SOIL Bacteria Useful to Farmers May Be Caused to Multiply

The greatest scavengers on earth are the minute living organisms which inhabit the first few inches of agricultural soils.  Although not visible to the naked eye, it has been demonstrated by the use of the microscope and other methods that they occur in enormous numbers when conditions are favorable. A rich soil may contain as many as 10 billions per ounce while a poor soil may only support about 15 millions per ounce. Many of these organisms are useful to agriculture in that they make plant food available out of the dead plant and animal remains that fall on or are put into the soil. Their most important contributions are a oradual supply of simple nitrogen compounds (nitrate and ammonia) and carbon-dioxide gas, two extremely essential materials for plant life. Not only do they alter material already in the soil but some of them actually add nitrogen compounds which they manufacture from the nitrogen of the air.

How can the farmer encourage the activities of beneficial soil organisms? Temperature and moisture usually can not be controlled except, of course, that water may be artificially applied and conserved by cultivation or mulching and excess water eliminated by drainage.  Other factors more capable of being controlled are the food supply of the organisms and plants, cropping systems, tillage, and the reaction of the soil. Stable manure and composts contain large numbers of beneficial organisms and not only add to the soil population but stimulate the activity and growth of those already there. Green manures on the other hand only furnish food for those in the soil.

Since 1 ounce of good stable manure may hold 12 billion organisms, an enormous number may be added by applying even 2 or 3 tons per acre. Soils are usually inhabited by desirable organisms although under conditions of a depleted food or moisture supply or other adverse conditions, many undoubtedly perish. With the addition of manure or compost, or the correction of the unfavorable circumstance the survivors multiply and start to work again.  Mineral fertilizers, especially phosphate, exert a favorable influence on the activities of the beneficial soil organisms. Living legume roots apparently stimulate soil organisms while those of mustard and cereals depress them.  Alternation of legumes with cereals is, therefore, one of the means to be used in assuring suitable conditions for the soil population. Plowing and cultivation will not only conserve moisture but will add air to the soil, thereby encouraging favorable bacterial action. Lime is an essential to legume nodule bacteria as well as to the plants on which they form nodules and it also favors the activities of most of the other unseen friends ®f agriculture.

Since most, of the beneficial organisms are universally distributed in agricultural soils and may be augmented by common farm practices there is no reason for going much beyond the farm to secure them.  The special preparations of these bacteria which have appeared for sale from time to time have not compared favorably with fertile soil and homemade compost. On the other hand, when a new legume is to be planted or the numbers of native nodule bacteria have been depleted by adverse conditions, it is necessary to introduce them artificially. This may be done by transferring field soil known to contain the proper organisms in abundance or by the application of artificially prepared cultures which are now easily procurable from commercial sources.