Geostatistical analysis of microrelief of an oxisol as a function of tillage and cumulative rainfall

Abstract

Surface roughness can be influenced by type and intensity of soil tillage among other factors. In tilled soils microrelief may decay considerably as rain progresses. Geostatistics provides some tools that may be useful to study the dynamics of soil surface variability. The objective of this study was to show how it is possible to apply geostatistics to analyze soil microrelief variability. Data were taken at an Oxisol over six tillage treatments, namely, disk harrow, disk plow, chisel plow, disk harrow + disk level, disk plow + disk level and chisel plow + disk level. Measurements were made initially just after tillage and subsequently after cumulative natural rainfall events. Duplicated measurements were taken in each one of the treatments and dates of samplings, yielding a total of 48 experimental surfaces. A pin microrelief meter was used for the surface roughness measurements. The plot area was 1.35 × 1.35 m and the sample spacing was 25 mm, yielding a total of 3,025 data points per measurement. Before geostatistical analysis, trend was removed from the experimental data by two methods for comparison. Models were fitted to the semivariograms of each surface and the model parameters were analyzed. The trend removing method affected the geostatistical results. The geostatistical parameter dependence ratio showed that spatial dependence improved for most of the surfaces as the amount of cumulative rainfall increased. RESUMO: A rugosidade da superfície pode ser influenciada pelo tipo e pela intensidade do preparo do solo, entre outros fatores. Em solos preparados o microrrelevo é aplanado consideravelmente com o acúmulo da chuva. A Geoestatística promove algumas ferramentas que podem ser úteis no estudo da dinâmica da variabilidade da superfície do solo. O objetivo desse estudo foi verificar se é possível aplicar geoestatística na análise da variação do microrrelevo do solo. Os resultados foram obtidos num Latossolo sob seis tratamentos de preparo do solo: grade de discos, arado de discos, escarificador, grade de discos + grade niveladora, arado de discos + grade niveladora e escarificador + grade niveladora. As medidas foram feitas logo após o preparo do solo e subseqüentemente após cumulativos eventos de chuva natural. Medições duplicadas foram feitas em cada tratamento para cada data, produzindo um total de 48 superfícies. Um rugosímetro de agulhas foi utilizado para as medidas da rugosidade da superfície. A área de cada parcela era 1,35 m por 1,35 m e as medidas espaçadas de 25 mm, produzindo um total de 3025 pontos por parcela. Antes da análise geoestatística, a tendência foi removida dos dados experimentais por dois diferentes métodos. Foram ajustados modelos aos semivariogramas de cada superfície, e os parâmetros desses modelos foram analisados. O método usado para remover a tendência influenciou os resultados geoestatísticos. O parâmetro geoestatístico razão de dependência mostrou que a dependência espacial aumentou para a maioria das superfícies com o aumento da precipitação pluvial acumulada. Palavras-...

Material type and roughness influence structure of inter‐tidal communities on coastal defenses

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