The role of white clover in the south european grazing systems: The Po Plain situation

Amedeo Reyneri, Carlo Grignani and Andrea Cavallero

Dipartimento di Agronomia, Selvicoltura e Gestione del territorio. via Michelangelo, 32, 10126 Torino, Italy

Abstract
Introduction
Role of white clover in permanent grassland
Pasture and animal production from grass/white clover mixtures
Pasture management
Environmental role of white clover
Conclusions
References

Abstract

The large spread of maize for silage has recently induced farmers to produce high quality forage from herbage. However, in the recent years, pure clover stands or Italian ryegrass/white clover mixtures, which were largely used on dairy farms for zero grazing utilization, have been substituted by pure stands of annual Italian ryegrass for silage conservation. Therefore nowadays, white clover plays a major role only as a basic component of temporary meadows and pasture and of permanent grasslands for less intensive animal husbandry (farms producing suckled calves or milk and calves). Animal production from grass/white clovermixtures in the western Po Plain ranges from 800 to 1300 kg liveweight gain ha^-1, and a range from 630 to 1100 g d^-1 head^-1 with heifers. Animal production is influenced more by N application and stocking rate than by grazing techniques or associated grass species. Control of white clover in order to preserve an adequate grass-clover balance is the main goal of meadow and pasture management. Rotational grazing and an alternation of grazing and mowing seems to increase white clover contribution. Strategic N application, the use of more vigorous grass cultivars and less competitive white clover cultivars, could contribute to an improved grass-clover balance.

Introduction

As in central and north Europe, white clover plays a key role in permanent and sown south European grasslands (Gonzàles Rodriguez, 1991; Paoletti and Parente, 1991; Papanastasis, 1994).

In the Po Plain (north Italy, 44°-46° N) the role of white clover has strongly changed in the last decades. With the reduction in the number of farms, over 45% in the last 20 years, there has been an increase in herd size and a concentration of animal production in technically developed farms sited in more favourable areas (Zuppiroli, 1988; Giau and Mosso, 1991). In the 70's and 80's, farm stocking rates have strongly increased by more than 30% and the necessity of a high forage production has meant introducing forage systems based on annual forage crops, especially maize for silage conservation (Giardini, 1988). In consequence, temporary grasslands now occupy only 50% of the previous surface, and permanent grasslands only 75% (Zuppiroli, 1988).

Until the end of 80's it was supposed that permanent and sown grasslands would quickly disappear from large areas, surviving only in marginal less favourable conditions and generally under less intensive farming.

Starting from the end of the 80's, and clearly in these last few years, the impressive increase in milk production per cow has pinpointed out the necessity of high quality forage resources (Succi et al., 1988); moreover, very intensive farming has become convenient and sustainable only for dairy enterprises. Both aspects have renewed interest on grassland as a technical and economical resource for less specialized animal production which tends to substitute mowing by grazing (Cavallero and Ciotti, 1991; Canale and Ciotti, 1995).

In a recent survey in the western Po Plain, Grignani and Acutis (1994) have reported that stocking rates are 3.8 cows ha^-1 for dairy farms, 2.4 cows ha^-1 for suckler cow enterprises, and 4.4 head ha^-1 for beef producers. The authors have pointed out that the first two types have 30% of farm surface as permanent or temporary grassland.

In such situations, the role of white clover in forage systems has radically changed. In most of southern Europe, and particularly in north Italy, and differently from central Europe, white clover is largely used in temporary grasslands, because pure grass stands have never been consistently developed in forage systems. The reasons of the failure of pure grass stands are due to the minor role of grazing, and to the higher yield of pure lucerne, of permanent grasslands or even of grass-legume mixtures (Cavallero and Ciotti, 1991; Annichiarico and Berardo, 1993). More recently, in intensive dairy farms clover pure stands or Italian rye-grass/white clover mixtures, which were largely used for cutting under zero grazing utilization or hay making, have been substituted by pure stands of annual Italian ryegrass for silage conservation (Canale and Ciotti, 1995).

Nowadays then, white clover plays a major role only in less intensive farming, as a basic component of temporary meadows and of permanent grasslands, for farms producing suckled calves or milk and calves; in these situations, white clover offers higher herbage quality and, where frequent irrigation is possible, higher and more steady productivity, particularly in summer.

Role of white clover in permanent grassland

White clover is the main legume of the permanent meadow of the Po Plain under irrigated and even non-irrigated situations (Bittante et al., 1985; Grignani, 1990). White clover presence under different environments and agricultural practices is reported in Table 1; its presence is on the average 16% and 10% respectively under fertile conditions (dominance of Italian ryegrass) and less favourable conditions (dominance of perennial ryegrass), representing over the 90% of all legumes in the sward.

Table 1. Vegetation types of permanent grassland and agricultural practices in the western Po plain

Main vegetation type		Italian ryegrass dominance					Perennial ryegrass dominance
Vegetation subtype		a	b	c	Mean		d	e	f	Mean
Season					Spr.	Sum.				Spr.	Sum.
		(presence %)
Trifolium repens		26	16	7	15	17	15	7	6	9	10
Other legumes		0	0	2	1	0	0	2	1	1	1
Dactylis glomerata		0	21	0	7	6	2	2	3	2	3
Lolium multiflorum		23	17	18	22	17	11	6	6	6	9
Lolium perenne		1	3	2	2	2	19	11	14	16	13
Poa trivialis		10	11	4	13	3	17	5	6	14	4
Setaria viridis		2	7	7	0	10	3	1	1	0	3
Echinochloa crus-galli		5	1	1	0	4	3	2	2	0	4
Other species		35	27	59	40	40	30	65	61	52	54
Agricoltural practices:
	- irrigation (no.)	5	5	4	5		4	3	0	2
	- organic fertilization (kg N ha-1)	200	170	290	220		210	120	150	160
	- mineral fertilization (kg N ha-1)	60	74	58	64		40	25	76	47
Herbage production (t ha-1 yr-1)		11.4	12.9	8.9	11.0		11.7	8.7	8.5	9.6

As expected the relative white clover abundance was positively correlated with the P₂O₅ and K₂O level in the organic fertilization and with the irrigation volume. If compared to central European meadows, Grignani (1990) has found a rather poor correlation of white clover presence with total distribution of N and its use with organic and inorganic fertilizations. White clover indifference to N application is largely due to competition between clover and grass; spontaneous clover in the Po Plain is a large or very large leaf type (ladino) that is able to compete with grass, even with highly productive Italian ryegrass (Paoletti and Parente, 1991; Annichiarico and Piano, 1993). The considerable petiole lenght of the ladino type (it can reach more than 60 cm in height), the faster regrowth during summer when temperatures are unfavourable to grass growth (mean temperature above 20 °C, and maximum mean temperature often above 30°C), and the absence of water stress, explains white clover competitiveness. Moreover, if compared with small leaf types, ladino has a better water stress tolerance if the stress is moderate as occurs in the irrigated lowlands (Thomas, 1984). Hence, in our conditions white clover could increase its presence from June to September, balancing the poor competitiveness during the spring and the autumn.

In permanent swards, white clover presence increases during summer (Table 1), but its seasonal fluctuation is more limited than in temporary swards (Cavallero and Cereti, 1985; Cavallero et al., 1993a); in permanent pastures wild warm season grasses, such as Setaria viridis, exert a strong competition and limit white clover spread, that otherwise woulf often become dominant. Hence, on temporary meadows, under 4-5 cuts year^-1 without water stress, white clover presence increases rapidly (Table 2), even faster when clover is associated with small sized grasses such as perennial ryegrass or less vigorous cultivars of cocksfoot and tall fescue.

Table 2. Effects of grass species on the evolution of white clover - ladino cv - presence in temporary meadows in three sites.

Site:	Carmagnola (1)		Caramagna (2)		Lodi (3)
Years after sowing:	First	Second	First	Second	First	Second
Associated grass:	(presence %)
Festuca arundinacea	40-55	50-80	15-20	20-30	19-38	24-41
Dactylis glomerata	20-35	20-45			9-54	8-65
Lolium perenne	40-60	55-80			30	50
Phleum pratense	20-25	20-25
Bromus Willdenowii	40	45

(1) Cavallero and Cereti, 1985; (2) Cereti, 1986; (3) Annichiarico and Berardo,

Pasture and animal production from grass/white clover mixtures

The role of white clover in north Italian pastures is partially different compared with central Europe. In the latter case the main issue about white clover is to improve forage quality and maintain a efficient animal production under low N fertilization (Wilman, 1989); in most southern european non Mediterranean lowlands, white clover presence is necessary to maintain a high herbage productivity mainly during warm seasons.

Hence, if compared with the production levels of central Europe, pure stands of white clover show higher productivity: under infrequent cutting it produces from 8 to 14 t ha^-1 yr^-1 DM in north Italian irrigated lowland (Parente, 1983; Cavallero and Ciotti, 1991; Paoletti and Parente, 1991) with LAI close to 2.0 (Grignani et al., 1993), and above 8 t ha^-1 yr^-1 in central Italian lowland (Parrini, 1975); if compared with pure grass stands, such levels of productiion are only 10-20% lower (Cavallero and Ciotti; 1991).

High productivity is due to a higher leaf appearance rate; in Wales it increases to 0.9-1.3 leaves per stolon tip in July (Wilman and Asiegbu; 1982) when in the same period in the Po plain the appearence rate is 1.0-1.6 leaves per stolon tip, and remains over 0.7 over six months (Grignani et al., 1993).

Under frequent cutting intervals, 4 weeks, white clover pure stands or mixtures have almost the same productivity, and under very frequent defoliations, every 10 days, clover could increase the herbage intake by cows. Cavallero et al. (1991), comparing three grass/white clover mixtures under continuous grazing, have reported better animal production from the mixture having the highest clover content, which allowed the highest liveweight gain in summer.

Animal production from grass/white clover mixtures in the western Po Plain ranges from 800 to 1300 kg liveweight gain ha^-1, and a range from 630 to 1100 g d^-1 head^-1 with heifers (Table 3). Animal production is influenced more by nitrogen application and stocking rate than by grazing techniques or grass species associated.

Table 3. Comparison between different grazing techniques and nitrogen applications with hei (CG, continuous grazing; RG, rotational grazing)

Grass in the mixtures:	Coocksfoot				Perrennial ryegrass			Tall fescu
Grazing techniques:	CG		RG	CG	CG		RG	CG
Nitrogen (kg ha -1)	120(2)	325(1)	120(2)	190(3)	120(2)	325(1)	120	325(1)
Clover (% by weight)	21	12	39	23	23	16	46	30
Grazing season (d)	193	207	193	210	193	207	193	205
Stocking rate (cows)	2.9	3.8	3.5	2.4	3.0	3.9	3.4	3.9
Liveweight gain (g head-1 d)	822	629	822	1100	822	683	822	705
Liveweight gain (g ha-1)	796	1157	960	792	838	1269	932	1301

Cavallero et al., 1990 (1), 1993 (2); Reyneri unpublished data (3)

Under continuous grazing and reducing N fertilization from 325 to 120 kg ha^-1 yr^-1, Cavallero et al. (1990, 1993b) obtained a reduction of 69 and 66% of liveweight gain per ha respectively, with cocksfoot-white clover and with perennial ryegrass/white clover mixtures (Table 3). With high N fertilization stocking rate is higher in April-June and September-October, and slightly lower in August; individual animal performances have been 22% higher than from high-N swards.

Steen and Laidlaw (1986) reported that animal production from a continuously stocked grass/white clover swards fertilized with 60 kg ha^-1 yr^-1 of N was 78% in the first three years and 86% in the fourth and fifth years of that of a similar mixture fertilized with 360 kg ha^-1 yr^-1. Similarly, Younie et al. (1986) reported a stocking rate of 72%, Stewart and Haycock (in Sheldrick et al., 1987), 74%, and Orr et al. (1990), with sheep, 76% of that on the high-N swards.

Hence, the advantage achieved with high N application is similar comparing environments at different latitude and with no or moderate water stress; differences between environments become clear considering that in Po Plain N application, even at a high rate, does not compromise clover presence in pasture (Table 3).

Comparing different grasses in mixtures, slight differences have been noticed; perennial rye-grass under continuous grazing and cocksfoot under rotational grazing seem to be more adaptable. With tall fescue mixtures uncertain results have been reported; Cavallero et al. (1991) reported high animal production, while Bergoglio (1986, and personal communication) and Cereti (1986) reported unsatisfactory results and the same management difficulty due to low palatability. In recent years, new tall fescue cultivars with a more palatable leaf blade have been introduced with promising response (very good resistence to trampling and drought) under rotational grazing (Reyneri, unpublished data).

Pasture management

A high animal production and the control of white clover in order to preserve an adequate grass-clover balance, are the main goals of the pasture management.

With regard to animal requirements and pasture composition, particularly to crude protein content, the target presence of white clover in the sward is rather variable; it could a presence of 10-25% in pasture for suckler cows or heifers to 15-30% for dairy cows.

A review of several Italian trials with different species, has reported that animal production is generally rather similar under continuous or rotational grazing techniques (Cavallero and Ciotti, 1991), but interactions between techniques and N distribution are sometimes evident. In the north-Italian plain grass/white clover swards grazed with heifers have given higher animal production under continuous grazing and under rotational grazing respectively with high N and low N fertilization (Table 3).

Although animal performance is rather similar under different grazing techniques, defoliation intervals clearly influence white clover presence (Table 3). In the continuously grazed pasture white clover presence ranged from 12 to 30%, while under rotational grazing it presence ranged from 39 to 46% (Cavallero et al.; 1993b). In both cases clover constantly increased its presence year after year. Either with high or low N input, in association with cocksfoot, white clover shows minor development, compared to the association with perennial ryegrass. As pointed out by Reyneri et al. (1993), the lesser competitive power is especially due to the shorter summer stasis in cocksfoot compared to perennial ryegrass.

The great morphological plasticity of cocksfoot stresses the modification of leaf size and stem angle (habitus) under different defoliation intervals. Hence, under continuous grazing herbage average height could be conveniently mantained 1 cm lower (6-7 cm) with cocksfoot mixture compared to perennial ryegrass mixtures (7-8 cm).

As it was noticed in central Europe (Laidlaw and Vertes, 1993), also in south Europe different defoliation intervals have clearly modified canopy structure and particularly white clover morphology (Table 4).

Table 4. Effects of utilization on composition and white clover morphology of two different grass-white clover mixtures (cv Regal, summer measurements).

Mixture:	Cocksfoot- white clover			Perennial ryegrass - white clover
Technique:	continuous g.	rotational g.	cut	continuous g.	rotational g.	cut
Stolon lenght (m m2)	2233	4000	1560	2667	4567	5500
Growing points (no. m2)	1720	1739	400	1852	2320	1350
Stolon internodes (cm)	0.8	1.2	1.5	0.6	1.2	1.8
Leaf blade: petiole	1.29	0.72	0.56	1.05	0.62	0.61

(Cavallero et al., 1993; Keynen et al., 1993)

Under rotational grazing with intervals between defoliations of 18-25 d, ladino type shows an extraordinary competitiveness, with a swift increase in presence. In these conditions, the larger leaf size of ladino matches a greater capacity of petiole elongation to place leaf laminae in the upper layer of the canopy; moreover in summer, stolen length is higher under rotational than under continuous grazing, allowing a greater spreader on the pasture surface. Despite leaf blade: petiol ratio strongly increasing under diminishing defoliation intervals, with 18-25 d between defoliations, ladino is more competitive compared any grasses (Cavallero et al., 1994). High N applications (350 kg ha^-1 yr^-1) reduces but does not considerably modify this behaviour (Cereti, 1986).

Reactions of white clover under different grazing techniques vary with climate and latitude. In grazing trials in Norway, Oyen and Pestalozzi (1994) found that white clover associated with perennial ryegrass was more abundant under continuous grazing than under rotational grazing; in the British Isles, Peel et al. (1987) found insignificant differences in clover presence with varying utilization techniques. On the contrary in warmer environments such as in the Po Plain and the Mississippi State, rotational grazing enhanced clover diffusion (Cavallero et al; 1993b; Brink and Pederson, 1993).

The rather seasonal pattern of herbage growth makes necessary to integrate grazing and conservation. The experiences stress the need for more flexible forage systems that could better fit the climatic annual variability. However, the mean proportion of the total area that has to be grazed respectively in spring, early summer and late summer-autumn is: 40:40-70:100% under continuous grazing, 30:50-80:100% under rotational grazing (Bergoglio, 1986; Cavallero et al, 1991 and 1993a). The 65-75% of the total herbage produced is then grazed and the remainder cut for silage or for hay (second cut). As it was referred by Hoden et al. (1987), during spring rotational grazing allows herbage to produce more, and a larger area could be cut for conservation. Compared with continuously stocked areas, an alternation of grazing and mowing can increase clover presence even more (Table 5). White clover spread is still enhanced by transferring animals to the aftermath, to a varying degree depending on the grass in the mixture. Clover cover increases from the association with cocksfoot to the one with perennial ryegrass, to the one with tall fescue, which is poorly competitive even with high N applications. Grazing after two cuttings result in a slowing down of clover spread, at least in the presence of grasses more active in summer, unlike the association with perennial ryegrass, that comes out even more unbalanced.

Table 5. Effects of utilization and grass in mixture on white clover presence

Grass in the mixture	Cocksfoot				Perennial ryegrass				Tall fescue
Nitrogen (kg ha-1 y-1)	120		325		120		325		325
Season	Spr.	Sum.	Spr.	Sum.	Spr.	Sum.	Spr.	Sum.	Spr.	Sum.
	(clover % by weight)
Continuously stocked	16	25	7	15	19	26	16	25	23	42
Stocked after 1 cut	18	38	10	25	21	40	21	27	28	52
Stocked after 2 cuts	18	24	18	22	21	60	23	28	25	36
Only cut	28	22	10	15	38	76	25	60	12	20

(Cavallero et al., 1991; Cavallero et al., 1993a)

Laidlaw and Steen (1988) suggest that in order to improve clover content in set stocked swards, spring overgrazing should be avoided and later animals should be transferred to the silage aftermath to allow the spring grazed area to be rested for some weeks. It can be argued that the same considerations could be adopted in the north Italian lowlands, with the basic difference that these management strategies have to be avoided in order to reduce white clover increase.

In order to achieve a more balanced pasture composition, medium leaved size types of white clover have been utilized in mixtures instead of the traditionally large leaved types. In tall fescue-white clover mixtures under grazing with heifers, cv. Huia, if compared with cv. Regal, showed a higher presence in spring, probably because of a better tolerance to winter cold, and a lower presence in summer and autumn (Table 6); the use of Huia could allow a more steady composition during the growing season, but the disadvantage is a rather poor productivity in July and August that explains the relatively low competition with the associated grass (Reyneri unpublished data). In swards stocked after one cut Huia showed the same behaviour. It was noticed that after few years wild white clover, better adapted to the lowland environment, progressively replaced Huia; hence, intermediate leaf size types are not a durable solution because they could only slow down the evolution of the pasture composition.

Under strip grazing, Italian rye-grass white clover mixture could be usefully utilized, avoiding defoliation intervals shorter than 3-4 weeks. The maintenance of Italian ryegrass in the pasture sward is assured, firstly, by self-reseeding during the summer cicle (grazing has to be suspended for one month and a cut has to be made) and secondly, by avoiding trampling damage under wet condition.

Vegetation balance is hard to mantain during the seasons and the years; large leaf types clover becomes often dominant if the natural reseeding of Italian ryegrass is not assured.

Table 6. Presence and structure of two white clover cultivars under different utilizations.

Grass in the mixtures:	Tall fescue
Cultivar	Regal		Huia
Season:	Spr.	Aut.	Spr.	Aut.
Only grazed (clover %)	12	22	18	9
Stocked after 1 cut (clover %)	14	31	11	12
Petiole lenght (cm)	16.3		5.8
Internode lenght (cm)	1.7		1.0
Lamina surface (cm2)	8.1		2.9

As was argued previously, most of the lowland permanent grasslands are dominated by the association between Italian ryegrass and white clover; the management guidelines for a correct utilization under more frequent defoliation are a central issue of the actual forage systems based on these resources. Management which fails to mantain a sufficient Italian ryegrass presence risks a degenerative evolution; Poa trivialis and other weeds take the place of ryegrass and productivity and herbage quality of pastures become soon inadeguate. In an irrigated permanent grassland, once utilized as meadow and dominated by Italian ryegrass (30-40%) and white clover (15-20%), after three years of grazing has become a Poa trivialis (15-20%) and white clover (25-50%) swards with too high a presence of weeds (35-45%) and without Italian ryegrass (1-3%) (Masoero et al., 1995; Bergoglio personal comm.). In this case, overseeding of Poa pratensis and perennial ryegrass could lead to a new sward structure, better adapted to a more flexible cutting-grazing utilization with shorter defoliation intervals.

Environmental role of white clover

However, in spite of the positive role of legumes in sustainable agriculture, there is some concern regarding N losses in case of high white clover presence and the consequent high N fixation rate (t'Mannetje, 1994); that could lead to a high NO^-₃ level in the soil, particularly at the end of the growing season. In England, comparing N^-₃ leaching of grass clover mixtures and N-fertilized pastures, Scholefield and Tyson (1992) concluded that the level of losses is likely to be similar and that the environmental advantage with the clover is that it does not cost fossil energy. Comparing a pure grass meadow receiving 240 kg ha^-1 yr^-1 of N, with a cocksfoot white clover pasture receiving 170 kg ha^-1 yr^-1 of N, first results from western Po Plain have pointed out higher N leaching from pasture (11 vs 42 kg ha^-1 y^-1) and similar losses from runoff (2 kg ha^-1 yr^-1); the difference seems to be related to excretal return (urine and dung) rather than botanical composition (Grignani pers. comm.). The same site, a 366 kg ha^-1 N yr^-1 fertilized maize for silage resulted in N losses above 150 kg ha^-1 yr^-1 and lucerne under 15 kg ha^-1 yr^-1.

Conclusions

The role of white clover in the south European grazing systems is under evolution.

The case of the Po Plain shows clearly that under intensive farming, forage system become simpler and based even more on maize and Italian ryegrass. Nowaday, grass white clover mixtures play a major role only on less intensive farms producing suckled calves or milk and calves. In these situations white clover contributes to increased herbage and animal production. Under more favourable conditions than central Europe, white clover exerts a strong competition. Therefore the control of white clover, in order to preserve an adequate grass/clover balance, is the main goal of the pasture management. Ladino types are too competitive, and intermediate leaf types are often less productive particularly in summer, when the clover contribution to herbage growth is crucial. More research is needed to fit sward management to the different animal requirements and environment conditions.

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