Humic Acid Mitigates the Negative Effects of High Rates of Biochar Application on Microbial Activity

Jiri Holatko,Oldrich Latal,Antonin Kintl,Muhammad Zafar-Ul-Hye,Tivadar Baltazar,Shah Fahad,Vaclav Pecina,Subhan Danish,Tereza Hammerschmiedt,Petr Sarec,Rahul Datta,Petr Novak,Martin Brtnicky,Ludmila Balakova

doi:10.3390/su12229524

Abstract

Objective: Biochar and a commercial humic acid-rich product, Humac (modified leonardite), represent soil amendments with the broad and beneficial effects on various soil properties. Their combination has been scarcely tested so far, although the positive impact of their interaction might be desirable. Materials and Methods: The dehydrogenase activity (DHA), microbial biomass carbon (Cmic), soil respiration (basal and substrate-induced), enzyme activities, total carbon (Ctot), and both shoot and root biomass yield were measured and compared in the short-term pot experiment with the lettuce seedlings. The following treatments were tested: the unamended soil (control), the Humac-amended soil (0.8 g·kg−1), the biochar-amended soil (low biochar 32 g·kg−1, high biochar 80 g·kg−1), and the soil-amended with biochar + Humac. Results: The effect of both amendments on the soil pH was insignificant. The highest average values of Ctot and Cmic were detected in high biochar treatment and the highest average values of basal and substrate-induced respiration (glucose, glucosamine, alanine) were detected in the low biochar treatment. The phosphatase activity and fresh and dry lettuce aboveground biomass were the highest in the low biochar + Humac treatment. Conclusions: Even though the combination of both biochar + Humac decreased the microbial activities in the amended soil (Cmic, DHA, enzymes, substrate-induced respiration) at the low biochar dose, they mitigated the detrimental effect of the high biochar dose on respiration (all the types) and the enzyme (phosphatase, arylsulphatase) activities. In contrast to the previously published research in this issue, the effects could not be attributed to the change of the soil pH.

Highlights

The term biochar is used for a heterogeneous material produced by pyrolysis of the selected raw material under controlled conditions
Research was conducted to compare the effects of two organic amendments, biochar and humic acids (HA) (Humac), and their combination on the soil microbial activity and the crop yield in the short-term pot experiment
We concluded that the combined application of both amendments exerted a positive effect on Cmic, Ctot (+157% and +166%, respectively), and lettuce crop yield (+26%) under experimental conditions in comparison with the control and the pure Humac treatment

Summary

Introduction

The term biochar is used for a heterogeneous material produced by pyrolysis of the selected raw material under controlled conditions. Biochar is produced from a wide variety of feed stock [1,2] Nowadays, it has been widely applied in various branches of anthropogenic activities: in the agriculture to increase productivity, management of soil health, and industry and technologies [3,4,5]. Soil rhizobacteria plays an significant role in phytoremediation of contaminated soil, increases nutrient uptake and promote plant growth and yield. One such co-amendment may represent humic acids (HA), which are the components of humus, a key factor in the persistence of soil organic matter (SOM) in soils. Biochar-derived HA seems to be important in the process of SOM enrichment in biochar-amended soils. The biochar-derived HA render increased aromaticity of low-temperature biochar whereas their interaction with high-temperature biochar has pore-blocking effects due to the extension of HA into pore throats, where they artificially lower the biochar surface area [11,12]

Methods

Results

Conclusion