Winter cereal root growth and aboveground–belowground biomass ratios as affected by site and tillage system in dryland Mediterranean conditions

Abstract

Understanding the interaction between crop roots and management and environmental factors can improve crop management and agricultural carbon sequestration. The objectives of this study were to determine the response of winter cereal root growth and aboveground–belowground biomass ratios to tillage and environmental factors in the Mediterranean region and to test an alternative approach to determine root surface area. Winter cereal root growth and biomass ratios were studied in three sites with different yield potential according to their water deficit (high yield potential, HYP; medium yield potential, MYP; low yield potential, LYP) in the Ebro Valley (NE Spain). At all sites, three tillage systems were compared (conventional tillage, minimum tillage, no-tillage (NT)). Root surface density (RSD), soil water content, yield components, and grain yield were quantified and shoot-to-root and grain-to-root ratios were calculated. RSD was measured with the use of image analysis software comparing its performance to a more common intersection method. Significant differences on RSD between sites with different yield potential were found being the greatest at the HYP site and the lowest at the LYP one. Shoot-to-root ratio was 2.7 and 4.6 times greater at the HYP site than at the MYP and LYP sites, respectively. Moreover, the grain-to-root ratio was significantly affected by site, with a ratio that increased with yield potential. Tillage had no significant effects on RSD at any of the sites studied; however, tillage did affect grain yield, with NT having the greatest yields. This study shows that in the Mediterranean dryland agroecosystems, winter cereals relative above- and belowground biomass growth is strongly affected by the yield potential of each area. NT in the Mediterranean areas does not limit cereal root growth and leads to greater grain yields. A highly significant linear relationship (P < 0.001; r 2 0.77) was observed between the root surface values obtained with the free-software image analysis method and the most common intersection method, showing it to be a reliable method for quantifying root density.