Abstract Portable X-ray fluorescence (pXRF) spectrometry offers valuable information for prediction models of soil fertility attributes spatial variation, although this approach is yet scarce in tropical regions. This study aims to predict and build spatial variability maps of soil pH, remaining phosphorus (P-Rem), soil organic matter (SOM) and sum of bases (SB) using pXRF results through stepwise multiple linear regression (SMLR) and Random Forest (RF) in a highly variable tropical area. Composite samples from soil A horizon were collected at 90 points throughout the campus of the Federal University of Lavras, Minas Gerais, Brazil, for pH, P-Rem, SOM, SB and pXRF analyses. RF predictions showed the highest accuracies, especially for P-Rem and SB (R² values of 0.66 and 0.55, respectively). Attributes that showed higher R² in punctual predictions also exhibited higher R² in spatial predictions. Data obtained from pXRF in tandem with RF can be used to assist prediction models for soil fertility attributes, consequently enabling the digital mapping of such attributes and helping to improve the knowledge about the spatial variability of such attributes in soils of tropical climate. This technique can therefore assist in the identification and orientation of adequate management practices in tropical agricultural practices.

ABSTRACT The present study aimed to evaluate the accumulation and distribution of Cu and Zn fractions in the profile of an Inceptisol by application of fungicides with a previous history of apple cultivation in southern Brazil. Stratified soil samples (0.0 – 0.025 m, 0.025 –0.050 m, 0.05 – 0.10 m, 0.10 – 0.15 m, 0.15 – 0.20 m and 0.20 – 0.40 m depth) were collected in two apple orchards (8 years old and 18 years old), and in a native pasture area adjacent to the orchards. The soil was subjected to analysis of physical and chemical properties and to chemical fractionation of Cu and Zn. The fractions of soluble, exchangeable, organic, residual and total Cu and Zn accumulated in the topsoil (0.0 – 0.025 m) of the orchards, being higher in the orchard cultivated for 18 years. Most Cu, especially in the topsoil of the 18 years old orchard, accumulated in the less stable organic fraction, which can potentiate toxicity to plants and transfer Cu e Zn to ground water. In deeper layers, Cu was also distributed in the residual and mineral fractions, which are more stable. Most Zn in the soil of the apple orchards was distributed in the mineral and residual fractions, which have low mobility and low potential toxicity to plants.

O objetivo deste trabalho foi avaliar os atributos microbiológicos e químicos de um solo com histórico de sete anos de aplicação de ureia e dejetos de suínos. No período de outubro de 2008 a outubro de 2009, foram coletadas amostras de solo na camada de 0-10 cm, as quais foram submetidas aos tratamentos: controle, sem aplicação de ureia ou dejetos; e com a aplicação de ureia, dejetos líquidos e cama sobreposta de suínos em duas doses, para suprir uma ou duas vezes a dose de N recomendada para a sucessão milho (Zea mays)/aveia‑preta (Avena strigosa). O carbono da biomassa microbiana (C‑BM) e a respiração basal (C‑CO2) foram analisados, e o coeficiente metabólico (qCO2) e o microbiano (qmic) foram calculados com os dados obtidos. Também foram determinados matéria orgânica, pH em água, P e K disponíveis, e Ca e Mg trocáveis. A aplicação do dobro da dose de cama sobreposta de suínos aumenta os valores de C‑BM e C‑CO2. O qmic e o qCO2 são pouco afetados pela aplicação de dejetos de suínos. A aplicação do dobro da dose de cama sobreposta de suínos aumenta os valores de pH em água e os teores de P disponível e de Ca e Mg trocáveis no solo.

The objective of this work was to evaluate the microbiological and chemical attributes of a soil with a seven‑year history of urea and swine manure application. In the period from October 2008 to October 2009, soil samples were collected in the 0-10 cm layer and were subjected to the treatments: control, without application of urea or manure; and with the application of urea, pig slurry, and deep pig litter in two doses, in order to supply one or two times the recommended N doses for the maize (Zea mays)/black oat (Avena strigosa) crop succession. The carbon of the microbial biomass (MB‑C) and the basal respiration (C‑CO2) were analyzed, and the metabolic (qCO2) and microbial quotient (qmic) were calculated with the obtained data. Organic matter, pH in water, available P and K, and exchangeable Ca and Mg were also determined. The application of twice the dose of deep pig litter increases the MB‑C and C‑CO2 values. The qmic and qCO2 are little affected by the application of swine manure. The application of twice the dose of deep pig litter increases the values of pH in water and the contents of available P and of exchangeable Ca and Mg in the soil.

As aplicações sucessivas de dejetos líquidos e cama sobreposta de suínos podem provocar o acúmulo de frações de cobre (Cu) e zinco (Zn) no perfil do solo. Este trabalho objetivou avaliar as formas e o acúmulo de Cu e Zn em um Argissolo Vermelho com histórico de aplicação de dejetos líquidos e cama sobreposta de suínos. Em março de 2010, após oito anos da instalação de um experimento localizado no município de Braço do Norte, Santa Catarina, SC, sobre um Argissolo Vermelho, foram coletadas amostras de solo nas camadas de 0-2,5; 2,5-5,0; 5-10; e 10-15 cm, em tratamentos sem a aplicação de dejetos e com a aplicação de dejetos líquidos de suínos e de cama sobreposta de suínos em duas doses para suprir uma e duas vezes a necessidade de N para a sucessão milho e aveia preta. O solo foi seco, moído em gral de pedra ágata e submetido à análise dos teores de Cu e Zn por EDTA 0,01 mol L-1 e ao fracionamento químico de Cu e Zn. A aplicação de cama sobreposta de suínos e dejetos líquidos de suínos aumentou os teores de Cu e Zn disponíveis na camada superficial do solo; entretanto, quando se aplicaram a dose (equivalente a 90 kg ha-1 de N) e o dobro da dose de cama sobreposta de suínos e o dobro da dose de dejetos líquidos de suínos o Cu e o Zn migraram até 15 cm de profundidade. O Cu no solo é acumulado especialmente na fração orgânica e residual e o Zn, preferencialmente na fração ligada aos argilominerais, especialmente nas camadas mais superficiais.

Successive applications of pig slurry and pig deep litter may lead to an accumulation of copper (Cu) and zinc (Zn) fractions in the soil profile. The objective of this study was to evaluate the Cu and Zn forms and accumulation in a Sandy Typic Hapludalf soil after long-term application of pig slurry and deep litter. In March 2010, eight years after initiating an experiment in Braço do Norte, Santa Catarina (SC), Brazil, on a Sandy Typic Hapludalf soil, soil samples were collected from the 0-2.5, 2.5-5.0, 5-10 and 10-15 cm layers in treatments consisting of no manure application (control) and with applications of pig slurry and deep litter at two levels: the single and double rate of N requirement for maize and black oat succession. The soil was dried, ground in an agate mortar and analyzed for Cu and Zn contents by 0.01 mol L-1 EDTA and chemically fractionated to determine Cu and Zn. The applications of Pig deep litter and slurry at doses equivalent to 90 kg ha-1 N increased the contents of available Cu and Zn in the surface soil layer, if the double of this dose was applied in pig deep litter or double this dose in pig slurry, Cu and Zn migrated to a depth of 15 cm. Copper is accumulated mainly in the organic and residual fractions, and zinc preferentially in the fraction linked to clay minerals, especially in the surface soil layers.