Theme 5: Drought--Oral Sessions

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The growing number of extreme weather events has created the need to identify tropical forage grasses with greater water use efficiency (WUE) to cope with water-limited conditions. WUE can be defined as the ratio of forage biomass produced per unit of water used. However, WUE is a dynamic ratio that changes according to environmental gradients (e.g., water or nutrient availability) or ontogenetic drift (e.g., changes in root to shoot biomass allocation across phenological stages). Furthermore, genetic improvement leading to greater WUE is likely to result in smaller plants that produce less than the required forage biomass to sustain good animal performance. Bearing that in mind, other alternatives for improving WUE must be taken into consideration. Grazing management is one among such alternatives. Results from a greenhouse experiment conducted with a number of forage grasses (Cenchrus ciliaris, Chloris gayana, Megathyrsus maximus, Urochloa spp.) at the Alliance of Bioversity-CIAT showed that different grazing intensities lead to various WUEs. Improved WUE values in grasses can be achieved through grazing management if it moderates the process of evapotranspiration by 1) reducing leaf area per plant; and 2) maintaining soil cover from pasture growth and productivity. Our results suggest that WUE in pastures planted with tropical forage grasses can be enhanced through moderate rotational grazing.

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Importance of Grazing Management in Improving Water Use Efficiency of Tropical Forage Grasses

The growing number of extreme weather events has created the need to identify tropical forage grasses with greater water use efficiency (WUE) to cope with water-limited conditions. WUE can be defined as the ratio of forage biomass produced per unit of water used. However, WUE is a dynamic ratio that changes according to environmental gradients (e.g., water or nutrient availability) or ontogenetic drift (e.g., changes in root to shoot biomass allocation across phenological stages). Furthermore, genetic improvement leading to greater WUE is likely to result in smaller plants that produce less than the required forage biomass to sustain good animal performance. Bearing that in mind, other alternatives for improving WUE must be taken into consideration. Grazing management is one among such alternatives. Results from a greenhouse experiment conducted with a number of forage grasses (Cenchrus ciliaris, Chloris gayana, Megathyrsus maximus, Urochloa spp.) at the Alliance of Bioversity-CIAT showed that different grazing intensities lead to various WUEs. Improved WUE values in grasses can be achieved through grazing management if it moderates the process of evapotranspiration by 1) reducing leaf area per plant; and 2) maintaining soil cover from pasture growth and productivity. Our results suggest that WUE in pastures planted with tropical forage grasses can be enhanced through moderate rotational grazing.