Evaluation of the throughfall and stemflow nutrient contents in mixed and pure plantations of acacia mangium, pseudosamenea guachapele and eucalyptus grandis.
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Universidade Federal de Viçosa
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The interception of the rainfall by the forest canopy has great relevance to the nutrient geochemistrycycle in low fertility tropical soils under native or cultivated forests. However, little is known about the modificationof the rainfall water quality and hydrological balance after interception by the canopies of eucalyptus underpure and mixed plantations with leguminous species, in Brazil. Samples of rainfall (RF), throughfall (TF)and stemflow (SF) were collected and analyzed in pure plantations of mangium (nitrogen fixing tree -NFT),guachapele (NFT) and eucalyptus (non-nitrogen fixing tree NNFT) and in a mixed stand of guachapele andeucalyptus in Seropédica, State of Rio de Janeiro, Brazil. Nine stemflow collectors (in selected trees) andnine pluviometers were randomly disposed under each stand and three pluviometers were used to measurethe incident rainfall during 5.5 months. Mangium conveyed 33.4% of the total rainfall for its stem. An estimativebased on corrections for the average annual precipitation (1213 mm) indicated that the rainfall s contributionto the nutrient input (kg ha-1) was about 8.42; 0.95; 19.04; 6.74; 4.72 and 8.71 kg ha-1 of N-NH4+, P, K+,Ca+2, Mg+2 and Na+, respectively. Throughfall provided the largest contributions compared to the stemflownutrient input. The largest inputs of N-NH4+ (15.03 kg ha-1) and K+ (179.43 kg ha-1) were observed underthe guachapele crown. Large amounts of Na+ denote a high influence of the sea. Mangium was the most adaptedspecies to water competitiveness. Comparatively to pure stand of eucalyptus, the mixed plantation intensifiesthe N, Ca and Mg leaching by the canopy, while the inputs of K and P were lower under these plantations.
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