Co-application of biochar and nitrogen fertilizer reduced nitrogen losses from soil.

Xiuwen Li,Forbes R Walker,Avishesh Neupane,Jennifer M Debruyn,Nourredine Abdoulmoumine,Sutie Xu,Sindhu Jagadamma,Dafeng Hui

doi:10.1371/journal.pone.0248100

Abstract

Combined application of biochar and nitrogen (N) fertilizer has the potential to reduce N losses from soil. However, the effectiveness of biochar amendment on N management can vary with biochar types with different physical and chemical properties. This study aimed to assess the effect of two types of hardwood biochar with different ash contents and cation exchange capacity (CEC) on soil N mineralization and nitrous oxide (N2O) production when applied alone and in combination with N fertilizer. Soil samples collected from a temperate pasture system were amended with two types of biochar (B1 and B2), urea, and urea plus biochar, and incubated for 60 days along with soil control (without biochar or urea addition). Soil nitrate N, ammonium N, ammonia-oxidizing bacteria amoA gene transcripts, and N2O production were measured during the experiment. Compared to control, addition of B1 (higher CEC and lower ash content) alone decreased nitrate N concentration by 21% to 45% during the incubation period while the addition of B2 (lower CEC and higher ash content) alone increased the nitrate N concentration during the first 10 days. Biochar B1 also reduced the abundance of amoA transcripts by 71% after 60 days. Compared to B1 + urea, B2 + urea resulted in a significantly greater initial increase in soil ammonium and nitrate N concentrations. However, B2 + urea had a significantly lower 60-day cumulative N2O emission compared to B1 + urea. Overall, when applied with urea, the biochar with higher CEC reduced ammonification and nitrification rates, while biochar with higher ash content reduced N N2O production. Our study demonstrated that biochar has the potential to enhance N retention in soil and reduce N2O emission when it is applied with urea, but the specific effects of the added biochar depend on its physical and chemical properties.

Highlights

Farmers rely heavily on nitrogen (N) fertilizers to improve crop yield because N is one of the primary nutrients that plants need for growth and productivity
Biochar 1 (B1) + urea treatment resulted in 19.7%, 71.3% and 36.9% lower N concentration than Biochar 2 (B2) + urea treatment on day 3, 10, and 30, respectively
Between day 3 and 10, biochar alone treatments resulted in negligible NAR from -0.21 to 0.35 mg N kg-1 day-1 in B1 treatment and -0.28 to 0.27 mg N kg-1 day-1 in B2 treatment, which were significantly lower than that in all the urea added treatments during that period (1.27– 12.3 mg N kg-1 day-1) (Table 3)

Summary

Introduction

Farmers rely heavily on nitrogen (N) fertilizers to improve crop yield because N is one of the primary nutrients that plants need for growth and productivity. In 2016, more than 144 million tons of fertilizer N was applied to agricultural lands across the world [1]. Less than 50% of the applied N is taken up by crops [2] and the rest is lost, potentially contributing to eutrophication, lake acidification, biodiversity loss, and global warming [3].

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