Carbon exchange in rainfed wheat fields: Effects of long-term tillage and fertilization under arid conditions

The adoption of no-till (NT) cultivation practices in field crops such as wheat (Triticum aestivum) may mitigate increasing global concentrations of atmospheric CO₂. Little information is currently available on the effects of rainfed wheat cultivation practices on the carbon exchange in arid regions. The goal of the present study was to quantify the long-term (13 years) effects of tillage and fertilization on soil CO₂ fluxes in wheat fields under arid climatic conditions (230mm rainfall), and evaluate the carbon turnover. It was hypothesized that adopting a NT practice would improve the carbon exchange in wheat fields under arid conditions. During 2007-2009, four different practices were studied in a Calcic Xerosol in Southern Israel: conventional tillage with fertilization (CT+F), conventional tillage without fertilization (CT), no-till with fertilization (NT+F), and no-till without fertilization (NT). CO₂ output as soil respiration efflux and CO₂ input as aboveground net primary production (ANPP) were calculated. The annual carbon loss as CO₂ efflux was higher under NT vs. CT practices both with fertilization (144.91 vs. 110.87gC m^-2y^-1) and without it (136.43 vs. 99.52gC m^-2y^-1). Similar trends were obtained for the carbon gain derived from wheat ANPP: 132.16 vs. 88.94gC m^-2y^-1 for the fertilized treatments, and 110.9 vs. 75.04gC m^-2y^-1 for the unfertilized practices under NT and CT, respectively. Furthermore, the physical soil-sealing layer, commonly found under CT practices due to raindrops' impact on the bare soil, highly affects the soil water regime, and also negatively affects soil gas exchange under CT. Our results clearly support the long-term advantages of adopting NT practices, where plant residues create a protective cover on the soil surface, in rainfed arid regions for all good reasons: better rainwater utilization and soil aeration, enhancing soil organic carbon content, and increasing yields.