Fertiliser and seasonal urine effects on N₂O emissions from the urine-fertiliser interface of a grazed pasture

Figures & data

Table 1 Basic soil properties (0–7.5 cm depth).

Soil properties	Value
pH	5.9
Total C (g kg^–1)	55
Total N (g kg^–1)	6.7
Olsen P (mg kg^–1)	30
Sulphate sulphur (mg kg^–1)	6
Potassium (cmolc kg^–1)	0.65
Calcium (cmolc kg^–1)	8.1
Magnesium (cmolc kg^–1)	1.57
Sodium (cmolc kg^–1)	0.14
Cation exchange capacity (cmolc kg^–1)	23
Total base saturation (%)	45

Table 2 Details of urine and fertiliser treatments applied to lysimeters.

Code	Treatment	Annual ^15N fertiliser rate (kg N ha^–1 yr^–1)	Urine (kg N ha^–1 yr^–1)
F0U0	Control	0	0
F2U0	^15N Urea 200	200	0
F4U0	^15N Urea 400	400	0
F0UA	Urine (autumn)	0	800
F2UA	^15N Urea 200 + Urine (autumn)	200	800
F4UA	^15N Urea 400 + Urine (autumn)	400	800
F0US	Urine (spring)	0	800
F2US	^15N Urea 200 + Urine (spring)	200	800
F4US	^15N Urea 400 + Urine (spring)	400	800

Figure 1 Timing of lysimeter treatment applications.

Figure 2 Daily and cumulative rainfall and cumulative drainage at experimental site over the duration of study. Note this does not include the 80 mm (8 × 10 mm) simulated rainfall applied after the split fertiliser applications.

Figure 3 Mean temporal N₂O emissions, daily rainfall and soil moisture from A, nil urine; B, autumn urine; C, spring urine treatments. F0, F2 and F4 = fertiliser rates of 0, 200 and 400 kg N ha^–1; and U0, UA and US = nil, autumn- and spring-urine applications, respectively. Bold arrows indicate urine + ¹⁵N fertiliser application, other arrows indicate split fertiliser applications. Error bars = LSR (5%), error is only shown if LSR is >5, n = 4. Note different y axis scales.

Figure 4 Mean cumulative recovery of N₂O-¹⁵N from ¹⁵N affected treatments. F0, F2 and F4 denote fertiliser rates of 0, 200 and 400 kg N ha^–1; U0, UA and US denote nil, autumn- and spring-urine applications, respectively. Bold arrows indicate urine + ¹⁵N fertiliser application, other arrows indicate split ¹⁵N fertiliser applications. Error bar = LSD (5%), n = 4.

Figure 5 Mean fertiliser contribution to the N₂O flux from ¹⁵N affected treatments, expressed as a percentage of the total N₂O flux. F0, F2 and F4 denote fertiliser rates of 0, 200 and 400 kg N ha^–1; U0, UA and US denote nil, autumn- and spring-urine applications, respectively. Bold arrows indicate urine + ¹⁵N fertiliser application, other arrows indicate split ¹⁵N fertiliser applications.

Table 3 Cumulative N₂O-N fluxes as a percentage of total N applied and as an emission factor for total N applied.

Treatment	Description	Cumulative N2O-N flux (g N2O-N ha^–1)	Cumulative N2O-N flux (% total N applied)	Emission factor (%) for total N applied
F0U0	0N urea, nil urine	766a	ND^1	ND^1
F2U0	200N urea, nil urine	1470a	0.74a	0.35ab
F4U0	400N urea, nil urine	1732a	0.43b	0.24b
F0UA	0N urea, autumn urine	5292bc	0.66ab	0.57a
F2UA	200N urea, autumn urine	6104b	0.61ab	0.53ab
F4UA	400N urea, autumn urine	6436b	0.54ab	0.47ab
F0US	0N urea, spring urine	4144c	0.52ab	0.42ab
F2US	200N urea, spring urine	3785c	0.38b	0.30ab
F4US	400N urea, spring urine	4332c	0.36b	0.30ab
LSD (5%)^1		1657	0.20	0.19

Different letters indicate a significant difference between treatments at the 5% (P < 0.05) level.

¹Not determined since zero N applied.

Figure 6 Mean cumulative N₂O emissions from all treatments. F0, F2 and F4 = fertiliser rates of 0, 200 and 400 kg N ha^–1; and U0, UA and US = nil, autumn- and spring-urine applications, respectively. Bold arrows indicate urine + N fertiliser application, other arrows indicate split fertiliser applications. Error = LSD (5%), n = 4.