Yield gap and the shares of climate and crop management in yield and yield variability of staple crops in West Africa. [O-3330b-01]

" Yield gap " (Yg) is a key concept of agricultural science for identifying the room for improvement of yields through better management of the agroecosystem. in rainfed agriculture Yg is the difference between actual yield (Ya) and the theoretical water limited yield (Yw) that would be achieved if solar radiation, temperature and precipitations were the only factor limiting the crop's growth and yield. Changes in Yw over regions and years are due to climate-soil interactions that are not easily modified by crop management, whereas changes in Yg are due to limiting factors that are typically within the scope of crop management such as nutrient availability, weeds, and pests. We provide an example of yield gap estimates in semi-arid a frica, using yield and other agronomic data collected in famers' fields of Senegal in 1990 and 1991 and from 2006 to 2012. i t illustrates how contrarily to what most people would expect climate is not, on average, what most limits yields in that region: yet, actual yields are on average a quarter of water limited yield, and this is due to constraints whose reduction is technically possible albeit subject to the economic and environmental relevance of doing so. Most studies dealing with the impact of climate change on agriculture in West a frica compare Yw under present and future climate as predicted by climate models. t he magnitude of those predicted long term changes in Yw by 2050 is down to –20% in the worst scenario combining a +6°C change with a -20% rainfall change. s uch changes in water limited yields are certainly concerning, but they are remarkably small compared to the potential +390% increase that would result from closing the current yield gap. When considering yield variations observed across plots and years, and not anymore regional averages over a few years, what strikes is the stability of observed yields compared to variations of Yw. We used crop model simulations with historical series of 20 years of weather data to compare yield distributions over years of a crop grown using 3 contrasted levels of fertilisation and no incidence of weeds, pests or diseases. For each fertilisation level, the simulated yield reached a maximum value the 'best year' of the series. t he three fertilisation levels were chosen so that the maximum simulated yield reached 0.25 Yw, 0.5 Yw, and 0.75 Yw respectively. t he resulting simulated yield distributions show that even if management allows increasing the median yield, in many years the climate is the main limiting factor and fertilising has no or a slight impact only. i n other words, the way the current climate limits crop production in this region is by making uncertain the output of investing for high yields. Buying fertilizers or working hard for manure collection, transport and distribution do not translate, a certain number of years, into more production. For farmers struggling for the daily subsistence of their family, that kind of risk may not be justified while alternative use of family resources in cash and labour force provide less risky ways to produce subsistence means. Until recently, in many farming systems of West africa, the growth in food needs due to population growth in rural areas was matched thanks to increases in cultivated or pasted areas rather than increases in crop yields or livestock pressure on land (i.e extension rather than intensification of crop or livestock activities). When rural families reached the limits of this strategy, migrations of many kinds of distance and duration became the adjustment variable to the gap between resources available from farming and population needs. T his suggests that for many, it is less risky to leave home than to intensify cropping or livestock systems. Anyway, as job opportunities for migrants from the rural zones are currently low in West african cities and elsewhere, there are legitimate concerns about the way this strategy may soon reach its limit as well. i n terms of climate change, the worst scenario for farmers of that region would be if crop intensification became even more risky under future climate than at present. t here is thus an urgent need for joint agronomic and climate research to go beyond the prediction of Yw or of yield under unchanged crop management and determine whether or not the future climate will increase the yield risks associated with crop intensification in that region. But this should not divert from designing and implementing policies incentive to such intensification under present climate, as this might be much easier now than later. (Texte intégral

Analysis of the relationship between start of the rainy season and farmer's soving date in the Niamey area and its impacts on the pearl millet yield

Relationship between start of the rainy season and farmer's planting date have been analysed at local scale through (i) in situ daily rainfall records and (ii) agronomical measurement provided by on-farm survey at plot scale for 10 villages network located on the mesoscale AMMA-CATCH Niger site during the 2004-2007 rainy seasons. Many classical empirical methods of monsoon onset dectection (e.g. Benoit, Kowal, Sivakumar, Ati, Marteau, Balme, Sultan) and numerical methods based on crop model SARRAH have been compared to the observed farmer's sowing date. Results show that SARRAH and Balme mean onset date are close to sowing date. But spatial and temporal variability of the sowing date is not correctly reproduced by any start of the rainy season. Nevertheless, almost 50% of the successful observed sowing date are in phase with the start of the rainy season defined by Sivakumar, Balme and SARRAH whereas about 40% of sowing are in advance comparing to Sivakumar or SARRAH onset date. Farmers' management of the sowing date is systematically based on risk strategy in order to ensure a maximum yield for most of the year. Thus, 23% of first sowing, usually earlier than the start of the rainy season, have failed and require re-sowing due to the intermittent dry spells and low rainfall intensity after sowing. Indeed, it causes a strong crop water stress during germination and panicle initiation. Otherwise, the start of the rainy season and sowing date does not seem to be the main factor of the yield variability, because these parameters explain only 10% and 16% respectively of the yield variation. However, mean yield appears to be affected by the delay of the start of the rainy season and/or latter sowing date which reduces grain yield of about 30% than ealier start of the rainy season or sowing

Channeling of Electrons in a Crossed Laser Field

In this article a new analytical description of the effective interaction potential for a charged particle in the field of two interfering laser beams is presented. The potential dependence on the lasers intensities, orientation and parameters of the particle entering the considered system is analyzed. It is shown for the case of arbitrary lasers crossing angle that for different values of projectile velocity the attracting potential becomes a scattering one so that the channel axes and borders interchange each other. In addition the projectile radiation spectral distribution is given and general estimations on the expected beam radiation yield are outlined

Enhanced third-order optical nonlinearity driven by surface-plasmon field gradients

Achieving efficient nonlinear optical frequency conversion in small volumes is key for future on-chip photonic devices that would provide a higher-speed alternative to modern electronics. However, the already intrinsically low conversion efficiency severely limits miniaturization to nanoscale dimensions. Here we demonstrate that gradient-field effects can provide for an efficient, conventionally dipole-forbidden nonlinear response, offering a new approach for enhanced nonlinear optics in nanostructures. We show that a {\em longitudinal} nonlinear source current can dominate the third-order optical nonlinearity of the free electron response in gold in the technologically important near-IR frequency range where the nonlinearities due to other mechanisms are particularly small. Using adiabatic nanofocusing to spatially confine the excitation fields, from measurements of the $2\omega_1 - \omega_2$ four-wave mixing response as a function of detuning $\omega_1 - \omega_2$, we find up to $10^{-5}$ conversion efficiency with a gradient field contribution to $\chi^{(3)}_{\mathrm{Au}}$ of up to $10^{-19}~\mathrm{m}^2 / \mathrm{V}^2$. The results are in good agreement with theory based on plasma hydrodynamics. Our results demonstrate an increase in nonlinear conversion efficiency with decreasing sample size that can offset and even overcompensate the volume decrease of conventional dipolar pathways. This will enable more efficient nonlinear optical devices and frequency converters and facilitate the extension of coherent multidimensional spectroscopies to the nanoscale.Comment: 14 pages, 4 figure

Superfluid 4He dynamics beyond quasiparticle excitations

The dynamics of superfluid 4He at and above the Landau quasiparticle regime is investigated by high precision inelastic neutron scattering measurements of the dynamic structure factor. A highly structured response is observed above the familiar phonon-maxon-roton spectrum, characterized by sharp thresholds for phonon-phonon, maxon-roton and roton-roton coupling processes. The experimental dynamic structure factor is compared to the calculation of the same physical quantity by a Dynamic Many-body theory including three-phonon processes self-consistently. The theory is found to provide a quantitative description of the dynamics of the correlated bosons for energies up to about three times that of the Landau quasiparticles.Comment: 5 pages, 3 figure

Hot electron driven enhancement of spin-lattice coupling in 4f ferromagnets observed by femtosecond x-ray magnetic circular dichroism

Femtosecond x-ray magnetic circular dichroism was used to study the time-dependent magnetic moment of 4 fs electrons in the ferromagnets Gd and Tb, which are known for their different spin-lattice coupling. We observe a two-step demagnetization with an ultrafast demagnetization time of 750 fs identical for both systems and slower times which differ sizeably with 40 ps for Gd and 8 ps for Tb. We conclude that spin-lattice coupling in the electronically excited state is enhanced up to orders of magnitude compared to equilibrium.Comment: added reference 24, clarified the meaning of photo-induced, emphasized that XMCD probes the magnetic moment localized at 4f electron

Anal incontinence after vaginal delivery or cesarean section.

INTRODUCTION: Uncertainties remain as to whether cesarean section is protective for short and long term development of anal incontinence. Our aim was to explore whether women who had only delivered vaginally were at greater risk of anal incontinence compared to nulliparous women and women who had undergone caesarean sections only. MATERIAL AND METHODS: Background information, medical history and data on anal incontinence (defined as fecal or flatus incontinence weekly or more) reported by women participating in a large population-based health survey in Norway (HUNT 3) during the period October 2006-June 2008, was collected and linked to data from the Medical Birth Registry of Norway. Anal incontinence prevalence was calculated and multivariable logistic regression analyses were applied. RESULTS: Mean age amongst the 12.567 women was 49.9 years. Age and educational level were similar in women with caesarean sections only and those with vaginal delivery and obstetric anal sphincter injuries (OASIS). Nulliparas and women with vaginal delivery and no OASIS were older and had higher educational achievements. One in four women with OASIS reported anal incontinence compared to one in six amongst the other women(p<.001). Age, educational level, diarrhea, constipation, birthweight and OASIS increased the risk of anal incontinence in all women. Parity was associated with anal incontinence in parous women only. No differences were found for fecal urgency. CONCLUSIONS: Women with vaginal deliveries complicated by OASIS were at increased risk of anal incontinence. However, no increased risk of anal incontinence was found in nulliparous women or women with cesarean sections only or vaginal deliveries not complicated by OASIS

Women's Empowerment and Reproductive Choices

The 1994 Cairo International Conference on Population and Development (ICPD) in their Programme of Action calls for promoting gender equality and equity and the empowerment of women. Furthermore, the conference also recognises the basic rights of all couples and individuals to decide freely and responsibly the number, spacing, and timing of their children, as well as the right to the information and the means to do so [Sadik (1994)]. The need for such a programme of action arose in view of the fact that in many countries, including Pakistan, women are generally least empowered and hence they have negligible rights to decide about the number of their children. According to the 1990-91 Pakistan Demographic and Health Survey, over 54 percent women either wanted to stop having children or wanted to wait at least two years before having another child [Ali and Rukanuddin (1992)]. However, in practice, all of these women were not protected; instead, only 12 percent were practising contraception [Shah and Ali (1992)]. The low incidence of family planning practice on the part of the women is not so much due to the dearth of family planning services; rather it is due to resistance by husbands, in-laws, and other peer pressures. Demographers like Caldwell (1982) and Cain et al. (1979) also contend that in patriarchal societies it is the patriarchy which militates against the fertility decline.

Marketing Percolation

A percolation model is presented, with computer simulations for illustrations, to show how the sales of a new product may penetrate the consumer market. We review the traditional approach in the marketing literature, which is based on differential or difference equations similar to the logistic equation (Bass 1969). This mean field approach is contrasted with the discrete percolation on a lattice, with simulations of "social percolation" (Solomon et al 2000) in two to five dimensions giving power laws instead of exponential growth, and strong fluctuations right at the percolation threshold.Comment: to appear in Physica