The great secret of legumes is they carry oxygen to their root tips

Dear Greg,

 

Thanks. That was an interesting article. The scientific world, though fascinated with microscopy, is slowing catching up. It could get better at connecting the dots, but it keeps identifying lots of dots anyway. Many things are clear from the overview that seem like momentous discoveries down in the tsunami of complexity.

 

The idea that we might get plants other than legumes to form nitrogen fixing nodules is bogus, though.

 

The great secret of legumes is they carry oxygen to their root tips, releasing oxalic acid that solublizes the lime complex. Calcium may be primary, but all the other cations, at least to molybdenum are activated as well. In 1971 I studied soil microbiology and found out about azotrophs. Later when I was farming I used the Tulane and Georgia Tech libraries to find out more. At the time over 800 species of Azotobacter were identified in the Nile Delta and over 600 in the Mississippi Delta. Azotobacters are responsible for nitrogen fixation around plant roots without nodulation. They require the alkaline complex in the soil to already be readily available while they specialize in energy utilization. They especially like high-carb root exudation, so they are found in and around C4 plants like maize or sugar cane where photosynthesis is tops. They don’t need nodules if the lime complex is in flux. Nodules are their prison. Many are also phosphorous solubilizers, which ensures they can metabolize carbs excreted at growing root tips. It takes most azotrophs 10 sugars for every amino acid  they produce, and this mob wastes not. Why would they limit themselves to nodules when their freedom allows them to do much more. Legumes are so famous for nitrogen fixation simply because they lift the availability of the lime complex so much. They leave activated lime behind for the next crop, so you see a good follow-on nitrogen response. But ideally we would just plant suitable legumes along with crops like sugar, maize and sorghum. Without wasting time rotating crops we would keep the lime complex in flux at the same time as growing a corn or sugar crop. Having done this I found that after a while the soybeans in my maize stopped nodulating because the azotrophs at large in the soil did a better job.

So much for getting cane and corn to nodulate when it’s less efficient.

Under the microscope, nature is fascinating. Its complexity is boggling. Wherever there’s a function there’s a piece of the puzzle. Yet, the overview is more enlightening if you want to know what is going on.

 

Best wishes,

Hugh Lovel