TY - JOUR
T1 - Herbage and nitrogen yields, fixation and transfer by white clover to companion grasses in grazed swards under different rates of nitrogen fertilization
AU - Enriquez-Hidalgo, D.
AU - Gilliland, T. J.
AU - Hennessy, D.
PY - 2016/12/1
Y1 - 2016/12/1
N2 - In grass–legume swards, biologically fixed nitrogen (N) from the legume can support the N requirements of the grass, but legume N fixation is suppressed by additional fertilizer N application. This study sought to identify a fertilizer N application rate that maximizes herbage and N yields, N fixation and apparent N transfer from white clover to companion grasses under intensive grazing at a site with high soil-N status. During a 3-year period (2011–2013), swards of perennial ryegrass and of perennial ryegrass–white clover, receiving up to 240 kg N ha−1 year−1, were compared using isotope dilution and N-difference methods. The presence of white clover increased herbage and N yields by 12–44% and 26–72%, respectively. Applications of N fertilizer reduced sward white clover content, but the effect was less at below 120 kg N ha−1. The proportion of N derived from the atmospheric N fixation was 25–70%. Nitrogen fixation ranged from 25 to 142 kg N ha−1 measured using the isotope dilution method in 2012 and from 52 to 291 kg N ha−1 using the N-difference method across all years. Fertilizer N application reduced the percentage and yield of fixed N. Transfer of N from white clover to grass was not confirmed, but there was an increased N content in grass and soil-N levels. Under intensive grazing, the maximum applied N rate that optimized herbage and N yields with minimal effect on white clover content and fixation rates was 60–120 kg N ha−1.
AB - In grass–legume swards, biologically fixed nitrogen (N) from the legume can support the N requirements of the grass, but legume N fixation is suppressed by additional fertilizer N application. This study sought to identify a fertilizer N application rate that maximizes herbage and N yields, N fixation and apparent N transfer from white clover to companion grasses under intensive grazing at a site with high soil-N status. During a 3-year period (2011–2013), swards of perennial ryegrass and of perennial ryegrass–white clover, receiving up to 240 kg N ha−1 year−1, were compared using isotope dilution and N-difference methods. The presence of white clover increased herbage and N yields by 12–44% and 26–72%, respectively. Applications of N fertilizer reduced sward white clover content, but the effect was less at below 120 kg N ha−1. The proportion of N derived from the atmospheric N fixation was 25–70%. Nitrogen fixation ranged from 25 to 142 kg N ha−1 measured using the isotope dilution method in 2012 and from 52 to 291 kg N ha−1 using the N-difference method across all years. Fertilizer N application reduced the percentage and yield of fixed N. Transfer of N from white clover to grass was not confirmed, but there was an increased N content in grass and soil-N levels. Under intensive grazing, the maximum applied N rate that optimized herbage and N yields with minimal effect on white clover content and fixation rates was 60–120 kg N ha−1.
KW - biological N fixation
KW - intensive grazing
KW - mixed sward
KW - N production
KW - perennial ryegrass
KW - Trifolium repens L.
UR - http://www.scopus.com/inward/record.url?scp=84949844770&partnerID=8YFLogxK
U2 - 10.1111/gfs.12201
DO - 10.1111/gfs.12201
M3 - Article (Academic Journal)
AN - SCOPUS:84949844770
SN - 0142-5242
VL - 71
SP - 559
EP - 574
JO - Grass and Forage Science
JF - Grass and Forage Science
IS - 4
ER -