Behaviour of bispyribac-sodium in aerobic and anaerobic rice-growing conditions with and without olive-mill waste amendment

Water and tillage management practices alone or in combination with organic amendments can alter the behaviour of pesticides. This study evaluates the sorption, persistence, and leaching of bispyribac-sodium (BYS) under anaerobic and aerobic rice-growing conditions with and without soil amendment by composted olive mill waste (OW). For this purpose, field experiments were conducted over three years. They involved six treatments: no-tillage and sprinkler irrigation (aerobic) without (NTA) and with OW application (NTAOW), tillage and aerobic without (TA) and with OW application (TAOW), and tillage and flooding without (TF) and with OW application (TFOW). In all three OW treatments, the amendment was applied in the first year. The K-f values were significantly greater in TF than in [NTA and TA] for the first and third years of the experiment by factors of [1.5 and 2.3] and [1.6 and 1.2], respectively. While in the first year K-f was 1.5 times greater in TF than TFOW, at the end of the experiment it was 1.6 times lower. In the non-amended treatments, the persistence of BYS was up to 1.9 times greater under anaerobic than under aerobic incubation conditions. Except for the NTA treatment in the third year, the persistence of BYS under aerobic incubation conditions (t(1/2) = 35.5-53.7 d) was enhanced when OW was applied to the soil (t(1/2) = 44.5-80.1 d). Under anaerobic incubation conditions, in the first year the BYS persistence was significantly reduced in NTA and TA when OW was added to the soil, but in TF it was enhanced. Conversely, in the third year the persistence of BYS was significantly increased in NTA and TA by OW addition, but decreased under TF management. BYS leaching was similar under the aerobic (TA and NTA) and anaerobic (TF) treatments in the first year, but was less under the TF treatment at the end of the experiment. Independently of the water and tillage management, the addition of OW significantly influenced BYS sorption and persistence, reducing the amount of the herbicide leached, although the magnitude of the effect depended on the time elapsed after its application to the soil. The use of OW could be considered as a strategy with which to reduce water contamination by BYS under aerobic and anaerobic rice-growing conditions, especially in the short term after application of this organic amendment.