SEASONAL-CHANGES IN PRODUCTION AND NUTRIENT CONTENT OF CYNODON-DACTYLON (L) PERS SUBJECTED TO WATER DEFICITS

Seasonal changes in water relations, production and mineral compositio n were studied in a sward of Cynodon dactylon (L). Pers, subjected to water deficits during a dry summer, and al recovery in autumn. The exp eriment was carried out under Mediterranean field conditions. Water de ficits during summer reduced total dry matter production by 60%, but i n autumn there were no differences between treatments. Compared to wel l-watered sward, the sward grown under drought showed an increase in p otassium, calcium and nitrogen of 55, 10 and 10% respectively. These d ifferences decreased with the arrival of autumn rains. Leaf osmotic po tential (Psi(pi)) fell during the dry summer to -2.8 MPa in well-water ed plants and to -4.2 MPa in stressed plants. In autumn there were no differences between treatments. Nevertheless, relative water content ( RWC) only decreased to 0.86 in droughted plants. In summer potassium c ontributed to the osmotic adjustment. In contrast, under water deficit s a decrease of 71% in sodium and, to a lesser but significant extent decreases in phosphorus, magnesium and chlorine was observed. Nitrogen , phosphorus and sulphur showed low concentrations during summer and i ncreased in autumn.