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Measurement of Fertilizer Phosphorus Residues and Its Utilization¹

ABSTRACT

A values and sodium bicarbonate (NaHCO₃) extraction soil tests were used to determine phosphorus (P) levels over 8 years on four soils which had been treated with 0, 100, 200, and 400 kg P/ha. The tests correlated highly with each other and indicated the decline of residual fertilizer-P over years as the soils were cropped. Reliable predictions for the duration of the beneficial effects of large amounts of fertilizer-P could be made for the two Manitoba soils where cropping was continuous (wheat-flax) but not for the Saskatchewan soils where fallow was included (wheat-fallow). By using the linear equation of NaHCO₃ soil tests vs. time (years), it was predicted that 100, 200, and 400 kg P/ha would last about 6, 9, and 13 years, respectively, before further fertilizer-P inputs were needed to maintain wheat production. Longer durations were predicted for 200 and 400 kg P/ha when curvilinear relationships were used, averaging 11 and 22 years, respectively, giving better economic feasibility. These soil testing techniques may be used on calcareous soils to minimize current fertilizer-P inputs for wheat where residual fertilizer-P has accumulated.

¹ Contribution from Agriculture Canada, Research Branch, Research Stations, Brandon, Manitoba and Swift Current, Saskatchewan.

² Research Scientists, Agriculture Canada, Brandon Research Station, Brandon, Manitoba, R7A 5Z7.

³ Research Scientists, Agriculture Canada, Swift Current Research Station, Swift Current, Saskatchewan, S9H 3X2.

Received for publication April 14, 1980. Accepted for publication June 30, 1980.