Biochar impact on nitrate leaching in upland red soil, China

Abstract

Positive effects of biochar on nitrate (NO3−–N) leaching have recently been demonstrated in many studies, which mainly focused on biochar mixed into soil samples in the laboratory. However, to our knowledge, studies on nitrate leaching from soil samples were directly taken from the field where biochar was added many years ago are relatively scarce. Therefore, a laboratory soil column method was used to study the influence of biochar on the process of vertical transport of nitrate. Breakthrough curves (BTCs) were obtained separately from each biochar treatment. The results were as follows: Biochar has a significant influence on the BTCs of NO3−–N. The initial time and total time increased incrementally with biochar application rate, whereas the cumulative amount of leached NO3−–N, peak concentration and water flux of the BTCs decreased at the same time. The C6 treatment (40 t/ha) significantly decreased the amount of leached NO3−–N. The measured values and simulated values obtained by CXTFIT 2.0 were highly significantly related, as shown by high correlation coefficients (r > 0.85**). A highly significant positive correlation (p < 0.01) was found between the initial time, total time and the application rate of biochar, while cumulative mass of leached NO3−–N, peak concentration and water flux showed a significant negative correlation (p < 0.01) with increasing biochar application rate. The results showed that the biochar added to soil could be an effective means of reducing nutrient leaching in soil column experiment in laboratory. CXTFIT 2.0 model was suitable in fitting the observed nitrate transport in upland red soils.