Effects of drought and salinity on maize phenology, morphology and productivity in a semi-arid environment

In a field trial in Tunisia, the effects of drought and salinity on maize phenology, shoot and root characteristics, and productivity were examined after the following treatments: two sub-optimal irrigation levels (70% and 35% ETM), with standard water quality; two levels of water salinity (3 and 6 g NaCl L-1) at 100% ETM, compared with optimal water supply (100% ETM, control) and standard quality. We demonstrate here that both drought and salinity greatly change phenology, with the result that both silking and physiological maturity are reached much earlier. The extreme condition is the most severe drought, resulting in 10 and 12 days anticipation respectively, although with compromised yield (-84% vs. controls). Irrigation at 70% ETM turned out to be a sustainable practice, with limited changes in phenology but with a fall in yield of 22%. The vegetative habitus of the plants was very stable towards salinity, although yield losses were considerable, i.e., 25% and 73% at moderate and high salinity, respectively, due to marked reduction of cob fertility. Extreme drought impaired root weight, whereas salinity did not affect this root trait. Principal component and discriminant analyses identified above-ground the number of kernels per ear and kernel weight, and below-ground the number of main roots as the key traits in sustaining maize productivity. We conclude that moderate water or salinity stress allows silking time to be scheduled, for more efficient water management in the sensitive growth stages of maize. Thorough screening of genotypes at below-ground level also seems to be helpful to improve water use efficiency and tolerance to conditions of extreme drought and salinity.