EFFECT OF CROPPING AND FERTILIZATION ON PLANT AND SOIL-PHOSPHORUS

Knowledge regarding the effects of long-term cropping practices and fertilization on the fate of P applied to the soil is required to aid in the prediction of how such practices Influence the quality and sustainability of the environment. A 24-yr crop rotation experiment, conducted on a Swinton silt loam (Aridic Haploboroll) in southern Saskatchewan, was used to determine uptake of P by crops, its distribution in grain and straw, and the rate of change and nature of the residual P in the soil. Phosphorus concentration in the grain relative to that in the straw was 7:1 to 12:1 for spring wheat (Triticum aestivum L.), 6:1 for pax (Linum usitatissimum L.), and 5:1 for lentil (Lens culinaris Medikus) and fall rye (Secale cereale L.). Grain P concentration was lowest in cereal crops (3.6 g kg(-1)) and highest in flax and lentil (4.4 g kg(-1)). Phosphorus removed annually with the grain increased with P fertilization and decreased with an increase in fallow frequency; it was 4.8 to 5.3 kg P ha(-1) for continuous wheat, 3.5 to 3.8 kg P ha(-1) for fallow-wheat-wheat, and 3.1 kg P ha(-1) for fallow-wheat. Trend analysis showed that fertilizer P increased the Olsen P levels in soil at rates of 1.0 to 1.7 kg ha(-1) yr(-1), but in the systems receiving no P, Olsen P remained constant and did not decline as suggested by a P balance sheet. Residual fertilizer P accumulated in labile forms, dominated by sorbed P and microbial P, rather than in forms dominated by Ca phosphate precipitates or other organic forms.