"In the last several years I have been making some soil experiments that I may write up when I am sure I know what I am talking about. In general, I may say I should prefer a soil slightly on the acid side for any and all tree and farm crops if I had an eye to future fertility. Lime breaks down vegetable matter and makes its constituent plant foods quickly available, but prevents a build-up of humus in the soil. The effect is very pronounced in times of drought, the alkaline soil crops drying up much more quickly than do those on acid soil. On the other hand, such soil elements as phosphorus seem to require the lime as a flux to prevent the phosphates from becoming fixed and unavailable to crops.
"In regard to peat moss, it is undoubtedly acid, but it is beneficial in its water-holding properties and in the comparatively slow release of its nutritive elements. Lime added to the peat will break it down rapidly and make it more available as a fertilizer, but until the decomposition reaches a certain point; its effect is to impoverish rather than to enrich the mixture. This seeming paradox can perhaps best be explained by some experiments I have been making with sawdust. A number of plots were prepared and given various treatments, including mixing one surface-inch of sawdust with the soil, and wheat was sown on the area.
"Wheat sown on the test plot without any treatment or fertilizer was normal for the poor clay soil on which the experiments were made. Where sawdust, only, was added, the wheat came up but sickened and produced no filled heads. The same was true where lime was added to the sawdust. Where heavy applications of nitrate of soda were added to the sawdust treated plots, both with and without lime, the 'sickness' disappeared and wheat was matured.
"My analysis of this, coupled with experiments in composting, leads to the following conclusion: During the period of decomposition of the sawdust (hastened, no doubt, by the lime), the bacteria of decomposition fed so heavily on the nitrates in the soil that the plants were starved. When the material had reached the condition of humus, the bacterial activity decreased to the point where fertility was restored.
"The above analysis accounts for the fact that coarse vegetable material, injures crops, when plowed under, for the current season. Fresh succulent material decays so quickly that it becomes almost immediately available, releasing its constituent plant food.
"With proper conditions of moisture and aeration, sawdust, when mixed with quickly decaying material like kitchen garbage, can be reduced to an excellent, usable humus in three summer months. In fact, it is then better material than if permitted to lie out in the weather for fifteen years.
"There is another factor I think important in tree growth, especially where summers are hot, and that is soil temperature.
"For any of our nut trees I should say that an acidity test of pH 6 to 7 would be entirely satisfactory. If the soil is infertile, some form of humus should be worked in at the time of planting. If much such material is used, some lime may be added. Better yet, wood ashes and bone meal will furnish potash, phosphorus, and the lime necessary to correct acidity and maintain the phosphorus in an available condition. Add to this, proper drainage and cool soil achieved by, first, cultivation, and later by heavy mulching, artificial shading, or shrubby undergrowth extended outside the root area, and your tree should 'go to town.' When the tree is large enough to shade its own root area it will take care of its own soil refrigeration. Nature knew what she was about when she planted trees in forests. Trees require warm heads (sunshine) and cool feet (shade), just the opposite from us humans."
Mr. Stoke's letter recalls a very ancient Arabian proverb connected with the date palm. "The date palm tree must have his head in hell and his feet in water." We are indebted both to Mr. Stoke and to the Arab scientists for many things.
Miss Mildred Jones' reply, fortunately, goes into other and equally important phases of the same subject. She says: "Anyone who is going to lime and fertilize nut trees should take at least a five year period for his work, using lime and fertilizer each year, and not dump it all in one year, then wait for results. He should study the return on a five year basis. One year is too short a term. Weather conditions can upset a program to the extent that both lime and fertilizer may not have their effect until the following year. Let those who really want to know, make graphs of growth in young trees and of nut production from older trees, in pounds, for five years, as against five of the same years during which trees similarly situated received no fertilizer or lime.