Soil conditions in the donga soils in subhumid zone in West Africa

Water erosion threatens large areas around the world. Donga is one of the witness of Gully erosion in northern Benin which induces serious threats to the natural habitats. This study was conducted to evaluate soil moisture content in different donga type (microdongas, mesodongas and megadongas) and its variation at different topographic level. The thermogravimetric soil moisture measurement technique was used for moisture estimation on saturated and unsaturated soil. Data were analyzed through ANOVA-test and T-test with SAS software. The results showed that soil moisture content varied according to donga types. On unsaturated soil, higher difference (2.75%, p-value =0.0328) was obtained in mesodongas at the middle followed by megadongas at the middle (2.6%, p-value = 0.034). On saturated soil, higher difference was obtained in mesodongas at the upstream (6.51%, p-value <.0001) at downslope (4.55%, p-value = 0.0032) and in the middle (4.32%, p-value = 0.0328) followed by microdongas at the upstream (2.25%, p-value <.0001). It is expected that this paper will be useful for the researchers looking for soil moisture information in sub arid and subhumid zone at different topographic level to develop afforestation strategies based on species that can make the best use of soil water.

Assessment of spectral indexes for estimating soil water content in the Brazilian Pantanal

The Pantanal is the largest floodplain of the globe occupying 138,183 km2 in Brazil. The fundamental ecological factor of interaction between the Pantanal ecosystems is the flooding regime. Connected to properties of the soil-plant-atmosphere system, knowledge on the soil water content becomes increasingly necessary. The high temporal and spatial variability of water content in the soil caused by the vast heterogeneity of soil texture, vegetation, topography and climate makes it a difficult physical variable to be measured. However, its spatial and temporal variability can be determined by recent modern techniques of remote sensing based on data obtained by microwave or infrared sensors. Thus, the aim of this study was to evaluate the accuracy of vegetation and soil water indexes through satellite images from Landsat 5 in the northern Brazilian Pantanal. The study was conducted in a pasture, experimental site in the Northern Pantanal in Mato Grosso state. Soil moisture was measured using a TDR probe installed at 10 cm depth in the period from 2009 to 2011. For comparison, spectral indexes and the surface temperature provided by Geological Survey (USGS) were used, these indexes are derived from bands ratios of satellite reflectance products Landsat 5 TM. The data evaluation was performed using some indicators: accuracy - Willmott index, Root Mean Square Error and the Mean Absolute Error. This study demonstrated that the application of remote sensing in the management of water resources is very promising. The indexes correlated with soil moisture measurement. Among the soil water indexes the NBR-2 showed related to soil moisture measurement. For both types of soils EVI had the highest determination coefficient, lowest errors and highest Willmott’s index of agreement.