Yield-depression effect of fertilizers and its measurement. II. Report on nutritional unbalance disclosed by field tests
1945
Willcox, O.W.
A survey of published field tests shows that in many cases persistent increase of the amount of fertilizer added to the soil results in depression of the normal yields of all kinds of crops, due to the creation of nutritional unbalance. Failure to preserve nutritional balance seems to be a major factor in repressing the fertility of the soil, and is one of the barriers to full exploitation of the known great inherent growth-energies of useful crops. Measures for correcting or avoiding nutritional unbalance require first of all a means of recognizing it and measuring its degree. Such a means is found in the use of the standard yield diagram, which is based on the Mitscherlich-Baule theoreum. On the South Carolina farms represented in the examples here given soil nitrogen is evidently in excess when its total amount exceeds 0.30 or 0.36 baule. Potash is out of balance when its amount exceeds 0.6 baule. In the Illinois soils considered, potash is not out of balance with corn and wheat when its average amount is about 2.0 baules. With soybeans, unbalance with potash begins at about 0.6 baule. Proof is cited that nutritional or agrobiologic unbalance arising from an excess of one nutrient (N for example) may be corrected by an additionof a deficient nutrient. This corrective effect is, of course, just another verification of the agrobiologic law that quantitative plant growth depends on a harmonic balance of all its factors.
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