Walbert Júnior Reis dos Santos

Pedotransfer functions for water retention in different soil classes from the center-southern Rio Grande do Sul State

Water retention in soil is used in many agronomic and environmental applications, but its direct measurement is time-consuming and expensive. Therefore, pedotransfer functions (PTFs) are alternatives to obtain this information faster and more economically. The objectives of this study were to generate and validate PTFs to estimate the water content at potentials of -33 kPa (field capacity) and -1500 kPa (permanent wilting point) for different soil classes from the central-south portion of Rio Grande do Sul State. The physical and chemical analyses database from soil surveys of the Celulose Riograndense Corp were used. The database is composed of particle size distribution (coarse and fine sand, silt and clay), soil organic matter, and water content data at the above mentioned potentials, besides other information concerning the behavior of the soil classes at field conditions. Firstly, the data were stratified by soil classes and depths, and then 70% of the data were separated for PTF generation and 30% for validation. PTFs were generated for each specific soil class and also general PTFs which were not stratified by soil class, by means of stepwise multiple regression. In most situations, PTFs for a specific soil class showed a better fit than the general PTFs. Proper adjustment of the data showed that the water retention values at potentials of -33 kPa and -1500 kPa can be estimated for the soils from the central-south portion of Rio Grande do Sul State that do not have such analyses through the use of PTFs.

Detailed soil survey of an experimental watershed representative of the Brazilian Coastal Plains and its practical application

This paper presents a detailed soil survey of an experimental watershed with representative pedoclimatic characteristics of the Coastal Plains in Espirito Santo State and its practical applications. For the pedological survey, 35 observation sites and three soil profiles were sampled and described, which were morphologically characterized and subjected to physical (particle size) and chemical analyses (routine and sulfuric acid digestion). The soil map was made using the geographic information system ArcGIS 9.3. This GIS software was also used to generate the digital elevation model (DEM) for identifying the slope classes. SAGA software was used to calculate the topographic wetness index (WI) which aided in a more accurate separation of Haplic Organosol from other soils. The predominant soil class in the watershed was the dystrophic/dystrocohesive Yellow Argisol (97%), containing morphological, chemical and physical characteristics representative of the most expressive Coastal Plains soils. Geoprocessing tools and techniques aided to make the watershed soil map.

Soil maps, field knowledge, forest inventory and Ecological-Economic Zoning as a basis for agricultural suitability of lands in Minas Gerais elaborated in GIS

Lands (broader concept than soils, including all elements of the environment: soils, geology, topography, climate, water resources, flora and fauna, and the effects of anthropogenic activities) of the state of Minas Gerais are in different soil, climate and socio-economics conditions and suitability for the production of agricultural goods is therefore distinct and mapping of agricultural suitability of the state lands is crucial for planning guided sustainability. Geoprocessing uses geographic information treatment techniques and GIS allows to evaluate geographic phenomena and their interrelationships using digital maps. To evaluate the agricultural suitability of state lands, we used soil maps, field knowledge, forest inventories and databases related to Ecological-Economic Zoning (EEZ) of Minas Gerais, to develop a map of land suitability in GIS. To do this, we have combined the maps of soil fertility, water stress, oxygen deficiency, vulnerability to erosion and impediments to mechanization. In terms of geographical expression, the main limiting factor of lands is soil fertility, followed by lack of water, impediments to mechanization and vulnerability to erosion. Regarding agricultural suitability, the group 2 (regular suitability for crops) is the most comprehensive, representing 45.13% of the state. For management levels A and B, low and moderate technological level, respectively, the most expressive suitability class is the regular, followed by the restricted class and last, the adequate class, while for the management level C (high technological level) the predominant class is the restricted. The predominant most intensive use type is for crops, whose area increases substantially with capital investment and technology (management levels B and C).

PEDOTRANSFER FUNCTIONS FOR WATER RETENTION IN THE MAIN SOILS FROM THE BRAZILIAN COASTAL PLAINS

Pedotransfer functions (PTFs) are equations used to estimate soil characteristics difficult to determine from other easily obtained ones. Water retention in soil is used in several agronomic and environmental applications, but its direct determination is time consuming and onerous, therefore PTFs are alternatives to obtaining this information more quickly and economically. The aims of this study were to generate a database and develop PTFs for water retention at potentials of -33 kPa (field capacity) and -1500 kPa (permanent wilting point) for Yellow Argisol and Yellow Latosol from the Brazilian Coastal Plains region. The Coastal Plains soils are mostly developed from Barreiras formation (pre-weathered sediments) and their main uses are sugarcane, livestock, forestry and fruticulture. The database to generate the PTFs was composed from the selection of information derived from scientific works and soil survey reports of the region. Specific PTFs were generated for each soil class, in their respective A and B horizons and for solum, through multiple regression by stepwise package of R language programming. Due to the small pedological variability (small number of soil classes containing great geographical expression) and mineralogical uniformity, usually observed in this environment, non-stratification of soil classes to create general PTFs presented similar or superior results compared to equations for each soil class. The adjustment of data demonstrated that water retention values at -33 kPa and -1500 kPa potentials can be estimated with adequate accuracy for the main soils of the Brazilian Coastal Plains through PTFs mainly from particle size distribution and secondarily from organic matter data.

SOIL MOISTURE SPACE-TIME ANALYSIS TO SUPPORT IMPROVED CROP MANAGEMENT

The knowledge of the water content in the soil profile is essential for an efficient management of crop growth and development. This work aimed to use geostatistical techniques in a spatio-temporal study of soil moisture in an Oxisol in order to provide that information for improved crop management. Data were collected in a coffee crop area at Sao Roque de Minas, in the upper Sao Francisco River basin, MG state, Brazil. The soil moisture was measured with a multi-sensor capacitance (MCP) probe at 10-, 20-, 30-, 40-, 60- and 100-cm depths between March and December, 2010. After adjusting the spherical semivariogram model using ordinary least squares, best model, the values were interpolated by kriging in order to have a continuous surface relating depth x time (CSDT) and the soil water availability to plant (SWAP). The results allowed additional insight on the dynamics of soil water and its availability to plant, and pointed to the effects of climate on the soil water content. These results also allowed identifying when and where there was greater water consumption by the plants, and the soil layers where water was available and potentially explored by the plant root system.

Soil moisture assessed by digital mapping techniques and its field validation

Tecnicas e ferramentas digitais podem auxiliar na predicao de propriedades do solo, a exemplo da umidade do solo, auxiliando no planejamento do uso e manejo de areas com fins agricolas e/ou ambientais. Nesse sentido, objetivou-se estudar indices de umidade, definir a resolucao espacial e selecionar o metodo de estimativa que melhor se correlaciona com dados de teor de agua medidos em campo, avaliando-se, ainda, a umidade em diferentes profundidades do solo e epocas do ano. Este estudo foi desenvolvido em uma paisagem com relevo forte ondulado e recoberta por Nitossolo no topo e no terco medio superior, e Argissolo no terco medio inferior, em altitude variando de 845 a 890 m, no sul do Estado de Minas Gerais, Brasil. Foram realizadas analises de correlacao linear de Pearson entre a umidade do solo determinada em campo, nas profundidades de 10, 20, 30, 40, 60 e 100 cm alem do armazenamento de agua na camada 0-100 cm, e os indices de umidade TWI (indice topografico de umidade) e SWI (indice de umidade SAGA) obtidos a partir de modelos digitais de elevacao em diferentes resolucoes espaciais. Na maioria das situacoes estudadas, o indice TWI com resolucao de 10 m condicionou melhores resultados, particularmente no periodo seco do ano. Neste estudo, apenas para a profundidade de 100 cm houve correlacao positiva e significativa, sugerindo que os indices de umidade sao indicados para estudos de dinâmica da agua em subsuperficie, auxiliando nos estudos de dinâmica hidrologica e no planejamento de uso e manejo do solo, especialmente no caso de plantas perenes com sistema radicular mais profundo.