Influence of liming on the spatial and temporal variability of Mehlich-1 extractable Fe in a rice field

The spatial variability and temporal stability of Fe extracted by Mehlich-1 was investigated on an acid rice soil, a typic Plintacualf, under different lime doses and redox potential (Eh) conditions in Corrientes, Argentina. Soil was sampled firstly in aerobic conditions, before sowing and then twice more in anaerobic conditions, i.e. 4 and 8 weeks after flooding. Three liming treatments were imposed: control (without any lime addition) and two dolomite doses (625 and 1250 kg ha−1). Ninety-six samples were taken for each sampling period and dolomite treatment. Flooding caused a decrease in Eh and an increase in pH. Increasing dolomite dose produced pH increase, while it enhanced Eh decrease, both in aerobic and in anaerobic conditions. Mehlich-1 extractable Fe was 4 to 12 times higher 8 weeks after flooding than in aerobic conditions. Increasing dolomite amendment slightly decreased Mehlich-1 extractable Fe in aerobic conditions, but sharply increased it in anaerobic conditions. Soil extractable Fe exhibited a rather strong spatial dependence over the three different study periods and for the three lime treatments, which was modelled by exponential and spherical models with low to moderate nugget effect. Kriging was useful in mapping variability of Mehlich-1 Fe, allowing description of microrregions with contrasting concentrations. Semivariogram parameters and kriging maps also showed a lack of temporal stability in the patterns of spatial dependence of extractable Fe for all the studied dolomite treatments.

Research Highlights
► Spatial and temporal variability of Fe was investigated on a paddy soil, under different lime doses and Eh.
► High spatial variability of Fe, pH, Eh found in a paddy soil in aerobic and anaerobic conditions.
► Sill values for extractable Fe rose when flooding increases.
► Lack of temporal stability in the patterns of Fe spatial distribution.