Nitrogen uptake of a perennial ryegrass-white clover pasture following strategic nitrogen fertiliser application during the cool seasons in the Western Cape province, South Africa

Labuschagne J. ; Hardy M.B. ; Agenbag G.A. (2009)


The effect of four fertiliser nitrogen (N) levels (0, 50, 100 or 150 kg N ha-1) applied as a single dressing in either autumn (late April), early winter (early June), late winter (mid July), early spring (late August) or late spring (early October) on fertiliser N recovery by a perennial ryegrass-white clover pasture five weeks after fertiliser N application was investigated. Herbage N yield (kg N ha-1 uptake) was determined for the pasture from herbage N yield of the perennial ryegrass fraction and the clover fraction. Increased fertiliser N rate resulted in increased perennial ryegrass N yields. Perennial ryegrass N yields tend to be lowest during winter (early as well as late winter). Pasture N yield responses were similar to the perennial ryegrass N yields. Except in 2001, higher clover N yields (kg N ha-1) were recorded when no fertiliser N was applied compared to treatments that received fertiliser N. Clover N yields did not differ in the 50-150 kg N ha-1 range and would therefore not influence pasture N yield in that range. Although season of application influenced N yields the response pattern was not consistent among the years covered by the study. Calculating the apparent N recovery rate (difference between N removed in fertilised plots and control plots) can serve as an important tool to evaluate the efficiency achieved with fertiliser N application. More research is needed to develop N removal as a management tool to be used in strategic N fertilisation programmes.

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