Abstract
The effects of a high biochar rate on soil carbon mineralization, when co-applied with excessive compost, have been reported in previous studies, but there is a dearth of studies focusing on soil nitrogen. In order to ascertain the positive or snegative effects of a higher biochar rate on excessive compost, compost (5 wt. %) and three slow pyrolysis (>700 °C) biochars (formosan ash (Fraxinus formosana Hayata), ash biochar; makino bamboo (Phyllostachys makino Hayata), bamboo biochar; and lead tree (Leucaena leucocephala (Lam.) de. Wit), lead tree biochar) were applied (0, 2 and 5 wt. %) to three soils (one Oxisols and two Inceptisols). Destructive sampling occurred at 1, 3, 7, 28, 56, 84, 140, 196, 294, and 400 days to monitor for changes in soil chemistry. The overall results showed that, compared to the other rates, the 5% biochar application rate significantly reduced the concentrations of inorganic N (NO3−-N + NH4+-N) in the following, decreasing order: lead tree biochar > bamboo biochar > ash biochar. The soil response in terms of ammonium and nitrate followed a similar declining trend in the three soils throughout the incubation periods, with this effect increasing in tandem with the biochar application rate. Over time, the soil NO3−-N increased, probably due to the excessive compost N mineralization; however, the levels of soil NO3−-N in the sample undergoing the 5% biochar application rate remained the lowest, to a significant degree. The soils’ original properties determined the degree of ammonium and nitrate reduction after biochar addition. To reduce soil NO3−-N pollution and increase the efficiency of compost fertilizer use, a high rate of biochar application (especially with that pyrolyzed at high temperatures (>700 °C)) to excessively compost-fertilized soils is highly recommended.
Highlights
As the biochar was added to the soil at rates equivalent to 2% and 5% of the total soil organic N, this gave 0.16 and 0.40, 0.21 and 0.54, and 0.19 and 0.48 mg waterextractable N kg−1 soil for ash, bamboo and lead tree biochar, respectively
Our study has indicated the significant role that a high biochar rate plays in reducing the ammonium and nitrate in soils, as well as its consistent effect on the pH and C/N
soil typesunder (Soil) with a lower pH and higher clay content may exhibit a reduced degree of decline, whereas a low proportion of clay facilitates the reduction of ammonium and nitrate in the soil
Summary
Biochar plays an important role in determining the N availability in soil, despite the low content of available N, as it may directly or indirectly influence N immobilization and mineralization, as well as nitrification [1]. The potential applicability of biochar in decreasing soil N losses was generally lower in tropical regions than in temperate regions [2], probably due to these areas’ high precipitation and warm temperature, which result in notable soil erosion, nutrient leaching, and the rapid decomposition of soil organic matter. The high precipitation levels (annually > 2500 mm) and warm temperature (annually around 23~25 ◦ C) are the two major detriments of Taiwan’s agricultural soils. %) of compost during intensive cultivation periods for short-term leafy crops, because of the relative low N mineralization rate and the low levels of nutrients in this compost compared with chemical and complete fertilizer Farmers in Taiwan usually apply a greater amount (2~5 wt. %) of compost during intensive cultivation periods for short-term leafy crops, because of the relative low N mineralization rate and the low levels of nutrients in this compost compared with chemical and complete fertilizer
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