Effects of intensification and diversification of crop rotation on soil structure and enzymatic activities at soil aggregates level

ROBLEDO B; GABBARINI L; WALL LG

Rosario

Congreso; 7th World Congress on Conservation Agriculture; 2017

CAAPAS-AAPRESID

No-till and crop rotation are basic components in conservation agriculture. In cooperation with the Project Chacra Pergamino ? AAPRESID, our Lab has been able to show that diversification and intensification of crop rotations (DIRC) modified soil biochemistry and soil biology parameters according to management (see posters by Covelli et al, Bedano et al, Ferrari et al, in this Congress), just 4 years after change of DIRC in those soils. The objective of this piece of work was to look how this differential DIRC modified the soil structure at the micro aggregate level, and how enzymatic activities were distributed within the micro aggregates. Two contrasting crop rotations (Maize-Soybean-Wheat-Soybean / Maize-Wheat-Soybean-Vicia-) with different index of intensification of rotation (IIR) (0.61 and 0.97) were taken for analysis at the different micro aggregate fractions. Wet sieving performed soil fractionation, to get the fractions 2000-250, 250-63, 63-20, 20-2, < 2 um. Soil enzymatic activities were performed by fluorometric method using 4-MUB-X substrates. Cellobiohidrolase, Chitinase, a-Glicosidase, b-Glucuronidase, Phosphatase, Sulfatase, Acyl-estearase and Leucin-amino-peptidase (7-AMC method) were determined to get an enzymatic profile of soils and soil fractions. The proportions of soil micro aggregates were significantly modified according to soil managements, with low variations between replicates. The biggest fraction 2000-250 um was significantly enhanced by DIRC. When enzymatic parameters (Km, Vmax) were analyzed according to fractions and soil management, it was found that different iso-enzymes would be selected at different aggregate fraction. The distribution of enzymatic activities related to degradation of cellulose and chitin varied differentially between different fractions, while other enzymatic activities more related to intermediate metabolism and P or S cycles remain more or less constant between fractions. It is worth noting that cellulase and chitinase activities were found to be good markers of DIRC. Considering that soil aggregates are the result of soil-microbial-fauna interactions, these results point out what fractions and/or biochemical services appeared to be more sensitive to change of soil managements, suggesting new pathways for future research at this level of soil organization to understand the mechanisms of soil function in conservative agriculture models.