Effect of Continuous Agriculture of Grassland Soils of the Argentine Rolling Pampa on Soil Organic Carbon and Nitrogen

Abstract

Long-term soil organic carbon (SOC) and soil organic nitrogen (SON) following cultivation of grassland soils (100/120-year tillage (T) + 20/30-year no tillage (NT)) of the Rolling Pampa were studied calibrating the simple AMG model coupled with the natural13C abundance measurements issued from long-term experiments and validating it on a data set obtained by a farmer survey and by long-term NT experiments. The multisite survey and NT trials permitted coverage of the history of the 140 years with agriculture. The decrease in SOC and SON storage that occurred during the first twenty years by a loss through biological activity was 27% for SOC and 32% for SON. The calibrated model described the SOC storage evolution very well and permitted an accurate simultaneous estimation of their three parameters. The validated model simulated well SOC and SON evolution. Overall, the results analyzed separately for the T and NT period indicated that the active pool has a rapid turnover (MRT ~9 and 13 years, resp.) which represents 50% of SOC in the native prairie soil and 20% of SOC at equilibrium after NT period. NT implementation on soils with the highest soil organic matter reserves will continue to decrease (17%) for three decades later under current annual addition.

Stover Quality and Soil Organic Carbon in Long‐Term Nitrogen‐Fertilized Maize

“…The higher C input in fertilized treatments did not increase the SOC because it could be more quickly degraded due to a decrease in C/N stover quality (Fig. 3) as has been previously suggested (Andriulo et al, 1999; Johnson et al, 2007; Milesi Delaye et al, 2013). The residues with high C/N ratio, typical of our non‐fertilized treatments would be degraded slowly, in contrast with the residues with low C/N ratio (Stevenson, 1986).…”

“…A high amount of mineral N availability is prone to loss by different pathways (runoff, leaching, denitrification, and volatilization). In addition, residual N may affect the dynamics of SOC between pools (Milesi Delaye et al, 2013) or cause a priming effect on SOC (Kuzyakov et al, 2000).…”

“…The model uses two coefficients: the first represents the mineralization rate of active soil organic matter (k) and the second represents the humification rate of crop residue input (k1). This model was developed and validated on long‐term experiments in the rolling pampas of Argentina (Andriulo et al, 1999; Milesi Delaye et al, 2013) and in the Northeast region of France (Mary and Wylleman, 2001).…”

Projection of Soil Organic Carbon Reserves in the Argentine Rolling Pampa Under Different Agronomic Scenarios. Relationship of these Reserves with Some Soil Properties

“…By contrast, the current level of intensification of the crop sequence (MWS) in rich SOC soils is the minimum to maintain soil fertility. An increased level of intensification through the implementation of cover crops of autumn-winter cycle and/or temporal pastures in this sequence is needed for the sustainability of the region [79]. The most promising alternative in poor SOC soils is the production of Miscanthus x giganteus as feedstock for the production of second generation biofuels.…”

“…We have previously found that climate change was a driving force of great potential impact on the productivity of agricultural production systems and on SOC evolution under similar scenarios in the same region [79]. Undoubtedly, many of the assumptions included during the modeling process will not happen in the medium term in case of climatic variations of high magnitude.…”