Soil Organic Carbon Pool Depletion Upon Land Conversion and No-till Cropping Systems Impacts On Carbon Sequestration and Soil Resilience As Indicators of Agronomic Productivity.

Conversion of native vegetation (NV) to agricultural ecosystems can induce drastic changes in soil organic carbon (SOC) and nitrogen (N) stocks. Thus, the present study conducted at two long-term experiments, one in a sub-tropical (PG site) and the other in a tropical region (LRV site) of Brazil, were aimed at: (i) assessing the change in SOC and N stocks upon conversion of NV to plow-based conventional tillage (CT), (ii) quantifying gains in SOC stock upon conversion of CT to no-till (NT) systems, and (iii) estimating the magnitude of SOC stock in relation to soil resilience and agronomic productivity. Conversion of NV to agricultural land use decreased the SOC stock by 0.58 and 0.67 Mg C ha^-1 yr^-1 in 0-20 cm depth at the PG and LRV site, respectively. At the PG site, soil under NT had 17.1 Mg ha^-1 more SOC than that under CT (0-20 cm), representing a sequestration rate of 0.59 Mg C ha^-1 yr^-1 and at the LRV site, rate of SOC sequestration (0-20 cm) ranged from 0.48 to 1.30 Mg C ha^-1 yr^-1. The fraction of C input by crop residues converted into SOC was ~ 20.5 % at the LRV and ~14.2% at the PG site. The SOC resilience index (RI) ranged from 0.29 to 0.79, and which increased with increase in C input among NT systems and the SOC sequestration rates at the LRV site. At the LRV site soybean yield increased 28 kg ha^-1 for every Mg ha^-1 in SOC stock to 1-m depth, and by 602 kg ha^-1 for every 0.1 increase in the RI. These data support the hypothesis that NT cropping systems with high C input have a large potential to reverse the process of soil degradation and SOC decline through positive benefits in the soil resilience and agronomic productivity.