Effect of Sweet Sorghum Root Depth on Final Yield in North Central Florida.

There is an increasing interest in developing cultivars with deeper root systems. Different traits, phenotyping techniques, and molecular markers that confer deeper roots have been identified. However, the depth of the root system that should be targeted by breeding programs remains unknown. We used the CERES crop model to evaluate the performance of 19 different root depth ideotypes over 24 years of historic weather data. We collected sweet sorghum growth data in the field for two years to modify the model equations associated with carbohydrate partitioning to stems and leaves. We used 39 additional data sets from 6 locations around the world planted on 6 different years with the same genotype. The model index of agreement (d-index) and normalized root mean square error (RMSEn) for stem weight were 96.11 and 19.24 respectively, 95.49 and 23.64 for total biomass weight and 99.78 and 4.7 for days from planting to maturity. There were no significant differences in final biomass production in ideotypes with root depths of 120cm or higher. However, there was a significant root depth by planting date interaction for yield increase. Thus, the minimum root depth to achieve the maximum yield was 120cm for May 1^st and June 1^st planting dates, but 140cm for the April 1^st planting date. Early planting was associated with higher risk of water deficit over the first two months after planting. The sensitivity analysis shows that radiation use efficiency and canopy extinction coefficient have an important interaction with root depth. To our knowledge, this is the first time that the CERES model is used to simulate sweet sorghum. However, the CERES model has been used for many different crops and environments. Therefore, this methodology can be easily applied in other cropping systems.