Biochar reduces short-term nitrate leaching from a horizon in an apple orchard.

Nitrogen leaching in croplands is a worldwide problem with implications both on human health and on the environment. Efforts should be taken to increase nutrient use efficiency and minimize N losses from terrestrial to water ecosystems. Soil-applied biochar has been reported to increase soil fertility and decrease nutrient leaching in tropical soils and under laboratory conditions. Our objective was to evaluate the effect of biochar addition on short-term N leaching from A soil horizon in a mature apple orchard growing on subalkaline soils located in the Po Valley (Italy). In spring 2009, 10 Mg of biochar per hectare was incorporated into the surface 20-cm soil layer by soil plowing. Cumulative nitrate (NO) and ammonium (NH) leaching was measured in treated and control plots 4 mo after the addition of biochar and the following year by using ion-exchange resin lysimeters installed below the plowed soil layer. Cumulative NO leaching was not affected by biochar after 4 mo, whereas in the following year it was significantly ( < 0.05) reduced by 75% over the control (from 5.5 to 1.4 kg ha). Conversely, NH leaching was very low and unaffected by soil biochar treatment. The present study shows that soil biochar addition can significantly decrease short-term nitrate leaching from the surface layer of a subalkaline soil under temperate climatic conditions.