Effect of increasing soil pH to near-neutral on phosphorus saturation index and water extractable phosphorus

Citation

Nyamaizi et al 2022. Effect of increasing soil pH to near-neutral on phosphorus saturation index and water extractable phosphorus. CSSS-ASSW 2022. May 23-27, 2022. Edmonton, Soil Science for Sustainable Development

Résumé

Soil pH influences phosphorus (P) dynamics and agri-environmental indicators used to monitor the risk of P loss from agricultural soils. We studied the effects of liming with calcium carbonate (CaCO3) to increase soil pH from acidic to near-neutral on i) degree of P saturation (DPS), the P saturation index (PSI), Mehlich-3 P (PM3) and water extractable P (Pw). Soils collected from a long-term highbush blueberry experiment were incubated at 22.5 °C for 93 days after CaCO3 amendment to increase initial pH values from 4.1 to 4.8, 5.5 to 6 and from 5.8 to 6.5. We observed a decrease of PM3 of 6, 8 and 10% respectively for each of the CaCO3 amended soils. The PM3 were classed as very high P with critical DPS > 25%, indicating increased risk of P loss with runoff. For soils with initial pH values of 5.8, Pw was 3.65 mg kg–1 which is in line with critical DPS > 25%, but decreased to 2.74 mg kg–1 with CaCO3. In contrast, CaCO3 decreased Pw from 1.17 to 0.86 and 1.47 to 1.39 mg kg–1 for soils with initial pH values of 4.1 and 5.5, respectively, but for soils with initial pH 4.8, CaCO3 increased Pw from 1.00 to 1.21, reflecting low PSI (5.2 to 6.1%). For soils with initial pH 5.5, high Mehlich-3 Al indicated high exchangeable Al which enhanced the fixation of phosphate ions in the solution, thus reducing Pw. Our results suggest using PM3 as an indicator of environmental risk likely underestimate potential P losses compared to Pw.

Date de publication

2022-05-23

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