Aporte de serapilheira em sistemas agroflorestais com palma de óleo na Amazônia Oriental

Abstract

Litterfall is a relevant compartment of natural and modified systems. However, natural environments conversion into minor diversified systems promotes dynamic´s changes in this net primary productivity (NPP) component. The oil palm (Elaeis guineensis Jacq.) is inserted in this conjuncture. Even with its economic importance at the global, national and regional levels, its expansion through monoculture is accompanied by negative social and environmental impacts. Being thus is fundamental the search for alternatives which enable its implementation and maintenance in accordance with guiding principles of sustainability. Thus, it is necessary to develop studies about the production of litterfall in more diversified agroecosystems, agroforestry systems (AFS), with the objective of obtaining models of systems that are closer to natural environments. In this study was evaluated litterfall production in agroforestry systems integrated to oil palm farming, and in successional forests. The nine study areas (each with 2 ha) are consolidated into three Demonstration Units (DUs); biodiverse agroforestry system (Bio-AFS), fertilizers agroforestry system (Fert-AFS), and successional forest (SF); located in Tomé Açu (PA) municipality. Litterfall samples were collected in 192 collectors, distributed in double tracks of AFS consorciated with oil palm’s double lines, since September 2016 to August 2017, in 36 plots. These samples were submitted to processing to determine the production in different fractions; cocoa (Theobroma cacao) and madre-de-cacao (Gliricidia sepium) leaf litterfall, in Bio-AFS and Fert-AFS; fine litterfall [leaves; petioles; woody material≤1.00cm (thin branches); reproductive and miscellaneous material; and thick litterfall [woody material>1.00cm (thick twigs)]. The successional forests had major annual production of fine, thick and total litterfall than all agroforestry systems. The SF-I had the largest contribution of fine and total litterfall (12,65 Mg ha-¹ year-¹ and 13,89 Mg ha-¹ year-¹) and SF-III had the largest thick fraction contribution (1,79 Mg ha-¹ year-¹). In relation the annual production of cocoa leaf litterfall, the Bio-AFS-I presented greater contribution (3,02 Mg ha-¹ year -¹) in comparison to Bio-AFS-II, and Bio-AFS-III. However, regarding madre-de-cacao leaf litterfall production , Fert- AFS-II presented greater contribution (1,80 Mg ha-¹ year -¹) in comparison to Fert-AFS-I, and Fert-AFS-III. The monthly litterfall production presented an unequal dynamics throughout the year. The contribution of fine and total litterfall was major in the drier and hotter months, differently the thick litterfall contribution, which was higher in the wetter months and with lower temperatures. There was a significant difference between successional forests and agroforestry systems, and between more diversified AFSs and less diversified AFSs, with regard to the annual litterfall production, being the higher annual production presented by the SF-I, and the minor presented by Fert-AFS-I (13,89 Mg ha-¹ year-¹ and 2,32 Mg ha-¹ year-¹). Significant difference was also observed between treatments, concerning the monthly litterfall production. The most diversified AFSs, in general, were superior to less diversified AFSs in annual litterfall production, being thus more similar the successional forests.