Alfalfa nutritive quality as influenced by drought in South-Eastern Oasis of Tunisia

Medicago sativa is the main perennial legume in many places in the world such as South-East Tunisian Oases. The widespread use of this species is due to its high adaptability, forage yield potential and to its good quality. Furthermore, the succession of drought years in South-East Tunisian Oases especially in Gabes influenced fodder distribution and digestibility. To a better understanding of the variation of the nutritive value of (Medicago sativa L.) plants, the effect of four drought levels (25%; 50%; 75% and 100% of field capacity) on nutritive quality was investigated for three populations [P1 (Gannouch); P2 (Chenini) and P3 (Tebelbou)] cultivated in these oases. Results showed that drought reduced leaves, shoots and roots dry matter, while this effect was more pronounced for above organs (values reached 1.2mg) than below organs (values reached 1.8mg). However, drought decreased phosphor, calcium, magnesium and nitrogen contents, neutral detergent fibre, acid detergent fibre and in acid detergent lignin content for P1 and P2, this stress enhanced potassium uptake, leaves shoots and roots shoots ratios especially for P3, values passed from 1.56 for control treatment to 2.06 for 25% of field capacity. This population seems to be the most resistant to drought by maintaining reduced leaf area and elevated ratios. This result indicates that Medicago sativa succeed to maintain a good nutritive value under stress conditions. To the best of our knowledge, it is important to study the effect of this stress on others varieties to more understand its effect on nutritive value.