Optimizing Conditions for the Measurement of Soil Inorganic Nitrogen with a Micro-Plate Reader

Abstract

There are numerous methods for measuring inorganic nitrogen (N) in soils, but many of these are complex or require expensive equipment. In order to seek an accurate and rapid measurement method, we optimized the conditions for soil inorganic nitrogen (N) (NH4+-N and NO3–N) determination with a micro-plate reader; a systematic study was carried out. The effects of extraction regent concentrations, ratios of extraction solution to the soil, extraction time, extracted solution storage methods and time, and reaction time on soil inorganic N measurement were investigated. Results showed that all tested conditions except the storage method had a significant effect on the determination of soil NH4+-N and NO3–N. Compared with the non-stored treatment, the value of the measured soil nitrate-nitrogen increased after being stored in a refrigerator for seven weeks, while that for ammonium-nitrogen content was reduced. The appropriate protocol was using extracting solution directly to determine the content of NH4+-N and NO3–N in soil (otherwise, keep it at room temperature), 1.0 mol/L KCl as the extraction regent, solution/soil ratio with 10:1, extraction for 45 min, and reaction for 25 min (only for NH4+-N). The recovery rate of adding standard solution was above 99% as it met the detection requirements.

Improved Method for Extracting Nitrites in Soil

“…Compared with un-buffered KCl, extraction with DIW significantly underestimated the NH4 + concentration in the three soils and the NO3 -concentration in the fluvo-aquic soil (Figure 2d-f). Tu et al (2021) [30] also found that the measured concentrations of NH4 + and NO3 -in KCl extracts were 1.6-2.6 and 1.1-1.8 folds higher than those in DIW, respectively. Lim et al (2018) [16] showed that DIW-extracted NO3 -concentrations were only 50-60% of those extracted by 2 mol L -1 KCl.…”

“…In recent years, a large number of studies have been conducted on the factors affecting the determination of soil NH 4 + and NO 3 − , including the extraction method [30], the concentration of the extractant [30], the storage method [31], the shaking time [30], etc. However, the effects of these factors on soil NO 2 − concentration have not been systematically reported.…”

“…Although most of the literature suggests that the shaking time for extracting NH4 + and NO3 -should be 60 min [30,36], some studies believe that the concentration of NO3does not change significantly after 15-30 min of shaking [37,38]. The NH4 + and NO3 -concentrations were relatively stable at the late stage of shaking (30-60 min), indicating that 30 min of shaking is long enough to quantitatively extract soil NH4 + and NO3 - [38].…”

“…Although most of the literature suggests that the shaking time for extracting NH 4 + and NO 3 − should be 60 min [30,36], some studies believe that the concentration of NO 3…”

Impact of biochars fabricated with typical feedstocks on soil environment and crop productivity: A case study with D. rubrovolvata

“…The pH and EC of the soil and biochar were determined using soil/biochar slurry to water (1:5, w/v) suspensions. The content of AN and NN in the soil and biochar was determined by extracting with potassium chloride solution and using a colorimetric method (Tu et al, 2021). The TN content in the soil was determined using the Kjeldahl method (Lin et al, 2020).…”