Effects of Root Architectural Diversity on Grain Sorghum Yield Under Irrigated and Rainfed Conditions.

The homogenous rooting system of a genetically uniform cropping system may be inefficient at exploiting the nutrient and water resources present in the soil profile. This study was performed to determine the effects, if any, of increased root architectural diversity on grain and forage biomass yields of grain sorghum [Sorghum bicolor (L.) Moench] under irrigated and rainfed conditions. Shallow and deep rooting monoculture plots were planted along with a high diversity plot containing an equal mixture of five shallow and five deep rooting genotypes under irrigated and rainfed conditions. This study was performed at The University of Florida Plant Science Research and Education Unit near Citra, FL using a split plot design with five replicates. The shallow rooting monocultures produced more grain (5.0 Mg ha^-1) than the deep rooting plots (4.1 Mg ha^-1) under irrigation. However the deep rooting monocultures produced more forage biomass (5.9 Mg ha^-1) than the shallow monocultures (5.2 Mg ha^-1). The high diversity treatment plots had grain yields that were in between those of the monoculture plots (4.7 Mg ha^-1), but produced more forage biomass than either monoculture (6.3 Mg ha^-1.) Under rainfed conditions the high diversity treatment had the highest loss of both grain and forage biomass yield, losing 25% of it’s total yield compared to the 14% drop for the deep rooting monocultures and the 23% lost in shallow monocultures. The monoculture plots produced less root mass under rainfed conditions than under irrigation, whereas high diversity plots produced more root mass under rainfed conditions. This change in root mass may explain the relative change in grain and forage biomass yield. Increased root architectural diversity did not appear to increase access to soil water, as it did not convey a relative yield advantage under rainfed conditions, and may even have a negative impact on yield.