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Soil water under lucerne phase and companion cropping systems.

Phil Ward1,2, Perry Dolling1,3, Diana Fedorenko1,4, Neil Fettell1,5, Rob Harris1,6, Brett Honeysett1,5, Roy Latta1,7, Anita Lyons1, Mark Peoples1,8 and Antony Swan8

1CRC for Plant-based Management of Dryland Salinity, University of Western Australia, 35 Stirling Highway, Crawley, WA 6914, www.crcsalinity.com.au
2
CSIRO Plant Industry, Private Bag No 5, Wembley WA 6913, Email phil.ward@csiro.au
3
Department of Agriculture and Food, Great Southern Agricultural Research Institute, 10 Dore St, Katanning WA 6317
4
Department of Agriculture and Food, 100 Bougainvillea Ave, Forrestfield WA 6058
5
NSW Department of Primary Industries, Agricultural Research and Advisory Station, PO Box 300, Condobolin NSW 2877
6
Department of Primary Industries, Rutherglen Centre, RMB 1145, Rutherglen VIC 3685
7
Department of Primary Industries, Walpeup Centre, Meridan Rd Walpeup, VIC 3507
8
CSIRO Plant Industry, GPO Box 1600, Canberra ACT 2601

Abstract

In southern Australia, lucerne (Medicago sativa) is the herbaceous perennial most likely to slow or halt the spread of salinity. To achieve this, it must: (1) reduce leakage and groundwater recharge; and (2) be widely adopted. In this paper, we examine the impact of lucerne on soil water storage for both phase (3-5 years of lucerne followed by an extended phase of cropping) and companion (simultaneous production of lucerne and crops) cropping systems. Production modelling, the role of lucerne management in minimising competition with a companion crop, and the influence of spatial arrangement on competition and crop yields are covered in related papers. Sites were established near Condobolin (NSW), Temora (NSW), Rutherglen (VIC), Esperance (WA), Katanning(WA) and Meckering (WA).Lucerne effectively depleted soil water below the root zone of annual crops and pastures at all sites under both systems, drying the soil by an extra 50-100 mm. The presence of a competing crop, lucerne suppression, supplementary irrigation and nitrogen addition, and lucerne winter activity rating, had at most minor effects on soil water extraction compared with water extracted by lucerne as a monoculture. Minimum lucerne density for soil water extraction varied between sites, but was always <12 plants/m2 The soil water depletion measured in these trials is likely to have a substantial impact on groundwater recharge and the rate of groundwater rise. We concluded that lucerne incorporation under either farming system will achieve desirable hydrological outcomes, and this expands the potential for broad-scale lucerne adoption.

Key words

Dryland salinity, recharge reduction, perennials

Introduction

In southern Australia, dryland salinity continues to expand as the landscape slowly comes to equilibrium with the changed hydrology induced by broad-scale clearing of native vegetation. In Western Australia alone, the area currently affected by dryland salinity is estimated at nearly 1 Mha, and in the absence of preventative action or prolonged decrease in rainfall, is expected to expand to between 2 and 4 Mha (McFarlane et al. 2004).

The most promising preventative action is the incorporation of perennial plants into current farming systems. Perennials often have the capacity to grow roots deeper than conventional annual crops and pastures, or can respond to out-of-season rainfall, or both. Consequently, many perennials can extract more water from the soil than conventional crops and pastures, allowing the soil to soak up more water at times of water excess, thereby reducing leakage and groundwater recharge. Substantial effort has been put into identifying suitable perennials for inclusion into farming systems, but at this stage, the best option by a considerable margin is lucerne (Medicago sativa).

The hydrological efficacy of lucerne has been demonstrated at many sites around southern Australia (Ward et al. 2006). Furthermore, lucerne fits well into existing farming systems, in which a period of several years (a phase) of lucerne pasture is followed by a phase of cropping, before returning to a lucerne phase. This is known as a phase rotation. However, despite lucerne’s hydrological efficacy and ready incorporation into farming systems, its adoption has been slow.

One of the major constraints to lucerne adoption is the cost of establishing the pasture, and further costs associated with lucerne removal prior to a cropping phase. However, there is another option. Since annual crops grow during winter and spring, and lucerne’s main growth period is late spring to summer, it may be possible to accommodate both crop and pasture production in the same 12-month period. Such a system, known as companion cropping, would involve sowing crops into established but suppressed lucerne pasture in late autumn or early winter, and harvesting the crop early in summer, leaving the lucerne to grow after crop harvest. In this farming system, there is no cost for lucerne removal, and the length of the lucerne phase is extended, increasing both the period of hydrological protection afforded by lucerne, and the interval between costs associated with lucerne re-establishment.

Companion cropping is already being trialed and adopted in some regions of southern Australia, but the impact of cropping and lucerne suppression on soil water extraction is not known. Similarly, the impact of cropping on lucerne plant density, and the effect of reduced lucerne plant density on soil water extraction, is poorly understood. In this research, we collate results from many trials in NSW, VIC, SA and WA, and compare soil water extraction by lucerne in a phase farming system with soil water extraction by lucerne in a companion cropping system. The role of lucerne plant density in maintaining a dry soil buffer is also investigated.

Methods

Trials comparing phase rotations with companion cropping systems were established in NSW near Condobolin and Temora, in VIC near Rutherglen, and in WA near Katanning. At the Condobolin and Rutherglen trials, treatments were set up to examine the impact of supplementary irrigation and nitrogen fertilizer addition. Nitrogen fertilizer was also investigated at the Temora site. Treatments at the Katanning site included the impact of lucerne winter activity (Humphries et al. 2004). At all sites, lucerne was established in the first year of the trial, and cropping commenced from the second year onwards. Soil water contents were measured with a neutron moisture meter at all sites.

Trials examining the impact of lucerne plant density on soil water extraction were established in WA near Katanning and Esperance (for details see Lyons and Latta, 2004), and Meckering. In all trials, lucerne was sown at 2, 4, and 8 kg/ha, and at 1 kg/ha for trials at Esperance and Katanning, in a randomized block design. Soil water extraction was measured with a neutron moisture meter.

Crop and pasture production, and spatial arrangement of lucerne within crops, were also investigated within this project, and are the subject of other papers presented at this conference (Fedorenko et al. 2006; Harris et al. 2006).

Results and Discussion

Soil water under phase and companion cropping systems

In all trials, lucerne was successful in establishing a large soil water deficit (SWD) in autumn compared with rotations that did not include lucerne. The magnitude of the SWD was in general agreement with previously reported values (Ward et al, 2006). Furthermore, there was little practical difference in the magnitude of the SWD created by lucerne grown as a monoculture, or grown in conjunction with grain crops (Table 1).

Soil water deficits for trials near Temora and Rutherglen were mostly generated by use of summer rainfall, rather than water uptake by lucerne from deeper in the soil. For these trials, the autumn soil water deficit was variable depending on the amount of summer rain received. Lucerne in trials near Condobolin and Katanning generated substantial soil water deficits in all years, due to water uptake from deep in the soil.

In general, soil water deficits created by lucerne were not strongly influenced by pre-crop or in-crop suppression of lucerne, nitrogen addition, or irrigation. Varieties with greater winter activity tended to produce slightly greater soil water deficits in the trial at Katanning (Humphries et al. 2004), but this effect was minor compared to the difference between the presence or absence of lucerne.

Lucerne density

Within the range of lucerne plant densities established in our trials (7-29 plants/m2), there was little difference in soil water extraction. All lucerne densities created larger soil water deficits than annual pastures for the second and subsequent years (Table 2). Significant differences in SWD at the Katanning trial indicated that densities below about 12 plants/m2 were less effective than higher plant densities. However, data from Meckering indicated the SWD kept on increasing with time despite densities falling to 3 plants/m2. Virgona (2002) concluded that a density of around 5 plants/m2 was a minimum for greater soil water extraction.

Table 1. Soil water deficits ( standard error) generated during the summer following various lucerne and crop treatments. Values for lucerne monoculture are in bold, companion cropping in italics, and crop monoculture in plain text. Codes represent treatments, with the “/” symbol used to separate growing seasons. L = lucerne; L* = lucerne terminated in the spring; B = barley; C = canola; T = Triticale; W = wheat; I = irrigated; S = lucerne suppression in crop; N = additional fertilizer nitrogen added; subscripts refer to lucerne winter activity rating.

Trial

Treatment code

SWD developed (mm)

Year 1

Year 2

Year 3

Year 4

Condobolin

L / L-I / L

1614

19910

17715

 
 

L / L / L-I

1592

1964

13929

 
 

L / B-I / W

1525

14813

8722

 
 

L / B / W-I

1524

1644

5214

 
 

L / B-L / W-L-I

1573

19613

17016

 
 

L / B-L-I / W-L

1592

1889

16720

 
 

L / B-L-N-S / W-L-N-S-I

15116

21920

19623

 
 

L / B-L-N-S-I / W-L-N-S

1565

19315

15014

 
           

Temora

L / L / L / L*

15415

14912

13621

12225

 

L / L / L-W / L-C

1657

14611

14214

15512

 

W / C / W / C

926

898

6910

15318

           

Rutherglen

L / L / L

954

1046

1207

 
 

L-I / L-I / L-I

1003

1113

1193

 
 

L-W / L-T / L-W

851

895

1032

 
 

L-W-I / L-T-I / L-W-I

825

1062

1131

 
 

W / T / W

6310

6114

8711

 
 

W-I / T-I / W-I

574

483

782

 
           

Katanning

L5 / L5 / L5 / L5

1794

2064

2183

2112

 

L10-W / L10-W / L10-W / L10-W

1635

1999

20410

2029

 

L5-W / L5-W / L5-W / L5-W

15111

1949

20311

20110

 

L2-W / L2-W / L2-W / L2-W

14116

18616

19515

19415

 

L0.5-W / L0.5-W / L0.5-W / L0.5-W

1368

17615

18614

18412

 

W / W / W / W

864

1124

967

10412

Table 2. Lucerne plant densities and autumn soil water deficits.

Trial

Sowing rate (kg/ha)

Year 1

Year 2

Year 3

Year 4

Density (/m2)

SWD (mm)

Density (/m2)

SWD (mm)

Density (/m2)

SWD (mm)

Density (/m2)

SWD (mm)

Esperance

1

131

533

121

433

91

614

71

494

 

2

182

545

162

446

111

605

81

525

 

4

241

444

241

415

121

566

102

446

 

8

271

452

363

432

121

592

111

462

 

Annual

0

502

0

322

0

392

0

321

                   

Katanning

1

152

7911

143

12813

121

1359

91

1254

 

2

191

8317

231

15621

163

16919

142

17621

 

4

253

887

273

1699

225

17110

175

17216

 

8

299

10715

286

16417

246

17418

176

18926

 

Annual

0

1077

0

987

0

1177

0

764

                   

Meckering

2

222

615

223

11311

151

15017

31

16714

 

4

362

647

343

11817

232

15020

71

17025

 

8

485

7710

413

12410

242

15217

113

17710

 

Annual

0

433

0

803

0

623

0

983

Under a companion cropping system, lucerne densities may decline more rapidly, especially where lucerne suppression is practiced (Latta and Lyons, 2006). Therefore, minimum lucerne densities for maintaining hydrological protection need to be established. Latta and Lyons (2006) demonstrated that for some soil types and climatic conditions in WA, lucerne densities of <5 plants/m2 in a companion cropping system were sufficient to maintain dry soil profiles. Our results also suggest that there may be variation in minimum lucerne density associated with soil type and climate, and further research would better quantify this important question.

Conclusions

Lucerne effectively generates large soil water deficits, thereby providing hydrological protection against deep drainage. Lucerne’s effectiveness was not affected by the presence of a crop in a companion cropping system. Furthermore, lucerne suppression, or the addition of supplementary nitrogen or water, did not substantially affect soil water extraction. Our research indicates that lucerne incorporated as part of a companion cropping system will be as hydrologically effective as lucerne incorporated as part of a phase rotation system. This increases the flexibility of lucerne in farming systems, and may lead to greater lucerne adoption in southern Australia.

Acknowledgements

Thanks to the CRC for Plant-Based Management of Dryland Salinity, and the Grains Research and Development Corporation, for supporting this research. We also wish to acknowledge other members of the research team not directly contributing to this paper, including Tom Bailey, Bill Bellotti, Clayton Butterly, Wen Chen, Michael Crawford, Jeff Hirth, Don Gaydon, Christopher Loo, Soheila Mokhtari, and Michael Robertson. Their thoughts and advice have been invaluable throughout the project.

References

Fedorenko D, Peoples M, Dolling P, Lyons A and Latta R (2006). Plant densities and spatial arrays in cropping systems that include perennials. Proceedings of the 13th Australian Agronomy Conference, Perth, Western Australia, September 2006.

Harris R, Clune T, Peoples M, Swan T, Bellotti W and Chen W (2006). The role of nitrogen and in-crop lucerne suppression for increasing cereal performance in companion cropping systems. Proceedings of the 13th Australian Agronomy Conference, Perth, Western Australia, September 2006.

Humphries AW, Latta RA, Auricht GC and Bellotti WD (2004). Over-cropping lucerne with wheat: effect of lucerne winter activity on total plant production and water use of the mixture, and wheat yield and quality Aust. J. Agric. Res., 55, 839-848.

Latta RA and Lyons A (2006). The performance of lucerne/wheat rotations on Western Australian duplex soils. Aust. J. Agric. Res. 57, 335-346.

Lyons A and Latta R (2004). Lucerne density studies in southern Western Australia in “Salinity Solutions – Working with Science and Society” Conference Proceedings, Bendigo 2004.

McFarlane DJ, George RJ and Caccetta PA (2004). The extent and potential area of salt-affected land in Western Australia estimated using remote sensing and digital terrain models. Proceedings of the 1st National Salinity Engineering Conference, Perth, Western Australia, November 2004.

Ward PR, Micin SF and Dunin FX (2006). Using soil, climate, and agronomy to predict soil water use by lucerne compared with soil water use by annual crops or pastures. Aust. J. Agric. Res. 57, 347-354.

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