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

Abstract

Abstract:The soil organic carbon (SOC) of the Argiudolls of the Argentine Rolling Pampa evolves rapidly. Currently, the soils richest in SOC are cultivated with intensified crop sequences (e.g. maize-double cropped wheat/soybean, MWS) under no tillage (NT) and the poorest ones with soybean monoculture (S) under NT. There are great uncertainties about the future projections of SOC reserves and soil fertility associated with changes in land use and management. The aim of this study was to predict soil fertility in 2032, by: a) validating the simple AMG model in long-term experiments of the Rolling Pampa, b) correlating the SOC and active carbon pools (SOCm and Ca, respectively) modeled for 2008 with some soil properties, and c) simulating the evolution of SOC reserves under different agronomic scenarios, using the AMG model, starting from rich and poor SOC soils of the Rolling Pampa. The AMG model was able to provide satisfactory simulation of the SOC reserves (R 2 = 0.87) and showed good quality of fit between Ca and particulate organic carbon (POC) and SOCm and structural stability index (SSI), indicating that the AMG model could project SOC reserves and soil fertility. In rich SOC soils, the maintenance or increase in mean crop yields (MWS NT and MWS with high yields under NT, MWS opt., respectively) caused no changes, whereas the conversion to S under NT reduced the SOC reserves by 12%. Maize residue removal caused 4.5% SOC loss in MWS NT and no changes in MWS opt. In poor SOC soils, the continuity of S under NT and the conversion to MWS NT produced no changes; the passage to continuous or periodic shallow tillage caused 6% SOC loss; and the conversion to Miscanthus x giganteus produced an increase of 9% in SOC.

Long‐term tillage impact on soil phosphorus under different crop sequences

“…These SOC data were published by Irizar et al. (2015) for NT and CP. In the case of MP, the data were not published.…”

“…At the surface layer (A horizon), previous studies have reported that the distribution of TP in all analysed crop sequences responded to the long‐term effects of the tillage systems on SOC (Andriulo & Milesi, 2014). Additionally, it responded to the distribution of crop residues in the profile (Franzluebbers, 2004; Irizar et al., 2015). Below the A horizon, the observed TP increase towards the centre of the Bt1 horizon (40–50 cm) (Figure 1) results from the increased clay percentage (Arzuaga et al., 2005; Hernández et al., 1995; O'Halloran, 1993) and to the P enrichment of the OM with increasing depth (Alvarez et al., 2018).…”

“…In S–S, it was observed that the soil inversion caused by CT results in the accumulation of a significant part of residues in the 10–20 cm layer; while in VT and NT, most of the above‐ground residues tend to remain more superficially (Allmaras et al., 1996). This differences in residues distribution have direct effects on SOC (Irizar et al., 2015) and TP concentration. Indeed, the correlation coefficient between the average SOC and TP concentrations was r = .89 ( p < .01) at 0–5 cm for NT and VT and r = .96 ( p < .01) at 10–20 cm under CT.…”

Cover crop mixtures increase ecosystem multifunctionality in summer crop rotations with low N fertilization

“…The stability index was calculated as the ratio between the dry weight of over-0.5-mm aggregates and the dry weight of 1-2-mm aggregates and expressed as a percentage (Kemper 1965). Aggregate stability was classified as unstable (<20%), moderately stable (20-40%), and stable (>40%) (Irizar et al 2015). Soil organic carbon was determined by wet digestion by Walkley-Black method (Nelson and Sommers 1982), SON was determined by Kjeldahl method (Mulvaney 1996), and POC by the method of Cambardella and Elliot (1992), replacing chemical dispersion in the original method by mechanical dispersion through water agitation of the soil sample with glass balls during 5 h at 40 rpm (Irizar et al 2010).…”