The use of acidifying materials on calcareous soils

1. Field, greenhouse, and laboratory experiments were conducted to determine the influence of acidifying treatments on yield and chemical composition of plants growing on various calcareous soils. 2. In a field experiment on Taylorsville silty clay loam, which contains 5 to 8% lime, the yields of wheat, potatoes, and sugar beets were not increased by sulfur, sulfur and manure compost, or phosphoric acid over the yields of comparable nonacidified treatments. In a 12-year study on Millville loam, which contains over 40% lime, sulfur and rock phosphate added to manure did not result in better yields than manure treatments alone. 2. In greenhouse studies the yields of alfalfa, barley, and corn growing on three different calcareous soils were not significantly increased by acidifying treatments, including two rates of sulfur, sulfuric acid, and phosphoric acid, over yields obtained from comparable treatments that were not acidifying. Irrigation water acidified to pH 3.0 by sulfuric acid decreased the yield of alfalfa. 3. In a greenhouse test with two calcareous soils and one noncareous soil, water acidified to pH 3.0 and to pH 5.0 with sulfuric acid had no significant effect on the yield or mineral content of tomato plants, but the treatments decreased the yield of alfalfa. Results on the noncalcareous soil were not appreciably different from those on calcareous soils. In this same experiment banded applications of sulfuric acid, dried manure, and treble superphosphate in various combinations showed no distinctive effects on calcareous soil compared with their effects the noncalcareous soil in regard to yield, or to iron, manganese, or calcium contents of tomato plants. The treatment means for all soils indicate that manure bands alone increased the concentration of iron in the plants. Sulfuric acid added to the manure further increased the content of iron but did not increase the manganese. Treble superphosphate decreased the iron and manganese contents. But the specific effects varied from soil to soil and indicate no distinctive benefits from the acid treatments on calcareous soils compared with a noncalcareous soil. 5. Alfalfa following the tomatoes was significantly decreased in yield by acidified irrigation waters. Phosphate content of alfalfa was significantly increased by the banded treatment combination of manure, sulfuric acid, and concentrated superphosphate. Other treatment effects were not significant. 6. Irrigation with waters acidified to pH 3.0, 4.0, 5.0, and 6.0 with sulfuric acid decreased the pH of three soils somewhat in proportion to the degree of acidity of the water used, but in no case was the pH of calcareous soils lowered below 7.0. 7. Water-soluble calcium determinations gave more consistent values in relation to the effects of sulfur and sulfuric acid treatments than did pH. Phosphoric acid decreased the pH of some soils but did not increase the calcium solubility. Farm manure treatments did not result in changes in either pH or soluble calcium in soils. The acidifying treatments showed no relationship to phosphorus soluble in a pH 5 acetate buffered solution. 8. A consideration of the results of this study and other reported investigations on the use of acidifying materials on calcareous soils indicates that there is insufficient evidence to date to warrant any widespread recommendation of such treatments for benefiting plant nutrition and growth. The value of acidifying agents in preventing phosphate reversion in calcareous soils has not been studied extensively enough to warrant conclusions.