La erosión es la principal forma de degradación en el mundo, en consecuencia de la pérdida de suelo, agua y nutrientes, provocando daños directos e indirectos. El objetivo de este trabajo es cuantificar las pérdidas de N, P y K por erosión hídrica en condiciones de lluvia simulada mediante la aplicación de seis pruebas de erosión en cultivo continuo de especies de ciclo estacional, incluyendo cultivos aislados y cultivos intercalados. El estudio se llevó a cabo en el campo en la Estación Experimental de Agronomía en Eldorado do Sul (RS), Brasil, en un Argisol Rojo Distrófico típico. Para el análisis de la pérdida de nutrientes, se aplicaron seis ensayos de erosión con lluvia simulada a los tratamientos entre finales de octubre y mediados de diciembre, utilizando el simulador de lluvia con brazos giratorios de Swanson. Las pérdidas de N y P se vieron influenciadas por las condiciones de la superficie, con la eliminación parcial de los residuos del cultivo y la no movilización del suelo. La excepción fue K, debido a su alta solubilidad en el suelo con baja actividad coloidal, que se perdió fácilmente en la escorrentía superficial del agua del suelo, independientemente de la cobertura total de la superficie del suelo por los residuos de los cultivos.
RESUMOA densidade do solo e a resistência mecânica à penetração (RP) influenciam o espaço poroso, interferindo diretamente no crescimento e produção agrícola das culturas. O objetivo do trabalho foi avaliar atributos estruturais de solos em agroecossistemas no semiárido, tendo a área de mata nativa preservada como referência e adotando como impeditivo ao crescimento das raízes o valor crítico de RP igual a 2 MPa. O estudo foi desenvolvido no projeto de Assentamento Terra da Esperança, no município de Governador Dix-Sept Rosado -RN, nos seguintes agroecossistemas: área de mata nativa preservada (AMNP), área de preparo intensivo (API), área de cultivo de cajueiro (ACCaju), Área coletiva de mata nativa (ACMN) e área agroecológica (AAG), coletando-se amostras nas camadas 0,00 -0,10 m e 0,10 -0,20 m, com estruturas deformadas e indeformadas para avaliação da densidade do solo (Ds), densidade das partículas (Dp), porosidade total (Pt) umidade gravimétrica (Ug) e a RP em campo, esta última com trinta leituras para cada agroecossistema supracitado. Os solos foram classificados como Cambissolo, com exceção da ACCaju, um Latossolo. A AMNP apresentou os maiores teores da fração argila em ambas as camadas e o maior valor de RP, com 1,56 MPA, explicada pela superfície consolidada e predominância da fração argila. ACCaju apresentou os menores valores da fração argila e maiores da fração areia, resultando assim em maiores valores de Ds. Já os valores da Dp foram próximos e a Ug foi considerada baixa. Os diferentes manejos adotados nos agroecossistemas não resultaram em impedimento ao crescimento das raízes.Palavras-Chaves: estrutura, assentamento rural, compacidade.
Mineralogical studies are incipient and necessary in the Apodi Plateau, Brazil. This study aimed to evaluate the interrelationship between the mineralogy of the clay fraction and its structural and chemical attributes and to differentiate two important pedo-environments in the semi-arid region of northeastern Brazil (Ferralsol and Cambisols of the Apodi Plateau-RN) using the multivariate technique. We evaluated the interrelationships between mineralogy and the structural and chemical attributes of the soil and differentiated between agroenvironments. We collected soil samples from six profiles in diagnostic horizons of the Ferralsols and Cambisols. In the mineralogical analysis of the clay fraction, X-Ray Diffraction was used to identify mineral peaks of clay and iron oxides. The physical and chemical properties of the soils were determined. The multivariate statistical technique was applied to process the data. The clay minerals identified were hematite, goethite, kaolinite, and illite. The principal component analysis allowed for the separation of environments according to soil density, Fed and Mg2+ for developed soils, and potassium, weighted average diameter, microporosity, total organic carbon, sodium, the sum of bases, calcium, total porosity, aeration, potential acidity, and Feo discriminated developing soils. This study revealed that the clay fraction influenced the structural attributes of the soil according to the degree of soil development. Two profiles presented atypical situations: High contents of crystallized iron in Cambisols and illite peaks in Ferralsolos. These mineralogical results are not commonly found in the literature, highlighting the potential for further studies. The answers concerning the mineralogy of semiarid soils in Brazil and the world show similarity.
Soil physical structure is related to porous space dynamics, which is affected by pedogenetic conditions, land uses, and agricultural practices. Thus, the objective of this work was to evaluate physical and structural attributes of Cambissolos under different uses in the Terra de Esperança Settlement Project, in Chapada do Apodi, Governor Dix-Sept Rosado, Rio Grande do Norte, Brazil, and detect the most sensitive attributes for the distinction of environments using multivariate analysis. The study areas with different land uses were: Native Forest Area 1 (NFA1), Native Forest Area 2 (NFA2), Native Forest Area 3 (NFA3) (reference areas), Conventional Management Area (CMA) Agroecological Area (AEA), and Cajaraneira (Spondia sp.) Orchard Area (COA). Areas with agricultural uses were characterized through physical and structural analyses, using disturbed and undisturbed soil samples collected from their 0.00-0.10, 0.10-0.20, and 0.20-0.30 m soil layers. The soil classes of the areas, according to the Brazilian Soil Classification System (SiBCS) were Cambissolo Haplico Carbonatico vertissolico (NFA1); Cambissolo Haplico Ta Eutrofico tipico (NFA2 and COA); Cambissolo Haplico Ta Eutrofico vertissolico (NFA3); and Cambissolo Haplico Carbonático tipico (CMA and AEA). The results of the attributes analyzed were expressed as mean of three replications per soil layer of each area, using multivariate analysis. Soil textures varied from sandy clay loam to clay. The total sand fraction presented negative correlations with clay dispersed in water, gravimetric moisture (GM), volumetric moisture (VM), total porosity determined (TPd) and microporosity (MiP); and positive correlations with soil density (SD), and basic infiltration rate (BIR), denoting pedogenetic influence. The SD presented significant correlation with GM, VM, TPd, MiP, macroporosity (MaP), aeration porosity (AP) and BIR, denoting its importance for the physical structure of the soil, and its dynamics. The most relevant attributes for the discrimination of the soil physical structure were the inorganic fractions clay and sand, porosity, degree of flocculation, aggregates, and soil mechanical resistance to penetration. The physical and structural attributes of the Cambissolos Haplicos were generally preserved, when compared to the current conditions of the NFAs, despite the different land use and managements. However, the soils of NFA1 (0.20-0.30 m layer), CMA, and AEA areas indicate fragility in aggregate stability and degree of flocculation due to the predominance of the sand fraction. The COA presented more favorable physical and structural conditions to the development of agricultural crops, especially on the surface layers, mostly influenced by their clay, TPd, AP, GM, VM, and soil mechanical resistance to penetration.
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