AGRICULTURAL LOESS SOILS ALONG A CLIMOSEQUENCE EVIDENCED DIFFERENT SUSCEPTIBILITY TO ACIDIFICATION BY SIMULATED N-FERTILIZATION

ITURRI, LAURA A.; BUSCHIAZZO, DANIEL E.

CATENA

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2018

0341-8162

Agricultural loess soils of the central region of Argentinashow acidification evidences linked to both climatic conditions and Nfertilization.Because of that, simulations to estimate the futureacidification trends under continuing N-fertilization, considering thedifferent neutralization capacities of the soils in this region, wereperformed. An equivalent number of protons to that produced by a constantapplication of 180 kg urea ha-1 year-1 (84 kg N ha-1 year-1) during 1,10, 30 and 50 years of fertilization, was added to unfertilized topsoilsamples of agricultural Haplustolls, Hapludolls and Argiudolls. Mostlyproton additions did not modify neither CEC nor the contents of bothamorphous and crystalline Al, Mn and Fe oxides. However, the Hapludolls,located in the transition zone of the climosequence, showed decreases intheir phyllosilicates crystallinity with the most acidifying treatmentsequivalent to 30 and 50 years of N-fertilization. This effect was lesspronounced in those soils placed in both the driest (Haplustolls) and themoist (Argiudolls) environments, due to the amount and composition of thesubstances and/or systems with acid neutralizing capacity that prevailed.Thus, the Haplustolls were the less affected soils by acidificationbecause their high amount of both free lime- and soil organic matter(SOM) as well as by the smectitic mineralogy of their fine mineralfractions, clay and silt. The Argiudolls were the soils with strongerneutralizing mechanisms given by both their high SOM and fine mineralfractions contents, though illitic. Therefore, the Hapludolls were themost susceptible soils to being acidified if N-fertilization continues,according to the low quantity of SOM and fine mineral fractions ofillitic mineralogy. From these results, the development and validation ofmathematical models were assessed in order to predict the soil buffercapacity and the future pH of the soils. The soil buffer capacity wasexplained 78% by both the cation exchange and dissolution reactions ofminerals accumulated in clays and silts, while pH values were explained75% by the cation exchange capacity as well as by the SOM, free-lime andclay and silt contents. The pH that the soils would have in the futurewere estimated 75% when it were used the outcomes of the simulations and57% with thenpH values of urea fertilized soils.