Changes in the Mineralisation of Nutrients and Sunflower Biomass in Soil Irrigated with Water from Oil Exploration in a Semi-Arid Environment

Wastewater from oil fields may be an option for irrigation, especially in regions which have low rainfall with high variability. The aim was to evaluate the composition and decomposition of shoot biomass from sunflower plants irrigated with water from oil wells,which had been subjected to filtering (FPW) and reverse osmosis (OPW), using groundwater (UGW) as a reference.Two tests were then carried out to evaluate decomposition of the residue. In the first test, residues produced with FPW, OPW and UGWwere incubated in soil and irrigated with groundwater (UGW). In the second test, residues from plants irrigated with UGW were also incubated,but irrigated with FPW, OPW and UGW. Significant differences were seen in the levels of Na, Mg and lignin in the residues with the use of FPW, showing greater levels for Na, and lower levels for Mg and lignin. The loss in biomass of the incubated residues was not significant in either test; this was not seen in the Mg e Nwith smaller losses than the biomass, or theNa, K e S with greater losses, especially when produced with FPW and OPW respectively. In the residue produced with UGW, differences were identified for Ca and Na, with the order of losses for type of water being UGW=FPW> OPW and OPW=UGW>FPW respectively. Irrigation using water from oil extraction alters the chemical characteristics of the soil and the composition of cultivated plants at a level sufficient to influence the rate of decomposition of the organic residue.