Resíduos de bauxita e da palma de óleo: potencial agronômico e ambiental para o condicionamento de solos ácidos.

Abstract

Agribusiness is one of the pillars for the positive result of the gross domestic product (GDP) in Brazil. The linear growth of this sector has generated greater demand for inputs that affect crop productivity. The use of alternative sources such as mining and agroindustry wastes can help in the alternative development of new products for use in soils. The association of bauxite residue (BR) with alkaline properties to oil palm waste, which are sources of organic matter and nutrients can characterize formulation with ideal conditions for soil conditioning. The first chapter aimed to evaluate the physicochemical properties (total N, organic carbon, cation exchange capacity, C/N ratio, nutrients and potentially toxic elements PTEs) as well as the potential ecological risk (PERI) of conditioners generated by BR increment under different oil palm organic residues. Thus, we defined a factorial with three doses of BR (25, 50 and 75%) and combined with two types of organic waste from palm oil production (1: palm oil mill waste POMW- fiber, bunch of empty fruits and blurs palm in ideal proportions for composting; 2: palm oil compost POC- mature compost of organic waste from oil palm) in 60 L containers and we evaluated after 90 days. The second chapter aimed to evaluate leaching of chemical elements, soil and groundwater contamination estimation, soil physicochemical characteristics and agronomic efficiency of formulation containing BR and oil palm residues in soil cultivated with Urochloa hybrid cv. Sabiá. The formulations were selected considering the parameters for soil conditioners, whose doses were (40, 80 and 120 t ha-1). PVC columns with a capacity of 5 kg were used, coupled with hoses and bottles adapted to facilitate drainage and collection of leachates. During 60 days simulated rainfall was applied aiming to saturate the substrate. After this period the hoses and bottles were removed and the columns started to be used as pots for growing Urochloa. The results indicated that the use of 25% BR associated with oil palm residues constituted a formulation that meets the requirements for soil conditioning. The higher the concentration of organic residues the higher the values of cation exchange capacity, water retention capacity, organic carbon, total N, nutrients, as well as lower sodicity and PTEs. The application of the formulations leached nine elements, however, neither in the leached solution nor in the soil was detected EPTs. The treatments neutralized Al3+ at the highest doses and also increased the base saturation (55.6%) in relation to the native forest soil (10.8%), as occurred with limestone (83%). They also raised soil pH (5.5) compared to native forest soil (4.7). Sabiá yields increased relative to native soil, matching limestone. Therefore, formulation containing BR and oil palm residues can be classified as soil conditioner, without impact on soil and groundwater contamination, besides increasing soil physicochemical parameters and grass production.