Organic matter and phosphorus dynamics under selected cropping systems in the South American tropics

abonos verdes absorption de substances nutritives agropastoral systems amendement organique andean region brachiaria dictyoneura calliandra calothyrsus colombia colombie crotalaria juncea disponibilidad de nutrientes engrais vert fallow systems feed grasses feed legumes fertilidad del suelo green manures harrowing hersage indigofera leguminosas forrajeras llanuras micorrizas arbusculares vesiculares mixed farming nutrient availability nutrient uptake organic amendments plaine plains rastreo rotation culturale rotational cropping sistemas con barbecho soil fertility soil organic matter soil types tipos de suelos tithonia diversifolia type de sol vesicular arbuscular mycorrhizae