The temporary injurious effect of excessive liming of acid soils and its relation to the phosphate nutrition of plants

Greenhouse studies were conducted with the purpose of determining the cause of the injurious effects of overliming on plant growth. The results obtained may be briefly summarized as follows: 1. Nine out of 10 acid soils ranging in pH from 4.4 to poorer growth of alfalfa when brought to pH values near neutrality than when lower amounts of calcium carbonate were used, the average decreased yields when the pH values were slightly above 7.0 being 46%. With five of the nine soils the overliming injury to alfalfa disappeared after the first year. 2. Corn grown on an acid Dekalb loam which had been limed to pH values of approximately 6.5 and 7.5 showed marked injury and developed a light green to purplish color characteristic of phosphorus starvation. Additions of manganese sulfate, magnesium sulfate, ferrous sulfate, iron humate, or large amounts of muriate of potash did not correct this condition. The additions of large amounts of mono-calcium phosphate, mono-potassium phosphate, or silica gel, however, overcame the injury. Likewise the substitution of increasing amounts of magnesium carbonate for calcium carbonate, up to 75%, markedly improved growth and produced normal leaf color where the largest amount was added. 3. The materials that overcame liming injury materially increased the water-soluble phosphate in the soil solution and soil extract. 4. In a comparison of four different liming materials added in sufficient amounts to bring an acid Dekalb loam to pH 7.0, corn and rape made much better growth with dolomitic limestone or calcium silicate than with calcium limestone or calcium carbonate; the plants in the latter cases likewise showed marked symptoms of phosphate deficiency. The differences thus obtained were found to be explained by the larger concentrations of water-soluble phosphate where the dolomitic limestone and calcium silicate sources had been used. When the liming materials were added in amounts to bring the soil to pH 5.8, no liming injury was obtained and there was little difference in growth from the use of the various liming materials. 5. The corn plants grown on the soil limed to pH 7.0 had a higher ash content and a lower percentage of magnesium and phosphorus on the ash basis than plants grown at pH 5.8. Excluding the dolomitic limestone treatment some evidence was obtained of a relationship between the injury from excessive liming and the calcium-phosphorus ratio of plants. 6. It is concluded that the temporary overliming injury obtained in these experiments is due to a disturbed phosphate nutrition.