Perhaps the greatest controversy in the gardening field during the past two decades has enveloped the relative merits of chemical nutrients and organic nutrients. The arguments have been so confusing for gardeners-even for those who are scientifically trained-that a thorough discussion of both "organic" and "inorganic" viewpoints is indispensable to any consideration of soils.
Most experienced plantsmen and soil specialists today occupy a middle ground, using organic and chemical materials as seems best suited to the needs of a particular soil, plant, or circumstance. But those who are at the extremes-violently pro-organic or anti-organic -press their arguments so vehemently as to almost drown out the moderates. The logical way to resolve this argument is to try to state both sides clearly and allow facts to speak for themselves.
Primitive man knew nothing about feeding plants. He simply and without awareness relied entirely upon native fertility or upon natural replacement of fertility for all of his crops. When a field became unproductive he merely moved on to fresh land. Nature's bounty was accepted without thought of how, what, or why. This approach, in basically the same form, continued through the centuries. The Greeks, Romans and those who came after them made some progress in plant feeding, with all of it based on natural manures and similar organic materials.
As the years passed, growers showed an increasing awareness of the need for replenishing the soil-restoring food elements that plants removed. It was not, however, until the experiments of Justus
von Liebig (1803-1873) that man really began to break away from dependence on natural manures. Liebig's discoveries came at a fortunate time for the human race, since new naturally fertile land for crops and pastures was running out.
EARLY CHEMICAL FERTILIZERS
Discovery of phosphorus and superphosphate as plant nutrients (one of the great scientific highlights of the nineteenth century) plus investigations of nitrogen, potash and other elements, resulted directly from von Liebig's work.
A fundamental error in much of the thinking of his day (and one which persists even today) was in considering soil as a bank into which deposits of fertilizer could be made and withdrawn at will. No account was taken of the role of soil organisms, the vital nature of humus, the self-regenerating capacity of soils and the need for replacing certain elements not yet proved essential to plant growth.
Because use of certain chemical elements resulted in large increases in crop yields, demand for these elements in even higher purities became so insistent that fertilizer manufacturers devoted more and more of their research and production to satisfying this demand. When these higher-analysis products became widely available, however, a point of diminishing returns was reached. Plants actually showed signs of doing less well when fed with these "pure" chemicals than when fertilized with natural manures or with fertilizers of lower purities.