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Non-parametric approaches such as the k-Nearest Neighbor (k-NN) approach are 9 nowadays considered as attractive tools for pedotransfer modeling in hydrology. 10However, non-parametric approaches have not been applied so far to predict water 11 retention of highly weathered soils in the humid tropics. Therefore, the objectives of this 12 study are: to apply the k-Nearest Neighbor (k-NN) approach to predict soil water 13 retention in a humid tropical region; to test its ability to predict soil water content at eight 14 different matric potentials; to test the benefit of using more input attributes than most 15 previous studies did and their combinations; to discuss the importance of particular input

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SUMMARYOver the past three decades, pedotransfer functions (PTFs) have been widely used by soil scientists to estimate soils properties in temperate regions in response to the lack of soil data for these regions. Several authors indicated that little effort has been dedicated to the prediction of soil properties in the humid tropics, where the need for soil property information is of even greater priority. The aim of this paper is to provide an up-to-date repository of past and recently published articles as well as papers from proceedings of events dealing with water-retention PTFs for soils of the humid tropics. Of the 35 publications found in the literature on PTFs for prediction of water retention of soils of the humid tropics, 91 % of the PTFs are based on an empirical approach, and only 9 % are based on a semiphysical approach. Of the empirical PTFs, 97 % are continuous, and 3 % (one) is a class PTF; of the empirical PTFs, 97 % are based on multiple linear and polynomial regression of n th order techniques, and 3 % (one) is based on the k-Nearest Neighbor approach; 84 % of the continuous PTFs are point-based, and 16 % are parameter-based; 97 % of the continuous PTFs are equation-based PTFs, and 3 % (one) is based on pattern recognition. Additionally, it was found that 26 % of the tropical water-retention PTFs were developed for soils in Brazil, 26 % for soils in India, 11 % for soils in other countries in America, and 11 % for soils in other countries in Africa.Index terms: physical soil properties, soil hydraulic properties, tropical soils, data-mining techniques.( Durante as últimas três décadas, as funções de pedotransferência (FPTs) foram amplamente utilizadas pelos cientistas para estimar propriedades de solos em regiões temperadas para responder à falta de banco de dados deles. Diferentes autores indicaram que poucos esforços foram dedicados à estimação de propriedades de solo nos trópicos úmidos, onde a necessidade de informações sobre as propriedades dos solos é ainda mais prioritária. Este artigo buscou proporcionar um inventário atualizado dos artigos, assim como trabalhos publicados recentemente em anais de congressos sobre FPTs com retenção de água para solos nos trópicos úmidos. Entre 35 publicações encontradas na literatura sobre as FPTs para a estimação da retenção de água dos solos nos trópicos úmidos, 91 % dos FPTs estão com base num enfoque empírico e somente 9 %, num enfoque semifísico. Das FPTs empíricas, 97 % são contínuas e 3 % (uma) é uma classe. Das FPTs empíricas, 97 % são com base em regressão multilinear e polinomial de n técnicas de ordenamento e 3 % (uma), no método k-NN; 84 % das FPTs contínuas são com base em pontos e 16 %, em parâmetros; 97 % das FPTs contínuas são baseadas em equação e 3 % (uma), no reconhecimento padrão. Adicionalmente, foi encontrado que 26 % das FPTs da retenção de água "tropical" foram desenvolvidas para solos no Brasil; 26 % , na Índia; 11 %, em outros países na América; e 11 %, em outros países na África.Termos de indexação: meteorização de solos, sol...