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Effects of pasture management and liming history on pasture and wheat performance in the central wheatbelt of Western Australia

Anyou Liu and Clinton Revell

Centre for Cropping Systems, Department of Agriculture Western Australia, Northam, WA 6401. www.agric.wa.gov.au Email aliu@agric.wa.gov.au

Abstract

Pasture is an integral component of farming systems in the Western Australian wheatbelt. However, the contribution of pasture to the performance of subsequent crops is often below its potential due to a low legume content in the pasture phase. Management techniques to improve the productivity of the legume component have been under test in a long-term rotation trial at a site near Northam since 1998. The site has a sandy loam soil with a baseline pH of 4.5 (CaCl2) and a long-term average annual rainfall of around 435mm. The effects of pasture management (legume mixture vs pure subclover) and previous liming application on pasture and following crop performance were examined. The legume mixture treatment showed a production advantage over pure subclover in years with an extended growing season. When the growing season was short, total pasture production from the legume mixture and pure subclover was similar. There appeared to be little effect of lime history on the production of either pasture treatment, but some residual effects were evident in cereal crops. Positive crop responses to improved pasture and applied nitrogen were identified at anthesis. However, good finish rains are required for this to be translated into grain yield. The results highlight the potential of using diverse legume mixtures to maintain legume stability and to increase production in the face of variable soil and climate conditions. Examination of the persistence of legume mixtures in pasture and crop rotations is continuing.

Key Words

legume pasture, legume mixture, farming system, wheat, lime

Introduction

Legume-based pasture is an integral component of farming systems in the Western Australian wheatbelt. Besides providing high quality feed for grazing animals, legume pasture has the capacity to fix nitrogen and provides opportunities for the control of some difficult weeds and diseases in subsequent crops. However, the current level of contribution of pasture to cropping systems is often below its potential due to variable and declining legume contents in pastures generally known as pasture deterioration (1). Management techniques to improve legume productivity therefore hold the key to profitability of such systems. The use of a mixture of diverse pasture legume species has been proposed as one way to increase and stabilise the legume component (5, 2, 3). In this paper, results from a long-term rotational trial examining the effect of pasture management and liming history on pasture and the following crop performance are summarised.

Methods

Treatment and experimental design

The site is situated at Jennacubine (3121S and 11640E), about 30 km from Northam. The soil is a sandy surfaced duplex with a background pH of 4.5 (CaCl2). An existing rotation trial at the site that commenced in 1996 was used for this experiment. The original trial incorporated subterranean clover and had lime application (2 t/ha) in 1996 as a main treatment, compared with nil lime. The plot size was 100 m by 100 m. Two new pasture treatments were introduced into the plots in 1999 and again in 2000 (Table 1). The first was a legume mixture treatment that included subterranean clover (Trifolium subterraneum cv Dalkeith), arrowleaf clover (T. vesiculosum cv Cefalu), biserrula (Biserrula pelecinus cv Casbah), gland clover (T. glanduliferum cv. Prima), pink serradella (Ornithopus sativus cv Cadiz) and yellow serradella (O. compressus cv. Santorini). The second treatment was pure subclover (T. subterraneum cv Dalkeith) sown at the same rate (15 kg/ha) as the combined legume mixture. The sequence of the rotation used was sown pasture, wheat, regenerating pasture, regenerating pasture and wheat (P-W-P-P-W). The rotation was repeated in two different years (1999 and 2000) to take account of seasonal variation. At each starting year of the rotation, pasture treatments were replicated three times. In 2000, the original plots were divided into two halves to allow legume mixture and subclover treatments to be sown within the same lime histories (Table 1). In this paper we report the results from the first two years of the rotation, i.e. sown pasture followed by wheat.

During the cropping year, nitrogen subplots with rates of 0, 25, 50 (kg/ha nitrogen in the form of urea) were applied to the wheat crop after seeding. The nitrogen plot size was 3 m by 3 m and replicated three times within each main plot.

Table 1 Plot history (lime) for new pasture treatments sown in 1999 and 2000.

Starting year of rotation

Plot history

1999

2000

2001

1999

limed

mixture

wheat

regenerating mixture

 

unlimed

subclover

wheat

regenerating subclover

2000

limed

--

mixture

wheat

 

limed

--

subclover

wheat

 

unlimed

--

mixture

wheat

 

unlimed

--

subclover

wheat

Climate conditions

The average annual rainfall at the site is 435 mm (110 year average). Actual rainfall recorded at the site over the term of experiment was 500 (397) mm, 289 (162) mm, 250 (242) mm for 1999, 2000, and 2001 respectively (May to October growing season rainfall shown in parenthesis). Seasonal conditions in 1999 were above average with good rainfall in October. Years 2000 and 2001 were below average. There was little rainfall after mid-September in 2000 and a six-week dry spell occurred after seedling emergence in 2001.

Site management, sampling and measurement

During the establishment phase, the pasture was allowed to grow without grazing until senescence to allow maximum seed production. Sheep were then introduced to remove the dry residue. During the season, several cuts were taken at key growth stages to estimate biomass production of each species. Following the pasture year, a wheat crop was sown into the paddock and managed in a way typical of local farm practice. After initial knockdown weed control and scarification, the wheat variety Carnamah was sown at 70 kg/ha plus 120 kg/ha superphosphate. Sampling was conducted both at anthesis to estimate dry matter production and at maturity to estimate grain yield.

Data analysis

Data were analysed using the statistical package Genstat Edition 5 using the split plot or the split-split plot model.

Results

Liming history

Limed plots had a significantly higher pH six years after lime application (Table 2). The limed soil also had a lower level of iron. Other measured soil properties between the two plots with different liming history were similar.

Table 2 Soil chemical properties in July 2001 6 years after liming in 1995 (Rotation sequence: 1995 pasture, 1996 wheat, 1997 pasture, 1998 pasture, 1999 wheat, 2000 pasture).

Paddock history

Nitrate N (mg/Kg)

Ammonium N (mg/Kg)

P
mg/Kg

K
mg/Kg

Sulphur
mg/Kg

Organic C
%

Iron
mg/Kg

pH_CaCl2

Unlimed

21.0

10.3

27.3

252.0

13.5

1.6

287.7

4.5

Limed

21.0

7.0

28.3

228.0

14.4

1.5

245.0

5.4

LSD(P=0.05)

ns

ns

ns

ns

ns

ns

21.4*

0.497*

Pasture production

In 1999 the legume mixture produced 50% more total biomass than pure subclover pasture, mainly due to the contribution from arrowleaf clover (Table 3a).

In 2000 there was no significant difference between the two pasture treatments in total pasture production (Table 3b). There was also no interaction between liming history and pasture treatment on pasture production. However, within the legume mixture treatment liming increased the contribution of gland clover and decreased the contribution from serradella.

Table 3a Pasture performance in 1999: legume mixture vs pure subclover (t/ha), 21 Oct 1999

Pasture

Subclover

Arrowleaf clover

Biserrula

Gland clover

Pink serradella

Yellow serradella

Grasses

Broad
-leaf

Total legume

Total

Mixture

0.43

2.82

0.66

0.25

1.00

0.67

0.31

0.15

5.84

6.29

Subclover

3.17

         

0.75

0.19

3.17

4.10

LSD(P=0.05)

1.09

         

ns

ns

2.09

0.98

Table 3b Pasture performance in 2000: legume mixture vs pure subclover (t/ha), 17 Oct 2000

History

Pasture

Subclover

Arrowleaf
clover

Biserrula

Gland clover

Serradella

All weeds

Total legume

Total

Unlimed

mixture

0.16

0.33

0.34

0.51

1.35

0.68

2.68

3.36

 

subclover

2.26

       

1.11

2.26

3.38

Limed

mixture

0.21

0.34

0.21

0.78

0.69

0.93

2.23

3.17

 

subclover

1.92

       

0.85

1.92

2.77

LSD0.05

Pasture

1.079

       

ns

ns

ns

LSD0.05

History

ns

ns

ns

0.107

0.275

ns

ns

ns

Pasture x History

ns

       

ns

ns

ns

Wheat production

Wheat biomass production at anthesis responded to N application in both years, but mainly from the 0 to 25 kg/ha N treatment (by about 18% in 2001) (Table 4a and 4b). Wheat following the pasture legume mixture produced more biomass in 2000 than wheat following pure subclover and was less responsive to applied nitrogen (Table 4a). Lime history did not affect biomass production at anthesis in 2001. There was no significant effect of pasture management and nitrogen application on grain yield in 2000 (Table 4a). However, in 2001 there was an indication of a lime nitrogen interaction in grain yield with yields at nil nitrogen being higher on limed subclover plots (Table 4b).

Table 4a Wheat DM at anthesis and grain yield in 2000 following two pasture treatments

Pasture

Biomass at anthesis (t/ha)

Grain yield (t/ha)

N-level

0N

25N

50N

0N

25N

50N

mixture

7.83

8.30

8.16

2.90

3.48

3.15

subclover

5.61

6.48

7.68

3.14

2.82

2.86

Biomass at anthesis: LSD (P=0.05): 1.14(Pasture), 0.60 (N-level), 0.93 (PxN)

Grain yield: LSD (P=0.05): ns (Pasture), ns (N-level), ns (PxN)

Table 4b Wheat biomass production at anthesis and grain yield in 2001 following four pasture/lime treatments

   

Biomass at anthesis (t/ha)

Grain yield (t/ha)

   

N-level (kg/ha)

N-level (kg/ha)

History

Pasture

0N

25N

50N

0N

25N

50N

Unlimed

mixture

6.62

7.39

8.97

4.05

4.27

4.47

 

subclover

5.06

7.16

7.59

3.69

4.06

4.76

Limed

mixture

6.67

7.40

7.94

4.14

4.81

4.33

 

subclover

6.84

7.90

8.14

4.49

4.61

4.46

Biomass at anthesis: LSD (P=0.05): ns (History), 0.434 (Pasture), 0.79 (N-level), 0.69 (HxP), ns (NxP), ns (HxN).

Grain yield: LSD (P=0.05): ns (History), ns (Pasture), 0.31(N-level, Fpr=0.075), ns (HxP), ns (NxP), 1.11 (HxN, Fpr=0.094).

Discussion and conclusion

The high soil pH maintained six years after lime application agrees well with other reports in WA environments (6). The higher productivity of the legume mixture compared to pure subclover in 1999 (the year with above average rainfall) indicates the potential of this approach to increase pasture production. However, it is unclear whether this pasture response is due to the additional species diversity or the history of liming. We suggest that the contribution from liming is minimal based on the pasture productivity data from 2000, in which there was no response to lime history for either pasture treatment. In addition, little difference was found in pasture and crop performance between the limed and unlimed treatments in the previous trial conducted before this experiment started (pers. comm. D Ferris). The extra pasture production from the legume mixture could be due to the ability of the individual species to create a larger canopy than subclover and an ability to better utilise stored soil moisture from deeper root systems. The extended growth period from the species mixture has further implications for extra green feed at the end of the season and higher levels of nitrogen fixation. The dry season of 2000 is not representative of the environmental conditions normally experienced in the area. Such conditions may limit the productivity of the species mixture. However, most of the species have the capacity to produce a persistent seed bank which should buffer the impact of seasons.

The response of the wheat crop to applied nitrogen indicates soil nitrogen is still a limiting factor for wheat production in the soil studied. Higher legume contents in pasture can alleviate the requirement for fertiliser nitrogen as shown by the lower N response in the 2000 crop after the species mixture treatment. The apparent lime response in the 2001 crop after subclover is difficult to explain. It was alleviated by nitrogen application, which is consistent with the view that liming can have a positive effect on the release of nitrogen from the organic pool (pers. comm. B. Bowden). The lack of a lime response following the legume mixture suggests these plots had a higher nitrogen status, perhaps from greater mineralisation of the residues of some species.

The response in grain yield was not always consistent with crop biomass measured at anthesis. This was notable in 2000 (following the good pasture year in 1999), when a significant difference in biomass production at anthesis did not result in a significant difference in grain yield. As suggested by Liu et al (4), a limited water supply at the end of the season is likely to have been the major reason for this.

The ability of species mixtures to persist in the rotation and their associated management techniques are still being evaluated.

Acknowledgment

We thank GRDC for the financial support, Candy Hudson, Christiaan Valentine and James Bee for technical support, David Ferris, Dr Mike Ewing for their initial contributions, and Murray & Fiona Siegert for having the trial on their property.

References

(1) Carter, E.D. (1982) Proceedings of the 2nd Australian Agronomy Conference. Wagga Wagga, p. 180.

(2) Cocks, P. S. and Bennett, S. J. (1999) Genetic Resources of Mediterranean Pasture and Forage Legumes (ed S. J. Bennett and P. S. Cocks). Kluwer Academic Publishers, Dordrecht, pp 9-19.

(3) Liu, A. and Revell, C. K. (2001) Proceedings of the 10th Australian Agronomy Conference. Hobart

(4) Liu, A., Ferris, D. G. and Revell, C. K. (2001) Proceedings of the 10th Australian Agronomy Conference. Hobart

(5) Oram, R.N. (1993) Alternative Pasture Legumes 1993 -- Proceedings 2nd National Alternative Pasture legumes Workshop. York, pp. 199-202.

(6) Tang, C. and Rengel, Z. (2001) Agribusiness Crop Update – farming systems for sustainability. Perth, pp.67-69

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