LIVING SOIL

Dominion, Volume 36, Issue 16, 14 October 1942, Page 4

LIVING SOIL

Unseen Workers By The

Million

GARDENERS’ MICROSCOPIC FRIENDS AND FOES (By I. D. Blair, M.Sc., Ph.D.)

Millions of microscopic workers, whose presence is unsuspected by the average person, are toiling in the top layers of garden soils. They are busy converting organic matter into plant food, oxidizing minerals so that plants can use them, and, by complicated chemical action within their own bodies, manufacturing growth-promot-ing substances which enhance the fertility of the soil. In this, the latest release from the New Zealand Association of Scientific Workers, Dr. Blair reviews some of the activities of these unseen workers. The soil is not a dead lifeless mass pf rock constituents —it is in a true sense a living system. Home gardeners should understand that the success of their efforts to cultivate so-called “higher l>lants” largely depend on _ activities of numerous groups of microbial organisms inhabiting soil to -the extent of hundreds of millions in a single soil, particle. These constitute the soil “micro-population and are largely responsible for chemical changes which must occur before plant growth can proceed successfully. Many of these changes liberate nutrient elements, making them available for plant growth, most notably the decomposition of nutritively rich organic matter of the humus type.

Our ordinary cultivation and gardening practices stimulate plant growth rot only insofar as the effect on physical texture is concerned but also through the effect they have on the soil insofar as it is an environment for microbial activity. Thus we now have the term “micro-climate” in reference to the soil; cultivation and manuring greatly, influence the micro-climate and depending on the charges therein so do the numbers and kinds of bacteria and fungi fluctuate. The state of the “soil micro-population” at any time can be considered as an index of soil fertility. Parasitic Organisms.

Normally micro-organisms assist higher plant growth by the role of the former in decomposition of organic residues, by the formation of nitrogenous materials and the transformation of minerals into a readily available condition. But another component of the micro-popu-lation comprises groups directly parasitic to plants and which thereby induce conditions associated with “disease.” Parasitism is a form' of nutrition enabling an organism to obtain its nourishment from the tissues of another living organism. Microbial parasitism of higher plants is evidenced by widespread occurrence of all manner of disease symptoms. They are known as plant pathogens in the soil, and cause damping-off, wilt and root-rot and most of our garden plants will from time to time exhibit evidence of such infections. There is no mutual interrelationship here between the higher and lower form of plant life, and either one must thrive at the expense of the other. It is the gardener’s aim to ensure that cultivated plants will thrive and to this end disense-producing organisms must be combated by methods of soil treatment, including (1) rotation of crops, siime soil pathogens accumulate as a result of continuous growth of disease-susceptible species or varieties. (2) Use of crop varieties possessing a natural or generic resistance to disease. (3) Use of chemicals in the form of protectant seed dusts, foliage sprays or soil fumigants. (4) Encouragement of a soil micro-climate conducive to beneficial organisms at file expense of harmful. To this important end our techniques of thorough cultivation, draining, manuring and weed-destruction all contribute.