Food security information on the Internet Parris, Thomas M
Environment : science and policy for sustainable development,
03/1997, Letnik:
39, Številka:
2
Journal Article
Recenzirano
Major Internet-accessible sources of information about the Nov 1996 World Food Summit and the issue of food security are highlighted. United Nations Food and Agriculture Organization ...(http://www.fao.org/wfs/homepage.htm); United States Department of Agriculture (http://ffas.usda.gov//ffas//food_summit/summit.html); (http://aceis.agr.ca/cb/fao/emain.html); United Nations Food and Agriculture Organization (http://www.fao.org); (http://apps.fao.org/default.htm)
A short-term experiment was conducted to determine the effects of reducing tree size on peach tree water use (TWU). Tree size was progressively reduced by de-branching an individual isolated tree ...over a 15-day period. TWU was measured at 15-min intervals using heat pulse sap flow sensors located at eight positions in the trunk sapwood. Measures of TWU were compared with estimates derived from reference crop evapotranspiration (ETo) and the area of shade cast by the tree on the soil surface (A SH). A SH was estimated prior to each de-branching event using a combination of photographs of the tree taken from the direction of the sun, and measures of fractional radiation interception in the area of shade cast by the tree. TWU and ETo averaged 39.5 l/day and 4.7 mm/day, respectively, in the 6-day period prior to de-branching. Effective canopy cover (ECC; estimated as A SH measured at solar noon) was 5.8 m2 in that period. Five de-branching events reduced TWU and ECC by >95%. To account for the daytime variation in A SH, we used effective area of shade (EAS), calculated from estimates of A SH at solar noon and 3 h each side of solar noon. K cb, the basal crop coefficient defined by Allen et al. Crop evapotranspiration: guidelines for computing crop water requirements (FAO irrigation and drainage paper 56). Food and Agriculture Organisation of the United Nations, Rome, 1998, was related to EAS by K cb = 1.05 EAS. These data for an isolated tree suggest that the transpiration component of orchard water use may be related to ETo using estimates of effective fraction of shade on the soil surface.
The main goal of this research was to estimate the actual evapotranspiration (ETc) of a drip-irrigated apple orchard located in the semi-arid region of Talca Valley (Chile) using a remote ...sensing-based soil water balance model. The methodology to estimate ETc is a modified version of the Food and Agriculture Organization of the United Nations (FAO) dual crop coefficient approach, in which the basal crop coefficient (Kcb) was derived from the soil adjusted vegetation index (SAVI) calculated from satellite images and incorporated into a daily soil water balance in the root zone. A linear relationship between the Kcb and SAVI was developed for the apple orchard Kcb = 1.82·SAVI − 0.07 (R2 = 0.95). The methodology was applied during two growing seasons (2010–2011 and 2012–2013), and ETc was evaluated using latent heat fluxes (LE) from an eddy covariance system. The results indicate that the remote sensing-based soil water balance estimated ETc reasonably well over two growing seasons. The root mean square error (RMSE) between the measured and simulated ETc values during 2010–2011 and 2012–2013 were, respectively, 0.78 and 0.74 mm·day−1, which mean a relative error of 25%. The index of agreement (d) values were, respectively, 0.73 and 0.90. In addition, the weekly ETc showed better agreement. The proposed methodology could be considered as a useful tool for scheduling irrigation and driving the estimation of water requirements over large areas for apple orchards.
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