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 8weeks after flooding. Three liming treatments were imposed: control (without any lime addition) and two dolomite doses (625 and 1250kgha-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 8weeks 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.