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EVALUATION OF THE CONVERSION FROM FOREST TO PASTURE 
USING REMOTE SENSING FOR SOIL FERTILILY ANALYSIS 
Izaya NUMATA'!, Joao V. SOARES', Getulio T. BATISTA? 
Dar A. ROBERTS, Oliver A. CHADWICK! 
‘University of California, Santa Barbara, Department of Geography, USA 
{numata; dar; oac@geog.ucsb.edu} 
? Instituto Nacional de Pesquisas Espaciais, INPE, Brazil 
{vianei; getulio@ltid.inpe.br } 
KEY WORDS: Multitemporal Analysis, Pasture Chronossequence, Dynamics of Soil Fertility, Land Use and Cove 
Change. 
ABSTRACT 
This study shows a application of remote sensing techniques for the evaluation of conversion from forest to pasture in 
the State of Rondonia, Brazil. The main objective of this study was to establish a pasture chronossequence for the 
analysis of the soil fertility dynamic by using multitemporal Landsat Thematic Mapper data over the State of Rondónia, 
in order to optimize the study site sampling in the field. The multitemporal classificaton of shade fraction image derived 
from spectral mixture analysiswas employed to identify the age of pasture. Using this approach, land cover change 
between 1987 and 1997 was divided into six age classes , including forest as a control for analysis of the dynamic of 
the soil fertility. 
1 INTRODUCTION 
The impact of the conversion of primary forest into pasture in the Amazon region has been discussed by many authors 
(Fernanside, 1983; Buschbacher, 1986). The continuous and rapid expansion of this kind of exploitation has been 
attributedto the short pasture caused by the rapid decay of soil fertility with time (Fernandes, 1980; Serräo et al., 
1982;Falesi & Veiga, 1987). The level of soil fertility in pastures varies greatly according to the age of the pasture 
settlement, besides soil type and management system (Serräo et al., 1982), as shown in Figure 1. To characterize the 
pattern of the degradation of pasture soil fertility and propose a better management procedure, for a sustainable 
development in this region, we require an better understanding of theof the dynamics of the soil fertility in the pasture 
chronossequence. Remote Sensing is a tool to render representative sampling for different stages of pasture.. 
Multitemporal remote sensing analysis has been used to characterize the process and the pattern of the land cover 
change (Alves & Skole, 1996). This approach can also describe the history of the land use and cover change and then 
the identification of the age of the certain land cover types (Adams et al., 1995; Lucas et al, 1996; Foddy et al. 1996; 
Roberts et al., 1998). 
For most of the studies on soil nutrient dynamics, the choice of sampling sites is based on interviews with ranch 
managers and owners (Uhl et al., 1988), or carried out in experimental fields (Teixeira & Bastos, 1989; Leónidas, 
1998). Remote sensing techniques could be used to expedite and develop a strategy for optimizing field sampling 
design at different scales, from local to basin-wide (LBA, 1996). 
This study presents a remote sensing approach for evaluating the conversion of forest into pasture, in the Amazon 
region, in order to optimize plans for soil sampling in the field. The approach was used to establish pasture 
chronossequences since the conversion of the forest to pasture, going from a recent conversion to more than 10 year-old 
pasture, using multitemporal Landsat TM data. 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 1033