Journal of Food, Agriculture & Environment, Vol.8 (2), April 2010 365 www.world-food.net Journal of Food, Agriculture & Environment Vol.8 (2): 365-369. 2010 WFL Publisher Science and Technology Meri-Rastilantie 3 B, FI-00980 Helsinki, Finland e-mail: info@world-food.net Received 8 January 2010, accepted 12 April 2010. Effects of phenological stages on forage yield quality traits in cocksfoot (Dactylis glomerata) M. Rezaeifard 1 *, A. A. Jafari 2 and M. H. Assareh 2 1 Islamic Azad University, Brojerd, Iran. 1/25 Griffith Street Everton Park, 4053 QLD, Australia. 2 Research Institute of Forests and Rangelands, Tehran, Iran. *e-mail: mo_rezaifard@yahoo.com Abstract In order to determine the effect of harvest date on yield and quality traits in cocksfoot (Dactylis glomerata), a split plot experiment was conducted using a complete randomized block design with two replications in Research Institute of Forests and Rangelands, Karaj, Iran, during 2004-2006. Five domestic genotypes, 10505 (Gorgan), 1773 (Sari), 1053 (Karaj), 1761 (Ormia) and 412 (Ardebil), and three foreign ones, IX (Russia), 1557 (Russia) and 1715 (USA), were sown in sub plots and five phenological stages (vegetative, heading, pollination, milky and dough seed stage) were considered as main plots. The data were collected and analyzed for dry matter (DM) yield, crude protein (CP), dry matter digestibility (DMD), water-soluble carbohydrates (WSC), acid detergent fiber (ADF) and total ash. Near Infrared Spectroscopy (NIRS) was used for estimation of the quality traits. The analysis of variance showed a significant effect of phenological stages on all traits (P≤0.01). The genotypes effect was significant on all traits except DMD, CP and total ash. The genotype × phenological stage interaction was non-significant for all of traits. For DM yield, the lowest and highest values of 2567 and 3607 kg ha -1 were obtained at vegetative and soft dough stages, respectively. In contrast, the average values of DMD and CP concentration ranged from 64.85 to 41.77% and from 22.86 to 9.72% at vegetative and dough seed stages, respectively. In general, DM yield, plant height, WSC and ADF values dramatically increased and DMD, CP and ash values decreased due to advancing plant maturity. For DM yield, IX (Russia), 1715 (USA) and 1053 (Karaj, Iran), with average values of 3871 to 4049 kg ha -1 , had the highest forage production. Among them, IX (Russia), with average values of 17.2 and 55.3% for CP and DMD, respectively, had highest quality. Based on DMD and CP yield per unit of area, the heading was recognized as the best harvest date in cocksfoot under conservation management. The regression equations were developed among phenological stages and all of traits. The results showed linear models for all of quality traits and quadratic equation for DM yield and stem number. Key words: Cocksfoot, Dactylis glomerata, phenological stage, yield and quality traits. Introduction The botanical composition of rangelands is variable in Iran. Cocksfoot (Dactylis glomerata L.) is one of the main perennial grasses that naturally grow in temperate pastures and rangelands in northern and western Iran. It is used for grazing and hay production. Cocksfoot grows at altitudes of 500-2900 m having more than 300 mm annual precipitation 1, 2 . The improvement of total annual yield, persistency, disease resistance and extended grazing season are important objectives in most herbage breeding programs. However, data from animal nutrition studies show the need to focus more attention on nutritive value in selection programs. Wheeler and Corbett 3 and Smith et al. 4 ranked forage traits in terms of their nutritional value for live weight gain and dairy production, respectively. Improved digestibility and increased water-soluble carbohydrate (WSC) content were the two most important criteria on each of the two lists 3, 4 . There is much published data which shows that digestibility is a major factor affecting intake 5 and animal performance 6 . Carlier concluded that WSC is completely digestible and has an important role in animal nutrition as primary source of the readily available energy necessary for efficient microbial fermentation in the rumen 7 . An adequate supply of soluble sugars is essential for good fermentation and protein utilization in the rumen, leading to improved feed efficiency and animal performance 8 . When considered as a separate characteristic, crude protein (CP) content was ranked as moderate or low priority in terms of quality objectives 3, 4 . However, with regard to the important interaction between WSC and CP in the efficiency of protein metabolism as discussed above, it is clear that the combined evaluation of both characteristics is desirable in relation to selection for improved nutritional value in herbage. Chemical composition of grasses changes with advancing maturity. As grass matures the proportion of the cell wall increases and the cell content fraction decreases. Both non-structural and structural carbohydrates make up approximately 50 to 80% of dry matter of forages 9 . Maturity and herbage age generally have a greater influence on forage quality than environmental factors. As plants advance in maturity, cell wall concentration within stems and leaves increases and the proportion of cell soluble content decreases. The rate of decline in digestibility of herbage is greatest during reproductive growth 10 . Breese and Thomas showed that small differences in maturity of cocksfoot could greatly affect digestibility 11 . ADF will increase by stem elongation, and as plant matures, cellulose and other structural carbohydrates will be collected in cell wall, which process is called lignification 11 . One of the factors that affect forage production is change in the ratio of leaf to stem. With the gradual growth of plant, the ratio of leaf