I was looking for information on using a disk harrow recently and came across an interesting web site:-
http://www.cigrjournal.org/index.php/Ejounral/searchThis is the address for the site's search engine. The articles are rather academic but cover many farming related topics so could be a useful source of advice if you have a problems and need advice.
The links on the search page will lead you to background information on the organisation's objectives and the range of topics covered. However, the search engine probably is the best way to find articles on anything specific.
I followed the advice at the bottom of the search page and entered [ disk AND harrow ] for my search.
The resulting articles didn't produce readable articles in 2 cases which is disappointing but others did open successfully which made the effort worthwhile.