Global changes in soil stocks of carbon, nitrogen, phosphorus, and sulphur as influenced by long‐term agricultural production

Abstract

Quantifying changes in stocks of C, N, P, and S in agricultural soils is important not only for managing these soils sustainably as required to feed a growing human population, but for C and N, they are also important for understanding fluxes of greenhouse gases from the soil environment. In a global meta-analysis, 102 studies were examined to investigate changes in soil stocks of organic C, total N, total P, and total S associated with long-term land-use changes. Conversion of native vegetation to cropping resulted in substantial losses of C (-1.6 kg m , -43%), N (-0.15 kg m , -42%), P (-0.029 kg m , -27%), and S (-0.015 kg m , -33%). The subsequent conversion of conventional cropping systems to no-till, organic agriculture, or organic amendment systems subsequently increased stocks, but the magnitude of this increase (average of +0.47 kg m for C and +0.051 kg m for N) was small relative to the initial decrease. We also examined the conversion of native vegetation to pasture, with changes in C (-11%), N (+4.1%), and P (+25%) generally being modest relative to changes caused by conversion to cropping. The C:N ratio remained relatively constant irrespective of changes in land use, whilst in contrast, the C:S ratio decreased by 21% in soils converted to cropping - this suggesting that biochemical mineralization is of importance for S. The data presented here will assist in the assessment of different agricultural production systems on soil stocks of C, N, P, and S - this information assisting not only in quantifying the effects of existing agricultural production on these stocks, but also allowing for informed decision-making regarding the potential effects of future land-use changes.

Effect of Large-Scale Cultivated Land Expansion on the Balance of Soil Carbon and Nitrogen in the Tarim Basin

“…Land reclamation from grassland and forest in the study area resulted in SOC and TN loss during the initial reclamation stages, but these recovered with increasing reclamation age ( Figure 5), which is in accordance with previous studies [18,60,61]. Anthropogenic disturbances frequently destroy the initial soil structure and accelerate the mineralization and decomposition process of SOM, which can intensify losses of C and N [62][63][64].…”

“…Land reclamation can alter the soil C and N bio-geochemical cycling and spatial-temporal characteristics of soil C:N ratios greatly [14][15][16][17]. The conversion from native vegetation to cropland decreases the input of vegetative tissues and increases soil temperatures to accelerate the litter decomposition and soil micro-organisms in the decomposition of soil C and N [18]. Reclamation activities can further cause C and N losses and change the soil C:N ratio [3].…”

The carbon sequestration potential of China's grasslands

“…, Kopittke et al. ), large‐scale SOC field inventories (Wertebach et al. ), and manipulative experiments (Del Galdo et al.…”

Quantitative assessment of microbial necromass contribution to soil organic matter

“…Since common fungal:bacterial ratios in soil are in the range of 0.5–5 (Bailey, Smith, & Bolton, ; Fierer, Jackson, Vilgalys, & Jackson, ), and the maximum content of nitrogen in bacterial necromass is 27% (see above), the amount of nitrogen from fungal and bacterial residues, together, may reach between 40.5% and 100% of the soil organic nitrogen pool. If we extend this calculation by speculating that also the average C/N ratio of 6.7 in microbial cells (Jenkinson, ; also see Box ) is sustained during soil necromass formation, and based on an average C/N ratio of soils at 11.5 (Kopittke, Dalal, Finn, & Menzies, ), this means that of total SOC the contribution stemming from microbial necromass may range from 23.6% to 58.3%. Alternatively, we may specify this calculation by taking into consideration that the C/N ratio varies between bacterial and fungal biomass.…”