1. Introduction
During the last five decades (1968-2018), the management of soils for soybean (Glycine max ) cultivation in Brazil has changed from a conventional system to the no-till (NT) system. The rate of conversion to NT was low in the 1970s and 1980s, but increased exponentially starting from the 1990s (Wingeyer et al., 2015). The area of soybean production under NT was ~35 million hectares (Mha) during 2017 and 2018 (Conab, 2018). During the transformation process, farmers and researchers focused on reducing disturbances to the soils and increasing the carbon (C) inputs because both of these changes exert strong direct and indirect effects on soil attributes (Cerri et al., 2012). The effects of NT on soil attributes could be both negative and positive, and the negative effects are primarily related to soil compaction. Nonetheless, much of the research indicates greater sustainability, more productivity and higher stability among crops in soil managed by NT than by conventional systems (Sa et al., 2014).
Soil compaction is a serious and persistent problem in NT areas, particularly in the Brazilian Cerrado region (Cecagno et al., 2016; Ryschawy et al., 2012). The most adverse impacts of compaction are an increase in soil resistance to penetration, reductions in the total porosity and water infiltration rate, increases in water runoff and erosion, and decreases in the plant available water (Reichert et al., 2016), and all of these impacts negatively affect crops (Krebstein et al., 2014). These problems can be reduced through the adoption of a system approach involving a high input of crop residues and a consequent increase in the soil organic carbon (SOC) content (Sa et al., 2014).
The input of biomass-C through a cover crop and/or crop residue in NT areas could be a viable option for increasing the total SOC stock (Daigh et al., 2014). The accompanying increase in SOC has positive effects on the chemical, physical (Andruschkewitsch et al., 2013, Steele et al., 2012) and biological properties of soils (Derpsch et al., 2014). Numerous studies on SOC stocks have confirmed their positive role in the vital functions of soil and have revealed that proper management is also pertinent to addressing current issues such as climate change and the increasing demand for food (Lal, 2015). In addition to obtaining data on total SOC stocks, it is also important to understand the different fractions of SOC and their effects on soil properties and crops’ response (Anghinoni et al., 2013; Cambardella and Elliott, 1992).
Soil water storage is an essential factor in agricultural production, and the available water capacity (AWC) is related to the physical attributes of the soil. Indeed, to achieve and sustain high productivity, the AWC of soil is an important edaphological property (Williams et al., 2016). Site-specific soil management systems can alter physical-hydraulic attributes (Basche et al., 2016). In particular, NT systems can strongly affect the water retention and structure of soils (Carducci et al., 2016; Rabot et al., 2018) as well as the quantity, forms and distribution of SOC (Tan et al., 2007). Thus, cropping systems can impact the AWC of the soil (Qi et al., 2011).
The strong need to harmonize productive, environmental, social and economic issues in agriculture has led to increased research based on a holistic approach to the agricultural system. In this context, the objectives of the present study were; i) to establish the relationships between physical properties and soybean yields, and ii) to determine the effects of the SOC contents on the soil physical properties in high-productivity environments under long-term NT management.