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Todds discussion of water needs for the farm


WATER NEEDS FOR ONE HECTARE The 1.8 meters of rainfall a year seems quite significant to me as a civil engineer. Most of the USA does just fine with agriculture given perhaps 0.8-1.2 meters rain a year, and no irrigation is needed to supplement that rain. Note that 1.8 meters of rain/year on a hectare comes to an average of 49 CM/day of water for that hectare. This makes me think again that the first guess at water use for the site at 50 CM per day may be more than we should plan. The area I live in has some of the most productive farm land in the USA and it receives 1.0 meters of rain a year and needs no irrigation. At say 1.0 m/yr of rain on a one hectare area that comes to 10,000 CM, or an average of 27 CM/day. Mexico City's annual rainfall is about 0.6 meters which equates to a daily average of 16 CM for a hectare. There I believe they need some irrigation. Thus, it seems logical in my mind if we bring water just to the plants and not spread it all about, as with rain, that one should be able to maintain agriculture with less than 27 CM/day for a hectare. Now you as an agronomist may have many reasons to push this number higher. Indeed in the USA we most often see only one crop each 12 months, while in these mini-farms in Mexico I suppose the plan is to have 2-4 crops a year.

Perhaps we can in the next few emails better define the annual water needs of these mini-farms. The last 2-3 days of e-mail helped a lot in addressing the desire for land slope and the geometry of the fish pond.


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