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<br />Comments to SWSI, November 3t 2003, by John Wiener <br /> <br />29 <br /> <br />2. ditch to gated pipe <br />3. pipe to gated pipe <br />4. pipe to surge valve <br />5.. furrow to sprin kfer <br />6. furrow to drip <br />7. furrow to subsurface drip <br />8. sprinkler to better sprinkler (e.g. Jow pressure or drag hose) <br />9. sprinkler to drip <br />10. sprinkler to subsurface drip <br />11. better sprin kler to drip <br />12. better sprinkler to subsurface drip <br />13. drip to subsurface drip <br /> <br />Structural changes to rand: <br /> <br />14. terracing, contouring <br />15. leveling <br />16~ altered tillage or conservation tillage. <br /> <br />Information management <br />17. Irrigation scheduling to meet needs by soU moisture <br />18. deficit irrigation (strategic deficits; tim i ng shortages) <br />19. fertilizer timing <br /> <br />Crop changes <br />20. change crops, crop mix, or rotation <br /> <br />Although the permutations of these factors would be intractable, farming does not appfy all of <br />them, and the scope of practical inquiry ;s considerably smaller. <br /> <br />What to do? An approach to the problem of estimating irrigation efficiency and <br />return flow obligations: <br /> <br />A. To the extent possible, a first step would be to narrow the range of crops and thus agronomic <br />factors which may be rerevant. Perhaps only a few need be consideredt such as fodder corn, <br />table or sweet corny alfalfat a hay crop, a smaU grain (oats?)t and a representative vegetable. <br /> <br />B. Second, the set of 20 changes noted could be narrowed as weflt using expert opinion and <br />experience to select the most likely or most common changes for a given basin or agricultural <br />region. <br /> <br />C.. Third, the soir and sub..soil properties could be considered, and representative types could be <br />identified if there is suffjcient representativeness in a given region. The Arkansas Valley, for <br />example, has underlying geologic and geomorphic uniformitYt but ditches have different areas of <br />soil types and soil processes which may be important varjabfes (e.g. the different salinity <br />conditions mapped by Gates at aL, as wen as different soils). <br /> <br />D. The integration of the fjrst three steps wourd be identificatjon of the- range of cases which can <br />be reasonabJy expected to cover a useful portion of current water use and potential transfers. <br />Although daunting in prospectt the extent of locaJ knowledge from agricultural extension and <br />USDA and other experts; as well as the prjvate sector, win quickly provide much of thjs~ <br /> <br />E. Taking the selected set of representative cases, the final question may be asked: can the <br />relevant irrigation and return flow conditions be adequately estjmatedt given the current state of <br />knowledge? <br />