Discussions regarding crops for calcareous soils/Guam
(2/9/02 - 2/12/02)

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postings: 3
countries: United States, Costa Rica
organizations/institutions/companies: CATIE, University of Guam, Univeristy of the Virgin Islands

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From: Frank Cruz
To: mulch-L@cornell.edu
Date: Feb 9, 2002
Subject: Crops for calcareous soils/Guam

Michael and mulch-L,

Hafa Adai from the pacific island of Guam, Please provide me with information on ECHO and other sources of info on cover crops. I am interested in learning more about potential cover crops and green manure crops for tropical climates.

I am working with farmers on northern Guam who are interested in working out a rotational scheme for papayas and bananas/plantains. They are very interested in including a legume cover crop if possible. They are on alkaline soils which are quite shallow. They irrigate during the dry season(6 months) and get 70+ inches of rain the rest of the year. Papayas are grown as annuals because of diseases. The major papaya diseases are Erwinia and Papaya Ring Spot Virus. The plantains grown are grown as an annuals because they do not ratoon well at all. They grow "Williams" bananas which last 5+ years in the ground. Any advise at all would be greatly appreciated.

Best regards.

Frank Cruz
Extension Horticulturist
University of Guam

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Date: Sat, 09 Feb 2002
To: mulch-L@cornell.edu
From: M McGuire
Subject: Crops for calcareous soils/Guam

Frank,

As you can see correspondence is not my strong point. Part of the delay was because I was still looking into some of these things myself. But let me tell what I know. I don't know much about papaya and plantain culture; I am doing it for the first time myself. There are some others on the mulch list who probably could help you out with specific questions; I am thinking about Larry Sell, Donald Kass, and Chuck Staver.

There are several tropical legume groundcovers recommended for orchards. After reading everything I could get my hands on, my short list for tropical, alkaline soils is:

• Jackbean, Canavalia ensiformis
• Mucuna deeringiana (NOT velvetbean = Mucuna pruriens)
• Butterfly pea, Clitoria ternatea

I have not been successful in actually *getting* any of these seeds yet, but I think I am close.

Tropical kudzu, Pueraria phaseoloides is also recommended by many, but others say there is too great a risk for it to escape and become a weed, especially in a small island environment. After seeing the ravages of Leuceana, johnsongrass, and coralvine (all introduced by the USDA station) on St. Croix biodiversity (or what was left of it after 300 years of cane extraction), I decided not to mess with that one.

Reputedly, Sesbania spp. have long been used for building fertility in alkaline soils in India, but I have not looked into it much yet. There are many species, most of them woody, and I don't know which ones would be appropriate for annual systems.

In terms of green manures for soil improvement in annual systems, it is hard to beat velvetbean (Mucuna pruriens), lablab bean (Lablab purpureus), and Crotalaria spp. (Crotalaria juncea, or sunnhemp, for alkaline soils) for tried and true species that work well in many, many environments. Pigeonpea (Cajanus cajan) is another, but you have to get a variety appropriate for your location and cropping system. But there are many more species out there.

In the long term, green manures work best in no-till systems. Roland Bunch has an excellent recent paper on this subject. From my experience, the key to no-till is getting or adapting equipment for managing the green manure biomass / mulch.

If you have more specific questions, don't hesitate to write back.

Mike McGuire
Virgin Islands

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Date: Tue, 12 Feb 2002
To: MULCH-L@cornell.edu
From: Donald Kass
Subject: Crops for calcareous soils/Guam

Dear colleagues,

I am technically out of this business on February 25 when I have to report for work as a microbiologist with the food and drug administration in Jamaica, NY but my experience with green manures on calcareous soils was that canavalia, pigeon pea and Arachis pintoi all grew well, even from seed that had been produced on acid soils. Other Phaseolus species should also do well. I would assume regular peanut, Arachis hypogaea, would also do well as it has a high Ca requirement.

The chapter by Duke in the ASA publication Crop Tolerance to Suboptimal Land Conditions, ASA Special Publication No. 32, does give ranges of pH tolerance for a great number of tropical crops and green manures. The range for Cajanus cajan is 4.3-8.4 and 4.3-8.0 for Canavalia ensiformis. He also lists a Canavalia plagiosperma, oblique Jackbean, which has a pH tolerance of 5.0-7.5.

Hope this is of some help,

Don
CATIE, Costa Rica