Application methods influence biochar–fertilizer interactive effects on soil nitrogen dynamics

Abstract

The potential nitrogen (N) losses from soils with fertilizer addition can be reduced when biochar is co‐applied, but this effect is influenced by the methods of biochar and fertilizer application. In a 60‐d laboratory incubation experiment, we investigated how two fertilizer application methods (surface placement and soil incorporation) affected N transformation in soils under the following treatments: control (soil with no biochar and urea [C]), biochar (150 mg N g−1 soil [B]), urea (150 mg N g−1 soil [U]), and the combination of B + U (75 mg N g−1 soil each B and U). Our results showed that at Day 30, the concentrations of soil NH4+–N and NO3−–N remained significantly higher for U but were relatively similar to control for biochar‐included treatments, indicating that the presence of biochar slowed the mineralization of urea during that period. The concentration of soil NO3−–N and cumulative N2O production under B + U treatment at 60 d was around two times higher for incorporation treatment compared with the surface treatment, indicative of a longer‐term N regulatory effect of biochar with the surface application method. Additionally, we observed a higher number of amoA gene transcripts when B + U was incorporated in the soil compared with applied to the surface at the later stage of incubation, indicative of higher potential nitrification activity. These results suggest that the surface application of B + U can be used as a slow release N source that can provide long‐term N supply to the crops, while the soil incorporation method could be used for crops that need low N at the beginning of the growth but require a substantial amount of it later. Surface co‐application of B + U can also be a good strategy to reduce soil N losses by slowing down ammonification, nitrification, N2O emission, and ammonia oxidizing bacteria activity.

Higher Biochar Rate Can Be Efficient in Reducing Nitrogen Mineralization and Nitrification in the Excessive Compost-Fertilized Soils

“…The soil N mineralization and immobilization rates are a function of the C and N pools available to microorganisms [12], and the immobilization of N occurs with an increasing C:N ratio. The immobilization of N has been reported following the addition of high C/N ratio biochar [9,29,41,42]. The raw C/N values of the three soils and compost were 8.5 (SAO), 4.8 (MAI), 5.9 (SAI), and 10.3 (compost), respectively.…”

“…However, at 57 weeks, a significant increase was observed only in the SAO soil, and an insignificant one in the MAI and SAI soils, indicating that the liming effect has been reduced (Table 4). Many reports have indicated that the inherent alkalinity of biochar could serve as a liming agent and leads to increased soil pH, especially for ameliorating the acidity of acidic soils [11,14,19,[24][25][26][27][28][29][30]. At the end of incubation, the soil pH increased by 0.01~0.24, 0.01~0.18, and 0.11~0.26 pH units for the SAO, MAI and SAI soils, respectively, and by 0.01~0.16, 0.03~0.13 and 0.06~0.26 pH units for the ash, bamboo, and lead tree biochars, respectively.…”

How do biochar size fractions and organic fertilizers interactively influence nitrous oxide emission from a tropical vertisol?

“…Few studies supported our result. For example, when soil was amended with BC + N (urea), higher NO 3 – produced through nitrification (X. Li et al., 2020). Similarly, BC was found to systematically stimulate nitrification and N 2 O emissions in a Haplic Calcisol (Martí et al., 2021).…”