Phosphate and Nitrate Release from Mucky Mineral Soils

• Published in: Open journal of soil science 2013-05, Vol.3 (2), p.107-114
• Main Authors: Leblanc, Michaël A., Parent, Léon E., Gagné, Gilles
• Format: Article
• Language: English
• ISSN: 2162-5360; 2162-5379
• DOI: 10.4236/ojss.2013.32012

High-organic (mucky) mineral soils make a small proportion of the Canadian agricultural land but are highly productive, especially for organic farming. Although these high-quality soils may release large amounts of nitrate and phosphate to the environment, there is yet no reliable agro-environmental indicator for managing N and P compared to the adjacent mineral and organic soils. Our objective was to quantify the N mineralization and P environmental risks of mucky mineral soils. Nine Canadian soil series (eight Orthic Humic Gleysols and one Terric Humisol with three variants) were analyzed for texture, pH(CaCl sub(2)), total C and N, oxalate and Mehlich-III (M-III) extractable P, Al and Fe, and water extractable P (P sub(w)). Soil texture varied from loamy sand to heavy clay, organic carbon (OC) content ranged from 14 to 392 g .OC.kg super(-1), total N from 1.21 to 16.38 g .N.kg super(-1), and degree of P saturation (DPS sub(M-III)) as molar (P/[Al + gamma Fe]) sub(M-III) percentage between 0.3% and 11.3%. After 100 d of incubation, soils released 31 to 340 mg.N.kg super(-1). The N mineralization rate was closely correlated to organic matter content (r = 0.91, p < 0.01). Sandy to loamy soils released 1.2 - 1.8 kg .N.ha super(-1).d super(-1) compared to 1.6 - 2.4 kg .N.ha super(-1).d super(-1) for clayey soils, 2.0 - 2.8 kg .N.ha super(-1).d super(-1) for mucky clayey soils and 2.6 - 2.7 kg .N.ha super(-1).d super(-1) for Humisol. For (P/[Al + 3Fe]) sub(M-III) ratios of mucky clayey soils below 4.5%, water-extractable P did not exceed threshold of 9.7 mg P sub(w) L super(-1). Mucky clayey soils could be managed for N similarly to Humisol and for P with (P/[Al + 3Fe]) sub(M-III) percentage not exceeding 4.5%.