Dry matter production, nutritive value and botanical composition of a perennial ryegrass white clover pasture applied with GA and N in successive periods in autumn and spring

Abstract

The effect of application of GA (GA) and nitrogen (N) fertiliser on dry matter (DM) production, botanical composition and nutritive value on a ryegrass – white clover pasture was examined in an autumn and spring trial at Lincoln, Canterbury, New Zealand. Each trial consisted of two periods. In Period 1, factorial combinations of GA (0 and 20g ProGibb SG©/ha) and N (0 and 50 kg N/ha) were applied to pastures and measurements made after 28 days. In period 2, each of the factorial combination of GA and N were splits and GA, N or nothing was applied, with measurements made after a further 28 days. In Period 1 in autumn, DM yield was not affected by application of GA but where N fertiliser was applied DM yield was greater (2152 kg DM/ha) than no N fertiliser applied (1496 kg DM/ha). GA did not affect clover, ME or CP content, but did increase stem length (68.5 vs. 60.5 mm). In period 2 in autumn DM yield was greater in GA treated than untreated pasture (875 vs. 528 kg DM/ha) but was similar to N fertilised pasture (712 kg DM/ha). GA increased clover yield above pasture treated with N or nothing (240 vs. 80 and 89 kg DM/ha) and altered many of the sward structure components including stem length, leaf length and leaf width. In period 1 in spring GA increased DM yield for mower cuts (1009 vs. 666 kg DM/ha) and quadrat cuts (1902 vs. 1653 kg DM/ha). GA caused the pasture to stand 40% taller than pasture not treated with GA (10.5 vs. 6.3 cm), and increased both ryegrass and clover content by 33 and 53% respectively. Pseudo stem length (73.1 vs. 55.1 mm) and leaf length (162.1 vs. 116.1 mm) were both increased 28 days after application of GA. N fertilised pasture had 44% more tillers than unfertilised pasture (15,815 vs. 8,875 tillers/m2). In period 2 in spring pasture treated with GA or N increased DM yield over control pasture (1331 and 1385 vs. 1072 kg DM/ha). Ryegrass content was higher at the end of period 2 in GA and N treated pastures than control pasture (916 and 1100 vs. 799 kg DM/ha). CP was lower in GA treated pasture at the end of period 2 (18.7%) than N fertilised (20.7%) or control pasture (19.4%). In both autumn and spring, there was no interaction between effects of application of GA in period 1 and period 2 indicating no yield decrease of carryover effect. Therefore results from this study confirm findings from previous authors the GA can increase yield of ryegrass white clover pasture without affecting pasture production in spring, and that GA has no adverse effects on pasture ME or nutritive value. As increase in DM yield was achieved with minimal change in CP from GA application over both periods. GA application may provide additional feed without increasing the N content of livestock diet. In turn, this may help reduce the high levels of urinary N excreted and subsequent nitrate leaching that is associated with application of N fertiliser.