Agronomic and physiological responses of sorghum, maize and pearl millet to irrigation

Abstract

Sorghum, maize and pearl millet were grown for fodder on a sandy loam soil under four irrigation schedules (i.e. irrigation at ID/CPE = 1.0 (S 0), 0.6 (S 1), 0.3 (S 2), 0.15 (S 3), where ID is irrigation depth, and CPE is cumulative evaporation from a USWB Class-A pan) during the hot dry season (May–July). Dry matter yield did not differ significantly among the three species under wet condition (S 0), but sorghum was superior to maize under all levels of water deficit (S 1, S 2, S 3). Sorghum also outyielded pearl millet under moderate moisture stress (S 1, S 2), but dry matter yields in the two species were similar under drought condition (S 3). Water-use efficiency was highest under wet (S 0), moderately stressed (S 2) and severely stressed (S 3) conditions in maize, sorghum and pearl millet, respectively. Apparent water use was highest from the upper soil layers, especially under frequent irrigation (S 0). Among stressed plants (S 3), maize extracted more water than the other species from the top soil (0–45 cm) and sorghum from the sub-soil (45–135 cm), while pearl millet had small water uptake from all layers of the soil profile. Increased frequency of irrigation generally resulted in higher profile water content, leaf water potential ( ψ L), leaf osmotic potential ( ψ π ), leaf turgor potential ( ψ P), leaf diffusive conductance (K L), leaf area index (LAI), evapotranspiration (ET), canopy net photosynthesis (P N) and dry matter yield in all species. ψ π decreased over time after planting, and irrigation only partially arrested the reduction in ψ π . ψ P generally declined with ψ L and at a more rapid rate in maize than in sorghum and pearl millet. Maize had higher ψ L and lower K L than sorghum and pearl millet. K L was correlated with both profile water content and ψ P in all species. There was significant positive linear association amongst LAI, ψ P, ET and P N in the three species. Sorghum had, however, higher P N and ET per unit LAI than maize and pearl millet. The dry matter yield was also positively linearly related to ψ P, K L, ET and P N in ascending order of prediction. Thus, P N seems to be the best parameter for assessing dry matter production in the three species. The study has emphasized that sorghum should be grown as fodder crop under inadequate and irregular water supply in semi-arid regions.