Abstract
Improving fertilizer nitrogen (N) use efficiency is central to sustainable and profitable grassland agriculture. A plot experiment with a control and fertilizer N (calcium ammonium nitrate, 25–50 kg/ha N) applied on nine occasions from February to September 2002 was conducted at two sites in southwest Ireland to assess N uptake and apparent recovery of fertilizer N (ARFN). Apparent recovery of fertilizer N after eight weeks varied from low in February (21%) and March (46%) to high from April to August (69–98%), indicating that high N use efficiency can be achieved in Irish grasslands at these times. Low recovery in spring suggested that N was applied in excess of immediate crop requirements. Note that N uptake and ARFN values from this study are likely to be somewhat conservative, particularly for spring applications. Over the 8 weeks during which growth was monitored, most (70%) of the grass yield and N uptake response to fertilizer N were in weeks 1 to 4 after application; however, a significant (30%) response occurred in weeks 5–8. This suggested that residual N availability following grazing at 4 weeks can be significant and that there may be scope to decrease N application rates in a grazing rotation. This can potentially improve N use efficiency and decrease N surpluses, with associated economic and environmental benefits. Apparent recovery of fertilizer N was closely related to soil temperature, with a 5.8% increase in ARFN with a 1 °C increase in temperature. Background (non-fertilizer) N supply contributed an average of 164 kg/ha per year (49%) taken up by the fertilized sward, highlighting the potential importance of soil N mineralisation to grassland productivity. Note that these results are for one year at two sites and that conditions may vary between years and at other sites and also that the experiment did not reproduce the cumulative effect of repeated fertilizer application over the grazing year.
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Claims 9
Claim · model-written summary
Apparent recovery of fertilizer N after eight weeks was low for February applications (21%).
Verbatim
t0“grassland”
e1“Apparent recovery of fertilizer N after eight weeks varied from low in February (21%)”
Claim · model-written summary
Apparent recovery of fertilizer N after eight weeks was low for March applications (46%).
Verbatim
t0“grassland”
e1“Apparent recovery of fertilizer N after eight weeks varied from low in February (21%) and March (46%)”
Claim · model-written summary
Apparent recovery of fertilizer N after eight weeks was high for applications from April to August (69-98%), indicating high N use efficiency can be achieved in Irish grasslands then.
Verbatim
t0“grassland”
e1“Apparent recovery of fertilizer N after eight weeks varied from low in February (21%) and March (46%) to high from April to August (69–98%)”
Claim · model-written summary
Low recovery in spring suggested that N was applied in excess of immediate crop requirements.
Verbatim
t0“grassland”
e1“Low recovery in spring suggested that N was applied in excess of immediate crop requirements”
Claim · model-written summary
Most (70%) of the grass yield and N uptake response to fertilizer N occurred in weeks 1 to 4 after application.
Verbatim
t0“grassland”
e1“most (70%) of the grass yield and N uptake response to fertilizer N were in weeks 1 to 4 after application”
Claim · model-written summary
A significant (30%) response of grass yield and N uptake to fertilizer N occurred in weeks 5-8.
Verbatim
t0“grassland”
e1“a significant (30%) response occurred in weeks 5–8”
Claim · model-written summary
There may be scope to decrease N application rates in a grazing rotation.
Verbatim
t0“grassland”
e1“there may be scope to decrease N application rates in a grazing rotation”
Claim · model-written summary
Apparent recovery of fertilizer N was closely related to soil temperature, increasing by 5.8% per 1 °C increase in temperature.
Verbatim
t0“grassland”
e1“Apparent recovery of fertilizer N was closely related to soil temperature, with a 5.8% increase in ARFN with a 1 °C increase in temperature”
Claim · model-written summary
Background (non-fertilizer) N supply contributed an average of 164 kg/ha per year (49%) of the N taken up by the fertilized sward.
Verbatim
t0“grassland”
e1“Background (non-fertilizer) N supply contributed an average of 164 kg/ha per year (49%)”