Electrical resistivity and modified Least Limiting Water Range for physical quality assessment in tropical soils

Abstract

The use of management that maximizes agricultural production and guarantee the provision of environmental services is increasingly necessary in the face of a scenario in which the demand for food increases, but natural resources become scarce. Within this context, the assessment of physical soil quality (PSQ) by methodologies that are sensitive to detect changes is essential. The objectives are: (i) to evaluate the potential of using electrical resistivity (ρ) to estimate soil moisture (θ) in tropical soils and (ii) to study the effect of conservationist management (deep tillage and maintenance of vegetated inter row with brachiaria) on the physical quality and water soil dynamic. The first article discusses the use of the geophysical method for estimating θ in Oxisol, in which the variation of ρ in terms of water loss in samples that were artificially compacted reaching increasing degree of compaction (DC) was evaluated in the laboratory. In the second and third article, it was evaluated how the deep soil preparation of an Ultisol, which presents a dense layer, can be beneficial for the soil water dynamics. In addition, it was evaluated how the use of different Citrus rootstocks can imply changes in environmental services due to changes in soil structure. Thus, for both articles, the treatments consisted of three rootstocks (Cravo Santa Cruz - CSC; Mandarin “Sunki Tropical” - ST; and Citrandarin Índio - CI) and native forest. For the second article, ρ was used to assess the spatial-temporal dynamics of θ, and from the generated images it was possible to infer about root development and water absorption by rootstocks. In the third article, the concept of drainable porosity (DP), which allows understanding about the underground recharge process, was incorporated into the Least Limiting Water Range (LLWR) in order to elucidate impacts of the management adopted in the agricultural aspects - by water analysis available for plant - and environmental - through the DP. In both studied soils, ρ proved to be a potential tool, presenting good accuracy for estimating θ. After model tests, the θ-ρ relationship was generally better described by the potential model. The θ showed greater influence on ρ than soil compaction. Among the rootstocks evaluated, the CSC was the one with the highest water absorption, due to the greater distribution of the root system. The deep tillage of the Ultisol was beneficial for the PSQ, as it favored the redistribution of water in the soil profile, evidenced by the lower θ in the deepest layers in treatments that were not subjected to preparation operations. In addition, it enabled good physical quality to the development of the plants, since in no case sampled, the average Ds was above that considered critical.