No matter what the particular ecosystem, we must replace plant nutrients to sustain our current rates of harvest. How we replace them depends on cost, on the accessibility of nutrient sources, and on philosophy. The replacement of choice is the one that provides the essential nutrient to the plant at a rate conducive to the health of the plant. Some critics of the use of commercial K fertilizers recommend substituting rock powders such as pulverized granite. But rock powders do not give up potassium rapidly enough to maintain healthy plant growth unless the rate of application is uneconomically high.
Farmers dislike wasting money no less than nonfarmers do.
Most farmers add fertilizer to soil in amounts determined by observations of plant responses and tests of soil and plant tissues. Soil nutrient losses enable plant growth. Judicious use of artificial fertilizers and soil conditioners counters soil nutrient depletion and, combined with soil conservation, is necessary to meet world food needs. Dr. Singer is a Professor of Soil Science, and Dr. Pettygrove a Cooperative Extension Specialist, in the Department of Land, Air and Water Resources, University of California, Davis.