The Economic, Ecological and Horticultural Aspects of Intercropping Nut
Plantings
By F. L. O'Rourke Michigan State College, East Lansing, Michigan
Mature nut trees are usually large trees, and large trees demand space. Young nut trees, therefore, must be planted relatively far apart from each other and for the first few years, at least, there is an abundance of unused land between the trees, which may be used for intercropping. The choice of just what crop or plants to use is often perplexing and should be considered for several aspects.
The economic factors are of prime importance. The cost of growing the crop, the specialized farm machinery and equipment needed, the availability of labor, the distribution of the seasonal labor demand, the time of the critical cultural practices or of harvesting, the potential market, and the expected price of the saleable product must all be considered.
The staple farm crops of the region are often preferable to specialty crops, particularly from the labor standpoint. Corn, wheat, oats, potatoes, and legumes can all be grown with a minimum of labor and the use of power machinery. There is less risk involved with farm crops than with specialities, both in securing an adequate crop and in the price received for the product. Fruit, vegetables and ornamentals often have very critical requirements. They must be sprayed, harvested, and shipped at exactly the right time or all the proceeds will be lost. Staple crops are not so demanding in either culture or harvesting.
The labor distribution throughout the season or even throughout the year must be considered and well planned in advance. No two crops should require exact and demanding attention at the same time. They should be chosen and planted so that a regular, even distribution of labor can be maintained with as little of a rush period as possible and yet with a minimum of idle time.
The general agricultural pattern of the region must be considered. In a sparsely settled grain and livestock region it would be quite inadvisable to grow strawberries or other crops which require a maximum of hand labor during a very brief period. Berries, however, may be perfectly well suited to sections where either transient workers or city children can be secured with little effort.
The crop should suit from the ecological viewpoint. It must not compete with the young, growing trees for mineral food and water, particularly during spring and early summer when the trees make most of their annual growth. On the other hand, if planted too close to the trees, some intercrops may be shaded too severely to produce a normal yield.
Success in intercropping is usually found between plants which are quite dissimilar in form and habit. Black walnuts and pasture grasses furnish a typical example. The long taproots of the walnuts penetrate deeply into the soil, while the grass roots are shallow and fibrous and feed in the soil surface layer. The aerial portions of these plants are likewise quite different, the walnuts tower high in the air, while the grasses form their crowns on the very surface of the ground. The light shade cast by the walnuts does not interfere with the photosynthetic activity of the grasses, but it is sufficient to discourage growth of broad-leaved weeds which have a higher light requirement than that of grass. This light shade also tends to provide a greater supply of available moisture for the grass, in that it reduces temperature and, consequently, water loss from the grass and soil by keeping down both transpiration and evaporation.
Experiments in both Tennessee and Ohio have shown that the quantity of grass produced from beneath walnut trees is greater than on equal areas in the open and that the quality, as represented by a larger protein content, is also higher. For this reason, one may well consider livestock as the income-producing portion of a walnut-pasture planting. Over one fourth of the agricultural land of the United States is devoted to pasture and much of the land is suitable for interplanting to walnuts, butternuts, and other pasture trees, as honey locusts and black locusts, all of which are known to improve the pasture grasses to some extent. The potential income which may be derived from such plantings over this vast acreage is enormous and is the more striking in that these pasture trees occupy a plane that is now idle and unproductive, that is, the area lying above the grass tops. The nuts produced on this "upper story" will represent almost all "clear profit" in that very little care need be given these walnut trees after they have been properly planted. Livestock guards will need to be placed about the trees at planting time and kept there until the trees have grown to the point where they may no longer be harmed by straddling and browsing.