RESUMEN

Denitrification and NH3 volatilization are the main removal processes of nitrogen in coastal saline soils. In this incubation study, the effects of wheat straw biochar application at rates of 0, 2, 5, 10 and 15% by weight to saline soil with two salt gradients of 0 and 1‰ on denitrification and NH3 volatilization were investigated. The results showed that the denitrification rates with 2, 5 and 10% biochar amendments decreased by 25.26, 33.07 and 17.50%, respectively, under salt-free conditions, and the denitrification rates with 2 and 5% biochar amendments under 1‰ salt conditions decreased by 17.74 and 17.39%, respectively. However, the NH3 volatilization rates increased by 8.05-61.73% after biochar application. The path analysis revealed the interactions of overlying water-sediment system environmental factors in biochar-amended saline soils and their roles in denitrification and NH3 volatilization. Environmental factors in sediment exerted much greater control over denitrification than those in overlying water. In addition, environmental factors exhibited an indirect negative influence on denitrification by negatively influencing the abundance of the nosZ gene. The comprehensive effects of the environmental factors in overlying water on NH3 volatilization were greater than those in sediment. The NH4+-N content, pH of overlying water and sediment salinity were the main controlling factors for NH3 volatilization in saline soils. Biochar application effectively regulated the denitrification rate by changing the environmental factors and denitrifying functional gene abundance, but its application posed a risk of increased NH3 volatilization mainly by increasing NH4+-N, EC and pH in overlying water.

Asunto(s)

RESUMEN

The spatial variability structure of soil attributes in a certain area might influence the semivariogram fitting model and, consequently, the attribute behavior mapping in this area leading to different decisions regarding crop management. This study aimed to identify, characterize and quantify the spatial variability of chemical attributes and the clay content in the superficial layer of a Gleysoils mapping unit (MU) at reconnaissance scale in the coastal plain of Rio Grande do Sul, through descriptive statistics and geostatistics and compare the results taking into consideration the existence of three Gleysoils mapping units at semi-detailed scale through the scaled semivariogram technique. A 403 ha area located in the Rio Grande do Sul Coastal Plain, in the city of Jaguarão was sub-divided into three mapping units (GL- o, GL-mo.lv and GL-lv), a sampling grid with 403 points, 100 m far one from another was established. In a 5 m radius around each sampling point, 10 sub-samples of disturbed soil were collected from the 0-0.20 m layer, making up a soil compound sample, and the following attributes were determined for each sample: pH in water, organic carbon, phosphorus, potassium, sodium, calcium, magnesium, aluminum, potential acidity and clay content. The cation Exchange capacity (pH=7.0) and base saturation were also calculated. The identification, characterization and quantification of the spatial variability of attributes from the soil Ap horizons were carried out through descriptive statistics and geostatistics, considering the mapping unit at the reconnaissance scale and the three units at the semi-detailed scale. In the geostatistics analysis, the scaled semivariogram technique was employed aiming to compare the spatial variability structure for each soil attribute in the total area and in the three MUs at the semi-detailed scale. Regarding the descriptive statistics, the Ap horizon attributes behavior in GL-lv was similar to that in the total area of the soil layer under analysis; however, when considering the spatial coordinates, the spatial variability structure of the GL-mo.lv attributes was the one that best described the attributes variability in the total area. The scaled semivariogram technique revealed that the spatial behavior of the attributes pH and exchangeable sodium was similar, regardless of the evaluation scale adopted or the factor used for the scaled semivariogram.

A estrutura de variabilidade espacial dos atributos do solo em determinada área pode influenciar o modelo de ajuste do semivariograma e, consequentemente, o mapeamento do comportamento do atributo nesta área induzindo a decisões diferenciadas de manejo agrícola. O objetivo deste trabalho foi identificar, caracterizar e quantificar a variabilidade espacial de atributos químicos e do teor de argila da camada superficial de uma unidade de mapeamento de Gleissolos em escala de reconhecimento na Planície Costeira do Rio Grande do Sul, por meio da estatística descritiva e da geoestatística e comparar os resultados levando em consideração a existência de três unidades de mapeamento de Gleissolos em escala de semi-detalhe por meio da técnica de escalonamento de semivariogramas. Uma área de 403 ha localizada na Planície Costeira do Rio Grande do Sul, no município de Jaguarão, foi subdividida em três unidades de mapeamento (GMve1, GMve2 e GXve), sendo estabelecida uma malha total de amostragem de 403 pontos, distanciados entre si de 100 m. Em um raio de 5 m em torno de cada ponto amostral, foram coletadas 10 sub-amostras deformadas de solo na camada de 0-0,20 m, constituindo uma amostra composta de solo, sendo determinados os seguintes atributos das amostras: pH em água, carbono orgânico, fósforo, potássio, sódio, cálcio, magnésio, alumínio, acidez potencial e o conteúdo de argila. Calculou-se também a capacidade de troca de cátions (pH=7,0) e a saturação por bases. A identificação, caracterização e quantificação da variabilidade espacial dos atributos dos horizontes Ap dos solos foram realizadas por meio da estatística descritiva e da geoestatística, considerando a unidade de mapeamento em escala de reconhecimento e as três unidades em escala de semi-detalhe. Na análise geoestatística foi usada a técnica de escalonamento dos semivariogramas, com a finalidade de comparar as estruturas de variabilidade espacial de cada atributo do solo na área total e nas três UMs em escala de semi-detalhe. Em relação à estatística descritiva, o comportamento dos atributos do horizonte Ap na GXve é semelhante ao da área total na camada de solo avaliada; entretanto, ao considerar as coordenadas espaciais, a estrutura de variabilidade espacial dos atributos na GMve2 é a que melhor descreve a variabilidade dos atributos na área total. A técnica de escalonamento dos semivariogramas mostra que o comportamento espacial dos atributos pH e sódio trocável é semelhante, independente da escala de avaliação adotada e do fator usado para o escalonamento dos semivarigramas.

Asunto(s)