Chemical Fractions And Predictions For Long-term Releases of Phosphorus In Typical Canadian Agricultural Soils

Withana Herath, Aruna
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University of Guelph

Phosphorus (P) pollution has been identified as the most significant agriculture-related threat to water quality impairment in Canada. One approach to reduce P pollution is to identify soils with high P loss potential and develop management strategies to minimize that risk. This thesis contributes towards greater understanding of short- and long- term P dynamics in soils to which different P sources had been applied (Chapters 3 and 4) and improvement in the P measurements for determining long-term P loss potential (Chapter 5). Chapter 3 evaluated immediate and residual effects of swine manure and fertilizer on soil P. Soils were sampled from Brookston clay loam in south-western Ontario, Canada which were treated with liquid (LM), solid (SM), composted (MC) manure and fertilizer, only in the corn phase. Soils were analyzed using a modified Hedley’s fractionation. All P sources influenced soil labile and moderately labile P in the year of application, while MC and SM showed significant residual impacts in the following year. Residual effects of MC and SM are beneficial for crops; however, there may be a P loss potential through leaching and runoff. Chapter 4 considered long-term effects of dairy manure slurry (DMS) and ammonium nitrate (AN) on soil P. Soils were sampled from south coastal region of BC, Canada, which were treated with DMS or AN at 50 or 100 kg NH4-N ha-1, and analyzed using a modified Hedley’s fractionation. DMS significantly increased labile and moderately stable P in surface soil, indicating short- and long-term impacts on P availability and loss potential. Chapter 5 analyzed a new test to predict long-term soil P loss potential. Soils were collected from four agro-ecological areas across Canada, and analyzed using Mehlich-3, Olsen, Resin strips (RMS), FeO-strips, and new procedures: various combinations of NaOH with and without EDTA, with four shaking periods. Statistically significant linear and quadratic relationships between the RMS and NaOH with EDTA-P indicated that the latter provide an efficient basis for predicting long-term soil P loss potential. A highly significant relationship between RMS-P and 0.025M NaOH with EDTA-P indicates this extractant was effective for measuring Total Releasable P.

soil phosphorus, environmental soil phosphorus testing, swine manure forms, dairy manure slurry