Changes in soil phosphorus pools induced by drainage in tropical peatlands: Evidence in monoculture and intercropping long-term systems

•Drainage in peatlands changes only inorganic P fractions in soil.•More than 70 % of soil P in peatlands are highly recalcitrant fractions.•P adsorption by the mineral matrix of soil can occur in peatlands.•Monocultive has little impact on phosphorus dynamics in soil in peatlands.•The intercropped, in the short term, may deplete soil P reserves in peatlands. Extensive areas of peatlands are drained around the world to create a favorable environment for food production, altering the natural anaerobic environment and nutrient dynamics in the soil. In this study, we used tropical peatlands subjected to monocultive (MC) of Manihot esculenta for 80 years and intercropped (IC) of Manihot esculenta and Cocos nucifera for 20 years and an area of natural vegetation (Forest), to estimate the effects of MC and IC systems maintained under drainage on the dynamics and accumulation of organic and inorganic fractions of P and on the potential of P adsorption by the soil. Our results showed that drainage predominantly altered inorganic fractions of P, having little influence on its organic fractions. In the short-term, the IC system reduced the total soil P content in subsurface by 35.6 and 37.9 % when compared with MC system and Forest, respectively, as a result of the reduction of all inorganic fractions of P. In all areas, regardless of the position in the profile, we observed the predominance of the highly recalcitrant residual P fraction (> 70 %) in the total P content of the soil. The adsorption process controlled P availability in peatlands subjected to drainage, reducing P availability only in the IC system. Based on our results, we indicate the MC of Manihot esculenta as the best cultivation system and we do not recommend of the IC system in tropical peatlands, as it presents serious risks of total depletion of the P content in soil. Our results provide new evidence on P dynamics in tropical peatlands subjected to drainage for long periods.