Mineral nutrition, soil factors and growth rates of Gmelina arborea plantations in the humid lowlands of northern Costa Rica
The purpose of this study was to determine the factors which are responsible for clearly visible growth irregularities in Gmelina arborea stands by relating growth rates to soil and site properties. All plantations under study, established on degraded pasture soils in the Atlantic lowlands of Costa Rica, showed the same growth pattern: very poor growth and chlorotic foliage of trees in mid-slope positions, and fast growth and healthy leaves of trees on hilltops and hillbases. The variation in site and soil properties and tree growth rates was analysed, using data from 24 sample plots in eight 3-yr-old plantations. Leaf samples were taken from 120 trees (five trees per site). Foliar analysis revealed that tree growth was highly dependent on the supply of N, P, K and S, indicating that poorly growing trees suffer from a multiple nutrient disorder. To identify the most restricting soil factor, simple correlations between growth rates and soil chemical and physical properties were applied to the entire data set. The best correlation was obtained with exchangeable soil K (r=0.78, P <0.001). Subdivision of the data set into plots on brown soils (eight) and plots on red soils (16) and subsequent correlation analysis resulted in much stronger relationships. Reductions in tree growth in mid-slope positions had different causes on the two soil types. On acid brown soils a combination of the soil variables Al saturation and bulk density explained 82 percent of variation in tree growth. Al saturation of up to 80 percent in brown soils inhibited nutrient uptake, particularly of N and P. The red soils were predominant on Ca-Mg-enriched, alluvial terraces and were among the first soils to be cultivated in the region. During agricultural use, and at the establishment of the tree plantations, the soils received dolomitic lime to reduce Al toxicity. Here, very low K/Mg ratios (less than 0.03) may induce k deficiency. Therefore, the best multiple regression model for tree growth rates on red soils is obtained with K/Mg ratio and thickness of the humic A-layer (r2 = 0.75, P <0.001). Inclusion of the variable bulk density resulted in a clear improvement to the model, explaining 91 percent of growth variability.
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| Format: | biblioteca |
| Published: |
Dic
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| Subjects: | GMELINA ARBOREA, ANALISIS DE TEJIDOS, SUELO TROPICAL, AFORESTACION, NUTRIENTES MINERALES, ANALISIS DEL SUELO, PROPIEDADES FISICO-QUIMICAS SUELO, TERRENO EN DECLIVE, ZONA ATLANTICA, COSTA RICA, |
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