Does conversion of forest to agricultural land change soil carbon and nitrogen? a review of the literature

Abstract

Soil carbon is a large component of the global carbon cycle and its management can significantly affect the atmospheric CO2 concentration. An important management issue is the extent of soil carbon (C) release when forest is converted to agricultural land. We reviewed the literature to assess changes in soil C upon conversion of forests to agricultural land. Analyses are confounded by changes in soil bulk density upon land‐use change, with agricultural soils on average having 13% higher bulk density. Consistent with earlier reviews, we found that conversion of forest to cultivated land led to an average loss of approximately 30% of soil C. When we restricted our analysis to studies that had used appropriate corrections for changes in bulk density, soil C loss was 22%. When, from all the studies compiled, we considered only studies reporting both soil C and nitrogen (N), average losses of C and N were 24% and 15%, respectively, hence showing a decrease in the average C : N ratio. The magnitude of these changes in the C : N ratio did not correlate with either C or N changes. When considering the transition from forest to pasture, there was no significant change in either soil C or N, even though reported changes in soil C ranged from −50% to +160%. Among studies that reported changes in soil N as well as soil C, C : N ratios both increased and decreased, with trends depending on changes in system N. Systems with increasing soil N generally had decreased C : N ratios, whereas systems with decreasing soil N had increased C : N ratios. Our survey confirmed earlier findings that conversion of forest to cropland generally leads to a loss of soil carbon, although the magnitude of change might have been inflated in many studies by the confounding influence of bulk‐density changes. In contrast, conversion of forest to uncultivated grazing land did not, on average, lead to loss of soil carbon, although individual sites may lose or gain soil C, depending on specific circumstances, such as application of fertiliser or retention or removal of plant residues.

Farm soil carbon monitoring developments and land use change: unearthing relationships between paddock carbon stocks, monitoring technology and new market options in Western Australia

“…Establishing or clearing plantations of forests fundamentally changes the soils physical, chemical and biological properties by modifying the quantity and type of organic carbon inputs, nutrient inputs, and stimulates SOC decomposition through soil disturbance (Murty, Kirschbaum et al 2002). It has been estimated that up to 39% of organic carbon in cultivated surface soils of Australia has been lost between 1860and 1990(Gifford et al, 1990 as cited in (Grace et al 2006).…”

“…Average declines in soil carbon stocks of around 30% can occur in the first 20 years after cultivation for some soils (Murty et al 2002). When soils are cropped, the associated biological and physical processes can result in a release of SOC over time, often up to 50% or more, depending on soil conditions and agricultural practices (Kirschbaum 2000); (Antle, Stoorvogel et al 2007).…”

Changes of anaerobic to aerobic conditions but not of crop type induced bulk soil microbial community variation in the initial conversion of paddy soils to drained soils

“…Maybe a similar SOC balance is acquired between above-and below-ground biomass, as well as inputs from root exudates and outputs from soil organic matter mineralization in RR, MM and SP (Nishimura et al, 2008;Darilek et al, 2010). Crop type, management intensity, environmental, climatic and site conditions, and time after land use change all influenced SOC sequestration (Jobbagy and Jackson, 2000;Murty et al, 2002). To better understand the effects of land use conversion from paddy to drained fields on soil properties, specific and detailed studies based on very similar site conditions are necessary.…”

“…Sun et al (2011) suggest an initial increase in soil nutrients (SOC and total N) within 10 years after rice conversion to vegetables, followed by stability in the nutritional status during an extended period of vegetable cultivation between 10 and 100 years. Land use conversion can have significant and long-lasting effects on soil properties and microbial communities (Murty et al, 2002). Consequently, the understanding of the conversion effects at different timescales is important and urgently required.…”

Agricultural land abandonment in Mediterranean environment provides ecosystem services via soil carbon sequestration

“…Depletion of soil C occurs within the first few decades of agricultural practices (Fernández-Romero et al, 2014;Murty et al, 2002), but several years are necessary for soil C recovery after agriculture abandonment (Alberti et al, 2008;Rühl et al, 2015). Agricultural soils are a source of CO 2 emission around the world, and this is accompanied by mismanagement that results in high erosion rates, soil aggregate loss, low infiltration rates, and changes in the soil biota (Bruun et al, 2015;Choudhury et al, 2016;de Moraes Sá et al, 2015;de Oliveira et al, 2015;Frossard et al, 2016;Gelaw et al, 2015;Leifeld and Mayer, 2015).…”