Comparison of two alkali trap methods for measuring the flush of CO₂

Abstract

Soil biological activity is a key feature of healthy soil. The flush of CO 2 during the first few days after rewetting of a dried soil is a rapid indicator of soil biological health, but variations in approach require testing and calibration. A 3-d incubation method (25 • C, 50% water-filled pore space, acid titration) was compared with a 4-d incubation method (∼20 • C, capillary wetted, electrical conductivity) from two long-term field experiments in Missouri (silt loam soils) and North Carolina (sandy loam and loamy sand soils). The two methods were related (p < .001) to each other (r 2 = .93, n = 211 for Missouri soils and r 2 = .68, n = 126 for North Carolina soils), but results differed in absolute value in an unexpected manner. Differences in incubation time (3 vs. 4 d), temperature (∼20 vs. 25 • C), and water delivery (50% water-filled pore space vs. capillary wetting) were major factors affecting relationships between methods. Time and temperature were predictable and scalable factors, but water delivery approach likely caused random variations specific to soil type. Both methods were able to discern depth stratification of soil biological activity, but subtle differences due to landscape position and soil texture were detected only with the 3-d method. We suggest that greater standardization of soil biological activity protocols based on key factors of soil moisture, temperature, and time of incubation be adopted to improve reliability and value to stakeholders.

Soil‐test biological activity with short‐term and long‐term carbon contributions

“…The methodological approach of using dried soil and relatively rapid analysis time were key attributes for its development as a soil testing approach (Franzluebbers, Haney, Honeycutt, Schomberg, & Hons, 2000). Also, it relies on natural decomposition of organic matter to yield a reliable estimate of respiratory activity when using a standardized laboratory approach (Franzluebbers & Veum, 2020).…”

Correlation between Carbon dioxide Evolution and Biological Quality Index of Long-term Nutrient Management Adopted Soils

“…Alkali trap method: For this, 100 g of soil amended with 15-ml of 1% of glucose and 35 ml of deionized water was placed in an air-tight bottle with a vial of 10 ml of 0.1N NaOH. The bottles were incubated at 30°C for 12 h. The unreacted alkali in the trap was quantified by back-titration with 0.1N HCl to determine the amount of CO 2 evolved from the soil (Franzluebbers and Veum, 2020).…”

“…In the present work, we related the measured SBQI of the soils of long-term nutrient management with the flush of CO 2 under laboratory conditions. The soil respiration rate or flush of CO 2 could be a potential indicator that could strongly relate several biological constituents including biologically active soil C and N fractions, water-soluble C, C and N mineralization and microbial biomass carbon (Morrow et al, 2016;Sciarappa et al, 2017;Franzluebbers, 2018;Franzluebbers, 2020;Franzluebbers and Veum, 2020). The relation was strong across the soil types and different management conditions; hence, it can be developed as a simple, rapid, and reliable method for testing biological quality.…”

“…To validate this concept to Indian agro-ecological conditions, in the present work, we have measured the CO 2 evolution from the soils under the influence of long-term nutrient management and assessed their relativeness to the biological attributes. Since all the four soils had distinct biological attributes as influenced by long-term nutrient management, the CO 2 evolved from these soils could easily be correlated with the biological quality of the soils (Franzluebbers and Veum, 2020). We have amended glucose uniformly in all the soil samples to accelerate the soil respiration at the earliest so that the result could be obtained quickly.…”

“…The recent works strongly correlate the CO 2 evolution following rewetting of dried soil (referred to as flush of CO 2 ) with mineralizable nitrogen and phosphorus of soil. Several studies used the flush of CO 2 to characterize soil biology as influenced by tillage, crop management, crop sequence (Morrow et al, 2016;Franzluebbers, 2018;Franzluebbers and Haney, 2018;Franzluebbers, 2020;Franzluebbers and Veum, 2020). In the present work, we assume that the CO 2 evolved from the soil samples may have a positive and strong correlation with soil biological attributes and by measuring the CO 2 , we can presumably derive the biological quality of the soil.…”