Determination of growth degree days (gdds) for growth stages and forage and seed production of berseem clover

Berseem clover is one of leguminoes forage crops which its yield performance depends on interactions among climatic, genetic and agronomical factors. This investigation was carried out in Karaj region to determine the growth degree days of different growth stages and seed and forage yield production of Berseem clover in four planting dates (16 March, 4 April, 25 April and 15 May). The results showed that 1060 (68 days) and 503 (25 days) GDDs are needed for forage production in the first and second cuts, respectively and 2000 GDD (120 days) for seed production. Among the different growth stages, branching and anthesis stages were the longest (31 days) and the primary leaf stage was the shortest (3 days) periods. The results demonstrated that the period from planting to the first cut was 75 days in the first planting date (the longest period), and 65 days in the third and forth planting dates (the shortest period). Although the longer period was needed to reach the first cut at the first planting date, its GDD (877 GDD) was lower than those of the third and forth planting dates (1132 and 1256 GDD respectively). This period was 25 days in all planting dates, but the GDDs accumulated during this period were 503.2 GDD. In general, Berseem clover needs 1563 GDD (93 days) for forage production with two cuts and 2000 GDD (120 days) for seed production. Based on these results, early planting date is recommended for forage and seed production.