2,712 research outputs found
âSupply and demand trends for fertilizer in Zimbabwe: 1930 to dateâ: Key drivers and lessons learnt
The fertilizer sector in Zimbabwe has evolved over the years in response to different policy changes based on the governmentâs priorities on agricultural development. The industry grew from the 1930s that targeted primarily large scale commercial farmers, through the liberalization period of the mid 1990s, and recent changes that have introduced controls on the marketing system. Since 2000, following the fast track land reform program, Zimbabwe has faced food insecurity challenges that have been exacerbated by the political and economic crises. This prompted the government to adopt policies that have reduced private sector interests in fertilizer supply. In this situation where explicit fertilizer markets have been absent, relief programs have been leading in facilitating deliveries of fertilizers to poorer smallholder farmers located even in remote areas. The supply of fertilizers in Zimbabwe has been driven by government policy, finance and infrastructure while the demand has primarily been a function of farmerâs capacity to acquire fertilizers, availability of water and farmers knowledge of fertilizer use. There is need for a policy shift that promotes a competitive fertilizer marketing to support a broader range of farmers in Zimbabwe leading to agricultural productivity growth. Investment in infrastructure is critical to reduce marketing costs and to boost fertilizer demand; policies that strengthen farmerâs capacity to acquire fertilizers and increase their knowledge on fertilizer use complemented by technologies that promote water use efficiencies are needed.Fertilizer, supply and demand, policy reform, consumption trends, Crop Production/Industries,
Conservation Agriculture Practices and Adoption by Smallholder Farmers in Zimbabwe
This study is based on a panel survey interviewing 416 farmers practising conservation agriculture for at least five cropping seasons. Farmers obtained higher yields on conservation agriculture plots than on nonconservation agriculture ones. The mean maize yield on conservation agriculture was 1546 kg/ha compared to 970 kg/ha for non-conventional draft tillage plots across all 15 districts. However, the contribution of conservation agriculture to total household food security requirements was limited due to small plot sizes. Labor and land still remains a major challenge that limits the expansion of conservation agriculture area. Winter weeding remains a challenge, with 63% of farmers practicing it. Application of residues is still limited (56% of farmers practising it). Fertilizer application is largely dependent on access to free fertilizer. The survey results show that the 78 % of the respondent farmers were initially selected by the NGOs and were provided with inputs such as seed and fertilizer. The other 22% of the farmers in the sample were selected as spontaneous adopters, who did not initially receive any NGO support to implement conservation agriculture practices. Eleven percent of the interviewed farmers had stopped conservation agriculture practices by the 2008/09 cropping season due to withdrawal of input support by NGOs. Research should continue to explore different recommendations for different areas as farmers face dynamic agro-ecological and soil environments. Conservation agriculture should not be introduced as a blanket technology for all areas, but should be flexible and adaptable to local conditions.conservation agriculture, planting basins, yield gains, adoption labor, and fertilizer, Farm Management, Research and Development/Tech Change/Emerging Technologies, Resource /Energy Economics and Policy,
Universal Baxterization for -graded Hopf algebras
We present a method for Baxterizing solutions of the constant Yang-Baxter
equation associated with -graded Hopf algebras. To demonstrate the
approach, we provide examples for the Taft algebras and the quantum group
.Comment: 8 page
\u3cem\u3eiac\u3c/em\u3e Gene Expression in the Indole-3-Acetic Acid-Degrading Soil Bacterium \u3cem\u3eEnterobacter soli\u3c/em\u3e LF7
We show for soil bacterium Enterobacter soli LF7 that the possession of an indole-3-acetic acid catabolic (iac) gene cluster is causatively linked to the ability to utilize the plant hormone indole-3-acetic acid (IAA) as a carbon and energy source. Genome-wide transcriptional profiling by mRNA sequencing revealed that these iac genes, chromosomally arranged as iacHABICDEFG and coding for the transformation of IAA to catechol, were the most highly induced (\u3e29-fold) among the relatively few (iac cluster were genes for a major facilitator superfamily protein (mfs) and enzymes of the ÎČ-ketoadipate pathway (pcaIJD-catBCA), which channels catechol into central metabolism. This entire iacHABICDEFG-mfs-pcaIJD-catBCA gene set was constitutively expressed in an iacR deletion mutant, confirming the role of iacR, annotated as coding for a MarR-type regulator and located upstream of iacH, as a repressor of iac gene expression. In E. soli LF7 carrying the DNA region upstream of iacH fused to a promoterless gfp gene, green fluorescence accumulated in response to IAA at concentrations as low as 1.6 ÎŒM. The iacH promoter region also responded to chlorinated IAA, but not other aromatics tested, indicating a narrow substrate specificity. In an iacR deletion mutant, gfp expression from the iacH promoter region was constitutive, consistent with the predicted role of iacR as a repressor. A deletion analysis revealed putative â35/â10 promoter sequences upstream of iacH, as well as a possible binding site for the IacR repressor
Signed zeros of Gaussian vector fields-density, correlation functions and curvature
We calculate correlation functions of the (signed) density of zeros of
Gaussian distributed vector fields. We are able to express correlation
functions of arbitrary order through the curvature tensor of a certain abstract
Riemann-Cartan or Riemannian manifold. As an application, we discuss one- and
two-point functions. The zeros of a two-dimensional Gaussian vector field model
the distribution of topological defects in the high-temperature phase of
two-dimensional systems with orientational degrees of freedom, such as
superfluid films, thin superconductors and liquid crystals.Comment: 14 pages, 1 figure, uses iopart.cls, improved presentation, to appear
in J. Phys.
Dynamics of Line-Driven Winds from Disks in Cataclysmic Variables. I. Solution Topology and Wind Geometry
We analyze the dynamics of 2-D stationary, line-driven winds from accretion
disks in cataclysmic variable stars. The driving force is that of line
radiation pressure, in the formalism developed by Castor, Abbott & Klein for O
stars. Our main assumption is that wind helical streamlines lie on straight
cones. We find that the Euler equation for the disk wind has two eigenvalues,
the mass loss rate and the flow tilt angle with the disk. Both are calculated
self-consistently. The wind is characterized by two distinct regions, an outer
wind launched beyond four white dwarf radii from the rotation axis, and an
inner wind launched within this radius. The inner wind is very steep, up to 80
degrees with the disk plane, while the outer wind has a typical tilt of 60
degrees. In both cases the ray dispersion is small. We, therefore, confirm the
bi-conical geometry of disk winds as suggested by observations and kinematical
modeling. The wind collimation angle appears to be robust and depends only on
the disk temperature stratification. The flow critical points lie high above
the disk for the inner wind, but close to the disk photosphere for the outer
wind. Comparison with existing kinematical and dynamical models is provided.
Mass loss rates from the disk as well as wind velocity laws are discussed in a
subsequent paper.Comment: 21 pages, 10 Postscript figures; available also from
http://www.pa.uky.edu/~shlosman/publ.html. Astrophysical Journal, submitte
Quantum Bit Regeneration
Decoherence and loss will limit the practicality of quantum cryptography and
computing unless successful error correction techniques are developed. To this
end, we have discovered a new scheme for perfectly detecting and rejecting the
error caused by loss (amplitude damping to a reservoir at T=0), based on using
a dual-rail representation of a quantum bit. This is possible because (1)
balanced loss does not perform a ``which-path'' measurement in an
interferometer, and (2) balanced quantum nondemolition measurement of the
``total'' photon number can be used to detect loss-induced quantum jumps
without disturbing the quantum coherence essential to the quantum bit. Our
results are immediately applicable to optical quantum computers using single
photonics devices.Comment: 4 pages, postscript only, figures available at
http://feynman.stanford.edu/qcom
The effect of pressure on statics, dynamics and stability of multielectron bubbles
The effect of pressure and negative pressure on the modes of oscillation of a
multi-electron bubble in liquid helium is calculated. Already at low pressures
of the order of 10-100 mbar, these effects are found to significantly modify
the frequencies of oscillation of the bubble. Stabilization of the bubble is
shown to occur in the presence of a small negative pressure, which expands the
bubble radius. Above a threshold negative pressure, the bubble is unstable.Comment: 4 pages, 2 figures, accepted for publication in Physical Review
Letter
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