RESPONSE TO N-FERTILIZER OF ITALIAN RYEGRASS GROWN ALONE AND IN MIXTURE WITH BERSEEM CLOVER UNDER CONTINENTAL IRRIGATED MEDITERRANEAN CONDITIONS

In a field experiment over three growing seasons, the potential benefi ts of planting berseem clover (Trifolium alexandrinum L) with Westerwo ld Italian ryegrass (Lolium multiflorum Lam.) were examined under irri gated continental Mediterranean conditions. Similar N rates (0, 30, 60 , 90 and 120 kg N ha-1 cut-1) were applied to both pure Italian ryegra ss stands and mixtures, each given three successive cuts. One previous ly unfertilized cut was performed in late winter. Species in the mixtu re were established at 50:50 seed ratio but the mean proportion of ber seem clover was 14%. Mean winter survival of berseem was 87% but 88% o f the plants had leaves damaged by the frost. Forage production varied with both N rate and cutting sequence in both the pure stand and the mixture but differences between the two types of swards were significa nt only at low levels of fertilizer N. Total DM production over the fo ur cuts in plots with N application of 0,90, 180, 270 and 360 kg N ha- 1 a-1 were 7.14, 9.51, 11.66, 13.91 and 14.36 t DM ha-1 a-1 in pure st and, respectively. Corresponding values for the mixture were 8.80, 10. 94, 12.90, 14.05 and 13.64 t DM ha-1 a-1. The mean response of Italian ryegrass in the range of 0-360 kg N ha-1 a-1 was 20 kg DM per kg N ap plied. The corresponding value for the mixture was 13 kg DM per kg N a pplied. At the berseem clover proportions reached in this work, N equi valence showed values of about 80 kg N ha-1 a-1. As rates of N increas ed from 0 to 120 kg N ha-1 cut-1, nitrogen concentration increased by 78%. In the applied range of N fertilizers, NO3-N was not affected.