Abstract
ABSTRACT Concerns about the negative effects of agriculture on soil physical quality and soil organic carbon (SOC) pools have spurred on the adoption of conservation tillage systems in tropical regions. This study aimed to evaluate the long-term impacts (16th year) of conventional (CT), minimum (MT) and no-tillage (NT) practices and different cover crops (sunn hemp and a bean/millet sequence) on soil physical properties and SOC content of a corn cultivated Ultisol in the northeast of Brazil. Soil bulk density (Bd), soil penetration resistance (SPR), soil aggregation, and total aggregate-associated carbon (C) (4-2 mm) were evaluated. Tillage practices exerted strong control on soil physical properties and total aggregate-C content but were influenced by cover crop species. Minimum tillage presented the lowest Bd, irrespective of cover crop, while NT with bean/millet sequence resulted in the lowest SPR. However, as regards soil aggregation and total aggregate-C, the results indicated that there were no differences between MT and NT, with both systems presenting greater mean weight diameter (MWD) and total aggregate-C content than CT. Total aggregate-C content in the 0.00-0.05 m soil layer in conservation tillage was increased by the adoption of a bean/millet sequence. Increased mechanical disturbance through CT practices was harmful to Bd, soil aggregation and SOC accrual. Overall, more conservative tillage practices and the proper choice of cover crops might yield greater soil quality. Low intensity of soil disturbances due to the adoption of MT favors soil aggregation and the accrual of SOC in weakly structured soils through increases in contact between organic and mineral particles while not causing significant destruction of soil aggregates.
Highlights
Soil degradation is a recurrent problem in tropical countries that implies declining ecosystem services and soil quality
Concerns about the negative effects of agriculture on soil physical quality and soil organic carbon (SOC) pools have spurred on the adoption of conservation tillage systems in tropical regions
The results provided here support the ideas behind conservation tillage systems, i.e. their benefits for soil quality
Summary
Soil degradation is a recurrent problem in tropical countries that implies declining ecosystem services and soil quality. Certain classes of soil are more prone to degradation, for instance, Inceptisols and Ultisols (Carvalho et al, 2014), soil mismanagement and land misuse, i.e. indiscriminate plowing and negative SOC budgets may exacerbate soil quality decline (Lal, 2015). Positive effects on soil porosity (Gao et al, 2017), aggregate stability (Moraes et al, 2016) and soil organic matter (SOM) stocks (Sá et al, 2009) across a wide range of soil types and climates are attributable to conservation tillage systems. The beneficial influence of conservation tillage practices, such as no or reduced soil disturbance, cover cropping and residue retention on soil physical properties and SOM apparently rely on site-specific interactions, post-adoption period, climate conditions, the properties of the former management system, and the choice of cover crop species (Derpsch et al, 2014; Hubbard et al, 2013). Most conservation tillage studies in Brazil have concentrated on Oxisols in the southern region (Moraes et al, 2016; Sá et al, 2009; Suzuki et al, 2013), while data to support the decision regarding the adoption of conservation tillage in northeastern Brazil are scarce
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