Linking water vapor sorption to water repellency in soils with high organic carbon contents

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The warming climate is rapidly changing the circumpolar region, presenting new opportunities and challenges for agricultural production in South Greenland. The warming climate is projected to increase the frequency of drought periods, but little is known about the soil-water retention (SWR) and the plant available water (PAW) of the agricultural soils in the region. This study aimed to measure the SWR and PAW of Greenlandic agricultural soils and evaluate the effect of organic carbon (OC) and clay (CL) content using pedotransfer functions based on OC and CL. The study included 464 South Greenlandic agricultural soil samples from 20 fields with a wide distribution in clay (0.016-0.184 kg kg −1 ) and OC contents (0.006-0.254 kg kg −1 ). Pedotransfer functions were successfully developed for estimating the gravimetric water content (w) at five soil-water potentials (−1500, −100, −30, −10, and −5 kPa) and PAW. The OC content was the primary variable governing the gravimetric water content at each soil-water potential, evidenced by R 2 values consistently above 0.80.The effect of OC on the gravimetric water content at −1500 kPa was close to the range reported in the literature, but OC effects were markedly higher between −100 and −5 kPa. Overall, this study highlights a substantial effect of OC on the PAW as a 1% increase in OC increased PAW by more than 4%, which is almost twice the value of a recent meta-study. Our study highlights the potentially dominating effects of organic matter on soil-water balance and availability in high-latitude agriculture.

Section: Resultssupporting

confidence: 81%

Organic carbon controls water retention and plant available water in cultivated soils from South Greenland

Weber

Blaesbjerg

Møldrup

et al. 2023

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“…The critical water content exhibited much less variability among the samples after conversion to pF, indicating that soil water retention has a normalizing effect on WR‐W curves. Further, a recent study showed that WR was intimately linked to the water vapor isotherms of soils from Denmark and Greenland with an OC ranging from 0.014 to 0.369 kg kg −1 (Hermansen et al., 2021). Hermansen et al.…”

Section: Resultsmentioning

confidence: 99%

“…Hermansen et al. (2021) were, among other things, able to predict WR AREA and W NON with high accuracy ( R 2 of 0.98 and 0.97, respectively) from the water content at 50% relative humidity. Therefore, desorption isotherms were applied to normalize SWR AREA to soil water retention.…”

Section: Resultsmentioning

confidence: 99%

“…Further, a recent study showed that WR was intimately linked to the water vapor isotherms of soils from Denmark and Greenland with an OC ranging from 0.014 to 0.369 kg kg −1 (Hermansen et al, 2021). Hermansen et al (2021) were, among other things, able to predict WR AREA and W NON with high accuracy (R 2 of 0.98 and 0.97, respectively) from the water content at 50% relative humidity. Therefore, desorption isotherms were applied to normalize SWR AREA to soil water retention.…”

Section: 4mentioning

confidence: 95%

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Glacial rock flour reduces the hydrophobicity of Greenlandic cultivated soils

Weber

Hermansen

Pesch

et al. 2023

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Soil water repellency (WR) is ubiquitous across Greenlandic cultivated fields, which may constrain agricultural production. Fine-grained glacial rock flour (GRF) is available in the surrounding landscape, which could serve as a soil amendment. We tested whether the application of GRF (rates of 0, 50, 100, 300, and 500 ton ha −1 ) reduced the WR across two field trials in South Greenland. The field trials, Upernaviarsuk (UP) and South Igaliku (SI), differed in clay (UP: 0.05-0.11 kg kg −1 ; SI: 0.03-0.05 kg kg −1 ) and organic carbon (OC) contents (UP: 0.04-0.13 kg kg −1 ; SI: 0.01-0.03 kg kg −1 ). We measured WR across gravimetric water contents (W) from oven-dry to the W where WR ceased (W NON ) to obtain whole WR-W curves. Most soils became hydrophilic around air-dry conditions at application rates of ≥300 ton ha −1 , likely due to increased clay:OC ratios. Application rates of ≥300 ton ha −1 generally reduced the trapezoidal integrated area of the WR-W curve (WR AREA ), W NON, and WR after heat treatments at 105˚C (WR 105 ) and 60˚C (WR 60 ). The WR 105 was significantly reduced in both fields at 500 ton ha −1 , while WR 60 was significantly reduced in UP at application rates of ≥300 ton ha −1 . The GRF effects were masked by texture and OC variations. Normalizing WR AREA to the water vapor sorption isotherms (utilizing the Campbell-Shiozawa model) revealed that GRF consistently reduced the normalized WR AREA . The SI field showed the largest reduction in the normalized WR AREA , likely due to its lower OC and clay contents. Thus, GRF could reduce WR across two Greenlandic field trials.

“…For eight soils without OM, Song et al (2022) suggested that water vapor sorption hysteresis for mineral soils was mainly due to the difference in cation hydration and dehydration for a w < ∼0.75, and the different sizes of narrow pore necks and connected pores for a w > ∼0.75. Zhuang et al (2008), Arthur et al (2020), andHermansen et al (2021) reported that the average hysteresis of SWVS increased with increasing SOC content. Arthur et al (2020) hypothesized that this is related to conformational changes in the structure of OM during the sorption process.…”

Section: Core Ideasmentioning

confidence: 98%

Effect of soil organic matter on sorption of water vapor and associated hysteresis

Xue

Chen

Arthur

et al. 2023

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In‐depth knowledge about the impact of organic matter (OM) on soil water vapor sorption (SWVS) and associated hysteresis related to various water activity (aw) levels is limited. The objective of this study was to elucidate the effect of OM on SWVS and sorption hysteresis for different aw levels. We measured water sorption isotherms and physicochemical properties of eight soils with varying clay (6‐47%) and OM (2.0‐7.8%) contents before and after OM removal. In general, OM increased SWVS, but the effect of OM on SWVS varied for different aw ranges. The presence of OM generally increased water vapor sorption during the adsorption process. For soils with OM content above 4.6%, the presence of OM decreased water vapor sorption during the condensation process. The local hysteresis (Hw) of soils with OM was higher than that of soils without OM for soils with OM contents above 3.4%. For aw < ∼0.75, the water vapor sorption hysteresis of soils with and without OM showed a significant correlation with cation exchange capacity (CEC), and the Hw values of soils with OM were lower than that of soils without OM for the same CEC. The OM can affect water vapor sorption and the associated hysteresis at low aw levels through adsorbed cations and organic functional groups, and at high aw levels through the structures of pores and OM.This article is protected by copyright. All rights reserved