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

Seasonal changes in water relations, production and mineral composition were studied in a sward of Cynodon dactylon (L). Pers, subjected to water deficits during a dry summer, and al recovery in autumn. The experiment was carried out under Mediterranean field conditions. Water deficits during summer reduced total dry matter production by 60%, but in autumn there were no differences between treatments. Compared to well-watered sward, the sward grown under drought showed an increase in potassium, calcium and nitrogen of 55, 10 and 10% respectively. These differences decreased with the arrival of autumn rains. Leaf osmotic potential (Psi(pi)) fell during the dry summer to -2.8 MPa in well-watered 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 contributed to the osmotic adjustment. In contrast, under water deficits 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 increased in autumn.