CO2 emission from soil in silage maize irrigated with wastewater under deficit irrigation in direct sowing practice

It is necessary to understand and measure the impact of tillage and irrigation practices on CO₂ emissions from the soil with an environmental sensitivity, while wastewater irrigation increases crop biomass yield. The main objective of the present study was to investigate the changes and reasons in CO₂ emissions from soil conventional and conservative tillage under different levels of wastewater irrigation. The CO₂ emission from tillage-sowing to harvest over the regular measurements with a EGM-5 infrared gas analyzer device was investigated with three replicates in three deficit irrigation levels (0%, 33%, and 67%) of domestic recycled wastewater in conventional tillage and direct sowing practices. Binary relationships of CO₂ emissions with H₂O emission, air temperature, and the soil temperature and moisture measured at three different depths (5 cm, 10 cm, 20 cm) were also investigated and strong (p < 0.01) positive linear correlations were determined. Wastewater irrigation and conventional tillage significantly increased CO₂ emissions compared to freshwater irrigation and direct sowing practice, while deficit irrigation practice decreased it. The direct sowing reduced seasonal CO₂ emissions ₂5.1% and 26.1% for per unit area (1 ha) of silage maize and per unit of fresh silage yield (1 kg), respectively, compared to conventional tillage. The lowest CO₂ emission per unit area and yield was determined in full irrigation treatment with freshwater in direct-sowing, while, in wastewater applications, it was determined in irrigation levels 33% per unit area and 67% per unit yield, under direct sowing. Thirty-three percent and 67% treatments in direct sowing resulted in less seasonal CO₂ emissions as 38.7% per unit area and 13.8% per unit fresh silage yield, respectively compared to full irrigation treatment with freshwater in conventional tillage. Mean CO₂ emissions in these treatments were found lower 17.9% per unit area and higher 17.8% per unit fresh silage yield compared to the full irrigation treatment with freshwater in direct-sowing. It was concluded that CO₂ emissions per unit yield could be decreased with 33% water saving under wastewater irrigation conditions, and could be achieved environmental additional benefits from more decreasing CO₂ emission by direct sowing also.