Dry matter (DM) production and crude protein (CP%)
of sheep urine patches in a grazed cocksfoot pasture (28
day rotation with 21±1 days regrowth) were measured
at Lincoln University from September 1999 to May
2001. Also, the DM response from artificial urine
patches was measured over time. The rate of nitrogen
(N) applied per hectare in an individual urine patch was
173 kg N/ha in autumn compared with 448 kg N/ha in
spring. This stimulated a maximum difference in DM
production between urine patches and controls over a 21
day period of 1970 kg DM/ha in spring (October).
Smaller differences were measured in summer (380 kg
DM/ha) and winter (370 kg DM/ha). The maximum
difference in CP% was also in spring being 27.0% for
urine patches and 18.7% for controls. DM production
differences were attributed to differences in net leaf
photosynthetic rate, which ranged from 23.5 in spring to
4.5 mol CO₂ m⁻² s⁻¹ in summer. Leaf photosynthetic
rate was limited solely by N supply in spring, by soil
moisture (mean soil volumetric water content in the top
500 mm < 20%) and leaf N content (< 3 %N) in summer
and mainly by low temperatures (< 9 ºC) but also N
supply in winter. The low temperature in winter also
meant the duration of urine patch response was 133 days
compared with 105 days in spring and 77 days in
summer. In a second experiment, the DM response of
cocksfoot to synthetic urine (300 kg N/ha) and irrigation
was examined in ungrazed areas (four 60-day regrowth
periods and one 110-day winter regrowth). From these
treatments, the maximum annual DM production for
cocksfoot with irrigation and N was 28.6 t DM/ha/yr
compared with 9.2 t DM/ha/yr for the control. The
addition of irrigation alone yielded 13.0 t DM/ha/yr
compared with N alone at 23.5 t DM/ha/yr. To overcome
the N stress in cocksfoot pastures a combination of
applied N in spring, tap rooted perennial legumes in
summer and annual clovers in winter is recommended.[Show full abstract]
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