Effects of urine patches and rest period on clover development in organic grass/clover sward

T. Baars and M.J.H. van Dongen

Louis Bolk Instituut, Department of Research in Biodynamic and Organic Agriculture, Hoofdstraat 24, 3972 LA Driebergen, The Netherlands

Introduction
Materials and methods
Results and discussion
References

Introduction

Recently the interest in organic farming in The Netherlands is growing. The Dutch government is especially interested in the question whether or not organic farming can be an alternative for conventional farming. One of the questions is to what extent are the results on nitrogen leaching, efficiency and total losses are better in organic dairy farming than in conventional farming. Especially, dairy farming on sandy soils is of interest because of the bigger losses to be expected. For this reason data were collected on the productivity of grass/clover leys on sandy soils under two grazing strategies and the effects of grazing and hence urination on nitrogen utilisation assessed. Therefore, urine patches were identified at three times in the year and the effect of urine on clover and nitrogen content and DM yield assessed.

Materials and methods

The one year experiment was caried out in 1990. After permanent pasture and one year in maize, tetraploid perennial ryegrass and white clover (cv. Barbian) was sown in September 1989 on a sandy soil. In April, 11 m³/ha slurry and in May, 25 t FYM/ha were applied. In March it was grazed by sheep for 17 days. Two management strategies were compared: "Grazing" (five times grazing, one cutting for silage in July); "Extra cut" (four times grazing, one cutting in July). In the "Grazing" managed field at three grazing times, urine patches were distinguished: each time 8 patches (urine-1= May, urine-2= August, urine-3= September). The patches were distinguished by colour, botanical composition and height and the position was marked by coordinates. At each harvest, DM yield, botanical composition and nitrogen content were assessed in the two management plots as well as in the marked urine patches.

Results and discussion

In Table 1 DM yield, nitrogen yield and clover content are given for every harvest of the two management strategies. There was an increase in clover content when a rest period of 9 weeks was included after the first grazing. Mean clover content was also higher in this treatment (40 % vs 28 %). It also influenced the clover content in early season the next year (35 % vs 20 %). High clover percentage in the first cut can thus be reached by adding an extra long rest period in the foregoing year. In several other experiments it has already been concluded that including cutting in continuous grazing is favourable to clover development (Wilkins, 1985; Curll et al., 1985). In this experiment it also resulted in higher DM yield and N-yield.

In Figure 1 the development of clover content is given under different conditions: Grazing, Extra cut, urine patches formed at three points of time (May, August, September). The urine affects the clover content in a negative way, especially when the urine patches are formed in early season, when clover content is low. At this time clover is almost completely reduced in the next cut (2 % vs. 21 %). It also diminishes clover development in the succeeding cuts. At all three urination times clover is reduced in the following grazing. In mid summertime (July/August) this reduction in clover content is less severe. It can be concluded that urine stimulates the growth of grass and inhibits the development of clover.

Only at the first urination time (May) is the nitrogen content higher in the urine patch than in the field (34 vs 26 gN/kg DM). Later in the season no differences in nitrogen content were measured. This in contrast to the DM yield which was 2-3 times higher in the urine patches compared with those in the field.

In all cases urine patches were invaded by clover stolon very rapidly. From the outline of a urine patch, caused in May (0, 88 m²), only 0, 22 m² was left in September.

Table 1. Yield (kg DM/ha), white clover content and nitrogen content at harvest.

Grazing management				Extra cut
harvest date	DM (kg/ha)	clover (%)	N (kg/ha)	harvest date	DM(kg/ha)	clover (%)	N (kg/ha)
02.05	1200	12	35	02.05	1200	12	35
28.05	1690	21	45
10.07	1410	24	40	10.07	4400	37	120
26.07	1020	30	38	26.07	1000	42	35
16.08	690	44	29	16.08	1100	62	51
17.09	2150	38	82	17.09	1990	48	79
total	8160	28	269	total	9690	40	320
1991				1991
06.05		20		06.05		35

Figure 1. Clover content (% in DM) during growing season under five treatments: Grazing, Extra cut, urine-1 (May), urine-2 (August) and urine-3 (September).

Due to the enormous concentrations of nitrogen and potassium in urine patches and due to the related leaching effects under such patches, housing of dairy cows overnight in the second half of the year, when clover content and nitrogen content is the highest, might be considered.

References

BAARS, T. and VAN DONGEN, M.J.H. (1992) De gevolgen van urine in enkele gras/klaverpercelen op zandgrond in 1990. Louis Bolk Instituut, Driebergen.

BAARS, T., OOMEN, G.J.M. and VAN DONGEN, M.J.H. (1992) Stikstofverliezen uit beweid gras/klaverland. (In: WERFF VAN DER, P.A. (ed.) (1992) Toetsing en nadere ontwikkeling van milieuvriendelijke bedrijfsvoering en bepaling van milieu-emissies van biologische gemengde bedrijven op zandgronden. Landbouwuniversiteit, Vakgroep Ecologische Landbouw, Wageningen).

CURLL, M.L. and WILKINS, R.J. (1985). The effect of cutting for conservation on a grazed perennial ryegrass/white clover pasture. Grass and Forage Science, 40, pp. 19-30.

WILKINS, R.J. (1985) White clover agronomy: responses to grazing management. In: Nutrition, agronomy & breeding of white clover. EC Workshop Johnstown Castle, Ireland, pp. 46-56.