Comparison of Drought Tolerance of Maize, Sweet Sorghum and Sorghum‐Sudangrass Hybrids

Abstract

AbstractIn drought‐prone environments, sweet sorghum and sorghum‐sudangrass hybrids are considered worthy alternatives to maize for biogas production. The biomass productivity of the three crops was compared by growing them side‐by‐side in a rain‐out shelter under different levels of plant available soil water (PASW) during the growing periods of 2008 to 2010 at Braunschweig, Germany. All crops were established under high levels of soil water. Thereafter, the crops either remained at the wet level (60–80 % PASW) or were subjected to moderate (40–50 % PASW) and severe drought stress (15–25 % PASW). While the above‐ground dry weight (ADW) of sweet sorghum and maize was insignificantly different under well‐watered conditions, sweet sorghum under severe drought stress produced 27 % more ADW than maize. The ADW of sorghum‐sudangrass hybrids significantly lagged behind sweet sorghum at all levels of water supply. The three crops differed markedly in their susceptibility to water shortage. Severe drought stress reduced the ADW of maize by 51 %, but only by 37 % for sweet sorghum and 35 % for sorghum‐sudangrass hybrids. The post‐harvest root dry weight (RDW) in the 0–100 cm soil layer for maize, sweet sorghum and sorghum‐sudangrass hybrids averaged 4.4, 6.1 and 2.9 t ha−1 under wet and 1.9, 5.7 and 2.4 t ha−1 under severe drought stress. Under these most dry conditions, the sorghum crops had relatively higher RDW and root length density (RLD) in the deeper soil layers than maize. The subsoil RDW proportion (20–100 vs. 0–20 cm) for maize, sweet sorghum and sorghum‐sudangrass hybrids amounted to 6 %, 10 % and 20 %. The higher ADM of sweet sorghum compared with maize under dry conditions is most likely attributable to the deep root penetration and high proportion of roots in the subsoil, which confers the sorghum crop a high water uptake capacity.