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Dryland lucerne seeding rates had no effect on pasture production.

Kieran Ransom

Department of Natural Resources and Environment, Bendigo, Vic 3550. www.nre.vic.gov.au Email kieran.ransom@nre.vic.gov.au

Abstract

Lucerne was sown at 1 and 3 kg/ha with subterranean clover at a site near Boort in north central Victoria to test the hypothesis that the dry matter production of lucerne is unaffected by seeding rate. Over 6 years, lucerne yields averaged 612 and 653 kg DM/ha per year for the 1 and 3 kg/ha seeding rates respectively, while the annual species component yielded on average 3112 and 3179 kg DM/ha per year, respectively. The 3 kg/ha lucerne produced significantly more dry matter in only the first 2 winter - spring periods. The data indicate little if any advantage from sowing lucerne at 3 kg/ha in this dryland environment.

Introduction

Lucerne is highly recommended for crop and livestock enterprises. In north central Victoria, the lucerne seeding rates used by farmers vary from 0.5 to 6 kg/ha, with an average of 2 kg/ha. Farmers using low (<2 kg/ha) seeding rates claim their lucerne yields are similar to, or better than those obtained with higher rates. This suggests that for lucerne at low plant densities, higher yields per plant compensate for the low densities. To test this hypothesis, lucerne was sown at two rates and growth per unit area measured regularly.

Method

A seeding rate experiment with lucerne was established at Fernihurst (14350’E, 3614’S), 15 km south of Boort in north central Victoria. The average annual rainfall forof the site is 396 mm, with an April-October average of 264 mm. The topsoil (0-10 cm) is a clay loam with a pHwater of 6.2 and an Olsen P of 4 mg/kg. The 40 ha paddock was subdivided into 3 equal sized sub-paddocks. In June 1985 the lucerne was sown with subterranean clover under a barley crop. One half of each sub-paddock was sown with 1 kg/ha, and the other half with 3 kg/ha of lucerne (Medicago sativa cv. CUF 101), both with subterranean clover (Trifolium subterraneum cv. Seaton Park and cv. Nungarin, each at 2 kg/ha). From August 1986 to August 1993, dry sheep rotationally grazed the 3 sub-paddocks at an average stocking rate of 4.5/ha. Pasture growth was measured at 6 weekly intervals using 6 pairs of sheep exclusion cages, with the cages from each pair positioned approximately 10 metres apart on the 1 kg/ha and 3 kg/ha lucerne blocks. There were 2 pairs of cages in each sub-paddock. They were shifted approximately 3 metres at the beginning of each measurement period to avoid sheep exclusion effects on production. Lucerne yields were estimated by cutting lucerne to 1 cm height using 1.0 m2 quadrats at the beginning and end of each period. Lucerne density was measured in each quadrat. Yields of annual pasture were estimated in 0.25m2 quadrats in the same manner as the lucerne yields. Pasture production was aggregated for each calendar season. All data were analysed by analysis of variance using Genstat 4.2 (1).

Results and discussion

Six years after the lucerne was sown, lucerne plant densities had declined to about 10% of their first year densities for both seeding rates (Table 1).

Table 1. Average densities (plants/m2) of lucerne sown at 1 and 3 kg/ha in 1985 (** = P<0.01, *** = P<0.001).

Seeding Rate (kg/ha)

1987

1988

1989

1990

1991

1992

1993

1

16.7

11.9

7.3

5.6

3.9

2.6

1.7

3

39.8

27.9

15.4

11.7

8.2

5.5

3.9

LSD(P=0.05)

5.3

3.7

2.3

4.1

2.0

1.7

1.1

 

***

***

***

**

***

**

**

Over this period, the 3 kg/ha lucerne yielded more (P<0.05) dry matter than the 1 kg/ha lucerne in only the winter - spring of the first two years (Table 2). When seasonal production was averaged over the 6 years, the 1 kg/ha lucerne produced 23% less dry matter than the 3 kg/ha lucerne in winter, with no differences at other times of the year (Table 2). However the average winter lucerne yields were so low (71 versus 92 kg/ha) that the additional 21 kg/ha of dry matter was unlikely to feed many extra stock. There were no significant differences between the two seeding rates in average spring production of lucerne, nor in the yields of the annual pasture component on any occasion.

Table 2. Effects of lucerne seeding rate on the yields (kg DM/ha) of the lucerne and annual pasture components at Fernihurst from 1986 to 1993. (ns = not significant, * = P<0.05, ** = P<0.01), and rainfall (mm), for 1987-1993.

 

Lucerne

Annual pasture

Rainfall

 

Lucerne seeding rate (kg/ha)

Lucerne seeding rate (kg/ha)

(mm)

Period

1

3

LSD(P=0.05)

1

3

LSD(P=0.05)

 

Summer-autumn 1986-87

407

476

128

ns

57

57

   

126

Winter-spring 1987

297

358

48

*

1196

1151

275

ns

161

Summer-autumn 1987-88

634

521

143

*

393

422

199

ns

235

Winter-spring 1988

210

292

71

*

2864

3241

1181

ns

262

Summer-autumn 1988-89

741

709

178

ns

1775

2003

545

ns

278

Winter-spring 1989

164

99

164

ns

3678

3836

1685

ns

218

Summer-autumn 1989-90

372

365

293

ns

41

83

42

ns

140

Winter-spring 1990

220

294

130

ns

2466

2310

657

ns

162

Summer-autumn 1990-91

285

305

94

ns

72

79

33

ns

103

Winter-spring 1991

162

187

83

ns

3519

3299

1415

ns

243

Summer-autumn 1991-92

160

146

61

ns

337

364

68

ns

145

Winter-spring 1992

107

147

47

ns

2570

2537

825

ns

337

Summer-autumn 1992-93

331

445

225

ns

104

139

64

ns

211

Autumn pooled

190

185

33

ns

397

450

145

ns

 

Winter pooled

71

92

16

*

1355

1374

194

ns

 

Spring pooled

122

137

31

ns

1360

1355

269

ns

 

Summer pooled

229

239

40

ns

0

0

     

The average water-use efficiency of the pasture (lucerne plus annual species) for the April-November growing season was 16 kg DM/mm, after allowing 70 mm for evaporation (2). This is considerably less than the 24 kg/mm monitored by the author on 60 paddocks in north central Victoria from 1993 to 1997. In the experiment reported in this paper, it is likely that annual pasture growth was severely constrained by the low soil phosphorus (3). Also, lucerne growth at the site may have been constrained by a saline (22,000 mg/kg total soluble salts) watertable that fluctuated between 0.6 m depth in winter and 2 m depth in summer. Lucerne roots were observed no deeper than 1.1 m depth in a soil pit dug and left open for 4 years. These data indicate no advantage from seeding lucerne at 3 kg/ha in this dryland environment. This result is similar to one from Condobolin in central west NSW where the cumulative production of lucerne over 20 months was 11.9, 9.1 and 9.6 t/ha for seeding rates of 1, 2 and 4 kg/ha, respectively (L. Roesner personal communication). These results suggest that the roots of lucerne sown at 1 kg/ha can just as effectively explore the soil volume and utilise all of the available soil water as the roots of lucerne sown at higher rates.

References

(1) Genstat 4.2. 2000. Lawes Agricultural Trust, Rothamsted Experimental Station.

(2) French, R.J. 1991. In: Dryland farming, a systems approach. Ed. V. Squires and P. Tow, p222-238. Sydney University Press, Sydney.

(3) Jones, H.R., Maling, I.R.and Curnow, B.C. 1984. Aust. J. Exp. Agric. Anim. Husb., 24: 579-585.

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