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Herbage production, nitrogen fixation and water use efficiency of ten annual pasture legumes grown with and without lime on an acid soil

Belinda Hackney1, Brian Dear1, Mark Peoples2, Gabrielle Dyce1 and Craig Rodham1

1EH Graham Centre for Agricultural Innovation (NSW Department of Primary Industries and Charles Sturt University), Pine Gully Rd, Wagga Wagga NSW 2650
Email: belinda.hackney@dpi.nsw.gov.au
2
CSIRO Plant Industries, GPO Box 1600, Canberra ACT 2601

Abstract

Herbage yield and nitrogen (N) fixation of ten temperate annual legumes, was measured when grown with and without lime on an acid soil. N-fixation of O. compressus and O. sativus was significantly lower on limed and unlimed treatments (average 3.4 kg N/tDM) compared to T. subterraneum (average of 18 kg N/tDM). T. michelanium, T. purpureum and T. vesiculosum fixed a similar amount of N to T. subterraneum in unlimed treatments but T. vesiculosum fixed significantly more N (28 kg N/t DM) than all other legumes in limed soils. Herbage production of T. purpureum and T. vesiculosum was very high, particularly in limed treatments (>9.5t/ha) and consequently the total quantity of N fixed was significantly higher (>220 kgN/ha) than for all other species (20-131 kgN/ha) except T. michelanium. Water use efficiency (WUE) of the two highest N-fixing legumes was amongst the highest of all species. The results indicate some new annual pasture legumes can fix large quantities of N and use growing season rainfall more efficiently than T. subterraneum, particularly where lime has been used to amend soil acidity.

Keywords

Trifolium, Ornithpus, Biserrula, Medicago

Introduction

Subterranean clover (Trifolium subterraneum) is the dominant annual legume species used in pasture and cropping systems in southern New South Wales (NSW) (Dear et al. 2003). Recently a wide range of new annual legumes have been developed and released for use in Australian farming systems (Nichols et al. 2007). Many of the new annual legumes have significant agronomic advantages over subterranean clover including higher production, improved pest tolerance, and better tolerance of difficult soil conditions including acidity and water logging (Nutt and Loi 2002, Nichols et al. 2007).

Use of pasture legumes in cropping rotations can increase soil N for the following crop and act as a ‘disease break’ in the cropping rotation (Dear et al. 2003). Pasture legumes also provide high quality feed either utilised directly or conserved for use in times of feed shortage. Farmers in central and southern NSW have indicated they will be increasing their use of pastures in their farming systems, particularly for reducing reliance on inorganic N sources for crops, but also as a means of increasing fodder conservation for improved drought preparedness (Hackney et al. 2008). Many of the annual pasture legumes developed in the past 15 years are well suited to this multi-purpose role.

Soil acidity affects 13.7 million hectares of agricultural land in NSW (Scott et al. 2000) with many soils also acidic at depth (Helyar et al. 1990). Pasture legumes used in farming systems with acid soils must cope with acidity and its associated toxicities per se, or demonstrate response to amelioration of soil acidity to justify farmers shifting their focus from a subterranean clover-based farming system to use of alternative legumes. The aim of this experiment was to assess N-fixation and growth (including efficiency of growth) of a range of annual pasture legume species in an acid soil with high levels of exchangeable aluminium (Al) and manganese (Mn), with and without use of lime, when grown as a one-year forage legume crop.

Materials and methods

The site was located at Binalong, NSW (34.671S, 148.632E, 480m a.s.l) where long-term average annual rainfall is 620 mm. In the year of the experiment, annual rainfall was 547 mm and growing season rainfall (GSR) 373 mm. GSR is the rainfall recorded from the autumn break until peak herbage production measurement in spring. The autumn break occurred on the 25th May 2004, and peak spring herbage production was measured on 23 November 2004. Wheat was sown at the site in the previous three years.

Ten annual legumes were sown on 24 May 2004 into a prepared seed-bed, plots 2 m x 8 m, in a randomised split-plot design replicated 3 times. Soil at the site was a sodosol (Isbell 2002). Prior to sowing, soil was collected from each replicate for analysis of pH and exchangeable cations. Analysis showed soils were acidic with high levels of exchangeable Al and Mn. Plots within replicates were split with lime (2.5t/ha) applied to half of the plot. Soil pH and exchangeable cations were analysed from each replicate (unlimed and limed) 12 months after lime application (Table 1). Annual legumes sown and their seeding rate were Ornithopus compressus cv. Avila (10kg/ha), O. sativus cv. Erica (10 kg/ha), Biserrula pelecinus cv. Mauro (7 kg/ha), Trifolium vesiculosum cv. Zulu II (8kg/ha), T. michelanium cv. Bolta (7 kg/ha), T. glanduliferum cv. Prima (7 kg/ha), Medicago murex cv. Zodiac (10 kg/ha), T. purpureum cv Electra (7kg/ha), T. hirtum cv. Hykon (10 kg/ha), and T. subterraneum cv. Goulburn (10kg/ha). Seeding rates were the typical rates used for each species grown as a one-year forage legume break crop. Prior to sowing seed of each species was inoculated and lime pelleted using the appropriate commercial rhizobium group. Molybdenum fortified single superphosphate (8.8 % P, 11% S, 0.05% Mo) was applied at 230 kg/ha with seed at sowing. Trifluralin (2 L/ha) was applied and incorporated prior to sowing. Clethodim and alpha-cypermethrin were applied at 2L/ha and 100 mL/ha to control annual grass weeds and red-legged earth mites respectively on 29 July 2004.

Peak spring biomass was assessed by a calibrated visual scoring system. Scores were calibrated by scoring 10, 0.25m2 quadrats across the scoring range (0-50), cutting the herbage in the quadrats and drying it at 70oC for 48 hours to determine dry weight. Herbage samples were collected from each plot (limed and unlimed) for analysis of total N content and the proportion of herbage N derived from N-fixation using the natural abundance technique (Unkovich et al. 1994, Dear et al. 1999). Annual ryegrass (Lolium rigidum) was used as the non-N fixing reference plant. WUE was calculated by dividing peak spring herbage yield by the GSR.

Table 1. Average soil pH, exchangeable Al and Mn12 months after experiment commencement in unlimed and limed (2.5 t lime/ha) treatments at Binalong NSW.

Treatment

Depth
cm

pH CaCl2

Exchangeable Al
%

Exchangeable Mn
cmol/kg

Unlimed

0-10

4.2

18

0.21

Unlimed

10-20

4.0

38

0.30

Limed

0-10

5.3

1

0

Limed

10-20

4.1

36

0.28

A spatial regular grid model was fitted using Genstat 10. Species and lime treatment were fitted as fixed effects and replicate as a random effect.

Results

Only four species, T. hirtum, B. pelecinus, M. murex and T. subterraneum, showed no significant increase in herbage production with addition of lime. Five species, O. compressus, T. michelanium, T. purpureum, O. sativus and T. vesiculosum, were as productive as T. subterraneum without lime addition and all except T. michelanium were more productive than T. subterraneum where lime was applied (Table 2).

No species x lime effect on tissue N content was found, but there was a significant effect of species alone with T. glanduliferum having the lowest tissue N content and T. vesiculosum the highest. All other species except O. sativus and T. hirtum had similar tissue N concentration to T. subterraneum. A significant species x lime effect on the proportion of tissue N fixed was found with the use of lime significantly increasing the proportion of tissue N fixed in T. subterraneum, T. hirtum, B. pelecinus, M. murex and T. vesiculosum. The proportion of tissue N fixed in O. compressus and O. sativus was not affected by lime addition and the lowest of all species in the limed treatment and amongst the lowest in the unlimed treatment.

Application of lime did not increase the calculated N fixed/t DM for either Ornithopus spp. but did increase fixation by B. pelecinus, though all three species were inferior to T. subterraneum in unlimed and limed treatments. Use of lime also significantly increased N fixed/t DM for T. hirtum, M. murex and T.vesiculosum. T. vesiculosum fixed significantly more N/t DM in the limed treatment compared to T. subterraneum.

Where no lime was added, calculated total N fixed per hectare was highest for T. subterraneum, T. purpureum, T. vesiculosum and T. michelanium. Except for T. subterraneum, addition of lime significantly increased total N fix/ha of all these species with T. vesiculosum having the highest N fix/ha overall. Total N fix/ha was also significantly increased with the use of lime on T. hirtum, B. pelecinus, T. glanduliferum and M. murex. Total N fix/ha of O. compressus and O. sativus was not affected by lime addition and was consistently low in the un-limed and limed treatments.

Where no lime was applied, no species showed significantly higher WUE than T. subterraneum. However, T. hirtum, B. pelecinus, T. glanduliferum and M. murex had significantly lower WUE. Where lime was applied O. compressus, T, purpureum, O. sativus and T. vesiculosum were significantly more efficient in utilising growing season rainfall compared to T. subterraneum. Use of lime also significantly increased the WUE of T. glanduliferum to a level where it was comparable to T. subterraneum.

Table 2. Herbage yield, tissue-N concentration, proportion of tissue-N fixed, N-fixation (kg N/t DM and kg N/ha) and WUE of 10 annual pasture legumes grown as a one year forage crop at Binalong NSW in 2004.

 

Tissue N (%)

Proportion of tissue N fixed (%)

Herbage yield
(kg DM/ha)

N fixed
kg N/t DM

Total N fixed
kgN/ha

Water use efficiency
kg DM/mm GSR

Botanical name

 

-L

+L

-L

+L

-L

+L

-L

+L

-L

+L

O. compressus

3.06c

10.7ab

8.20a

5831defg

9439hij

3.06a

2.17a

17.1a

20.1a

14.1cde

25.5ij

T. michelanium

3.04c

67.6f

70.4f

5507cdef

7847ghi

19.5fghij

22.1ij

108cd

177ef

15.1cdef

20.7ghi

T. purpureum

3.04c

58.3ef

71.6f

7481fgh

10189j

17.3fghi

21.4hij

130de

222fg

19.8fg

27.0j

O. sativus

2.76b

23.4bc

11.5ab

5935efg

9269hij

5.4ab

3.11a

34.2a

34.0a

19.9fgh

25.1hij

T. subterraneum

3.19c

44.9d

59.7ef

7457fgh

6081efg

16.6efgh

19.6ghij

134de

131de

16.7efg

15.8defg

T. hirtum

2.70b

32.1cd

65.6f

3558abc

5146cde

9.06bc

18.8fghij

32.6a

90.7cd

11.3bcd

14.7cdef

B. pelecinus

3.65d

5.53a

41.9d

3860abcd

4800bcde

3.57a

14.5def

13.2a

68.3bc

10.5bc

13.2cde

T. glanduliferum

2.34a

49.6e

60.4ef

2740a

5955efg

11.7cde

14.6defg

32.9a

89.9bcd

7.41ab

15.7cdefg

M. murex

3.14c

43.5d

66.4f

2892ab

3443abc

11.2cd

22.8j

15.9a

60.9abc

4.72a

7.4ab

T.vesiculosum

3.90e

41.3d

66.5f

6457efg

9803ij

16.0defg

28.2k

124de

277g

16.3defg

26.9j

LSD (5%) interaction

ns1

13.8

2066

5.10

55.0

5.21

LSD (5%) species

0.23

         

Numbers within main columns followed by the same letter are not significantly different at p=0.05. 1ns=not significiant

Discussion

This experiment found on strongly acid soils with high levels of exchangeable Al and Mn, several annual legumes produced similar quantities of herbage and fixed similar amounts of N as T. subterraneum. With addition of lime, T. vesiculosum, and T. purpureum were superior to T. subterraneum in herbage production, WUE and N-fixation/ha (T. vesiculosum was also superior on a kg N-fixed /t DM basis).

In this experiment T. subterraneum showed no increase in herbage production and total N-fixation with use of lime. T. subterraneum responses to lime have frequently been reported (e.g. Scott and Cullis 1992), however, many other studies have shown little impact of lime on production (e.g Evans et al. 1990). The herbage yield increases in response to lime in this experiment for T. michelanium, T. glanduliferum and T. vesiculosum concur with previous studies (Evans et al. 1990, Hayes 2003, Cripps et al. 1988), and indicate greater suppression of growth of these species in strongly acid soils compared to T. subterraneum.

Herbage production and WUE of O. compressus and O. sativus was amongst the highest of all species in this experiment. However, N-fixation in both unlimed and limed plots was poor, yet Ornithopus showed no indication of N-deficiency and tissue N-content was similar to T. subterraneum. These results suggest that both Ornithopus spp. may have been scavenging rather than fixing N. Low N-fixation may also have been due to ineffective nodulation due perhaps to poor survival of rhizobia in this soil or low viability of rhizobia used in the inoculation process. Other experiments (e.g. Ovalle et al. (2006)), reported relatively high N-fixation of O. compressus (91 kg N/ha). Herbage production increases of 61% and 32% were recorded for O. compressus and O. sativus respectively with addition of lime. The magnitude of these increases were surprising given the reputation of Ornithopus spp. for acid soil tolerance. However other studies (e.g. Michalk 1994) reported significant increases in herbage production of Ornithopus spp. with the use of lime. Ornithopus spp. are known to be sensitive to Mn (Jenkins 2004) and exchangable Mn levels at this site were above the threshold level (0.20 cmol/kg) where yield reductions in sensitive species are known to occur (Bromfield et al. 1983). Bromfield et al. (1983) additionally reported that the threshold level for yield suppression by Mn was lower (0.10 cmol/kg) where conditions of high exchangeable Al also occurred. At this site exchangeable Mn in the unlimed treatment and in the limed treatment at 10-20cm was above both threshold levels and exchangeable Al was also high. While no indications of Mn toxicity were observed on the unlimed plots, there may still have been suppression of production and perhaps of N-fixation.

While N-fixation Ornithopus spp. was unaltered by lime addition, N-fixation of B. pelecinus (kgN/t DM and kg N/ha) increased significantly with liming but was still inferior to T. subterraneum. Poor N-fixation but high total tissue N in the unlimed treatments suggest B. pelecinus was scavenging rather than fixing N. Poor N-fixation may have been due to the same factors suggested for Ornithopus spp. B. pelecinus has significant potential in Australian farming systems due to its adaptation potential and ease of seed harvest (Nichols et al. 2007). However, on the basis of this research further clarification of its ability to fix N is warranted.

Of the annual legume species evaluated in this experiment, T. vesiculosum, T. purpureum and T. michelanium had a significant advantage over T. subterraneum in herbage production, N fixation and WUE when used as a high density legume break crop on acid soils with lime amendment. Rising inorganic N costs and decreased reliability of growing season rainfall mean producers need to choose legumes for cropping rotations that can fulfil a number of roles. While other legumes such as Ornithopus spp. appear well suited to fulfilling the high productivity, high WUE criteria, further research is required to better define their N fixation capability. Additional research is also needed to better define the N-fixing capability of B. pelecinus.

References

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Cripps RW, Young JL, Bell TL, Leonard AT (1988) Effects of lime and potassium application on arrowleaf clover, crimson clover and coastal bermudagrass yields. Journal of Production Agriculture 1: 309-313

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