Implications of grass-clover interactions in dairy pastures for forage indexing systems. 4. Canterbury

Figures & data

Figure 1. Average monthly maximum temperatures (A) and minimum temperatures (B), and total rainfall (▪) plus irrigation water applied (▪) (c) from March 2012 to May 2015. The grey bars represent data during the experiment while the black lines represent the 30-year means.

Table 1. Seasonal and total annual adjusted herbage accumulation (kg DM/ha) from pastures sown with (plus) or without (minus) clover, and receiving High or Low rates of nitrogen (N) fertiliser annually.

	Nitrogen treatment		Clover treatment		s.e.d.	N × clover treatment									Statistical significance P-values
	High	Low	Plus	Minus		High N plus clover		High N minus clover		Low N plus clover		Low N minus clover		s.e.d.	Nitrogen	Clover	N × clover
Early spring 2012	1400	1220	1290	1340	87	1350		1450		1230		1220		124	.067	.585	.523
Late spring 2012	3720	2710	3250	3180	168	3680		3750		2820		2600		237	<.001	.693	.392
Summer 2012/2013	4130	3350	4400	3070	153	4380	a	3870	b	4430	a	2270	c	217	<.001	<.001	<.001
Autumn 2013	2880	2270	2970	2190	82	3040	a	2730	b	2900	ab	1650	c	116	<.001	<.001	<.001
Total annual 2012/2013	12,130	9550	11,910	9780	383	12,450	a	11,820	a	11,370	a	7730	b	541	<.001	<.001	.002
Winter 2013	1110	670	950	830	33	1150		1070		750		590		47	<.001	.003	.264
Early spring 2013	2000	1340	1850	1490	57	2107		1820		1530		1160		80	<.001	<.001	.803
Late spring 2013	3060	2280	2810	2530	76	3120	a	3010	a	2510	b	2050	c	107	<.001	.003	.036
Summer 2013/2014	3740	3030	4040	2740	263	4240		3240		3830		2240		372	.019	<.001	.285
Autumn 2014	2970	2530	3130	2370	102	3200	a	2750	b	3060	ab	2010	c	145	.001	<.001	.012
Total annual 2013/2014	12,880	9860	12,780	9970	364	13,870	a	11,890	b	11,690	b	8040	c	515	<.001	<.001	.042
Winter 2014	1140	840	1080	910	36	1180	a	1100	a	980	b	710	c	51	<.001	<.001	.022
Early spring 2014	1880	1760	2020	1610	80	1980	ab	1780	b	2070	a	1450	c	112	.153	<.001	.021
Late spring 2014	3360	2170	3070	2450	83	3530	a	3190	b	2610	c	1720	d	118	<.001	<.001	.006
Summer 2014/2015	4790	4360	5590	3560	145	5340	b	4250	c	5850	a	2870	d	204	.011	<.001	<.001
Autumn 2015	3340	2940	3360	2920	88	3480		3200		3240		2650		125	<.001	<.001	.111
Total annual 2014/2015	14,510	12,070	15,120	11,450	251	15,510	a	13,510	b	14,740	a	9390	c	355	<.001	<.001	<.001

Notes: s.e.d., standard error of the difference between means. Nitrogen × clover treatment means with different letters within a row are significantly different. There was no winter herbage accumulation recorded in 2012, therefore ‘Total annual 2012/2013’ is the sum of growth for the seasons early spring, late spring, summer and autumn only.

Table 2. Seasonal and total annual adjusted herbage accumulation (kg DM/ha) from pastures sown with eight different perennial ryegrass cultivars with contrasting morphology and heading dates.

	Perennial ryegrass cultivar
	Abermagic AR1		Alto AR37		Base AR37		Bealey NEA2/6		Commando AR37		Kamo AR37		One50 AR37		Prospect AR37		s.e.d.	Statistical significance P-value
Early spring 2012	1260	bc	1320	ac	1190	bc	1180	c	1450	ab	1540	a	1200	bc	1370	ac	88	<.001
Late spring 2012	3330		3290		2930		3120		3290		3280		3230		3240		145	.135
Summer 2012/2013	3680		3530		3660		4060		3780		3460		3850		3880		200	.079
Autumn 2013	2360	bc	2560	ac	2600	ac	2770	ab	2340	c	2500	ac	2690	ac	2810	a	135	.003
Total annual 2012/2013	10,640		10,700		10,380		11,130		10,860		10,780		10,960		11,300		369	.301
Winter 2013	590	b	940	a	960	a	1040	a	700	b	690	b	1110	a	1090	a	61	<.001
Early spring 2013	1540	b	1540	b	1610	b	1620	ab	1670	ab	1740	ab	1770	ab	1880	a	83	<.001
Late spring 2013	2760		2630		2470		2590		2710		2720		2800		2690		119	.168
Summer 2013/2014	3490		3450		3290		3580		3030		3110		3650		3520		224	.067
Autumn 2014	2580	cd	2730	bd	2790	ac	2860	ac	2450	d	2650	bd	3060	a	2910	ab	104	<.001
Total annual 2013/2014	10,950	bc	11,290	ac	11,120	bc	11,690	ac	10,560	c	10,920	bc	12,370	a	12,080	ab	400	<.001
Winter 2014	650	c	1060	b	1040	b	1180	ab	800	c	760	c	1320	a	1130	b	58	<.001
Early spring 2014	1680	b	1850	ab	1700	ab	1690	ab	1940	a	1930	a	1890	ab	1860	ab	79	.001
Late spring 2014	2840	ab	2990	a	2460	b	2470	b	3000	a	2900	ab	2780	ab	2650	ab	147	<.001
Summer 2014/2015	4620		4570		4450		4760		4260		4500		4710		4740		203	.211
Autumn 2015	3180		3220		3160		3010		2900		2990		3320		3350		160	.059
Total annual 2014/2015	12,960	a	13,690	a	12,820	a	13,110	a	12,900	a	13,070	a	14,020	a	13,740	a	432	.037^1

Notes: s.e.d., standard error of the difference between means. Cultivar means with different letters within a row are significantly different. There was no winter herbage accumulation recorded in 2012, therefore ‘Total annual 2012/2013’ is the sum of growth for the seasons early spring, late spring, summer and autumn only.

¹While the P-value for total annual dry matter yield in 2014/2015 was significant, use of the more-conservative Tukey's LSD test indicated cultivar means were not significantly different from each other. In the Results and Discussion sections, the main effect of cultivar is therefore considered to be non-significant.

Figure 2. Significant nitrogen (N) × cultivar interaction detected in the seasonal adjusted herbage accumulation data during winter 2013. Pastures were sown with eight different perennial ryegrass cultivars and received High (▪) or Low (□) rates of N fertiliser annually. The error bars indicate the maximum standard error of the difference for comparing N treatment means for a cultivar as well as cultivars within each N treatment.

Table 3. Seasonal nutritive value characteristics from pastures sown with (plus) or without (minus) clover, and receiving High or Low rates of nitrogen (N) fertiliser annually.

	Nitrogen treatment		Clover treatment			N × clover treatment									Statistical significance P-value
	High	Low	Plus	Minus	s.e.d.	High N plus clover		High N minus clover		Low N plus clover		Low N minus clover		s.e.d.	Nitrogen	Clover	N × clover
Crude protein concentration (% DM)
Late spring 2012	12.8	10.9	12.5	11.1	0.31	13.0	a	12.5	a	12.1	a	9.8	b	0.44	<.001	<.001	.013
Summer 2012/2013	15.2	14.3	17.1	12.4	0.72	16.1	ab	14.3	b	18.1	a	10.5	c	1.01	.221	<.001	.002
Autumn 2013	21.6	18.6	21.3	18.9	0.38	22.4	a	20.9	b	20.2	b	17.0	c	0.54	<.001	<.001	.038
Late spring 2013	19.3	16.8	19.5	16.6	0.36	19.9	a	18.7	b	19.1	ab	14.4	c	0.51	<.001	<.001	<.001
Summer 2013/2014	16.6	16.0	18.3	14.3	0.67	17.7	a	15.5	b	18.9	a	13.1	c	0.95	.416	<.001	.018
Autumn 2014	27.6	23.9	26.2	25.3	0.55	27.4	a	27.8	a	24.9	b	22.9	c	0.78	<.001	.152	.049
Late spring 2014	15.6	15.3	16.5	14.3	0.50	16.6		14.6		16.5		14.1		0.71	.594	<.001	.670
Summer 2014/2015	17.5	14.4	18.7	13.3	0.34	19.2	a	15.8	c	18.1	b	10.8	d	0.48	<.001	<.001	<.001
Autumn 2015	22.1	22.9	23.9	21.0	0.27	22.9	b	21.2	bc	24.9	a	20.8	c	0.39	.021	<.001	<.001
NDF concentration (% DM)
Late spring 2012	46.8	45.5	45.5	46.9	0.52	46.4		47.2		44.6		46.5		0.73	.030	.022	.368
Summer 2012/2013	53.0	52.6	51.2	54.4	0.60	52.7	b	53.3	b	49.8	c	55.5	a	0.84	.585	<.001	<.001
Autumn 2013	46.8	45.5	45.2	47.1	0.53	46.6	a	47.0	a	43.8	b	47.2	a	0.74	.031	.003	.018
Late spring 2013	49.8	46.4	48.8	47.4	0.98	49.1	a	50.5	a	48.6	a	44.3	b	1.39	.005	.182	.013
Summer 2013/2014	47.3	48.2	46.8	48.7	0.44	47.2	b	47.5	b	46.5	b	49.9	a	0.62	.074	.001	.005
Autumn 2014	47.8	48.6	47.4	49.0	0.46	47.9	b	47.6	b	46.8	b	50.4	a	0.65	.092	.004	<.001
Late spring 2014	43.4	43.2	42.5	44.0	0.25	42.7		44.1		42.3		44.0		0.36	.519	<.001	.442
Summer 2014/2015	53.9	54.1	52.9	55.1	0.80	53.4		54.5		52.5		55.7		1.13	.827	.020	.223
Autumn 2015	47.8	51.9	47.8	51.9	0.34	46.7	c	48.9	b	48.9	b	54.9	a	0.48	<.001	<.001	<.001
ME density (MJ ME/kg DM)
Late spring 2012	12.5	12.7	12.7	12.5	0.07	12.6		12.5		12.7		12.6		0.09	.051	.069	.868
Summer 2012/2013	11.7	11.2	11.6	11.3	0.09	11.7	a	11.7	a	11.5	a	10.9	b	0.12	<.001	.004	.003
Autumn 2013	12.0	12.2	12.2	12.1	0.07	12.0		12.1		12.3		12.1		0.09	.032	.311	.130
Late spring 2013	12.3	12.8	12.5	12.7	0.10	12.3		12.3		12.6		13.0		0.14	<.001	.082	.114
Summer 2013/2014	12.3	12.3	12.3	12.2	0.07	12.2	ab	12.3	ab	12.4	a	12.2	b	0.09	.923	.387	.039
Autumn 2014	12.1	12.3	12.2	12.2	0.08	12.1		12.2		12.4		12.1		0.12	.190	.302	.065
Late spring 2014	12.8	12.9	12.9	12.9	0.04	12.8	b	12.9	b	13.0	a	12.8	b	0.06	.076	.107	.020
Summer 2014/2015	11.6	11.2	11.4	11.4	0.09	11.6		11.7		11.2		11.1		0.12	<.001	.910	.309
Autumn 2015	12.0	11.7	11.9	11.7	0.04	12.1		12.0		11.8		11.5		0.06	<.001	<.001	.124

Notes: NDF, neutral detergent fibre; ME, metabolisable energy; s.e.d., standard error of the difference between means. Nitrogen × clover treatment means with different letters within a row are significantly different.

Table 4. Seasonal nutritive value characteristics from pastures sown with eight different perennial ryegrass cultivars.

	Perennial ryegrass cultivar																	Statistical significance P-value
	Abermagic AR1		Alto AR37		Base AR37		Bealey NEA2/6		Commando AR37		Kamo AR37		One50 AR37		Prospect AR37		s.e.d.
Crude protein concentration (% DM)
Late spring 2012	11.4		11.6		12.3		12.2		11.0		11.6		12.3		12.3		0.65	.337
Summer 2012/2013	15.9	a	14.0	b	14.8	ab	14.2	ab	15.2	ab	15.6	ab	14.6	ab	13.7	b	0.61	.003
Autumn 2013	19.6	ab	20.2	ab	20.2	ab	19.4	b	20.6	ab	20.8	a	20.1	ab	19.9	ab	0.44	.031
Late spring 2013	18.9	a	18.1	ab	18.2	ab	17.4	ab	17.0	b	17.7	ab	18.4	ab	18.5	ab	0.58	.036
Summer 2013/2014	16.2	ac	16.1	bc	15.4	c	15.9	bc	17.7	ab	18.3	a	15.2	c	15.6	bc	0.73	<.001
Autumn 2014	25.3	b	25.6	ab	25.6	ab	25.5	ab	27.0	a	26.6	ab	25.2	b	25.3	b	0.47	<.001
Late spring 2014	15.9		15.1		16.0		15.6		15.5		14.3		15.4		15.8		0.83	.592
Summer 2014/2015	15.1		15.6		15.6		16.1		16.4		16.9		15.5		16.5		0.69	.156
Autumn 2015	21.8	b	21.9	ab	21.9	ab	22.2	ab	23.5	ab	23.7	a	22.2	ab	22.5	ab	0.59	.001
NDF concentration (% DM)
Late spring 2012	43.1	c	47.6	b	43.4	c	42.5	c	50.1	a	50.6	a	44.3	c	47.8	b	0.68	<.001
Summer 2012/2013	50.3	c	54.2	ab	51.8	bc	51.3	c	54.7	a	54.3	a	51.3	c	54.5	a	0.78	<.001
Autumn 2013	42.4	c	47.0	ab	44.9	b	44.9	b	47.5	a	47.1	ab	47.5	a	47.8	a	0.75	<.001
Late spring 2013	46.8	cd	48.6	ac	46.8	cd	46.6	d	49.7	a	50.3	a	47.2	bd	49.1	ab	0.63	<.001
Summer 2013/2014	49.9	a	44.8	d	47.9	b	47.6	bc	46.0	cd	48.3	ab	48.3	ab	49.2	ab	0.61	<.001
Autumn 2014	46.1	d	49.0	ab	47.7	bd	46.8	cd	47.8	ad	48.5	ac	49.5	ab	50.0	a	0.69	<.001
Late spring 2014	41.4	de	43.8	ac	42.3	ce	40.5	e	44.6	ab	45.9	a	43.2	bd	44.4	ab	0.69	<.001
Summer 2014/2015	51.1	b	55.5	a	53.7	ab	53.8	ab	55.3	a	53.9	ab	53.7	ab	55.0	a	0.93	<.001
Autumn 2015	47.3	c	51.1	a	50.0	ac	48.1	bc	50.4	ab	50.5	ab	51.0	a	50.7	ab	0.91	<.001
ME density (MJ ME/kg DM)
Late spring 2012	13.0	ab	12.5	c	13.2	a	13.3	a	11.9	d	11.8	d	12.8	b	12.4	c	0.09	<.001
Summer 2012/2013	11.7	ab	11.3	c	11.9	ab	12.0	a	11.0	cd	10.9	d	11.6	b	11.1	cd	0.10	<.001
Autumn 2013	12.3	b	12.1	bc	12.6	a	12.7	a	11.8	de	11.6	e	12.0	cd	11.8	de	0.08	<.001
Late spring 2013	12.6	b	12.5	bc	12.9	a	12.9	a	12.3	cd	12.2	d	12.7	ab	12.4	cd	0.08	<.001
Summer 2013/2014	12.6	ab	12.4	bc	12.6	ab	12.6	a	12.0	e	11.7	f	12.3	cd	12.1	de	0.07	<.001
Autumn 2014	12.3	ab	12.1	bc	12.5	a	12.6	a	12.1	bd	11.8	d	12.1	bc	12.0	cd	0.10	<.001
Late spring 2014	13.0	cd	13.0	bc	13.2	ab	13.3	a	12.5	e	12.3	e	13.0	bc	12.7	d	0.08	<.001
Summer 2014/2015	11.7	a	11.3	bd	11.7	a	11.6	ab	11.0	d	11.1	d	11.5	ac	11.2	cd	0.11	<.001
Autumn 2015	11.9	bc	11.8	cd	12.1	ab	12.3	a	11.6	de	11.5	e	11.8	cd	11.7	ce	0.09	<.001

Notes: s.e.d., standard error of the difference between means. Cultivar means with different letters within a row are significantly different.

Figure 3. Significant clover × cultivar interactions detected in neutral detergent fibre (NDF) concentration data during (A) summer 2012/2013, (B) late spring 2013 and (C) summer 2014/2015, and in metabolisable energy (ME) density data during (D) summer 2012/2013 and (E) summer 2013/2014. Pastures were sown with eight different perennial ryegrass cultivars with (●) or without (○) clover. The error bars indicate the maximum standard error of the difference for comparing clover treatment means for a cultivar as well as cultivars within each clover treatment.

Figure 4. Seasonal botanical composition of pastures during late spring (LSp), summer (Sum) and autumn (Aut). The four treatments were: HN+c, High nitrogen (N) plus clover; HN-c, High N minus clover; LN+c, Low N plus clover; and LN-c, Low N minus clover. Components include perennial ryegrass (grey), white clover (white), unsown species (black) and dead material (diagonal lines).

Table 5. Seasonal perennial ryegrass and white clover content (% of above residual herbage DM) of pastures sown with eight different perennial ryegrass cultivars.

	Abermagic AR1		Alto AR37		Base AR37		Bealey NEA2		Commando AR37		Kamo AR37		One50 AR37		Prospect AR37		s.e.d.	Statistical significance P-value
Perennial ryegrass
Late spring 2012	75	b	81	ab	86	a	78	ab	86	a	84	a	82	ab	83	ab	2.6	.015
Summer 2012/2013	72	ab	71	ab	75	a	71	ab	67	ab	64	b	71	ab	73	ab	3.2	.019
Autumn 2013	82		85		84		85		82		79		80		83		2.5	.087
Late spring 2013	90	ab	89	ab	90	ab	87	b	91	ab	91	ab	88	ab	92	a	1.4	.020
Summer 2013/2014	75	a	78	a	82	a	79	a	73	a	74	a	80	a	82	a	3.3	.033
Autumn 2014	90	ab	86	ac	90	a	89	ac	85	bc	85	c	87	ac	87	ac	1.6	<.001
Late spring 2014	90		91		91		89		91		91		90		88		2.0	.747
Summer 2014/2015	76		73		79		71		70		74		75		74		4.5	.487
Autumn 2015	76		77		81		75		73		73		77		73		3.3	.260
White clover
Late spring 2012	12	ab	5	b	12	ab	14	a	6	ab	9	ab	9	ab	6	ab	2.8	.010
Summer 2012/2013	30		29		30		35		36		42		31		27		4.8	.084
Autumn 2013	17		10		13		15		16		18		12		12		3.5	.084
Late spring 2013	9	ab	8	ab	8	ab	13	a	8	ab	11	a	7	ab	3	b	2.1	.005
Summer 2013/2014	24	ab	26	ab	19	ab	27	ab	31	a	30	ab	20	ab	16	b	4.6	.017
Autumn 2014	11		14		10		11		14		12		11		13		2.4	.526
Late spring 2014	9		6		5		9		8		7		9		8		2.0	.124
Summer 2014/2015	26		31		23		33		35		37		28		31		7.6	.717
Autumn 2015	23	ab	21	ab	18	b	26	ab	27	ab	27	ab	21	ab	33	a	4.5	.038

Notes: s.e.d., standard error of the difference between means. Cultivar means with different letters within a row are significantly different. White clover content is from the ‘with clover’ treatments only.

Table 6. Perennial ryegrass and white clover population density in pastures sown with (plus) or without (minus) white clover, and receiving high or low rates of nitrogen (N) fertiliser annually.

	N treatment		Clover treatment			Statistical significance P-value
	High	Low	Plus	Minus	s.e.d.	Nitrogen	clover
Perennial ryegrass tiller density (tillers/m^2)
Autumn 2013	8873	6646	7087	8431	417.7	<.001	.007
Autumn 2014	6806	6568	5943	7431	275.2	.404	<.001
Autumn 2015	5208	5160	4640	5729	231.6	.840	<.001
White clover growing point density (points/m^2)
Autumn 2013	904	1674			85.2	<.001
Autumn 2014	469	1117			198.1	.015
Autumn 2015	221	414			81.2	.064

Notes: s.e.d., standard error of the difference between means. White clover growing point density data are from the ‘+ clover’ treatment only. Growing point density data and s.e.d. are from the analysis without square root transformation, while the statistical significance is from the square root transformed data.

Table 7. Perennial ryegrass and white clover population density in pastures sown with eight different ryegrass cultivars with contrasting morphology and heading dates.

	Cultivar																	Statistical significance P-value
	Abermagic AR1		Alto AR37		Base AR37		Bealey NEA2/6		Commando AR37		Kamo AR37		One50 AR37		Prospect AR37		s.e.d.
Perennial ryegrass tiller density (tillers/m^2)
Autumn 2013	9057	ab	7581	cd	7035	d	5438	e	8272	bc	9563	a	7343	cd	7784	cd	386.3	<.001
Autumn 2014	7495	a	6493	ab	5977	bc	5037	c	7420	a	7553	a	7102	ab	6418	ab	392.2	<.001
Autumn 2015	5126	ab	4986	ab	5163	ab	4096	b	5757	a	5586	a	5080	ab	5679	a	357.9	<.001
White clover growing point density (points/m^2)
Autumn 2013	1388		1404		1320		1370		1350		1300		1146		1036		170.5	.251
Autumn 2014	814		1034		804		916		634		636		822		682		172.1	.041
Autumn 2015	446		190		204		386		418		284		298		312		113.9	.105

Notes: s.e.d., standard error of the difference between means. Cultivar means with different letters within a row are significantly different. White clover growing point density data are from the ‘+ clover’ treatment only (mean of two nitrogen levels). Growing point density data and s.e.d. are from the analysis without square root transformation, while the statistical significance is from the square root transformed data.

Table 8. Density (number/m² (Log N + 12/m²)) of CRW in pastures sown with (plus) or without (minus) white clover, and receiving High or Low rates of nitrogen (N) fertiliser annually.

Year	Treatment				Clover × N interaction
	Plus clover		Minus clover
	High N	Low N	High N	Low N	s.e.d.	P-value
2013	21 (3.3)	71 (4.2)	9 (2.9)	15 (3.1)	11.6 (0.20)	.020
2014^a	31 (3.5)	52 (3.9)	2 (2.6)	2 (2.56)	11.2 (0.25)	.229
2015	40 (3.7)	106 (4.9)	4 (2.7)	5 (2.7)	25.7 (0.09)	.005
2016	37 (3.8)	35 (3.7)	5 (2.8)	14 (3.1)	4.5 (0.13)	.031

Note: CRW, clover root weevil.

^aFewer than half the plots infested by CRW; data analysis unreliable.