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ABSTRACT
Increases in soil test values (Bray P-1) resulting from annual applications of P fertilizer were approximately 1 pp2m for each 4 pp2m of P added in fertilizer during a 3-year period on six field experiments. In another field experiment, soil tests were made over a 5-year period following a single fertilizer application, and again the addition of approximately 4 pp2m of fertilizer P was required to increase the P-1 soil test by 1 pp2m. These results also indicated that the soil test values, though still changing, were sufficiently stable to be reliable 1 year after the application. When a more variable group of soils were incubated in the laboratory for 49 weeks, additions ranging from 2 to 10 pp2m of P were required to increase the soil test value by 1 pp2m.
1 Contribution from the Agronomy Department, University of Illinois, Urbana.
2 Associate Professor, Professor, and former Research Assistant now at ENSP, New Delhi, India, respectively.
Received for publication November 11, 1970. Accepted for publication February 25, 1971.
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