Dry matter yield and tiller development of perennial ryegrass/white clover swards in response to autumn applied nitrogen : A dissertation submitted for partial fulfilment of the requirement for the degree of Bachelor of Agricultural Science with Honours

Abstract

The timing of N application in autumn determines the pasture response. A field experiment was conducted to investigate effects of N fertiliser rate (O (N1) and 100 (N2) kg N/ha) and defoliation height (40 (Hl) and 80 (H2) mm) applied on two dates in autumn (10 March (01) and 7 April (02), 2010) on perennial ryegrass/white clover swards over two regrowth periods at Lincoln University. The total yield response was greater for D1 than D2 (1557 vs 557 kg DM/ha) with the majority of this response occurring in the first regrowth period. N increased the leaf appearance rate (LAR) of ryegrass by about 15-23% but doubled the leaf elongation rate (LER) and daughter tiller appearance rate in the first regrowth period, and increased the LER by 29% and tiller populations by 1200/m² in the second regrowth (These differences would have contributed to a faster rate of canopy development for light interception and photosynthesis. The lower N response for D2 than D1 was associated with a lower LAR, LER and daughter tiller appearance in days (but constant in thermal time), which would have slowed canopy development. Average growth rates of the swards expressed in degree days were slower for D2 than D1 in the first regrowth (2.3 vs 4.4 kg DM/ha/°Cday), possibly due to changes in radiation use efficiency. Yield responses to N were not affected by defoliation height. Therefore time of application was the main factor that influenced the N response because it determines the temperatures that the swards experience.