Biochar addition affected nutrient leaching and litter decomposition rates in boreal sandy soils

Sanna Saarnio,Riitta Kettunen

doi:10.23986/afsci.89559

Abstract

Effects of biochar addition on litter decomposition rates, nutrient leaching and soil moisture were tested in two boreal agricultural soils; a sandy till and a medium fine sand. Three litter bags were buried in soil basins, which were stored in the dark for 31 and 19 weeks in the sandy till experiment and medium fine sand experiment, respectively. Once per each temperature period, the soil was saturated in order to collect excess water for nutrient analyses. Biochar increased the decomposition rate of N-rich litter but did not affect the decomposition of N-poor litter. PO43--P and NO2--N were released from the biochar to the leached water and thus leaching of PO43--P, NO2--N and total P was increased in the soil with the finer texture. However, biochar retained water after heavy irrigation and leaching of PO43--P and total P was not increased on the coarser soil. Although pure biochar adsorbed NH4+-N from nutrient solutions, NH4+-N leaching from both soil types was generally not affected by biochar. Leaching of nitrate NO3--N and total N was decreased on both soils due to retention by the biochar.

Highlights

Biochar addition may affect cycling of carbon (C), nitrogen (N), phosphorus (P) and other nutrients in soils in many ways
The amounts of PO43--P (127–366 μg l-1) and total P (128–381 μg l-1) leached from the pure biochar were very high (Fig. 1), in comparison to the amounts leached from biochar mixed in the soil
The pure biochar significantly adsorbed NH4+-N (9–47% of the applied amount), NO3--N (5–31%) and total N (5–34%) when the nutrient solutions were allowed to percolate through the biochar, whereas leaching of excess NO2--N, PO43--P and total P from the pure biochar was evident

Summary

Introduction

Biochar addition may affect cycling of carbon (C), nitrogen (N), phosphorus (P) and other nutrients in soils in many ways. We hypothesised that biochar addition 1) decreases nutrient (N, P) leaching, especially from soils with low organic matter content, 2) decreases the decomposition rate of new organic litter (just added in soil) and 3) increases soil moisture content albeit with a smaller increase in soils with finer texture and better initial water holding capacity. We hypothesise that these changes would lead to decreased agricultural nutrient loading to watercourses during the non-vegetated phases of the field

Methods

Results

Discussion

Conclusion