The Effect of Liming on the Utilization of Soil and Fertilizer Phosphorus by Several Crops Grown on Acid Organic Soils

The effect of liming two strongly acid Rifle peat soils on the growth and absorption of soil and fertilizer phosphorus by field beans, sudan grass, and corn was studied under greenhouse conditions. The dry weight of field beans was markedly increased by applying up to 12 tons of CaCO₃ per acre. In contrast, the growth of corn was depressed when more than 3 tons of CaCO₃ per acre was applied. Liming had little or no effect on the yield of sudan grass. Concentrated superphosphate (49% P₂O₅ tagged with P³²) mixed with the organic soils was very effective in increasing the growth of corn, but less benefit was noted with field beans and sudan grass. The phosphorus content of plants was progressively depressed by successive increments of CaCO₃. Distinct phosphorus deficiency symptoms were evident on corn grown in soil receiving the highest lime rate. The use of superphosphate eliminated all signs of phosphorus starvation in corn and significantly increased the phosphorus content of each crop at all lime levels. It is suggested that the depression in percent plant phosphorus caused by liming was due to a decrease in the proportion of H₂PO₄⁻ to HPO₄⁼ ions in the soil solution. The percent of plant phosphorus derived from fertilizer was generally progressively reduced by increasing amounts of lime. At the rate of 50 pounds of P₂O₅ per acre, this percentage was approximately ½ that found in plants receiving the 200-pound P₂O₅ per acre application. Though the amount of fertilizer phosphorus absorbed by corn was many times that by field beans, the percent of fertilizer derived phosphorus in the two crops was quite similar at any given lime-superphosphate level. Laboratory studies indicated that liming followed by 6 months of moist incubation had little effect on the amount of phosphorus extractable in a dilute hydrochloric acid-ammonium fluoride solution.