Hay yield and nitrogen harvest in smooth bromegrass mixtures with alfalfa and red clover in relation to nitrogen application

An experiment was conducted in order to investigate hay yield and nitrogen harvest in binary smooth bromegrass (Bromus inermis Leyss cv. Tohum Islah) mixtures with alfalfa (Medicago sativa L. cv. Kayseri) and red clover (Trif olium pratense L. cv. Tohum Islah) in Erzurum, Turkey for 5 years between 1 991 and 1995. The Hay yield, nitrogen harvest, protein concentration and la nd equivalent ratio (LER) in the mixtures with alternating rows of 1:1, 2:1 and 1:2 of smooth bromegrass with alfalfa and red clover were compared to those in pure legume stands without any N-fertilizer application or pure sm ooth bromegrass stands that received 0, 50, 100 and 150 kg ha(-1) N. The mi xtures had no N fertilization apart from 40 kg N ha(-1) in the establishmen t year. The dry matter production in all the mixtures receiving no N fertil izer application was higher than in pure legume stands. Pure grass stands w ere sustained only with the application of 150 kg ha-l N. The highest hay y ields were obtained from the mixtures of smooth bromegrass (Sb) with red cl over (Rc) (2Rc 1Sb) (14.65 t ha(-1)) and with alfalfa (A) (1A 1 Sb) (14.49 t ha(-1)). Although N application increased Sb yields in pure stands, the h ighest yields obtained with N fertilization were still lower than the yield s in the mixtures without N application. The superiority of the mixtures wa s also reflected by their large N harvests (e.g. 355.9 kg N ha(-1) in 2Rc 1 Sb plots) compared to pure Rc (317.8 kg N ha(-1)), pure A (294.3 kg N ha(-1 )) and pure Sb stands that received 150 kg N ha(-1). The nitrogen harvest i ncreased in pure Sb plots as the N doses applied increased. Furthermore, th e protein concentration of the hay from the mixtures (158.2-165.7 mg g(-1)) was equal to that of the purl A stands (165.7 mg g(-1)) and higher than th at of pure Sb stands (122.9 mg g(-1) at 150 kg N ha(-1) application) althou gh the hay from pure Re plots had the highest protein concentration (179.3 mg g(-1)). The LER values were also higher in the mixtures (e.g. 1.28 in 1A 1Sb and 1.28 in 2Rc 1Sb plots) compared with the pure stands. The mixture plots also had a more balanced temporal distribution of hay. The grass comp onent was more productive in early spring, whereas the legume fractions gre w better in the summer. In conclusion, for a sustainable production of high -quality hay and greater N harvests without using N fertilizers, binary mix tures of Sb with A in alternating rows (1A 1Sb) were recommended for long-p urpose stands and in alternation with double red clover rows (2Rc 1Sb) for short purpose stands under similar conditions. N application could be elimi nated in the grass-legume mixtures without any yield depression. (C) 1999 E lsevier Science B.V. All rights reserved.