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How To Experiment With Fertilizers

( Originally Published 1915 )



How to Experiment with Fertilizers.—To determine what element or plant food is most needed, select an area of level ground of uniform texture, tilth, and former treatment. Avoid underdrains, back furrows and dead furrows which might affect the yield of one of the experiments. After the ground is uniformly prepared, mark off plots and set a strong stake at the corner of each. The plots are most convenient when long and narrow and separated from each other by a 2- or 3-foot strip for a walk. A plot 8 by 34 feet is approximately equal to a square rod. A plot 16 by 34 feet—two square rods—is better. Five different treatments may be given on as many different plots. These should be compared with a check plot having no treatment (Fig. 76). The average of two experiments is more accurate, of course, than the result from one experiment. Therefore twelve plots are recommended.

Plot 1 may be treated with an even application of one pound of nitrate of soda, plot 2 with one pound of acid phosphate, plot 3 with three-fourths of a pound of nitrate of potash, and plot 4 with 25 pounds of finely pulverized calcium limestone. Plot 5 may have an application of the first three mixed. Plot 6 is to have no treatment. This treatment of the five plots is equal to a dressing of 600 pounds per acre of a high-grade complete fertilizer. On plots 1, 2 and 3 the treatment consists of a single element of the fertilizer. If there is a suspicion that the soil needs more of one element and not any of the others, the amount of that element may be increased to something like 4 or 5 pounds for a square rod and used on another plot. By comparing the weight of the products from these strips, we may learn the relative values of the different commercial fertilizers.

There are many things that make an experiment with fertilizers go wrong. It is very hard for the busy farmer to get reliable results. But this work in school may do much to give the child something of the scientific attitude of mind, careful weighing of evidence, suspension of judgment, truthful statement of just what was found, etc.

Plants as Fertilizers.—What good do the clovers, vetches, alfalfas, cowpeas and other leguminous crops do ? The answer to that question is indeed an interesting study for any school. The teacher should remember that an intelligent use of the legumes may mean a life of prosperity and happiness, or no knowledge of them may mean a life of wretched poverty for nearly one-half of the boys and girls in her classes. To begin with, it may be interesting to teach them that few plants get enough air and water to allow them to reach their best possible size and quality. Now the roots of such plants as mammoth clover and alfalfa go far down into the ground; the former may penetrate six feet, the latter nine feet, or more. After the tops are plowed off the decaying roots act as sponges to hold air and water. During rainy weather the decaying roots absorb the surplus water and then during the dry times gradually dole it out as needed to the growing plant roots. Think of placing lamp wicks nine feet long all over one's field to hold air and water until needed, then to bring it to the surface.

These are only the incidental results of the legumes. If a field has been worked for some time it may become sour or poisoned from the plants that have been growing on it. The clovers do more than any other class of plants to restore fertility to the soil. If the field gets too sour it seems that alsike is the only clover that will do well, then, after the alsike clover is plowed and the field worked a year or so, the other clovers may grow. Nor is this the great mission of the clovers. All the legumes have a function which the botanists call commensalism or symbiosis. This means that they live together for support. Now the little clover roots are the messmates of certain kinds of bacteria which differ for the different kinds of clover; that is, alfalfa and sweet clover messmate with one kind of bacteria, other clovers with other kinds, cowpeas (Fig. 77) with another, beans with another, etc.

The farmer in the new agriculture will be just as sure to have a library on agriculture and to read it as is the teacher to have one on pedagogy, the lawyer on law, or the doctor on medicine. Perhaps the most readable book on the soil is Fletcher's " Soils." I close this chapter with a paragraph from that book.

" The greatest problem in farming is that of maintaining the fertility of the soil. The fertility of the soil is its power to produce crops. It is not mere plant food; it is water, air, sunlight, plant food, temperature, soil bacteria and all of the other factors and conditions which make a soil habitable for plants.

" It is concerned with the texture of the soil as much as with its richness, and its water-moving power as much as its composition. Plant food is but one of many conditions necessary to the growth of crops, and often it is the least essential condition. The fertility of the soil is the sum of all the conditions that make it possible for the seed to sprout, the blade to spread and the ear to ripen. It is the inherent power of the soil to produce crops.

" The problem of maintaining or restoring the fertility of farm soils, then, is much broader than that of merely adding plant food to them. It depends upon plowing, harrowing, rolling, cultivating, draining, irrigating and other tillage and cultural operations, fully as much as upon manuring, fertilizing, fallowing and the like. A really comprehensive discussion of the soil fertility should consider all the ways in which soil is handled or is acted upon by natural forces, as well as means of enriching it, and of conserving natural richness."

Enough has been said, I hope, to enable the teacher to see that much of the study of the soil has to be left until the year given to the subject in the high school or college. President Wallace of the National Conservation Congress says : " Farmers with knowledge of how to maintain and increase the productivity of the soil are soon to be the nation's greatest need."



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