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 flax ( 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.