Effect of cover crop management on soil organic matter

doi:10.1016/j.geoderma.2005.01.019

Geoderma

Volume 130, Issues 3–4, February 2006, Pages 229-239

https://doi.org/10.1016/j.geoderma.2005.01.019 Get rights and content

Abstract

Characterization of soil organic matter (SOM) is important for determining the overall quality of soils, and cover crop system may change SOM characteristics. The purpose of this study was to examine the effect of cover crops on the chemical and structural composition of SOM. We isolated humic substances (HS) from soils with the following cover crop treatments: (a) vetch (Vicia Villosa Roth.)/rye (Sesale cereale L.), (b) rye alone, and (c) check (no cover crops) that were treated with various nitrogen (N) fertilizer rates. CPMAS-TOSS (cross-polarization magic-angle-spinning and total sideband suppression) ¹³C NMR results indicated that humic acids (HA) from soils under rye only were more aromatic and less aliphatic in character than the other two cover crop systems without fertilizer N treatment. Based on the DRIFT (diffuse reflectance Fourier transform infrared) spectra peak O/R ratios, the intensities of oxygen-containing functional groups to aliphatic and aromatic (referred to as recalcitrant) groups, the highest ratio was found in the HA from the vetch/rye system with fertilizer N. The lowest ratio occurred at the vetch/rye system without fertilizer N treatment. The O/R ratio of fulvic acids (FA) can be ranked as: vetch/rye without fertilizer>vetch/rye with fertilizer>no cover crop without fertilizer>rye alone (with or without fertilizer) soils. Both organic carbon (OC) and light fraction (LF) contents were higher in soils under cover crop treatments with and without fertilizer N than soils with no cover crop. These chemical and spectroscopic data show that cover crops had a profound influence on the SOM and LF characteristics.

Introduction

Soil organic matter (SOM) is a very reactive, ubiquitous component in soils. It is an important soil quality attribute, which influences the productivity and physical well-being of soils. Cover crops have been used to improve soil quality and reduce nonpoint sources of nutrient pollution, e.g., NO₃⁻ (Daliparthy et al., 1994). Thus, it is important from both an economic and environmental standpoint to determine how cover crop systems influence SOM characteristics and the biogeochemical cycling of carbon.

SOM contents and properties are a function of agricultural practices and the amounts and kinds of plant residues returned to the soil (Mann, 1985, Doran et al., 1987, Cheshire et al., 1990, Campbell et al., 1999, Ding et al., 2002). Based on data from long-term research plots of seven different locations (distributed in KY, MN, NE, OR, WV) in the USA, Doran (1980) reported that numbers of microbes, microbial biomass and potentially mineralizable N were greater for no-tillage than for conventional tillage in the 0–7.5 cm depth. However, these trends were generally reversed in the 7.5–15 cm depth, probably because conventional tillage moves some SOM to lower soil depths, which benefits microbial growth. Consequently, when the top 15 to 30 cm of soil under no-tillage is considered, often no net effect was observed (Doran, 1980, Angers et al., 1997). Wander and Traina (1996a) showed that SOM in crop rotation with cover crops was significantly higher than without cover crops. However, Lal et al. (1991) in a similar study reported no or minimal change of SOM content. The reason for not detecting any SOM change could be due to natural soil heterogeneity (Wander and Traina, 1996a).

In addition to SOM quantity, the quality (e.g., structure and composition) and distribution of individual fractions (e.g., humic acids, polysaccharides) can be important to the maintenance of soil fertility and structure. Monreal et al. (1995) observed a higher lignin dimer to lignin monomer ratio in continuous wheat rotation and this ratio decreased from large to small aggregate sizes, indicative of the change in the quality of SOM. Wander and Traina (1996b) used diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy to examine functional groups of SOM fractions and reported that the ratios of reactive to recalcitrant fractions in HA best reflected overall SOM bioavailability. They also reported that the ratios in FA, LF and litter were useful in distinguishing temporal impacts of farming systems on SOM lability. They concluded that the characteristics and distribution of individual SOM fractions may provide a means for assessing management impacts on SOM quality that can be tied to soil productivity, and they specifically emphasized that further work is needed to determine how SOM composition changes with tillage and cropping practices.

DRIFT detects molecular vibrations and is useful for functional group analysis and for identification of molecular structures of SOM (Stevenson, 1994). But it cannot be used to quantify carbon contents of structural groups (e.g., aromatic-C). In contrast, ¹³C NMR spectroscopy provides quantitative data for structural components (Mao et al., 2000). NMR has been successfully used to characterize SOM by many scientists (Wilson, 1987, Schnitzer et al., 1991, Preston, 1996). Thus, it would be advantageous to use both NMR and DRIFT to characterize SOM under different cover crop systems.

The primary objective of this research was to evaluate the impact of cover crop systems on SOM in New England (USA), which was never investigated before. We chose to examine SOM fractions obtained using alkali extraction (HA and FA) and physical fractionation. The specific objectives are: (1) to determine structural and compositional changes of HS (HA and FA fractions) caused by cover crop systems using NMR and DRIFT, and (2) to evaluate the light fraction (LF) variability as affected by cover crop systems with or without fertilizer N treatment.

Section snippets

Site description and sampling

Since 1990, cover crop experiments have been conducted in the Connecticut River Valley at the Massachusetts Agricultural Experiment Station Farm in South Deerfield, Massachusetts (USA). The soil in these plots is a fine sandy loam (coarse, mixed, mesic Fluventic Dystrudept) and low in SOM (∼2%). Its upper 0.6 m is homogeneous, overlaying inclined layers of coarse and fine material to great depth. Three cover crop treatments with four N rates (applied to corn after cover crop incorporation) were

Yields of organic carbon and light fraction materials

With no fertilizer N treatment, the OC content was the highest in the vetch/rye system and lowest in the soil without cover crop (Table 2). However, with nitrogen fertilizer, OC in vetch/rye appeared to decrease (from 15.1 to 13.0 kg m⁻³). After 10 years field experiment, OC differences were significant between the cover crop systems (both vetch/rye and rye alone) and no cover crop systems with or without fertilizer treatments. The OC content was significantly affected by the fertilizer N

Discussion

Cover crops have long been recognized to play an important role in sustainable agriculture due to their functions in preventing soil erosion, improving soil productivity, contributing nutrients to succeeding crops, and suppressing weeds. However, the relationship between SOM characteristics and cover crop management practices is not well understood. Although the mechanisms affecting the sequestration of organic matter in soil are complex (Doran et al., 1987, Campbell et al., 1991, Campbell et

Conclusions

Organic carbon was higher in soils under both vetch/rye and rye alone management systems than under no cover crop. This was due to low input of plant residues into the soil under no cover crop system. Yields of LF material under different cover crop systems were strongly dependent on the fertilizer N rates. For no N fertilizer treatments, LF content changes were minimal. However, with fertilizer N application, the LF content changes were substantial under different cover crop systems. All DRIFT

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Effect of cover crop management on soil organic matter

Abstract

Introduction

Section snippets

Site description and sampling

Yields of organic carbon and light fraction materials

Discussion

Conclusions

Soil Tillage Res.

Geoderma

Soil Biol. Biochem.

Diffuse reflectance and transmission Fourier transform infrared spectroscopy of humic and fulvic acids

Soil Sci. Soc. Am. J.

Effect of crop rotations and fertilization on soil organic matter and some biochemical properties of a thick Black Chernozem

Can. J. Soil Sci.

Soil quality–effect of tillage and fallow frequency. Soil organic matter quality as influenced by tillage and fallow frequency in a silt loam in southwestern Saskatchewan

Soil Biol. Biochem.

Labeled and native sugars in particle size fractions from soils incubated with 14C straw for 6 to 18 years

Soil Sci.

Infrared spectroscopy

Dairy manure application to alfalfa: crop response, soil nitrate, and nitrate in soil water

Agron. J.

Soil organic matter as affected by tillage management

Soil Sci. Soc. Am. J.

Soil microbial and biochemical changes associated with reduced tillage

Soil Sci. Soc. Am. J.

Influence of alternative and conventional agricultural management on soil microbial process and nitrogen availability

Am. J. Altern. Agric.

Expectations of cover crops for sustainable agriculture

Quantitative characterization of humic substances by solid-state carbon-13 nuclear magnetic resonance

Soil Sci. Soc. Am. J.

Labeled and native sugars in particle size fractions from soils incubated with ¹⁴C straw for 6 to 18 years