Variabilidade espacial da rugosidade superficial do solo medida com rugosímetros de agulhas e laser

Abstract

RESUMOA variabilidade espacial da rugosidade superficial do solo foi estudada a partir de uma grade de dados pontuais medidos com instrumentos de diferentes graus de precisão. Para a medição da rugosidade utilizou-se um rugosímetro laser, em condições de laboratório, sendo as leituras realizadas antes e após a aplicação de diferentes quantidades de chuva (0 mm, 10 mm, 55 mm, 85 mm). Nas condições de campo (pastagem e superfície arada) utilizou-se um rugosimetro de agulhas, e as leituras foram realizadas em quatro datas distintas. Verificou-se alta dependência espacial para a rugosidade superficial, com os dados obtidos em ambos os métodos e em todos os tratamentos. Os parâmetros dos semivariogramas obtidos com os dados do rugosímetro de agulhas apresentaram grandes variações nas diferentes datas, devido à forma de distribuição e ao tamanho dos agregados. Isso indica a dificuldade de encontrar um modelo tridimensional, representativo do microrrelevo, em condições de campo. Verificou-se grande semelhança em todos os semivariogramas obtidos a partir dos dados do rugosímetro laser (superfície simulada) indicando que, apesar das alterações na rugosidade superficial, não foram observadas modificações no comportamento da dependência espacial com a aplicação de diferentes quantidades de chuva. Palavras-chave: microrrelevo, semivariograma escalonado, geoestatística, agregados do solo. ABSTRACT SPATIAL VARIABILITY OF SOIL SURFACE ROUGHNESS MEASURED BY PIN AND LASER RELIEFMETERSThe spatial variability of the soil surface roughness was analysed by instruments of different precision degrees in a grid of data points. For measuring the roughness it was used a laser reliefmeter before and after application of different amounts of rain (0 mm, 10 mm, 55 mm, 85 mm) in the laboratory. At field conditions (pasture and ploughed surface) a pin reliefmeter was used at four different dates. The results showed a great spatial dependence of soil surface roughness in both methods and for all treatments. The great variation of semivariogram parameters obtained with pin reliefmeter data for all different dates was due to the distribution and size of soil aggregates. This indicates how difficult it is to obtain a representative tridimensional microrelief model at field conditions. All other semivariograms obtained with laser reliefmeter data (simulated surface) were similar among themselves, indicating that despite the alterations in the soil surface roughness, the spatial dependence pattern did not change with different amounts of rain.

Evolution of the soil surface roughness using geostatistical analysis

“…All semivariograms were fitted to spherical model, confirming this model as the one of the useful for parameters of soil and plant (CAmBArdellA et al, 1994;souzA et al, 2001;siqueirA et al, 2008). The fact that in this study all the data have been fitted to spherical model, confirms that although there have been changes in soil surface roughness caused by the different amounts of simulated rain, it was not detected changes in spatial variability pattern, according to pAz gonzález et al (1998) and BertolAni et al (2000).…”

“…In addition, runoff will start well before all depressions are filled. Water and sediments storage in depressions during rain causes that rough surfaces erode at slower rates than smooth surfaces under similar conditions (eltz and norton, 1997;BertolAni et al, 2000;Bertol et al, 2006;CAstro et al, 2006).…”

“…Soil surface roughness decay is influenced by height and intensity of rain, runoff, stability of aggregates, soil density and soil porosity (eltz and norton, 1997;pAz gonzález et al, 1998;BertolAni et al, 2000;Bertol et al, 2006;CAstro et al, 2006). Moreover, knowledge of soil surface roughness provides information on soil structural quality, because of its influence on the speed and degree of degradation of the upper most soil surface layer (Bertol et al, 2006).…”

“…However, as pointed out by HuAng and BrAdford (1992) and Bertol et al (2006) RR describes only the vertical component of roughness, namely the distribution of height of clods and depressions, without taking into account the spatial component, or the location of clods and depressions. Soil surface roughness is usually evaluated using a pinmeter, at the centimeter scale, or by laser-scanner, at the millimeter scale (eltz and norton, 1997;BertolAni et al, 2000;dArBoux et al, 2002;Bertol et al, 2007;VidAl Vázquez et al, 2007), which provides measurements of microdepressions and microelevations present in the soil surface.…”

“…BertolAni et al (2000) studied the spatial variability of soil roughness and emphasized the importance of geostatistical parameters for a better understanding of mathematical models of soil roughness. Moreover, geostatistics is useful for analyzing the evolution of surface water retention during rainfall events.…”