UTILIZATION BY PLANTS OF PHOSPHORUS IN FARM MANURE

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Abstract
By means of radiophosphorus, the utilization by plants of P from manure and superphosphate, when these 2 P sources were applied separately and together, was detd. in a greenhouse expt. using Italian rye grass as the indicator crop. The P fertilization had little effect on the yield of the rye grass. The P content of the plants increased greatly with successive cuttings and, in general, the plants that received manure contained a higher % of P than those receiving only superphosphate. The P content of the plants was lower when the fertilizer materials were placed in a band than when they were incorporated into the soil. The percentage of P in the plants derived from the added fertilizer varied from 28 to 67 in the 1st cutting, and from 20 to 46 in the 3d cutting. In all treatments, with the exception of protein-bound P, the proportion of P in plants derived from added fertilizer decreased with time. The P from superphosphate was somewhat more available than that from manure, particularly in the 1st cutting. Incubating superphosphate with manure for 22 days had neither a beneficial nor a detrimental effect, as compared with direct appln. to the soil of superphosphate and manure immediately after mixing of the 2 materials. Incubation of manure for 22 days slightly increased the availability of P. In the 1st cutting, utilization by plants of applied P was higher in treatments involving band placement than in treatments in which the fertilizer material was mixed with the soil. By the end of the 2d and especially the 3d cutting, the band placement proved less efficient than the uniform mixing throughout the soil. The protein-bound P in manure was only 20-30% as efficient as the P in superphosphate or in manure taken as a whole. The applied P recovered by plants in the 3 cuttings varied, with treatments, from 8 to 12% except for the protein-bound P, of which only 2% was recovered despite the lower rate of appln. The recovery of applied P by plants agreed remarkably well with that obtained by extraction of the soil with 1% citric acid soln. Isotopic exchange and biological conversion of P may decrease the specific activity of P in the plants and affect the interpretation of results.