The common misconception about plowing or tilling is that it helps hold moisture and organic material, when the fact is that it does the opposite in most cases. When you break the soil or disrupt the natural organic layer on the top of the soil you allow water to do lots of damage. It compacts the soil badly causing major run off, it literaly seals the soil. This is also why you see crack forming in soil. By not disrupting the organic layer of the soil profile you provide cusioning for when water hit....the dried soybeans, grass, whatever act like a wick for the water when it rains. The organic material also provides a protective layer for microbes and fungi to flourish(which are crucial in plant gowth and organic material break down). Leaving the organic layer undisturbed will save you money on fertilizer, as well. Since the rain or irrigation can't compact the soil it allows for more breakdown of organic material making more Natural or Oraganic fertilizer. The roots will also have more room to grow with less compacted soil. I could spend a little more time on details but then you be reading forever. If you have any questions PM me and I'll try to help ya out. also I'm not saying there is never a time to till the soil, because sometimes you need to break the ground initially to get started. No till is the way to go from a conservationists prospective, and why not there are to many benefits to list.