Long-term effects of grazing intensities on soil aggregation and organic matter in a no-tilled integrated soybean-cattle system

Watershed management practices such as prescribed fire, harvesting and understory mastication can alter the chemical composition and thickness of forest detritus, thus affecting the quantity and quality of riverine dissolved organic matter (DOM). Long-term effects of watershed management on DOM composition were examined through parallel field and extraction-based laboratory studies. The laboratory study was conducted using detritus samples collected from a pair of managed and unmanaged watersheds in South Carolina, USA. Results showed that dissolved organic carbon (DOC), total dissolved nitrogen (TDN) and ammonium (NH4+-N) concentrations were higher in water extracts from the unmanaged watershed than from the managed watershed (P<0.01). Pyrolysis gas chromatography–mass spectrometry analysis showed that water extracts from the unmanaged watershed contained more aromatic compounds than extracts from the managed watershed. For the field study, monthly water samples were collected for 1 year (2015) from the paired watersheds. DOC and TDN concentrations, as well as DOM aromaticity, were significantly higher in the unmanaged watershed than in the managed watershed for most of the year (P<0.05) and were linked to detrital thickness, precipitation and flow patterns. The formation potential of two regulated disinfection by-products was lower in the unmanaged watershed for most of 2015 (P<0.05). From this study, it appears that long-term watershed management practices may alter detrital mass and chemistry in ways that improve water quality.

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Organic matter characteristics and water-stable aggregation of a sandy loam soil after 9 years of wood-residue applications

Canadian Journal of Soil Science ◽

10.4141/cjss93-011 ◽

1993 ◽

Vol 73 (1) ◽

pp. 115-122 ◽

Cited By ~ 14

Author(s):

A. N'dayegamiye ◽

D. A. Angers

Keyword(s):

Organic Matter ◽

Sandy Loam ◽

Term Effect ◽

Long Term Effects ◽

Wood Residue ◽

Organic C ◽

Soil C ◽

Wood Residues ◽

Heavy Fractions

The long-term effects of wood-residue applications on soil properties are not well documented. This study was undertaken to characterize the organic matter and aggregation of a sandy loam after 9 yr of biennial application of wood residues (tree clippings) at rates of 25, 50 and 100 Mg ha−1 with and without nitrogen fertilization. Carbon (C) and nitrogen (N) contents of the whole soil were determined as well as the C content of the density fractions and of the fractions soluble and insoluble to Na4P2O7. In comparison with the control, the whole-soil C content was 16–24% higher following application of wood residues alone and 16–37% higher for application of wood residues supplemented with nitrogen. The treatments had no effect on soil water-stable macroaggregation (> 250 μm). Wood-residue applications had no effect on the humic material (soluble in Na4P2O7) but favored the humin-C content (the fractions insoluble in Na4P2O7) by 25–60% relative to the control. The light-fraction organic matter was on average 68% larger, and the heavy fraction 17% larger, in the treated soils than in the control. On average, 80% of the differences in total organic C induced by residue application could be attributed to differences in the humin and heavy fractions. The long-term effect of wood-residue applications to the soil was, therefore, reflected in an accumulation of the more stable organic matter present as heavy and humin fractions. In addition, the differences in the light fractions suggested a short-term effect of wood-residue applications.Key words: Light and heavy fractions, wood residues, organic C, water-stable aggregates, humic acids, humins

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