CONICET | Buscador de Institutos y Recursos Humanos

Empiric evidences indicate that N-fertilization linked with no-till decreased pH values of loess soils of the Pampas. On soil samples from the topsoil of four N-fertilized (F) and non-fertilized (NF) paired Mollisols within a climosequence (from ustic to udic moisture regimes) were measured the extent of pH decreases, their effects on some chemical- and mineralogical properties as well as their H+ buffering substances. Results indicated that both F- and NF soils showed, although incipient, acidification evidences, being differences between pHW and pHKCl higher than 1.0. Moreover, N-fertilization produced higher pH decreases, but particularly in soils with udic water regimes, in agreement with both their higher N-doses and the longer N-fertilization periods. F ustic soils showed both less crystallized illite- and kaolinite-like clay minerals as well as higher contents of amorphous Al oxides than the NF pairs. It remain unclear if the higher contents of amorphous Al coming from the denaturalization of phyllosilicates, from the transformation of the abundant volcanic glasses present in these soils or from both. Cation exchange capacity and the percent of base saturation showed no changes between fertilization treatments, probably due to the large influence of soil organic matter (SOM) on exchange properties of the studied soils. If pH decreases due to both N-fertilization and no-till continue, soils placed in both the moistest- (Argiudolls) and the driest extremes of the climosequence (Haplustolls) will be the less affected because their buffer substances. Udic soils content high SOM and illitic clays and silts, which have high capacity to neutralize H+ while ustic soils contain free lime and high density charged clay minerals. The most affected soils would be those placed in the transition zone of the climosequence (Hapludolls), which content low amounts of the substances with buffer capacity.