Matching crop row and dripline distance in subsurface drip irrigation increases yield and mitigates N2O emissions

Intensive irrigation and nitrogen (N) fertilization are often linked to low N-fertilizer efficiency, and to high emissions of the greenhouse gas nitrous oxide (N2O). Efficient irrigation systems (e.g. subsurface drip irrigation [SDI]) combined with N-fertigation in a no-till agroecosystem can promote N-use efficiency, thereby curbing N2O emissions without depressing crop yield. Yet, crop type and SDI plant settings (and management) such as dripline spacing may determine the agronomic and environmental performance of SDI. In this two-year field study on maize (Zea mays L.) - soybean (Glycine max [L.] Merr.) rotation with conservation agriculture management (notill and cover crops), we investigated the effects of three different irrigation/fertilization systems (SDI with a narrow dripline spacing (70 cm) + fertigation with ammonium sulphate, SDI with a large dripline spacing (140 cm) + fertigation with ammonium sulphate, and sprinkler irrigation [SPR] + granular urea application) on yield, N-fertilizer efficiency, and N2O emissions in a fine-textured soil. We hypothesized that SDI systems (especially with narrow dripline distance) would increase yield and mitigate N2O compared with SPR, and particularly for maize due to its higher water and nutrient demand. We found that SDI increased maize yield (+31%) and Nfertilizer efficiency (+43-71%). These positive results were only observed during the drier year in which irrigation supplied ca. 80% of maize water requirements. The narrower dripline spacing mitigated N2O emissions compared with sprinkler irrigation (by 44%) and with the wider spacing (by 36%), due to a more homogeneous distribution of N in soil, and to a lower soil moisture content. Soybean yield and N-use efficiency were not affected by the irrigation systems. We also found that SPR enhanced cover crop residue decomposition, thus promoting the release of C and N into the soil and increasing N2O emissions. Overall, our study provides important insights on key management decisions that define the sustainability of novel irrigation systems; in particular SDI with a 70 cm dripline distance should be promoted for maize to increase productivity and decrease N2O emissions in fine-textured soils.