Divergent influence of degree of base saturation of soils on the availability of native, soluble, and rock phosphates

The influence of hydrogen- and calcium-saturated exchange material separated from bentonite, peat, and mineral soils on the availability of rock phosphate to oats, corn, millet, and buckwheat grown in quartz cultures was investigated. The influence of degree of base (calcium) saturation on the availability of native and applied soluble phosphates in 13 Michigan soils was also studied in the laboratory. It is concluded as follows: 1. The addition of hydrogen-saturated exchange material from bentonite and organic and inorganic soils greatly increased the availability of rock phosphate to crops like oats, millet, and corn which otherwise do not feed well on it. This was evidenced by increased yields and a higher phosphorus and a lower calcium content of plants. Calcium-saturated exchange material from bentonite was beneficial in this way. 2. Hydrogen-saturated exchange material from bentonite did nearly so markedly affect the availability of rock phosphate to buckwheat wheat, a crop which takes up large quantities of calcium and normally feeds well on rock phosphate. 3. It is concluded that, in accordance with the law of mass a hydrogen-saturated exchange material greatly increases the availability of rock phosphate to crops low in calcium, such as oats, corn, and millet, but not, generally, to crops high in calcium, such as wheat. 4. Increase in base saturation through the application of lime to seven soils resulted over a period of 1 to 20 days in significant increases in amounts of readily available soil phosphates. In two soils there were slight increases. With the same soils, lime helped to preserve the availability of added soluble phosphates. 5. Increasing additions of lime to five acid soils consistently the power of these soils to fix added soluble phosphate in a difficulty soluble form. 6. The results support the contention that an increase in base saturation of soils lowers the immediate availability of rock phosphate to crops like corn and oats but, on the other hand, tends to keep native soil phosphates and those added as soluble salts in the form of calcium phosphate rather than the less available basic iron phosphates.