March 16, 2015-03-20
Doctoral Thesis MATIAS EZEQUIEL DUVAL
Department of Agronomy, Univeridad Nacional del Sur, Bahía Blanca, Argentina
Director Dr. Juan Galantini
Comisión Investigaciones Científicas (CIC), CERZOS (UNS CONICET)
CONTENT, QUALITY AND DYNAMIC OF SOIL ORGANIC FRACTIONS AS INDICATORS OF SOIL QUALITY UNDER NO-TILLAGE SYSTEMS
The intensification of agriculture, with a gradual degradation of Argentina’s soil, has increased erosion processes and loss of fertility. The aim of this dissertation was to analyze different soil parameters, either alone or combined, to serve as sensitive indicators in the assessment of different management practices on sites with different climate and soil conditions. The study sites are located in Bengolea and Monte Buey (Córdoba), Pergamino (Buenos Aires) and Viale (Entre Rios). Good agricultural practices, Poor agricultural practices and natural environment (reference) at each site were evaluated. During the period from September 2009 to September 2012 soil sampling was performed in the months of February and September, in which it was determined: total organic carbon (COT), total nitrogen, pH and available phosphorous. A series of physical and chemical methods of fractionation to obtain organic fractions with different characteristics and cycling time was applied. Also a number of physical properties related to the size and distribution of pores, water availability and their relationship to soil management practices were analyzed. COT levels in AN decreased from the East (28 g kg-1 in Viale) to West (14 g kg-1 in Bengolea) following the rainfall and texture gradient of sites. Relationships between different labile organic fractions with COT in AN showed differences among sites, reflecting different dynamics according to the characteristics of the environment in different localities. COT levels in 0-20 cm depths of agricultural soils were 6-42% lower than AN where soybean frequency was one of the main factors causing these declines. In general, the labile organic fractions showed differential sensitivity. Those with higher lability (COPg and CHs) showed differences related to land use, while intermediate lability (COPf and CHt) were useful to highlight the changes due to agricultural practices. Between agricultural managements, both cropping intensity and crop type in the rotation changed the content and distribution of COT and its fractions. The sensitivity to temporal variations and management was higher in the labile organic fractions that in the COT. In turn, the magnitude of variability was different between fractions, where temporal fluctuations increased in the following order COM < COT < COPf ≤ CHt < CHs ≤ COPg. The combination of information from different soil attributes through indices such as COT/clay, stratification index and C pool index allowed a better differentiate the effect of use and management. The physical properties were degraded by agricultural managements with higher values of bulk density, influenced by texture, lower macroporosity and air capacity, without finding a physical indicator to different agricultural practices on all sites.