This week I've been thinking about legumes. Renowned for their N fixing ability (which varies quite a bit by species and of which the time scale of benefits remains unclear), their grains, or beans, often go underappreciated in American culture. Despite the intense focus on soil microbial communities in this lab's research, we aren't exploring the impact of adding legumes into a rotation on specific microbial community attributes. Is understanding microbial community diversity and activity trends in the grass-legume rotation part of the key to unlocking the mysterious "rotation effect," part of which remains undescribed even with all of our new understandings about soil fertility.
Part of what has spurred this renewed interest, on my part, are several anecdotes about a recent swell of interest from California growers in growing garbanzo beans. This interest may be due to a strong garbanzo bean market. Or, perhaps growers are becoming more and more interested in diversifying their crop rotations and markets. It may be important to quantify how adding in a pulse crop (legume harvested for its seeds, or grains) into California crop rotations affects soil quality.
Growers worldwide have known that including legumes in their rotations was beneficial for their soils and crop yields. A manifestation of this ancient observation is the paired grain+bean dishes present in most ancient cultures. Rice + soybean in China. Two of the famous "three sisters" in Native American cultures that cultivated crops -- corn + beans. Rice and lentils in the Middle East.
Part of the problem with pulse crops in modern times is that beans have declined in popularity and low demand has created relatively low prices for bean crops growers produce. This has been changing for garbanzo beans, which have enjoyed new popularity with the proliferation of hummus. First found on grocery co-op shelves, then popularized by the recent healthy food movement to become ubiquitous in any grocery store deli, demand for hummus, and garbanzo beans by extension, has grown enormously. This has spread to other varieties of the legume.
Innovation in bean-based products, from George Washington Carver's peanut butter to the transformation of the soybean into tofu, has driven the expansion of cultivation of certain legumes and (in some cases) diversified crop rotations. Perhaps that time is drawing near in California cropping systems.