled through vegetation before its land-to-rivers transfer. By accumulating in terrestrial plants to a similar extent as some major macronutrients (0.1–10% Si dry weight), Si becomes largely mobile in the soil-plant system. Litter-fall leads to a substantial reactive biogenic silica pool in soil, which contributes to the release of dissolved Si (DSi) in soil solution. Understanding the biogeochemical cycle of silicon in surface environments and the DSi export from soils into rivers is crucial given that the marine primary bio-productivity depends on the availability of H4SiO4 for phytoplankton that requires Si. Continental fluxes of DSi seem to be deeply influenced by climate (temperature and runoff) as well as soil-vegetation systems. Therefore, continental areas can be characterized by various abilities to transfer DSi from soil-plant systems towards rivers. Here we pay special attention to those processes taking place in soil-plant systems and controlling the Si transfer towards rivers. We aim at identifying relevant geochemical tracers of Si pathways within the soil-plant system to obtain a better understanding of the origin of DSi exported towards rivers. In this review, we compare different soil-plant systems (weathering-unlimited and weathering-limited environments) and the variations of the geochemical tracers (Ge/Si ratios and d30Si) in DSi outputs. We recommend the use of biogeochemical tracers in combination with Si mass-balances and detailed physico-chemical characterization of soil-plant systems to allow better insight in the sources and fate of Si in these biogeochemical systems

In Intertidal Gastropod Community Malalayang Beach Manado North Sulawesi

This study aims to determine the density and relative density of gastropods and diversity index of the community as well as evenness and dominance index in the intertidal beach Malalayang), Manado in North Sulawesi. Gastropods were sampled using quadrate with size 1x1m2 placed systematically and disproportionately on dead coral sandy substrate, mix mud, rocks slightly sandy substrate, and substrate-sized stones. The study found that there has been a change in the amount of 30 species of gastropod species (Manginsela, 1998) increased to 69 species. While the density of gastropods contained in the intertidal beach of Malalayangis ranging from 13,63individu / m2to currently 2,73-13,63individu / m2 and relative density ranging from 11.22% - 42.78%. Diversity index of organism is high with a value of H '= 2.81497. Evenness index of gastropods in Malalayang Beach intertidalcould be categorized fairly even and almost evenly. Meanwhile, the low dominance values ​​C = 0.2132, indicating that the area has good conditions as a place to live, and yet there is competition, which means, food or a place is suitable for gastropods to live. The intertidal area of Malalayang Beach Manado North Sulawesi substrate are mainly in the form of sandy coral, slightly muddy and rocky. Keywords: gastropod, distribution A B S T R A K Penelitian ini bertujuan mengetahui kepadatan, kepadatan relative dari masing-masing jenis gastropoda serta indeks keanekaragam komunitas gastropoda, kemerataan dan indeks dominansi di intertidal Pantai Malalayang (di belakang Minanga Hotel), Manado Sulawesi Utara. Pengambilan contoh gastropoda menggunakan kuadrat ukuran 1x1m2 yang ditempatkan secara sistimatis dan proporsional pada substrat karang mati berpasir campur lumpur, substrat bebatuan sedikit berpasir substrat batu-berukuran. Hasil penelitian menemukan telah terjadi Perubahan jumlah spesies gastropoda dari 30 spesies (Manginsela, 1998) meningkat menjadi hanya 69 spesies. Sedangkan kepadatan gastropoda yang terdapat di intertidal pantai Malalayang dari berkisar 13,63individu/m2 saat ini 2,73-13,63individu/m2 dan kepadatan relatif berkisar 11,22% - 42,78%. Keanekaragaman jenis organisme tergolong tinggi dengan nilai H' = 2,81497. Kemerataan jenis gastropoda pada intertidan Pantai Malalayang Manado Sulawesi Utara termasuk kategori cukup merata dan hampir merata. Sedangkan, Dominasi rendah yakni nilai C = 0

Explicit solutions to the Korteweg-de Vries equation on the half line

Certain explicit solutions to the Korteweg-de Vries equation in the first quadrant of the $xt$-plane are presented. Such solutions involve algebraic combinations of truly elementary functions, and their initial values correspond to rational reflection coefficients in the associated Schr\"odinger equation. In the reflectionless case such solutions reduce to pure $N$-soliton solutions. An illustrative example is provided.Comment: 17 pages, no figure