Searching for criteria for the selection of efficient tree species for fallow improvement, with special reference to carbon and nitrogen
1995
Schroth, G. | Kolbe, D. | Pity, B. | Zech, W.
Planted fallows are a potential means for regenerating soil fertility in the humid tropics. N-fixing leguminous trees are often recommended for this purpose, but precise criteria for efficient fallow trees do not exist. A combined field and laboratory study was undertaken, including 9 tree species of five years age, of which 6 were N-fixing, and a spontaneous fallow dominated by Chromolaena odorata on a Ferralic Cambisol in the Central Cote d'Ivoire. Although the trees differed widely in growth, litterfall and root mass, differences in total soil C and N were small. Soil respiration and N-mineralization were measured by incubating topsoil in the laboratory. The initial CO2-flush after rewetting differed significantly between species, but non-significant differences afterwards indicated comparable stability and size of the labile C pools of the soils. Total N-mineralization differed significantly between species, with highest values for the control. There was no relationship between the ability of the plants to fix N and N-mineralization or total N-accumulation in the soils. To test the effect of the trees on a subsequent crop, rice was grown in pots filled with topsoil from all plots. Total above-ground dry matter of the rice differed significantly between species and was significantly correlated with N-mineralization in the soil and N-concentration in the rice leaves. N-mineralization was closely related to the amount of litterfall for 7 of the 9 tree species, and to root-mass for the 6 N-fixing tree species. Litterfall and root mass are identified as potential criteria for fallow tree efficiency, but the long-term effect of high N-mineralization rates on available soil-N pools needs further investigation. The importance of soil biological measurements in comparison to chemical soil tests for the assessment of fallow effects is stressed.
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