A soil compaction diagnosis method for occasional tillage recommendation under continuous no tillage system in Brazil

Soil compaction has reduced crop yield under continuous no-tillage systems (NTS), and occasional tillage has been suggested as a mitigating measure. The aim of this study was to suggest a moisture content range ideal for diagnosing and monitoring soil compaction and propose a criterion based on PR for making decisions regarding recommendation of occasional tillage. After 10 years of cultivation under NTS, soil management practices were tested for mitigating soil compaction, combining occasional tillage (subsoiling or chisel plowing) and chemical soil conditioning (limestone or agricultural gypsum). Undisturbed soil samples were collected at three depths, and PR was measured at seven soil matric potentials at 1.5 years after the installation of the experiment. Five PR models were tested in accordance with soil moisture content and validated for each treatment and soil depth. The yields of soybean (2015/2016 and 2017/2018 crop seasons), maize (2016/2017 crop season), common bean (2017 second crop), and wheat (2018 second crop) were evaluated. Occasional tillage with subsoiling or chisel plowing under continuous NTS led to an increase in grain yield in the three subsequent years. An ideal range of soil water content for diagnosis of compaction (IRDC) in a continuous NTS area between the matric potentials of -0.03 and -0.50 MPa, preferentially -0.10 MPa, was suggested, unlike the value of field capacity suggested in the literature. Based on the IRDC, a method was proposed for diagnosis and monitoring of soil compaction in continuous NTS areas exhibiting restricted grain yield for the purpose of making decisions regarding occasional tillage. An example of application of this method was tested and was successful.