Soil carbon, nitrogen dynamics, and energy, carbon budgeting in response to uncultivated land management with crop biomass in the southwestern US

Uncultivated agricultural land management by leaving biomass of the last crop planted in the field can prevent soil health degradation over time. However, the effects of different uncultivated land management practices on soil organic carbon stock, total nitrogen stock, and soil health changes remain unclear. A field experiment from June 2021 to September 2023 investigated the effects of integrated crop residue-uncultivated land management. The treatments include winter wheat in fall then uncultivated with entire crop biomass left in the farm (WT); corn in summer then uncultivated with biomass (CT); bare or no vegetation (BT); and continuous annual irrigated winter wheat (CWT). The study focused on investigating changes in soil organic carbon (SOC), soil inorganic carbon (SIC), total carbon (TC), and total nitrogen (TN) in 100 cm soil depth and quantifying cost budgeting, energy budgeting, and carbon budgeting in various treatments. The results showed that the highest SOC stock for 0–100 cm soil depth (115.2 Mg/ha) with an increase of 49.6 % was observed in CWT. However, the SIC stocks in CWT were 37.4 %, 52.4 %, and 36.3 % lower than those in BT, CT, and WT, respectively. No significant differences in TN stocks were observed between the four treatments after 3-year implementations of land management, WT showed slightly higher TN stock in 100 cm depth than the other three treatments. Considering the budgets of cost, energy, and carbon, although CT had the highest net returns of 7726.3 US$/ha, WT increased surface coverage thereby enhancing the net energy (275776.4 MJ/ha), energy use efficiency (12.0), energy profitability (10.97), carbon efficiency (12.41) and carbon sustainability index (11.41), accompanied by second highest net returns of 6610.6 US$/ha. Planting winter wheat in one season and then leaving the land uncultivated, with the entire biomass left on the land, not only reduces soil degradation but also improves carbon and energy efficiency. This approach could be an effective solution for land management and groundwater conservation in the Lower Rio Grande Valley.