The fixation of phosphates by clay soils
1934
Scarseth, G.D. | Tidmore, J.W.
The results may be briefly summarized as follows: 1. Maximum plant response to phosphate fertilization on highly colloidal acid and calcareous soils was not obtained until the applications of the phosphates were requvalent to 1,800 and 2,000 pounds of superphosphate per 2 million pounds of soil, respectively. 2. The efficiency of the various phosphates used, as measured by plant response, decreased rapidly with the time of contact with the soil. 3. In the acid soil, di-calcium phosphate was slightly more available than mono-calcium phosphate. The relative efficiencies for mono-calcium, tri-calcium, mono-ammonium, ferric phosphates. and superphosphate were 100, 57, 110, 25, and 117, respectively. 4. Calcium carbonate greatly decreased the availability of readily soluble phosphates and the crop yield when applied immediately before planting to the acid clay soil, whereas after equilibrium was established and CaCO3 was no longer present in the soil the availability of the phosphates increased as shown by the yield of sorghum. Calcium carbonate decreased the availability of tri-calcium phosphate as measured by plant growth. 5. In general, the more soluble the phosphate used the more rapid was the rate of fixation. On the other hand, relatively insoluble phosphates were fixed slowly but were inefficient in supplying available phosphorus to the plants.
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