Alley Cropping in the Temperate Zone...

Agroforestry has long been appreciated by farmers and researchers in the tropics. The success of agroforestry techniques in the tropics has caught the attention of researchers in the developed world, and they are now exploring its potential use in temperate zones. This interest is illustrated by two conferences on agroforestry which took place in North America over the past year: "the first conference on agroforestry in north america" held in Guelph, Ontario, Canada, and "the planning for agroforestry symposium" in Pullman, Washington, U.S.A.

Dr. Rhonda Janke, Agronomy Coordinator at the Rodale Research Center in Maxatawny, Pennsylvania, is initiating two evaluations of the potential for agroforestry in the temperate zone. The purpose of the first study is to determine which species of perennial, woody, nitrogen-fixing plants have characteristics necessary for their success in an alley cropping system in a temperate climate.

Alley Crop Species Screening

Dr. Janke plans to test the feasibility of alley cropping N-fixing trees with vegetables- high-value crops in Pennsylvania. Some of the vegetables she is considering include: corn, peppers, tomatoes, and lettuce. Preliminary research and background reading revealed more than 60 winter-hardy N-fixing woody species from all over the world. About 30 were chosen-among many other criteria-for their rapid growth habit and their tolerance to the humidity of Pennsylvania. These species will be planted at the Rodale Research Center to be screened for their positive and negative characteristics for alley cropping with vegetables. Planting starts in 1990 and will continue in 1991. Most of the trees will be started from seed, and 3 to 4 will be propagated vegetatively. Some of the N-fixing species are listed at the end of the article. Salix (Willow) species and Gleditsia triacanthos (Honey Locust), both non N-fixing trees, will be included in the trial for comparison. Experimental units in the screening trial will consist of blocks of five trees to be subjected to various treatments.

Questions this trial will attempt to answer include the following:

  • Do they survive the winter in Pennsylvania?
  • Do they grow fast enough to establish in 2 to 3 years, and regrow at a rate which would permit at least one clipping for mulch per year? What is the optimal height and time at which to coppice each species, and can the cutting be mechanized?
  • Are the species weedy? Do they re-sprout beyond the base of the stem? Are they easy to reproduce from seed?
  • Does the leaf mulch suppress crop or weed growth? Do the leaves provide necessary nutrients to the crops?
  • What is the best strain of Rhizobia or Actinomycete for each species in the climate of eastern Pennsylvania and where can it be obtained?

    Demonstration Trial

    In addition to the species screening being conducted at the Rodale Research Center, Dr. Janke is establishing a demonstration trial at the new Working Tree Center, located at the original 70-acre Organic Gardening Experimental Farm, near Emmaus, Pennsylvania. From the trees in the screening trial Dr. Janke selected three for the demonstration trial which showed the greatest potential. She choseCaragana arborescens, (Siberian Peashrub),Robinia pseudoacacie, (Black or common locust) and Saphora japonica (Japanese pagoda tree) for their promise as rapid growing, nitrogen-fixing species, to alley crop them with vegetables. Planting was begun in 1989 and continues in 1990. These trees will be managed in a uniform fashion while various vegetable crops will be grown depending on farm needs. Nitrogen-fixing trees can be included in agro-ecosystems as wind-breaks, wildlife habitat to attract beneficial insects, and as border plantings in a home garden. They double as a source of mulch and a means of stabilizing soil in vegetable production systems on sloping and marginal land.

    The nitrogen-rich biomass collected from prunings can be used as mulch and/or compost. The trees can be coppiced mechanically using a brush-hog or other heavy mower which, when modified can the mulch from the trees to the vegetable bed. Trees can be coppiced by hand when used for boarders and wind-breaks. According to Robert Rodale, "understanding the role of trees is a first step toward solving some major problems which could improve our future prospects on earth."

    All trials involving trees are long-term studies which are not expected to yield significant results for several years. If you have experience with any of the species mentioned above, or any information about other projects on agroforestry in temperate regions, please write to Dr. Janke.

    Dr. Rhonda Janke, Agronomy Coordinator
    Rodale Research Center
    R.D. 1 P.O. Box 323
    Kutztown, PA 19530 U.S.A.