Beans as Green Manure
MEXICO CITY - Feb 25/15 - SNS -- Growing regional crops such as velvet bean for green manure can have a dramatic impact on yields of crops such as corn, according to a paper published in the January-February 2015 issue of Agronomy Journal by researchers at the INBIOTECA- Universidad Veracruzana, Xalapa, Mexico.
Scientists grew velvet bean on fields from May through November. They then cut the leaves and stems, leaving them on the fields. Two weeks later, they planted maize or corn. Harvests the following May showed a 60% increase in maize yields.
The researchers said this rotation reduced need for chemical fertilizers and herbicides. Allowing the cut leaves and stems to dry in place added more nitrogen and phosphorus to the soil. Additionally, the leaves' calcium helped stabilize the pH of the soil. While growing, the leaves shaded the soil, preventing weeds, and saving time and money. The velvet bean also protected the soil from weathering due to erosion.
Leaving the leaves on the soil makes use of "green manure." According to lead researcher Angel Ortiz-Ceballos, green manure is "an herbaceous, shrubby or woody plant material that is incorporated into the soil when it is still green or before it reaches full maturity. Green manure is used to improve or maintain the soil reservoir of nutrients which are used by plants and soil organisms."
Because green manure increases soil organic matter, it encourages the presence of other helpful organisms. One such organism is the earthworm. They make tunnels in the soil and excrete nutrients into the soil. The soil is softer, more porous, provides a more favorable microclimate, and makes more nutrients available for other crops.
Long History in Tropical Areas
Ortiz-Ceballos' research provides the science behind local practices. "Velvet bean has been used in southern Mexico for over 40 years by the Chontal and Popoluca indigenous peoples," says Ortiz-Ceballos.
"They observed that when plots where velvet bean had been abundant were clear-cut to grow maize, yields were higher. Others realized that grasses were scarce in sites where velvet bean was abundant, and thought velvet bean could be used to get rid of weed grasses growing in maize plots. Thus, they innovated the winter harvest by introducing the corn-velvet bean rotation system."
Velvet bean has multiple uses in Mexico. Its seeds are brewed to make infusion drinks (like coffee), and are often referred to as "nescafe" or "pica-pica mansa." The leaves, stems and seeds are fodder for cattle, pigs, chickens, turkeys, or sheep.
Velvet bean (Mucuna pruriens) was described in a separate paper by researchers from Italy as a vigorous annual climbing legume originally from southern China and eastern India and now grown in tropical regions of Asia, America, Africa, and the Pacific Islands. Pods are typically used as a vegetable for human consumption and the leaves as animal fodder.
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