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CIFOR-ICRAF s’attaque aux défis et aux opportunités locales tout en apportant des solutions aux problèmes mondiaux concernant les forêts, les paysages, les populations et la planète.

Nous fournissons des preuves et des solutions concrètes pour transformer l’utilisation des terres et la production alimentaire : conserver et restaurer les écosystèmes, répondre aux crises mondiales du climat, de la malnutrition, de la biodiversité et de la désertification. En bref, nous améliorons la vie des populations.

CIFOR–ICRAF publishes over 750 publications every year on agroforestry, forests and climate change, landscape restoration, rights, forest policy and much more – in multiple languages.

CIFOR–ICRAF addresses local challenges and opportunities while providing solutions to global problems for forests, landscapes, people and the planet.

We deliver actionable evidence and solutions to transform how land is used and how food is produced: conserving and restoring ecosystems, responding to the global climate, malnutrition, biodiversity and desertification crises. In short, improving people’s lives.

Dynamics of density fractions of macro-organic matter after forest conversion to sugarcane and woodlots, accounted for in a modified Century model

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Soil organic matter (SOM) is the major controlling factor of soil fertility for low external input agriculture. However, most models describing SOM dynamics are based upon pools which are not directly measurable. We developed a SOM submodule for the CENTURY model based on Ludox particle size density fractions. The turnover rates of these easily measurable fractions were determined by assessing their 13C isotope signatures in a chronose-quence under surgane after rainforest conversion.The net monthly decomposition rates of light (L), intermediate (I) and heavy (H) fractions of macro-organic matter (150 m – 2 mm size) under sugarcane cultivated for 2–10 years following forest removal ranged from 0.0162 and 0.0154 month1 for forest-derived L and I fractions to 0.0118 month1 for H fractions, while for unfractionated forest soil organic matter it was 0.0068 month1. The soil carbon of the CENTURY model was reconstructed and the ‘slow’ (SOM2) pool was divided into L, I, H and R fractions, where the R (resistant) fraction represents the 50–150 m size fraction. The modified CENTURY model simulated the dynamics of L, I and H fractions as well as total organic carbon (C%) under sugarcane with a coefficient of determination (R2) of 0.90, 0.95 and 0.98, respectively. Without further adjustments the model was applied to woodlots of Gliricidia sepium and Peltophorum dasyrrachis. The model accounted for 60% of the variation in measured light (L) fraction in the 0–5 cm layer under Gliricidia and Peltophorum, but only for 40% of the variation in the I and H fraction data. Results thus show some progress in linking SOM models to measurable soil organic matter fractions, but are not yet satisfactory for the heavier fractions, more strongly associated with mineral particles. Experimental data for these fractions show a considerable spatial variability, possibly linked to activity of soil fauna, not covered by the model

DOI:
https://doi.org/10.1016/S1573-5214(00)80005-6
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