Vetiver breaks wind (!) and nurtures banana trees

Alrighty, then! Back to business--monkey business, that is.

California's "Dr. Banana," Doug Richardson, has worked with bananas and Vetiver for many years. A couple of years ago he and I chatted about Vetiver, bananas, and Hawaii's climate. I wondered whether Vetiver's proven effectiveness as a moisture barrier would contribute to mold in Hawaii banana trees. Doug assured me that Vetiver is an interesting chameleon. When conditions are wet, Vetiver acts as a wick to release moisture; it retains moisture during dry times.

Enjoy the following excerpts from a recent exchange between Doug and Criss Juliard, and John Greenfield's response:

From Criss:

Vetiver surrounds banana plantations as a windbreak along the coast in Morocco; in Senegal, we set up an erosion trial on a banana plantation. On a slight 3-degree slope, we planted one-half hectare with Vetiver hedgerows following the contour, and, next to it, one-half hectare without. Surprisingly, the banana trees planted next to the hedges produced ripe bunches about 4-6 weeks earlier than those without. We concluded that the Vetiver hedges retained moisture and made that moisture available to the plant, both strategic conditions for better growth and yield. While neither plot had drip irrigation, both had received the same amount of gravity-fed water.

In Senegal, I gave some vetiver plants to a plant pathologist friend, who transplanted them near some of his banana trees. He was surprised to observe the superior growth and development of the trees near the vetiver, compared to those further away from it, even though he didn't water the vetiver. When he dug a small trench around one of the banana trees to check its roots, he found its root system decidedly turned towards the vetiver, and concluded that a symbiotic relationship had developed between the two plants. He suspected that vetiver roots were better at dispersing water than his own watering regime. One of the problems we faced early in our relationship with Senegalese banana growers was their preference for flood irrigation. Slowly, large and small plantations converted to drip irrigation, measured and timed. Senegal has now been transformed from net importers of bananas to net exporters! Candidly, part of that shift resulted from the persistent civil disruptions in neighboring Ivory Coast countries that could no longer supply the Senegalese banana market.

I hope your expanded banana plantation is highly successful. Try installing Vetiver on some parts and not on others. In Morocco we've been planting bananas using a technique we learned in Lebanon. Plant a banana plant at each corner of a square meter (3') hole, and install an irrigation outlet at each hole. We found that planting the banana plant 50 cm below the surface eliminated nematode problems, and that one simple tie around the four grown trees eliminated the need for individual “tutors” and the risk of anything touching the bananas.

Doug's response:

I tried to obtain some photo images of a banana/Vetiver planting I did in California in 1999. In my experience, bananas and Vetiver work very well together. However, I found Vetiver's beneficial influence was not limited to bananas. Along with bananas, I planted dozens of other subtropical fruit trees that are considered marginal specialty crops in our area. Almost without exception their growth exceeded our expectations.

I agree that Vetiver greatly improves the moisture regime for the plants in its vicinity but I suspect that an equally powerful factor is the microbiological activity in the rhizosphere of the Vetiver and its attendant impact on the nutritional status and vigor of nearby plants. Vetiver's potential as a nurse crop has been touted in the literature and my experience is consistent. Its use as a windbreak is also a strong contributing factor to the rapid development of plants grown with Vetiver. I have used drip irrigation and microjets with bananas, and both produced acceptable results. Some papers suggest that drip is superior to sprays in the subtropics because it doesn't wet and cool the banana's pseudostems in our heat-deficient environment. However, the sprays provide more humidity. I need more time with a new planting to discern.

John's observations:

Let me add my 10 cents' worth. In the 1950s I set up two large banana plantations on sugar estates that were being closed in Fiji. We didn't use Vetiver because the plantations were on alluvial plains in a 6,000mm rainfall area too wet for sugar cane, but ideal for bananas. Bananas need about 40 litres of water a day to reach full production in nine months. The humidity created by high rainfall or too much irrigation encourages Cercospora leaf spot which affects the bunches reaching maturity. Once the tree has thrown a bunch it no longer will produce leaves, and Cercospora can wipe out the essential leaves before the bunch has filled out or ripened.

Irrigation is costly, and, in your case, Criss, Vetiver hedges would do a great job conserving moisture and holding it in the root zone, without humidity problems. But I think that another factor may be in play, and that is the role played by Vetiver’s Mycorrhiza in stimulating banana growth.

Moisture conserved by Vetiver hedges planted across the slope will stimulate and sustain the crops grown by subsistence farmers, and will become increasingly important as the global recession expands. Developing countries will have to support themselves as aid agencies exhaust their funds. Using Vetiver hedges to conserve moisture in Andhra Pradesh, India, farmers actually produced an excellent crop of millet in an area that had been declared a drought disaster.

Criss:

Your 10 cents is always worth more than a gold mine!

Bananas and proper drainage:
I have not lived in areas with 6,000mm rainfall, but Cercospora leaf disease devastated plenty of small Senegalese banana farms because of overwatering, excess dampness in the roots, and poor soil drainage. Specialists in the Caribbean suggest that healthy banana plants need less than the 40 liters you suggest; they recommend 14 liters/day, spaced over a period of not less than four hours. Bananas that get more water than that are prone to root-based diseases, at least Grand Nain, the variety we were battling. We used raised beds with deeply planted Vetiver. During the rains, Vetiver absorbed and evapo-transpired excess water; during the dry season, Vetiver reduced drought stress by maintaining humidity in the root zone.

Mycorrhiza:
At the time, I was not familiar with Mycorrhiza mycelia and the way it worked. As you addressed, mycelia increases roots' ability to absorb nutrients from the soil beyond those the root system can grasp on its own. Nabil El Chowk, my partner in Morocco, has been researching for several years the effect of inoculating plants with Mycorrhiza mycelia he collects from and near roots in different parts of parched lands, where plants grow in a continuous state of stress. He explained to me that Mycorrhizae found near and in vetiver roots have unusual capacities to increase growth and survival of fruit trees, vegetables and ornamental flowers grown on the farm. www.cropdevelopment.org

So our challenge is how to add to our already bulging Vetiver tool box that the plant not only improves food crop production through soil moisture retention, but also establishes a symbiotic relation, examined through a unique Mycorrhiza in and near Vetiver roots, that allows food crops to develop more efficiently in poor soils. Doug simply refers to the phenomena as the “microbiological activity in the rhizophere.” How do we better market these two advantages in regions where Vetiver is most needed?