Pattern of crop development in fertilised and unfertilised grass/clover swards grown for silage

David Younie¹ and Andrea Giordano²

¹ Scottish Agriculture College, 581 King Street, Aberdeen, Scotland AB9 1UD

² Universita di Torino Facalta di Agraria, Torino, Italia

Introduction
Materials and methods
Results
Discussion and conclusions
Acknowledgements
References

Introduction

The dynamics of grass and clover fractions in grazed grass/white clover swards have received considerable research attention. In contrast, the pattern of development of grass and clover in swards grown to a more mature stage for herbage conservation has been largely ignored. Relative levels of silage yield at a single cutting date have been reported, e.g. by Younie and Wightman (1992) and Bax and Niessan (1992) while Wilhelmy et al. (1991) described changes in growth parameters over time during the early part of the season (to the end of May). The experiment described here was carried out to determine the pattern of vegetation development in uninterrupted growth in fertilised and unfertilised grass/clover swards during May and June.

Materials and methods

The experiment was carried out in 1992 at Craibstone, Aberdeen, Scotland on an established sward on sandy loam soil of Countesswells Association, Countesswells Series. The 8-year-old sward was comprised almost entirely of perennial ryegrass (cvs Bastion. Talbot, Meltra. Preference) and white clover (cv. Milkanova). Assessment of clover content in early April 1992 indicated a ground cover of 10.6% and a population density of 2028 growing points/m² The experiment was a 5 x 2 factorial with five cutting dates (at fortnightly intervals) and two fertiliser nitrogen (N) rates. The first cut was taken on 6 May and the final cut on 1 July. Fertiliser N was applied at nil (FO) or 120 kg N/ha (F120). A second cut was taken from all plots at a single date (4 August) four weeks after the final cutting date of the initial sequence.

Plot size was 6.0 m x 1.5m and there were four replications. Herbage yield was measured by Agria reciprocating blade fingerbar mower leaving a 4 cm stubble height. Components of yield were assessed by hand separation. In vitro D value (DOMD) and crude protein content in the herbage were measured at the final three cutting dates.

Results

Dry matter yield increased significantly with time and with fertiliser addition (Table 1). The relative advantage in yield of F120 over FO was greatest (46%) at the first cutting dale and least (17%) at the fourth cutting date on 16 June.

Table 1. Effect of cutting date and N level on yield (t DM/ha)

Cutting date	N level		Mean
	FO	F120
6/5	1.4	2.6	2.0	***
20/5	3.7	5.5	4.6	***
4/6	6.3	8.4	7.4	**
16/6	9.3	11.2	10.2	**
1/7	10.9	14.2	12.6	*
Mean	6.3	8.4	7.4	***
			***

Clover content in F120 was, as expected, significantly lower than in FO (Table 2), but cutting date also had a significant influence, particularly in FO, where clover content peaked at the second cutting date on 20 May and then declined to its lowest level at the final cutting date.

Table 2. Effect of cutting date and N level on clover content (% in DM)

Cutting date	N level		Mean
	FO	F120
6/5	13.7	7.1	10.4	*
20/5	21.9	6.7	14.3	*
4/6	15.0	5.7	10.4	*
16/6	16.4	1.8	9.1	*
1/7	10.8	4.1	7.4	NS
Mean	15.6	5.1	10.3	***
			***

These changes were accompanied by an increase in the percentage of flowering tillers in ryegrass from zero on 20 May to over 90% on 1 July in both FO and F120 and resulted in the patterns of crop development shown in Figures 1 and 2.

Fig 1: Contribution of grass and clover to total herbage yield over time (Treatment FO)

Fig 2: Contribution of grass and clover to total herbage yield over time (Treatment F120)

(DOMD) was consistently higher (8% on average) in FO and than in F120 (Table 3).

Table 3. Effect of cutting date and N level on DOMD

Cutting date	N level		Mean
	FO	F120
4/6	72.2	65.6	68.9
16/6	66.4	60.6	63.5
1/7	58.2	56.9	57.6
Mean	65.6	61.0

Discussion and conclusions

During the late May/early June period, when grassland is commonly cut for silage in Scotland, the unfertilised grass/clover sward achieved the same level of DM yield and DOMD yield approximately eight days later than the fertilised sward. A delay in cutting at the first cut will normally restrict yield at the second cut, but in this experiment, total two-cut yield (from first cut plus the second cut on 4 August) was greatest in those treatments cut at later dates in the May/June cutting sequence.

The proportion of clover DM in the total herbage was not a constant during the uninterrupted growth of the silage crop. Clover content increased during May as temperature improved, but subsequently declined as total herbage yield increased - the increasing yield being primarily a consequence of the development of flowering tillers in ryegrass.

Despite this gradual reduction in clover content, the feeding value (in terms of DOMD) of an unfertilised grass/clover sward cut eight days later than a fertilised sward would not necessarily be lower. In this experiment. DOMD as well as DM yield of FO were higher on 16 June than F120 on 4 June. A delay in the date of cutting the first cut thus appears to be a practical solution to the disadvantage, perceived by most farmers, of lower silage yields in unfertilised grass/clover swards.

Acknowledgements

SAC receives financial support from the Scottish Office Agriculture and Fisheries Department Andrea Giordano was funded by the ERASMUS Programme of the CEC.

References

BAX. J.A. and NIESSAN, A.M. (1992). Protein content of grass/white clover silage. British Grassland Society Third Research Conference. Greenmount College.

WILHELMY, B., KORNHER, A. TAUBE. F. and WULFES. R. (1991). Changes in quality parameters during growth of pure grass swards and mixed grass clover swards as influenced by level of fertiliser. In White Clover Development in Europe. Meeting of FAO Co-operative Research Sub Network on Lowland Pastures and Fodder Crops, Polcenigo, Italy, 1991. REVR Technical Series. 19, 185-190.

YOUNIE, D. and WIGHTMAN, P.S. (1992). Herbage production over eight years from clover-based and intensively fertilised swards under grazing and silage management. British Grassland Society. Third Research Conference. Greenmount College.