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Depletion of Nursery Lands.
When the the crop is removed, even the roots are taken out of the soil. For four or five years, the land receives practically no vegetation which can rot and pass into humus; and then, the trees are dug in the fall, often when the soil is in unfit condition, and this fall digging amounts to a fall plowing. The soil, deeply broken and robbed of its humus, runs together and cements itself before the following summer; and it then requires three or four years of "rest" in clover or other herbage crop to bring it back into its rightful condition. This resting period allows nature-if man grants her the privilege to replace the fiber in the soil, and to make it once more SO open and warm and kindly that plants can find a congenial root-hold in it.
The following synoptical sketch of the causes of the so-called wearing-out of nursery lands will serve to bring the question of productivity of lands into its proper relationships and perspectives :*
a. The fertility of the soil.-There are two analytical means of determining the fertility of the land. One method determines the chemical constitution, and the other the mechanical or physical condition.
Chemistry determines the amount and kind of plant-food in the soil, but it cannot tell just how useful this food may be to the plant. This depends upon the physical condition of the land, or upon the relation of the soil to warmth, moisture, air and mechanical constitution. The plant is not simply a passive agent, taking in the food which is presented to it, but it is actively engaged in searching for and appropriating food.
* L. H. Bailey, before American Association of Nurserymen, at Chicago, as reported in Garden and Forest, June 24, 1896.
The actual fertility of the soil depends, therefore, upon the plant as well as upon the land. The better and more comfortable the plant, the more food it can appropriate from a given soil; hence that soil is practically the richer. The chemist does not determine the physical conditions which make the plant comfortable and active. In other words, the amount of plant-food in the soil is only one of the elements in the fertility of the land.
In most instances as much depends upon the physical condition of the soil as upon its chemical constitution, and in many cases even more depends upon it.
Soil is derived from two sources-rock and organic matter. Each is essential to it. Without the rock matter it
would lose body and staying qualities. Without the organic matter it would lose life, or "heart" and activity.
Nature adds the organic matter to the soil by growing plants upon it and then incorporating their remains with it. Everywhere the process of soil-building is now going on. The longer the soil is in crops the richer it becomes, although the relative amount of mineral matter which it contains may be decreasing at the same time.
Nature makes the soil richer, then, both by fining and digesting the mineral matter and by ameliorating its physical condition through the incorporation of humus or organic matter.
This fining process must ultimately cease, but the addition of humus never ceases. The final and complete enrichment of the soil, therefore, must come largely as the result of the incorporation of humus with it.
The chief value of this humus is not to directly afford plant-food, but to improve the conditions of temperature, moisture, aëration and the like.
b. Man's treatment of the land.-Man's chief desire is to use the organic products of the land. He consumes the plant product. As a consequence, cultivated soils soon tend to become hard, dense, heavy and lifeless, and the more clay-like the land the more pronounced is the result.
The Best Nursery Lands.
The best and richest farm soils are those which are loamy-that is, those which are friable, soft and dark-colored. This loamy condition is brought about largely by the addition of stable-manures and green crops.
Every ordinary soil tends to lose its humus sooner than its mineral plant-food, and most so-called exhausted soils are injured in their physical condition rather than exhausted of their fertility.
It follows, therefore, that the addition of mere plant-food cannot entirely restore the generality of worn-out lands. The physical condition must always receive first attention. The addition of concentrated fertilizers is not a fundamental corrective of poor lands in the vast majority of cases. It should be considered as a supplement to the treatment of the land by means of tillage and cropping.
If man's reward from the cultivation of the land is so unlike nature's, it follows that one cannot copy the practices of nature in the treatment of the land. Yet, in every generation, there are men who proclaim that because nature neither plows nor tills, therefore man should not. The only infallible guide to the proper treatment of the soil is experience, not mere science, nor speculation; but science explains the laws and directs the application of them when once perience has discovered them.
In fact, experience is law, for experience that persists is that which gives consecutively uniform results under like conditions. All experience proves that frequent tillage and the addition of humus quickly and invariably ameliorate and improve the soil. It is folly to attempt to controvert the facts by mere speculation. On the other hand, experience proves that the addition of chemical fertilizers does not invariably visibly benefit the soil; therefore, the value of such applications must depend upon local or transient conditions.
c. The nursery lands.-The best nursery lands, at least in New York state, are those which contain much clay. soil is the most easily injured by unwise or careless ment and by the loss of organic matter.
The nursery crop occupies the land for three to five years. During all this time the land receives no addition of organic matter, and finally even the roots are taken out of it. In very many cases the trees are planted and dug when the soil is wet or very dry, and, it is therefore, quickly and very seriously injured in its "grain," or its physical condition.
Nurserymen find that if the land is rested in clover or grass for a few years it will again grow trees. This rotation, like all others, is a means of ameliorating the physical condition of the soil as well as the chemical condition of it. A part of the rotation must aim at the incorporation of humus. Therefore, every famous rotation has a "rest" crop in it.
An incidental advantage of any rotation is the variety of tillage imposed by it. A rotation of tools and of methods and seasons of working the land, is often as important as the other results of alternate cropping.
Extended figures of chemical analyses * of nursery stock show that the amounts of potash, phosphoric acid and nitrogen which such stock removes from the land is really very small, and less than that removed by similar bulk or weight of corn or wheat. Experiments now being made show that the addition of concentrated or chemical manures to heavy nursery lands does not promise very important results; but there are greater hopes from experiments in the sowing of crimson clover and other cover crops in the nursery rows, and in the use of stable manures. There are instances of excellent results following the addition of stable manure to nursery lands between the trees in the fall. One piece of land so treated has grown excellent plum trees for twenty consecutive years. There is no necessary reason why nursery stock should not follow nursery stock as well as wheat follow wheat, except that the land is usually more clay-like, the rotation or cropping is longer, and the addition of humus or fiber to the soil is less.
d. The conclusions.-The difficulty, then, is not one of amount
* Consult 10th Rep. N. Y. State Exp. Sta. (1891), and Bull. 103, Cornell Exp. Sta.; also Rep. Amer. Assoc. Nurserymen, 1896, 43-45.
Treatment of Nursery Lands.
of plant-food so much as of the availability of that food by improving the physical conditions of the soil. The soil must be warm, soft, mellow, and the plant must be comfortable.
The trouble is, not that nursery trees take so much from the soil, but that the rotation is too long, the fiber is burned out of the soil, and much of the working of the land is untimely.
Certain lands are not readily injured by nursery cultivation, and these may grow several continuous crops of trees. Now and then the nurseryman can augment the growth of his stock by extra attention to tillage (it is assumed that he always tills well), and by the addition of some quick nitrogen compound, as nitrate of soda; but these are generally only temporary correctives. The complete or fundamental corrective for nursery land is rotation; but the length of this rotation may often be shortened, or even entirely reduced, by the judicious intercultural use of stable manures and cover crops.
The conclusion was
made that the physical condition of the soil is a subject of greater or earlier importance than its chemical constitution; that the value of rotation of crops lies largely in its ameliorating effect upon the physical condition, and that nursery lands are no exception in demanding such rotation. Instead of thinking it strange that trees do not readily follow trees, we should rather think it strange if they did. Because the crop is of several years' duration, it becomes necessary that the alternating cropping should also be extended. A system of rotations must be practiced in blocks of years, not in single years. But this alternating cropping can be greatly. shortened by giving greater attention to the addition of fiber to the soil while the nursery stock is growing. There are instances in which the alternation may be made short, and some in which there need be hardly any. Professor Bailey said that he did not look for a general corrective of the depletion of nursery land, therefore, by the addition of concentrated or chemical fertilizers, but by better management of the lands.