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Revista Brasileira de Ciência do Solo

On-line version ISSN 1806-9657


NAKAGAWA, Fábio Keiti et al. Estimating subsoil resistance to nitrate leaching from easily measurable pedological properties. Rev. Bras. Ciênc. Solo [online]. 2012, vol.36, n.5, pp.1491-1498. ISSN 1806-9657.

Leaching of nitrate (NO3-) can increase the groundwater concentration of this anion and reduce the agronomical effectiveness of nitrogen fertilizers. The main soil property inversely related to NO3- leaching is the anion exchange capacity (AEC), whose determination is however too time-consuming for being carried out in soil testing laboratories. For this reason, this study evaluated if more easily measurable soil properties could be used to estimate the resistance of subsoils to NO3- leaching. Samples from the subsurface layer (20-40 cm) of 24 representative soils of São Paulo State were characterized for particle-size distribution and for chemical and electrochemical properties. The subsoil content of adsorbed NO3- was calculated from the difference between the NO3- contents extracted with 1 mol L-1 KCl and with water; furthermore, NO3- leaching was studied in miscible displacement experiments. The  results  of  both  adsorption  and leaching  experiments  were  consistent  with  the  well-known  role  exerted  by  AEC  on  the nitrate behavior in weathered soils. Multiple regression analysis indicated that in subsoils with (i) low values of remaining phosphorus (Prem), (ii) low soil pH values measured in water (pH H2O), and (iii) high pH values measured in 1 moL L-1 KCl (pH KCl), the  amounts of surface positive charges tend to be greater. For this reason, NO3- leaching tends to be slower in these subsoils, even under saturated flow condition.

Keywords : anion exchange capacity; remaining phosphorus; retardation factor.

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