A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Spatial variation of soil properties in a 63 ha low productivity Amazon pastureC.E.P. Cerri a,* , M. Bernoux b , V. Chaplot c , R.L. Victoria a , J. M. Mellilo d , B.J. Feigl a ,M.C.Piccolo a , C.C. Cerri aa Centro de Energia Nuclear na Agricultura (CENA), Universidade de Sao Paulo, CP.96.13400-970 Piracicaba, SP, Brazilb Institut de Recherche pour le Développement (IRD), URO41-SeqC, at CENAc IRD at Ambassade de France, BP06, Ventiane, RPD Laosd The Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts,USA.* Corresponding author: Centro de Energia Nuclear na Agricultura, Universidade de SaoPaulo, CP.96. Piracicaba, Brazil. E-mail: cepcerri@cena.usp.br; fax: +55 19-3429-4610.The present study investigates the spatial variation of soil chemical and physicalproperties in a 63 ha pasture area located at Nova Vida Ranch, Rondonia, Brazil. Aregular 25 m grid was used for collecting a total of 2,955 soil samples at the 0 to10, 10 to20 and 20 to 30 cm layers. Soil samples were analyzed for total carbon and nitrogen, δ13 C and δ 15 N, pH in H 2 O, pH in KCl, clay, silt, and sand contents. Conventionalstatistical methods and geostatistics were performed in order to analyze soil propertiesspatial dependence. Mean, standard deviation, skewness, and kurtosis for all measuredvariables were evaluated. All variograms generally were well structured with a relativelylarge nugget effect. Total C, total N, pH in H 2 O, pH in KCl, δ 13 C and δ 15 Nsemivariograms were best fitted by spherical models, while clay and sand contents werebest fitted by exponential models. Two types of validation (“Jackknife” or crossvalidationand external validation) were conducted, indicating a lack of bias for the usedprediction models. Models were used to interpolate the values at unmeasured locations