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University of KwaZulu-Natal (2015)

Water use of selected sorghum (Sorghum Bicolor L. Moench) genotypes.

Hadebe, Sandile Thamsanqa

Titre : Water use of selected sorghum (Sorghum Bicolor L. Moench) genotypes.

Auteur : Hadebe, Sandile Thamsanqa.

Université de soutenance : University of KwaZulu-Natal

Grade : Doctor of Philosophy (Crop Science) 2015

Résumé
Water scarcity is a major limitation to crop production in sub–Saharan Africa (SSA). Under these conditions, determining and predicting crop yield response to water in rainfed agriculture is useful for improving water productivity and food security. This study aimed to determine water use characteristics and water use efficiency of different sorghum genotypes as well as to model water use of such sorghum genotypes for extrapolation to other rainfed agro–ecologies. A review of water use of major cereal crops was conducted to gain insight into strategies to improve water productivity under arid and semi–arid agro–ecologies. To quantify water use and determine water use efficiency (WUE) of sorghum under different environmental conditions three sorghum genotypes, namely, PAN8816 (hybrid), Macia (open–pollinated) and Ujiba (landrace) were planted at two sites (Ukulinga and Mbumbulu) under rainfed conditions in 2013/2014 and 2014/15 seasons. Furthermore, PAN8816, Macia, Ujiba and IsiZulu (landrace) genotypes were planted at Ukulinga under early, optimal and late planting dates to determine sorghum water use characteristics (morphological, physiological, phonological and yield). Field trials planted at Ukulinga in 2013/14 were used to calibrate the AquaCrop model for PAN8816, Macia and Ujiba. Model testing was conducted using observations from three planting dates at Ukulinga during the 2014/15 season. Thereafter, PAN8816 and Ujiba crop files were used to use AquaCrop to extrapolate to other rainfed agro–ecologies in South Africa (Deepdale, Richard’s Bay and Ukulinga) and develop best management recommendations for rainfed sorghum production. During the 2013/14 season, WUE was significantly lower at Mbumbulu (7.49 kg ha-1 mm-1) relative to Ukulinga (11.01 kg ha-1 mm-1). This was attributed to low total available water at Mbumbulu. Macia had higher WUE (10.51 kg ha-1 mm-1) relative to PAN8816 (9.34 kg ha-1 mm-1) and Ujiba (7.90 kg ha-1 mm-1), however differences were not significant. During the 2014/15 season, sorghum genotypes adapted to low water availability through reduced canopy size and duration, low chlorophyll content index and stomatal conductance, as well as hastening phenological development. The AquaCrop model satisfactorily predicted yield response to water for the studied sorghum genotypes during calibration and testing. When applied for scenario analysis, the model performed well for the range of agro–ecologies considered. This study confirmed drought tolerance and high WUE of sorghum and it is concluded that sorghum is uniquely suitable and adapted to production under semi– and arid agroecologies of SSA. Furthermore, the study confirmed the use of the AquaCrop model as a cost–effective, relatively accurate tool to predict sorghum yield response to water.

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