Impacts of fresh and aged holm-oak biochar on clomazone behaviour in rice cropping soils after transition to sprinkler irrigation

Abstract

Although alternative practices to traditional flooding rice cultivation urgently need to be implemented in water-stressed regions, these can modify soil properties, thereby affecting the environmental behaviour of pesticides. One of the most extensively used herbicides in rice cropping is clomazone. A field experiment covering two years was conducted to evaluate how fresh and aged holm oak biochar (BH) influenced clomazone's behaviour in rice cropping after transition from flooding to sprinkler irrigation with different tillage systems. The experiment involved traditional flooding irrigation and tillage either without (FT) or with (FTBH) first-year BH addition, and four treatments more where sprinkler irrigation had been in use for 3 years – sprinkler irrigation and tillage without (ST) or with (STBH) first-year BH addition, sprinkler irrigation and no-tillage without (SNT) or with (SNTBH) first-year BH addition. The measurements done in the first and second years after BH application were taken to constitute the temporal variability (i.e., “fresh” and “aged” effects, respectively). Adsorption-desorption, dissipation, and leaching studies were carried out under laboratory conditions using soils from the field experiment. The Kd (partition coefficient) values were 1.2, 1.1, and 1.1 and 1.5, 1.2, and 1.2 times greater in SNTBH, STBH, and FTBH than in the corresponding unamended soils for the fresh and aged years, respectively. The clomazone persistence was only significantly affected by BH addition in the treatments under sprinkler irrigation. Under anaerobic incubation conditions the application of BH led to an increase in the t½ (half-live) values from 19 and 26 d and from 22 and 21 d in SNT and ST, to 36 and 35 d, and to 25 and 31 d in the corresponding amended soils for the fresh and aged years, respectively. However, under aerobic conditions, while for the fresh year t½ values increased from 37 and 41 d in SNT and ST to 40 and 52 d in the corresponding amended soils, for the aged year these values were not significantly affected. The management regimes significantly influenced clomazone leaching, with the total leached values showing the following trend: ST = SNT > FT = STBH = SNTBH > FTBH. Therefore, the use of BH as organic amendment may be an effective tool to greatly reduce water contamination by clomazone in rice fields under conventional tillage and flooding irrigation, but also under sprinkler irrigation, particularly after BH aging under no-tillage practices.