Examining the land leveling impacts on the physical quality of lowland soils in Southern Brazil

Highlights

• Land leveling effects were assessed in lowland topsoil attributes.

• Leveling negatively affected most of the evaluated soil physical quality indices.

• Soil hydraulic-energy indices were successfully used as physical quality indicators.

Abstract

The use of irrigation systems in rice and other crops cultivated under aerobic conditions in lowland leveling soils has increased worldwide. This study aimed to evaluate the impact of land leveling operations on the soil physical quality (SPQ), mainly on water retention and aeration in a lowland soil in Southern Brazil. A 10 × 10 m-grid was established before and after land leveling in a 1.0 ha-experimental area, where disturbed and undisturbed soil cores were sampled to measure soil texture, organic carbon, bulk density, water retention curve, total porosity, macro, and microporosity at each point location in the 0–0.20 m soil layer. Based on the Spearman correlation results, land leveling negatively affected the majority of the evaluated soil physical properties and SPQ indices. The hydraulic-energy-based indices significantly correlated with other physical properties before and after leveling operations, indicating their capacity to capture the soil structure changes. Likewise, the absolute aeration energy index (A_a-pF) strongly correlated with microporosity emphasizing its application to examine SPQ in land leveling areas. Semivariogram models were fitted to measured data for kriging a spatial variability map for each soil property. Land leveling increased all practical ranges and the goodness-of-fit of the hydraulic-energy indices, decreasing their degree of spatial dependence. The maps of the hydraulic-energy indices were useful to identify regions where key-properties and other SPQ indices presented similar behavior becoming additional tools for farmers to mitigate negative effects of leveling on the SPQ to increase the soil water storage, infiltration, and crop water use efficiency.

Introduction

Land leveling has been used worldwide as an agricultural practice on lowland soils mainly cultivated with rice fields under anaerobic conditions (Parfitt et al., 2014, Brye et al., 2006, Linh et al., 2017, Marzolff and Pani, 2018). In recent times, the use of sprinkler irrigation in aerobic systems that cultivate rice, soybean, sorghum, and maize in lowland soils has been increased in the south of Rio Grande do Sul state/Brazil and in other countries such as Pakistan (Kahlown et al., 2007), Italy (Spanu et al., 2009), USA (Vories et al., 2017), and India (Mandal et al., 2019). Under aerobic conditions, water can be saved when soil management (e.g., land leveling), conservation practices (e.g., no-tillage), and crop rotation are adopted. Despite these findings, there is a lack of knowledge about the effects of land leveling on SPQ and production systems cultivated in lowland soils under aerobic conditions, as these topics have not been thoroughly explored.

Due to the intense traffic of machines during the cutting, filling, smoothing, and shaping operations on the soil surface, land leveling strongly affects the physical-hydraulic and chemical properties of the topsoil surface layer (Aschonitis et al., 2012, Öztekin, 2013). Leveling operations may cause an increase in bulk density and a decrease in organic carbon content in lowland soils (Brye et al., 2004, Martínez-Casasnovas and Ramos, 2009, Öztekin, 2013; Timm et al., 2020). Furthermore, the effective arable layer for crop development can be decreased exposing subsoil layers mainly in cutting operations in shallow lowland soils.

The soil water retention curve (SWRC) is a key soil hydraulic function that can also be used as a soil quality indicator (Rickson et al., 2012). In addition, several soil quality indices (SQIs) are derived from SWRC and allow the assessment of soil physical quality (SPQ). The pore size distribution (PSD) function (Reynolds et al., 2009), hydraulic-energy indices, and functions of aeration and water retention (Armindo and Wendroth, 2019) are examples of derived SQIs to be applied in the SPQ analysis under agricultural practices, such as land leveling. In this regard, this study aimed to examine the effect of land leveling operations on the water retention and aeration behavior of a lowland soil in Southern Brazil. We hypothesize that the water retention and aeration behavior of lowland soils in aerobic environments are affected by land leveling operations which impact their hydraulic-energy-indices.