Diazotrophic population and soil nitrogen dynamics following coapplication of biochar with inorganic fertilizer in the humid tropics

Muhammad Farid Azlan Halmi,Khanom Simarani

doi:10.1590/1678-4499.20210017

Abstract

Nutrient loss from the weathering process is a major challenge for tropical agriculture. Biochar with nutrient retention capacity has been proposed as an amendment to retain plant-available nutrients. Meanwhile, information on diazotrophic population responses to biochar application in the humid tropics is still poorly explored. A field study was carried out over three cropping cycles of maize in a typic paleudults of Peninsular Malaysia. During the first cropping cycle, the soil was amended with palm kernel shell biochar (PK), rice husk biochar (RH), palm kernel biochar with fertilizer (FPK), rice husk biochar with fertilizer (FRH), fertilizer (F), and control soil (C). Soil samples were taken at each harvesting stage and analyzed for pH, cation exchange capacity (CEC), total N, ammonium (NH4+–N), nitrate (NO3––N), microbial biomass N, and urease activity. Total and active diazotrophs were quantified from soil DNA and RNA, respectively, employing quantitative polymerase chain reaction (qPCR) amplification of the nifH gene. Palm kernel shell and rice husk biochars maintained a significant NH4+–N and NO3––N, respectively, during the second cropping cycle. Both biochars promote the total and active diazotrophic population. A detrimental impact on the nifH transcript was detected from fertilization even when biochar was co-amended. Two possible land management options for tropical soil were proposed from the overall data. First, the application of fertilizer with biochar can reduce N loss against weathering. Second, the application of biochar alone may improve biological N2 fixation in tropical soils.

Highlights

The acidic soil in the humid tropics is naturally deficient in plant nutrients due to high weathering in this climatic region
During the first cropping cycle, the soil was amended with palm kernel shell biochar (PK), rice husk biochar (RH), palm kernel biochar with fertilizer (FPK), rice husk biochar with fertilizer (FRH), fertilizer (F), and control soil (C)
The simultaneous enhancement of pH and cation exchange capacity (CEC) is expected as it is frequently reported by various recent field studies (Hale et al 2020; Halmi et al 2018; Oladele et al 2019a) on the amelioration effect of biochar in the humid tropics

Summary

Introduction

The acidic soil in the humid tropics is naturally deficient in plant nutrients due to high weathering in this climatic region. Intense weathering from continuous high rainfall constrains crop production by causing rapid N loss from the soil through leaching and surface run-off. High dependency on N fertilizer and its excessive application may cause detrimental environmental impacts, such as ammonia volatilization and eutrophication via nitrate leaching (Moura et al 2016). A growing body of evidence supports the application of biochar, a thermal degradation organic product from pyrolysis (Lehmann et al 2011), as an amelioration solution for the problematic highly weathered soil in the humid tropics. Supplementation of biochar with fertilizer may further enhance the amelioration effect, as biochar can hold the applied N and prevent it from leaching (Oladele et al 2019a; Uttran et al 2018), and mitigate N loss against weathering

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Results

Conclusion