I don't know anything about synthetic innoculants. What I've used is a naturally occurring soil microbe that works with the bean plant to fix nitrogen from the atmosphere - plants can't do that by themselves. If you've been growing beans successfully in the space in the past, the bacterium is already there and you don't need the innoculant - it will just continue to reproduce itself every year. If you do add the innoculant, it won't make your beans grow any better 'cause the ecosystem will only support a certain amount of the bacteria and the extra will just die off. If you're starting a new plot and want to make sure your beans have what they need, you have nothing to lose but $$ by adding the innoculant - it's organic. If your soil was previously used, say, to grow a chemically treated lawn, you probably don't have much of any healthy life in your soil and you need the innoculant in the first year. The only way to know for sure is to pull up a plant halfway through the growing season and see if it has lots of node on its roots (this is the clearest picture I could find www.agweb.com/assets/1/9/NewsMainImage/nod
). If it doesn't have the nodes, it's not able to fix nitrogen and you need to innoculate the soil, but it's too late for that year. So my take on it is why wait to find out? Oh, and if you have lots of clover volunteering on the soil before you turn it into a bean patch, that's just as good to know as having beans grow well there - if clover likes it, it's innoculated.
| December Minutes: 1,176