Effect of tillage systems on soil properties, water dynamics and greenhouse gas emissions in a continuous irrigated maize crop in semi-arid conditions

Resum

The use of conventional tillage (CT) for continuous maize crop (Zea mays) is widely practiced by local farmers in Northwest Spain. This includes a frequent soil ploughing and disturbance to prepare the seedbed and to control weeds before sowing. Conversion from CT to no-tillage (NT) would not only help increase soil organic carbon (SOC), reduce soil erosion and CO2 emissions but also can improve soil water content (SWC), lower the carbon footprint (CFP) and environmental impacts. For these reasons it was interesting to evaluate the effect of CT and NT on various aspects of the production cycle of a continuous irrigated maize crop in Castile and Leon. Therefore, this study was carried out from 2011 to 2017 in Zamadueñas’s experimental field, located in the Spanish province of Valladolid. The experimental design included four random blocks where the main factor studied was tillage systems. Under CT, the seedbed was prepared with a mouldboard plough followed by a spring cultivator, while only an herbicide (glyphosate) was applied under NT system for weeds control. The different soil properties were determined by collecting soil samples up to 100 cm soil depth after the maize harvest in 2011, 2015 and 2017. The SWC was monitored during the maize production cycle and CO2 emissions were measured at different intervals from 2011 to 2017. Finally, the assessment of the carbon footprint (CFP) included the agricultural inputs of the maize production process, the N2O emissions which were estimated using the methodology suggested by IPCC (2006) and SOC changes. The evaluation of the soil properties revealed that some soil parameters such as bulk density, pH, available phosphorus and extractable potassium could not only be affected by tillage systems but also by the combination of the experiment conditions and the climatic variations from year to year. Nevertheless, the soil organic matter was significantly higher under NT system than CT thanks to the addition of crop residues and the non-disturbance of the soil surface. The results showed that NT treatment presented higher SWC especially in the first 50 cm and 100 cm soil depth than CT system during the 3-year study. Tillage system did not show significant differences in the assessment of water productivity. However, the mean water use efficiency and irrigation use efficiency were 4.0 and 4.5% higher under NT system than CT system. In 2017, SOC stock was 36% greater under NT than CT, with a rate of 1.6 and 1.1 Mg ha-1 yr-1 respectively at 0-10 cm depth. The SOC stock of the top 30 cm soil layer was 13% greater under NT system than CT. CO2 emissions were significantly affected by tillage systems in short and long terms and were significantly higher under CT than NT system. Moreover, the results obtained showed that the emissions from the agricultural inputs of fuel and electricity inputs (direct energy) and machinery use were higher under CT system while the ones emitted from synthetic fertilizers, pesticides, water applications and maize seed (indirect energy) were greater under NT treatment. The highest N2O emissions were produced by the application of the highest rates of N fertilization. The absence of soil disturbance combined with crop residue retention increased the SOC accumulation in the topsoil layer, promoted the accumulation of moisture in the soil during drought period, reduced CO2 emissions without drastically decreasing maize grain yield and helped minimizing the carbon footprint and the impact on climate change.