Comparison of nitrate leaching from oats and Italian ryegrass catch crops following simulated winter forage grazing: a field lysimeter study

Figures & data

Table 1. Key soil fertility (0–7.5 cm) and physical properties for the Balmoral soil.

Soil analysis	Value	Soil depth (cm)	Soil bulk density (g cm^−3)	Stone volume (%)	Soil porosity (%)	Soil texture^a
pH	6.1	0–10	1.14	11	58	Stony ZL
Olsen-P	33 µg mL^−1	10–20	1.57	30	42	Stony ZL
Exch-Ca	8.1 cmol^+ kg^−1	20–30	1.90	51	29	Stony SL
Exch-Mg	0.5 cmol^+ kg^−1	30–40	2.05	54	24	Stony S
Exch-K	0.4 cmol^+ kg^−1	40–60	1.96	51	27	Gravelly S
Exch-Na	0.2 cmol^+ kg^−1
CEC	16 cmol^+ kg^−1
Reserve-K	3.6 cmol kg^−1
Sulphate-S	4 µg g^−1
Organic-C	45 g kg^−1
Total-N	4.0 g kg^−1
Organic-S	5 µg g^−1
Base saturation	65%

^aZL – silt loam; SL – sandy loam; S – sand.

Table 2. Lysimeter treatment ID (It. ryegrass – IR; oats – OT) and urine application rates.

	Treatment schedule
Treatment ID	Crop	Urine rate (kg N ha^−1)
IR: Control	It. ryegrass	0
IR: U350		350
IR: U700		700
OT: Control	Oats	0
OT: U350		350
OT: U700		700

Table 3. Major tasks and dates for the field lysimeter experiment.

2013–2014
Task list	Date
Lysimeters installed	15 January 2013
Kale transplanted	15 February
Kale cut	14 June
Surface trampled	15 June
First urine application	26 June
Volatilisation expt. started	26 June
First leachate collection	27 June
Second urine application	3 July
Volatilisation expt. finished	1 August
Oats sown	18 August
It. ryegrass sown	16 September
Control It. ryegrass lysimeters re-sown	7 October
Oats harvested	22 November
First ryegrass harvest	1 December
Kale sown and fertiliser applied	6 December
Kale harvested	30 May 2014
Lysimeters deconstructed	31 May

Table 4. Mean daily winter (June–August), spring (September–November), summer (December–February), and autumn (March–May) soil, air, solar radiation, and evapotranspiration values for 2013–2014 compared with recent LT 2000–2016 averages.

Climate variable	Winter		Spring		Summer		Autumn
	2013–2014	LT	2013–2014	LT	2013–2014	LT	2013–2014	LT
Soil temperature (°C)	5.9	4.8	10.6	10.3	16.0	16.3	11.1	10.8
Air temperature (°C)	6.6	5.6	11.7	11.4	15.8	15.6	11.2	11.4
Solar radiation (MJ ha^−1 )	5.8	5.8	17.1	17.5	22.3	21.6	9.3	10.1
Evapotranspiration (mm)	0.8	0.8	3.0	3.2	4.7	4.5	1.6	1.9

Figure 1. Daily rainfall, simulated rainfall/irrigation and cumulative rainfall for 2013–2014 and mean cumulative drainage for It. ryegrass (IR) and oats to November from the commencement of treatment application.

Figure 2. Nitrate concentration vs. cumulative drainage following the June/July urine applications (0, 350, and 700 kg N ha⁻¹) for the It. ryegrass (A, top) and oats (B, bottom) lysimeter treatments. Time scale approximate only. Standard error bars (±1 SE) shown.

Table 5. Total inorganic-N leaching (, , and total-N), drainage and inorganic-¹⁵N leaching losses for It. ryegrass and oats urine treatments (control, 350, and 700 kg N ha⁻¹) to the end of the winter–spring drainage period.

Treatment		^bInorganic-N leached (kg N ha^−1)			Drainage (mm)	Inorganic-^15N leached (kg N ha^−1)
Crop	Urinary-N			Total-N	Winter/Spring			Total ^15N
It. ryegrass	Control	46a	2a	48a	351b	6a	0a	6a
	350	167bc	26ab	192b	369b	93b	19b	112b
	700	264d	85c	349d	433c	167d	66c	233d
Oats	Control	11a	0a	11a	321ab	3a	0a	3a
	350	131b	41b	172b	332ab	78b	31b	109b
	700	193c	81c	280c	295a	126c	68c	194c
Crop		**	ns	*	***	*	ns	ns
Urinary-N		***	***	***	ns	***	***	***
Crop × urinary-N		ns	ns	ns	***	ns	ns	ns
^aLSD (5%)		52	28	62	41	32	24	43

^aLSD: least significant difference (P < .05) at crop × urine rate level.

^bMeans followed by a letter in common are not significantly different according to Duncan’s multiple range test (P < .05).

Table 6. Annual total-N and ¹⁵N inorganic-N leaching loss (, , and total), gaseous-N loss (NH₃-N and N₂O-N), DM N content and soil-¹⁵N for It. ryegrass and oats urine treatments (control, 350, and 700 kg N ha⁻¹).

Treatment		^bInorganic-N/^15N leached (kg N ha^−1)						Gaseous-N/^15N loss (kg N ha^−1)				DM N/^15N content (kg N ha^−1)				Soil-^15N (kg N ha^−1)
Crop	Urinary-N rate	Nitrate		Ammonium		Inorganic-N		Ammonia/dinitrogen		Nitrous oxide		Tops		^dRoots		^eTotal
	kg N ha^−1	N	^15N	N	^15N	N	^15N	^cNH3		N	^15N	N	^15N	N	^15N	^15N
It. ryegrass	0	52a	6a	2a	0a	53a	6a	1a	5a	1.9a	0.1a	34b	1a	31b	0.4a	11a
	350	171b	94b	26ab	19b	197b	114b	11b	43b	6.4b	3.1b	83c	12b	41c	4.1d	110b
	700	274c	170c	85c	66c	359d	236c	28c	56c	12.0d	6.7c	100c	25c	40c	6.3e	137c
Oats	0	30a	2a	0a	0a	30a	2a	–	5a	1.4a	0.1a	44a	11b	18a	0.2a	12a
	350	172b	84b	41b	31b	213b	115b	–	52c	8.7c	3.8b	88b	15b	21a	2.0b	93b
	700	251c	142c	81c	68c	337c	210c	–	65c	11.3d	5.6c	98b	30c	23a	3.0c	158c
Crop		ns	ns	ns	ns	ns	ns	–	ns	ns	ns	ns	**	***	**	ns
Urine rate		***	***	***	***	***	***	**	***	***	***	***	***	**	***	***
Crop × urine rate		ns	ns	ns	ns	ns	ns	–	ns	ns	ns	ns	ns	ns	ns	ns
^aLSD (5%)		49	29	28	24	61	43	10	12	2.4	1.3	16	8	7	0.9	23

^aLSD: least significant difference (P < .05) at crop × urine level.

^bMeans followed by a letter in common are not significantly different according to Duncan’s multiple range test (P < .05).

^cAmmonia volatilisation measurements from bare soil, no crop present.

^dOats’ roots refers to subsequent kale crop.

^eTotal-N includes organic and inorganic N.

Figure 3. Oats and It. ryegrass DM production (A) and ¹⁵N uptake (B) to the end of the winter–spring period (December 2013) after winter (June 2013) application of ¹⁵N-labelled urine. Standard error bars (±1 SE) shown.

Figure 4. Summed total (%) of ¹⁵N recovered in drainage, soil, plant, and gaseous-N fractions from applied ¹⁵N-labelled urine or water. Standard errors (±1 SE) for total ¹⁵N recovery shown.