Soil is a natural resource that has been affected by human pressures beyond its renewal capacity. For this reason, large agricultural areas that were productive have been abandoned due to soil degradation, mainly caused by the erosion process. The objective of this study was to apply the Universal Soil Loss Equation to generate more recent estimates of soil loss rates for the state of São Paulo using a database with information from medium resolution (30 m). The results showed that many areas of the state have high (critical) levels of soil degradation due to the predominance of consolidated human activities, especially in growing sugarcane and pasture use. The average estimated rate of soil loss is 30 Mg ha -1 yr -1 and 59 % of the area of the state (except for water bodies and urban areas) had estimated rates above 12 Mg ha -1 yr -1 , considered as the average tolerance limit in the literature. The average rates of soil loss in areas with annual agricultural crops, semi-perennial agricultural crops (sugarcane), and permanent agricultural crops were 118, 78, and 38 Mg ha -1 yr -1 respectively. The state of São Paulo requires attention to conservation of soil resources, since most soils led to estimates beyond the tolerance limit.

A erosão acelerada constitui importante processo de degradação da qualidade das terras agrícolas. Comumente, a perda física de solo é computada, negligenciando-se os efeitos econômicos dessas perdas, que podem ser estimados empregando-se métodos de valoração econômica. Este trabalho teve por objetivo aplicar o método Custo de Reposição, para valoração econômica das perdas de nutrientes por erosão de um Latossolo Vermelho Distroférrico típico. Foram analisados dados de perda de solo e de nutrientes provenientes de dois ensaios realizados no município de Campinas (SP). No Ensaio I (1990-1996) foram testados oito tratamentos, um por parcela, e as repetições ocorreram no tempo. No Ensaio II (2003-2005), foram testados dois tratamentos, com quatro replicações, sendo analisadas duas safras. Para o Ensaio I ocorreram diferenças significativas entre tratamentos para perdas de solos e de nutrientes. O tratamento "plantio direto" foi o que melhor preveniu as perdas por erosão, enquanto que "aração morro abaixo" foi o que mais intensificou esse processo. A intensidade de erosão não teve influência sobre as produtividades de milho, que não se diferenciaram entre tratamentos, assim como também os custos de reposição de nutrientes. Para o Ensaio II, não foram caracterizadas diferenças significativas entre tratamentos para nenhum atributo analisado, podendo ter ocorrido efeito residual do Ensaio I (anterior). O método Custo de Reposição pode ser aplicado como um indicador na avaliação da sustentabilidade de sistemas de manejo do solo. Mas, em ensaios de longa duração, a variação anual dos preços de fertilizantes e de mão-de-obra pode mascarar os efeitos devidos aos tratamentos em si.

Soil compaction may interact with available soil water and aeration porosity, affecting root and crop growth. Most commonly, soil compaction status is assessed by penetration resistance (PR) tests. The Least Limiting Water Range (LLWR) is an indicator of soil structural quality that appraises the simultaneous effects of water availability, aeration, and PR on plant growth. High resolution PR microprofiles are commonly acquired for LLWR assessment. Multifractal analysis of these microprofiles provides a new opportunity to investigate highly localized heterogeneity at the scale of small soil cores. The objectives of this work were to characterize the scaling properties of depth‐dependent PR microprofiles using multifractal analyses and to explore the effects of soil bulk density and water potential on the degree of multifractality of these PR data series. Disturbed soil cores from a clayey Oxisol (Rhodic Hapludox) were assayed at seven different levels of bulk density (ρb) in the range of 1.00–1.60 kg dm−3 and at six different matric potentials (ψ) from −6 to −1500 kPa, yielding 42 treatments. Each treatment was replicated three times and three PR microprofiles were recorded per soil core, so that 378 PR data series were analyzed. Singularity and Rényi spectra revealed the multifractal behavior of PR microprofiles, and the multifractal approach provided considerable detailed information on their depth‐dependent structure. Rényi spectra and singularity spectra of PR microprofiles, and specially the branches accounting for the most negative statistical moments, depended on ρb and ψ. Effects of bulk density on multifractal parameters were modeled by a linear equation, while water potential effects were modeled by an exponential relationship to log (−ψ). Increasing ρb gradually reduced the degree of multifractality. Increased dryness increased the degree of multifractality, notably near the wilting point, while higher water contents near field capacity showed no significant effects on the degree of multifractality.

ABSTRACT:The soil is a key component of the Earth System, and is currently under high pressure, due to the increasing global demands for food, energy and fiber. Moreover, the management of agricultural systems is often inadequate and ignores the agricultural suitability of lands, and particularly the vulnerability of soils. This paper demonstrates the application of the concept of the Soil Lifetime Index (SLtI) for the entire state of São Paulo, at a spatial resolution of 30 m. The SLtI methodology represents a tolerance criterion and a diagnostic tool to assess the level of soil degradation by water erosion, based on estimated soil loss rates and on an average soil renewal rate. Two approaches were applied to determine: i) the remaining time (years) until the solum (horizons A + B) is removed by water erosion to a critical depth of 1.0 m (original approach); ii) the remaining time (years) until the top 0.25 m of the nutrient-rich soil surface is removed by water erosion (new approach). Several areas in the state have reached a very critical soil depletion level, due to the predominance of consolidated agricultural activities, mainly of sugarcane and livestock production (as in the mesoregions of Ribeirão Preto, Bauru, Assis, Itapetininga and Araraquara). Only 35 % of the study area is in conserved state; 65 % of the study area is in the state of resource degradation, requiring intervention to diminish soil loss rates -and of this total, SLtI is zero in 1 and 0.25 % of the study area, respectively, for the original (critical depth of 1 m) and the new approach (0.25 m). It was estimated that at the current soil loss rates, within 100 years, 20,000 km 2 of the total area of the state of São Paulo (248,209 km 2 ) will have reached the critical depth of 1.0 m, and the top 0.25 m of the soil surface from an area of approximately 76,000 km 2 will have been completely removed if the current pace of resource exploitation is maintained.

In evaluation of soil quality for agricultural use, soil structure is one of the most important properties, which is influenced not only by climate, biological activity, and management practices but also by mechanical and physico-chemical forces acting in the soil. The purpose of this study was to evaluate the influence of conventional agricultural management on the structure and microstructure of a Latossolo Vermelho distroférrico típico (Rhodic Hapludox) in an experimental area planted to maize. Soil morphology was described using the crop profile method by identifying the distinct structural volumes called Morphologically Homogeneous Units (MHUs). For comparison, we also described a profile in an adjacent area without agricultural use and under natural regrowth referred to as Memory. We took undisturbed samples from the main MHUs so as to form thin sections and blocks of soil for micromorphological and micromorphometrical analyses. Results from the application of the crop profile method showed the occurrence of the following structural types: loose (L), fragmented (F) and continuous (C) in both profiles analyzed. In the Memory soil profile, the fragmented structures were classified as Fptμ∆+tf and Fmt∆μ, whose micromorphology shows an enaulic-porphyric (porous) relative distribution with a great deal of biological activity as indicated by the presence of vughs and channels. Lower down, from 0.20 to 0.35 m, there was a continuous soil volume (sub-type C∆μ), with a subangular block microstructure and an enaulic-porphyric relative distribution, though in this case more compact and with aggregate