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Universidad Nacional del Sur (2017)

Dinámica de la cobertura de residuos en suelos bajo siembra directa : relación con la humedad del suelo y la transformación de las fracciones orgánicas lábiles

López, Fernando Manuel

Titre : Dinámica de la cobertura de residuos en suelos bajo siembra directa : relación con la humedad del suelo y la transformación de las fracciones orgánicas lábiles

Auteur : López, Fernando Manuel

Université de soutenance : Universidad Nacional del Sur

Grade : Doctor en Agronomia 2017

Résumé
The semi-arid region of the southwest of Buenos Aires province -Argentina- (SOB), has climatic and edaphic characteristics that differentiate it from the central Pampean region. Since the large expansion of no tillage (NTill) in the SOB, it is needed a more detailed knowledge of several factors that affect both the productivity and the sustainability of agroecosystems. Furthermore, due to the importance of surface residues in NTill, it is necessary to determinate factors that affect its dynamics. The objective of the thesis was to generate information about the current state of soils under NTill in the SOB and surface residues dynamics, to achieve an adequate implementation of this practice in the region. It was proposed to evaluate different factors related to surface residues, soil physical properties, soil organic carbon (SOC) cycling and nutrient availability. From the study of surface residues (123 sites) and physical fertility (17 sites), it was possible to establish that most soils under NTill in the SOB would not have an adequate soil cover and porosity. Although it is not possible to attribute the loss of physical fertility to NTill management, the way it has been implemented in the region has not been able to guarantee an adequate soil cover and porosity. Soil respiration (SR) presented important variations in different soils under NTill of SOB that would have different effects on SOC cycling. Due to SR during summer-autumn fallow, potential C-CO2 losses could be very high. Consequently, continuous wheat (Triticum aestivum L.) cultivation with chemical fallow would produce large C-CO2 losses. The differences in SOC balances would be influenced by soil type, precipitations during fallow period and crop C contribution. Increased soil cover under NTill caused higher SR and greater nitrogen (N) and phosphorus (P) availability for crops. The increase in nutrient availability would be due to better conditions for organic matter mineralization during fallow period. However, due to the increase of heterotrophic microbial activity, it would be necessary to study the effect of increasing surface residues on potential C-CO2 losses during chemical fallow. Although NTill management in the SOB represented a great change compared to conventional tillage systems, it would be necessary to advance in new practices that allow the adequate implementation of NTill in the SOB. Due to low soil cover and absence of crop rotations, it would not be possible to define the current NTill management as conservation agriculture (CA). The transition from NTill management to the integration of the other CA principles is complex and represents a holistic change, requiring the adaptation and / or generation of management practices to each situation. Increasing soil cover, decreasing fallow periods and adaptation of crop rotations would be valid tools to improve NTill management in soils of the SOB. Furthermore, the implementation of these practices would lead to increase C sequestration, that would help to revert soil degradation in the region.

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Page publiée le 16 mars 2020