Organic farming enhances soil carbon and nitrogen dynamics in oil palm crops from Southeast Amazon

The expansion of oil palm (Elaeis guineensis Jacq, Arecaceae) crops threatens tropical rainforests. It negatively impacts a series of ecosystem services and functions, including carbon (C) sequestration and dynamics, as well as nutrient cycling. Such negative impacts have pressured companies to adopt conservationist practices in palm oil production. And yet the conversion from conventional to organic farming has gained space in the last decade, studies assessing the effects of organic oil palm crops on ecosystem functioning are still scarce. Here, we assessed how alternative farming practices affect organic matter dynamics in oil palm crops. We compared oil palm crops under conventional (CP) and organic (OP) farming in Southeast Amazon. We also sampled lowland dense ombrophilous forest (floresta densa de terra firme, FT) as reference. Soils were sampled at 0-10, 10-20, and 20-30 cm depth intervals to determine soil physical-chemical properties and C and nitrogen (N) concentrations and stocks. The highest soil C and N concentrations were found at 0-10 cm interval in CP and OP. We detected no variation in soil C and N stocks within depth intervals in FT and CP, while OP had higher soil C and N stocks at the 0-10 cm interval. When comparing OP and CP crops, soil C concentrations and stocks did not vary within zones or depth intervals. All OP zones had higher soil N concentrations and stocks than their conventional counterparts, and we found a variation within depth intervals. Our results show that organic farming has positively influenced organic matter dynamics. Organic oil palm crops preserved and even increased C and N sequestration.