Distinguishing functional pools of soil organic matter based on solubility in hot water.

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Date: May 2021
From: Soil Research(Vol. 59, Issue 4)
Publisher: CSIRO Publishing
Document Type: Report
Length: 7,287 words
Lexile Measure: 1520L

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Abstract :

Evidence is emerging that the solubility of soil organic matter (SOM) in water is a key factor regulating the turnover of carbon (C) and nitrogen (N). We used data from a field trial with a wide range of treatments in a case study to: (1) examine the link between SOM solubility and bioavailability and (2) evaluate whether low water-solubility is a factor contributing to the persistence of refractory SOM. The trial was established in 2000 on a silt loam (Udic Dystocrept) at Lincoln, New Zealand to identify management practices that maintain SOM following the conversion of long-term pasture to arable cropping. The following land use treatments were sampled (0-7.5,7.5-15 and 15-25 cm) in 2013: (1) long-term ryegrass-white clover pasture; (2) arable cropping rotation, managed using either intensive, minimum, or no tillage; and (3) continuous bare fallow (plots maintained plant-free using herbicide; not cultivated). The bioavailability of SOM was determined by measuring C and N mineralisation in a 98-day incubation at 25[degrees]C (soil maintained near field capacity) and water solubility was assessed by measuring hot-water-extractable C and N (16-h extraction at 80[degrees]C). After 13 years of arable cropping, C stocks (to 25 cm) were 11 t [ha.sup.-1] less than in pasture soil (decrease of 14%). Tillage 'intensity' had no effect on C stocks in the top 25 cm. Large losses of C were observed in the bare fallow treatment (19 t C [ha.sup.-1] less than pasture soil). The bioavailability of SOM (C[O.sub.2]-C mineralised as a proportion of soil C) also declined under arable cropping and bare fallow. The relationship between total C and mineralised C had a significant (P Keywords: bioavailability, land use effects, long-term fallow, recalcitrance, soil organic matter solubility.

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Gale Document Number: GALE|A671306822