ECHO (Educational Concerns For Hunger Organization) has free downloadable technical documents for any/everyone who wants them. Go to ECHOnet.org. find the Agriculture tap, at the bottom of the list select ECHO Downloads. From there you can find whatever you might want from appropriate technology to Zia Holes as the name of their book suggests.
Note: you must provide an email address each time you download a file.
Attached is one of my favorite files so far, but there are many many more that I haven't gotten to yet.