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Sulla (Hedysarum coronarium) production sown with cover crops

Carolyn de Koning1, Peter Schutz1 and Jake Howie2

1. SARDI, Turretfield Research Centre, Rosedale, South Australia, 5350, Email Carolyn.dekoning@sa.gov.au; peter.schutz@sa.gov.au
2.
SARDI, Waite Institute Precinct, PO Box 397, South Australia, 5001, Email jake.howie@sa.gov.au

Abstract

Sulla growth can be slow in the first year and production may be lost or greatly reduced adding to the expense of establishment. Under-sowing sulla with a cover crop maybe a way of maximising production during the establishment year by providing winter grazing and/or a grain crop to harvest. But when moisture is limited pasture legume establishment under cover crops can be poor or totally fail. The aim of this experiment was to measure the effect of various cover crop species (wheat, barley and forage brassica) sown at different rates on the dry matter production, seed yield and plant survival of sulla. A key finding of the study was that cereal cover crops enhanced the over summer survival of sulla plants. Cereal cover crops in spring were very competitive with sulla significantly reducing sulla dry matter production by 28% - 53%. Sulla seed yield was unaffected by cover crops. The added advantage of cereal cover crops in this study was their ability to suppress weeds and their capacity to produce enough dry matter for winter grazing.

Key Words

Hedysarum coronarium, sulla, cover crops, cereals and forage brassica

Introduction

Sulla (Hedysarum coronarium) is a short-lived perennial forage legume that has provoked a lot of interest in Australia due to its ability to produce non-bloating, good quality, high dry matter forage with reputed anthelmintic properties (Neizen et al. 1995 and 1998). Growth of sulla in the establishment year can be slow (Crocker 2008) and as a consequence production could be lost or reduced during the first year adding to the expense of establishment. The use of cover crops sown with sulla maybe a viable option to establish this species. Nevertheless, cover crops can increase the risk of establishment failure mostly due to competition effects under dry conditions (Norton and Koetz 1998, Dear et al. 2010). In wetter districts the under-sowing of forage legumes with cover crops may be a way of minimising the expense of establishment (Carter et al. 1992). Cover crops could either be grazed in winter and/or grain harvested from them in early summer. Sometimes cover crops are used to protect lucerne seedlings from wind damage (Lattimore 2008). Potentially cover crops may also be used to protect sulla seedlings from the abrasive action of wind-blown sand particles. Very few studies have been done in Australia with cover crops and sulla. Forage oats have been tested as a cover crop with sulla but were found to be too competitive (de Koning et al. 2008). Other cover crop species such as wheat (Triticum aestivum), barley (Hordeum vulgare) and forage brassica (Brassica napus) need to be evaluated and their influence on sulla production and survival measured.

Methods

The experiment was sown at Turretfield Research Centre, Rosedale, South Australia (Long. 138o50’E, Lat. 34o33’S). The soil type was a Red Brown Earth with pH 7.8 (in water). The long-term average annual rainfall is 468 mm with long-term average growing season rainfall of 324 mm (May – Oct.). The total rainfall for 2009 was 464 mm and the growing season rainfall was 347 mm. Three species of cover crop (wheat variety “Yitpi”, barley variety “Keel” and forage brassica “Titan”) were each sown at three rates. The cereals were sown at 10, 40 and 80 kg/ha and the brassica was sown at 0.5, 1.5 and 3 kg/ha. The highest sowing rate used for the cereals and the forage brassica represent the average rate used in the district for sowing monoculture crops. In mixtures of vetch and cereal the 40 kg/ha sowing rate is commonly used for the cereals. A cone-seeder (sowing width 1.5 m) with 15cm tine spacing was used to sow the cover crop and sulla on 29 May 2009. Plots were 1.5 x 6m and cover crop species sown in a south to north direction using one sowing width. The “Wilpena” sulla seed (slurry peat inoculated, then lime coated) was sown at 7.5 kg/ha across the cover crop plots in an east to west direction using four sowing widths to complete a 6m plot. There were 10 treatment plots including the control (no cover crop sown) and three replicates (total 30 plots). Treatments were randomised using SpaDes (Spatial Design Generator). Plant numbers of sulla and cover crop were counted on 14 August 2009 using one quadrat (50 x 100cm) per plot. Dry matter of sown species and weeds was measured on 14 August 2009 and 22 October 2009 by cutting herbage to ground level in one quadrat (50 x 100cm) per plot. Individual plant weight was calculated using the dry matter yield per quadrat divided by the number of plants per quadrat taken on 14 August 2009. Samples were hand-sorted separately into sown species and weeds and dried in the oven for 24 - 48 hours at 80oC. Seed yield of sulla and grain yield of cereals was measured by hand-harvesting on 21 December 2009 one quadrat (50 x 100cm) per plot and threshing the component species separately.

Data was analysed using ANOVA in “Statistix 8” and natural logarithm transformation made where appropriate (see Tables 1 and 2).

Results

Significant differences in the number of cover crop plants established were due to differences in sowing rate. This was particularly the case for the cereals (Table 1). There were no significant differences in sulla plant numbers (grand mean = 74 plants/m2 - data not shown) or sulla dry matter yield in winter (14th August 2009). However, individual sulla plant weight was influenced by cover crops. Sulla plants were lighter when grown with barley sown at 80kg/ha and heavier when sown with brassica at 0.5 kg/ha compared to “no crop” sulla plants. Total dry matter production was greatest for barley cover crop treatments sown at 40 and 80 kg/ha (1902 kg/ha and 1784 kg/ha respectively compared to “no crop” 737 kg/ha). The brassica sowing rates and “no crop” treatments produced the least total dry matter. Plots were not sprayed to control weeds so that the influence of cover crop species and sowing rates could be measured for each treatment. Weed biomass (composed mostly of Capsella bursa-pastoris, Echium plantagineum, Hordeum leporinum and Lolium rigidum) was greatest in all three brassica sowings, wheat and barley sown at 10kg/ha and the “no crop” control. Barley sown at 80 kg/ha had significantly suppressed weeds (only 5 kg DM/ha weeds). Wheat at 40 and 80 kg/ha and barley at 40 kg/ha also had good suppression of weeds.

Table 1: Production of sulla and various cover crop species sown at different sowing rates measured on 14 August 2009 at the Turretfield Research Centre, Rosedale, South Australia.

Cover crop/

Sowing rate kg/ha

Sulla

g/plant

Crop

g/plant

Crop

no./m2

Sulla

kg DM/ha

Crop

kg DM/ha

Weeds

kg DM/ha

Total

DM kg/ha

Brassica 0.5

0.68

1.34

9

537

116

246 a

899

Brassica 1.5

0.50

0.94

27

336

248

133 abc

717

Brassica 3.0

0.53

0.88

37

387

321

199 ab

907

Wheat 10

0.61

1.48

31

390

458

201 ab

1049

Wheat 40

0.40

1.06

77

260

820

49 bcd

1129

Wheat 80

0.45

0.78

146

341

1114

57 d

1512

Barley 10

0.60

1.51

37

463

543

153 ab

1159

Barley 40

0.40

1.54

105

280

1596

26 cd

1902

Barley 80

0.31

0.81

187

259

1520

5 e

1784

No crop

0.50

0

0

470

0

267 a

737

LSD (P=0.05)

0.16

0.62

16

n.s.

280

*

373

* Natural log transformed data, treatments followed by the same superscript letter are not significantly different, back-transformed data presented. n.s = not significant.

Sulla dry matter production in spring was significantly reduced by both cereal species sown at 40 and 80 kg/ha and barley at 10 kg/ha compared to the control (Table 2). Weed dry matter was dramatically reduced by all cereal treatments, particularly wheat and barley sown at 80 kg/ha. The forage brassica treatments had no influence on weed competition. Total dry matter measured in October 2009 was lowest for barley sown at 80 kg/ha (4888 kg/ha) when all other treatments had yielded between 6050– 7496 kg/ha. No significant differences were found in sulla seed yield. Cover crop grain yields were significantly higher where crops were sown at higher rates. Barley was the most productive in grain yield compared to wheat. The forage brassica did not produce seed. Sulla adult plant numbers to survive into autumn 2010 were greatest for all three barley treatments and for wheat sown at 80 kg/ha. There were no significant treatment effects on sulla seedling regeneration in autumn 2010 (Grand mean = 32 seedlings/m2 - data not shown).

Table 2: Production of sulla and various cover crop species sown at different sowing rates measured on 22 October 2009 at the Turretfield Research Centre, Rosedale, South Australia.

Cover crop/

Sowing rate kg/ha

Sulla

DM kg/ha

Cover Crop DM kg/ha

Weeds

DM kg/ha

Total

DM kg/ha

Sulla seed

kg/ha

Cover crop grain kg/ha

Sulla adult plants/m2

Brassica 0.5

4227

225 b

1932 a

6384

59

0

2 d

Brassica 1.5

3733

290 b

2027 a

6050

80

0

5 cd

Brassica 3.0

4280

231 b

2507 a

7018

99

0

6 bcd

Wheat 10

3520

3248 a

728 b

7496

44

713 d

8 abc

Wheat 40

3213

3586 a

514 bcd

7313

15

1323 cd

7 bcd

Wheat 80

2733

4234 a

339 cd

7306

63

1951 bc

15 ab

Barley 10

3293

2627 a

606 bc

6526

39

1166 d

9 abc

Barley 40

2960

3848 a

614 bc

7422

79

2109 ab

13 abc

Barley 80

2133

2498 a

257 d

4888

13

2704 a

22 a

No crop

4587

0

1910 a

6497

72

0

7 bcd

LSD (P=0.05)

1181

*

*

1425

n.s.

*

* +

* Natural log transformed data, treatments followed by the same superscript letter are not significantly different, back-transformed data presented. n.s. = not significant, + Adult plants /m2 counted on the 16.4.10

Discussion

The key finding of this study was that cereal cover crops sown with sulla appeared to enhance the over summer survival of sulla plants. This finding contrast with those of Norton and Koetz (1998). They found cover crops had negative effects on lucerne establishment. Cover cropping will be risky in drier environments and the probability of establishment failure greater (Norton and Koetz 1998, Dear et al 2010). Growing season conditions were favourable during this study possibly leading to increased survival of sulla plants. In addition, cereals may have provided partial shade, acted like mulch or reduced wind therefore reducing transpiration from sulla plants during summer. It should be noted that the cereals in this experiment were not grazed or harvested. Grazed or harvested cereal cover crops may not offer protection to adult sulla plants in summer and this warrants further investigation.

This study also showed that cereal cover crops could provide extra winter feed. Grazing will need to be carefully monitored as sulla is highly palatable and may be grazed in preference to the cereal. Another advantage of cereal cover crops shown was their ability to reduce weed biomass. Similarly, Verano (1976) found that weed numbers were always lower in plots with cover crops of wheat and barley under-sown with lucerne. Cover crops or “nurse crops” are a way to control weeds without the use of herbicides (Lattimore 2008). We did not graze or cut the cover crops in winter. Grazing cover crops in winter may reduce their ability to suppress weeds and this should be tested.

Sulla plants in this study managed to grow to the same height as the cereal cover crop and were green while the cereal plants had senesced (Figure 1). This will present problems if the intention is to harvest the grain from the cereal cover crop. Green sulla plants will be taken into the cereal harvester possibly reducing grain quality and causing problems physically harvesting the crop. Forage brassica at the sowing rates used did not offer any advantages and plots were heavily infested with weeds. Barley was the most productive cover crop by growing the highest quantity of dry matter and yielding the most grain. This is probably due to more barley plants established than wheat. Under favourable seasonal conditions as found in this study a reasonable grain yield can be obtained from the cover crop. Further studies on cover crops with sulla are warranted that include cutting and or grazing the cover crop in winter, trials on lighter textured soils, impact on second year sulla production, wider range of cover crop species, different row spacing and a range of sowing rates for sulla.

Figure 1: Sulla with a barley cover crop in late spring, note the senesced barley and the height of the sulla.

Acknowledgements

Thankyou to Pastures Australia (A collaboration between AWI, GRDC, MLA, RIRDC & Dairy Australia) for providing funding for this work.

References

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