Sampling and TDR probe insertion in the determination of the volumetric soil water content

• Published in: Revista Brasileira de Ciência do Solo 2003-08, Vol.27 (4), p.575-582
• Main Authors: Teixeira, W.G, Schroth, G, Marques, J.D, Huwe, B
• Format: Article
• Language: eng ; por
• Subjects: Amazon; AMAZONAS; AMAZÂNIA; AMOSTRAGEM; dieletric properties; Earth sciences; Earth, ocean, space; Exact sciences and technology; FERRALSOL; FERRALSOLES; FERRALSOLS; LATOSSOLO AMARELO; MUESTRA; Oxisols; PROPIEDADES FÍSICO - QUÍMICAS SUELO; PROPRIEDADE FÖSICO-QUÖMICA; PROPRIÉTÉ PHYSICOCHIMIQUE DU SOL; SAMPLING; SOIL CHEMICOPHYSICAL PROPERTIES; SOIL MOISTURE CONTENT; SOIL SCIENCE; Soils; Surficial geology; time domain reflectometry; UMIDADE DO SOLO; ÉCHANTILLONNAGE
• ISSN: 0100-0683; 1806-9657; 0100-0683; 1806-9657
• DOI: 10.1590/S0100-06832003000400001

Volumetric soil water content (theta) can be evaluated in the field by direct or indirect methods. Among the direct, the gravimetric method is regarded as highly reliable and thus often preferred. Its main disadvantages are that sampling and laboratory procedures are labor intensive, and that the method is destructive, which makes resampling of a same point impossible. Recently, the time domain reflectometry (TDR) technique has become a widely used indirect, non-destructive method to evaluate theta. In this study, evaluations of the apparent dielectric number of soils (epsilon) and samplings for the gravimetrical determination of the volumetric soil water content (thetaGrav) were carried out at four sites of a Xanthic Ferralsol in Manaus - Brazil. With the obtained epsilon values, theta was estimated using empirical equations (thetaTDR), and compared with thetaGrav derived from disturbed and undisturbed samples. The main objective of this study was the comparison of thetaTDR estimates of horizontally as well as vertically inserted probes with the thetaGrav values determined by disturbed and undisturbed samples. Results showed that thetaTDR estimates of vertically inserted probes and the average of horizontally measured layers were only slightly and insignificantly different. However, significant differences were found between the thetaTDR estimates of different equations and between disturbed and undisturbed samples in the thetaGrav determinations. The use of the theoretical Knight et al. model, which permits an evaluation of the soil volume assessed by TDR probes, is also discussed. It was concluded that the TDR technique, when properly calibrated, permits in situ, nondestructive measurements of q in Xanthic Ferralsols of similar accuracy as the gravimetric method. A umidade volumétrica do solo (teta) no campo pode ser avaliada por métodos diretos e indiretos. Dentre os métodos diretos, o gravimétrico é considerado altamente confiável e, conseqüentemente, preferido. As principais desvantagens deste método são: a grande demanda de trabalho para a amostragem do solo e os procedimentos posteriores no laboratório, uma vez que, por ser um método destrutivo, não permite reamostrar o mesmo local posteriormente. Ultimamente, a técnica da reflectometria no domínio do tempo (TDR) vem sendo amplamente usada como um método indireto não-destrutivo para avaliação de teta. Neste estudo, avaliações do número dielétrico aparente do solo (épsilon) e amostragens para determ