Phosphorus status of a soil in a long-term experiment
An experiment that was established in 1982 to assess placement of P fertilizer on the yield of continuous barley was terminated in 2004, after annual application of P (30 kg ha-1) was discontinued in all but one treatment in 2001. Total removal of P during the first 20 years of the experiment (615 kg P2O5 ha-1) was virtually equal to total P application (600 kg P2O5 ha-1); however, when removal by the control that was fertilized with N only was subtracted from the total removal, a residual P component of 474 kg P2O5 ha-1 was obtained as a result. In spite of this, discontinuing P fertilization after 20 years of annual application of 30 kg P2O5 ha-1 resulted in significant reduction in barley grain yield that was greater in the treatments that P was seedrow placed (21%) than either banded (12%) or 1/3 seedrow placed and 2/3 banded (15%). Four week burial of PRS™ probes in 2006 allowed us to ascertain the reasons for these differences that reflected management and P placement practices. The use of PRS™ probes allowed us to interpret over 90% of variations both in P removal and yield of barley over the duration of the experiment.
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