Abstract

Key Words

Introduction

Within Australia it has been estimated that approximately 2.5 million hectares are salt affected, with the potential to increase to 15 million hectares. Much of this salt-affected land lies within Western Australia; however the recent National Land and Water Resources Audit indicated that the greatest increases in salinity are likely to occur in New South Wales and Victoria. This report also found that half of the salt-affected land within Australia is used for sheep production. One of the major limitations to production from saline land is the lack of commercial forage species that can be used successfully on these areas. The halophytic grass Distichlis spicata cv. yensen-4a has been grown successfully as a sheep forage at dryland sites in the Western Australia wheat belt (personal observation). The aim of this research was to investigate the potential of this grass for forage production in south-eastern Australia when irrigated with saline irrigation water.

Methods

A field experiment was conducted at Undera in the Goulburn Valley of northern Victoria; the annual average rainfall of this area is 460 mm, and irrigated dairying is it’s main industry. Four salt-tolerant grasses (Leptochloa fusca, Puccinellia cilliata, Paspalum vaginatum and Distichlis spicata cv. yensen-4a) were established with 20 kg P/ha and 18 kg N/ha during the summer of 2000. Treatments consisted of moderately-saline and highly-saline irrigation water, replicated four times. The saline irrigation water came from the evaporation basins of the Serial Biological Concentration experiment located at the same site. Irrigation water was applied whenever the cumulative evaporation minus rainfall reached 60 mm; at each irrigation, the electrical conductivity (EC) of each source of irrigation water was recorded.

Plots (2 m x 1 m) were harvested when there had been sufficient growth by cutting two quadrats (25 cm x 25 cm) from each plot to a height of 20 mm. After being dried at 70°C and weighed, the samples were analyzed for protein and ash content and in-vitro dry matter digestibility (IVDMD). Analyses of variance were performed on the data using GenStat (Lawes Agricultural Trust, Rothamstead Experimental Station). Where appropriate, data were log₁₀ transformed to stabilize variances.

Results

The average EC’s of the moderately-saline and highly-saline irrigation water were 21.7 dS/m and 62.5 dS/m, respectively. Soil EC values (1:5 in water) increased significantly from a pre-irrigation average of 1.49 dS/m, to 2.55 dS/m and 5.25 dS/m after the moderately-saline and highly-saline saline irrigation water, respectively, had been applied.

Salinity overall did not affect the protein contents (P>0.15) of the grasses (Table 1). Distichlis protein contents were lower than Paspalum and Leptochloa at each harvest (P<0.05). The Leptochloa and Paspalum ash contents were significantly higher than the Distichlis ash contents in all harvests (P<0.05). Overall, the ash content was found to increase significantly with salinity (P<0.05). Distichlis IVDMD’s were found to be significantly lower than Leptochloa and Paspalum in all harvest (P<0.05). Salinity treatment was found to increase IVDMD in the first and third harvest (P<0.05), but not in the fourth harvest (P>0.3). The digestibility results presented in this paper have not been corrected for their soluble ash contents, and as such, may have been over-estimated.

Table 1. Protein and ash contents and digestibility of three grasses irrigated with moderately-saline and highly-saline water. The log₁₀ transformed digestibility data for Harvest 4 are in parentheses.

¹ No statistical analyses were conducted on the second harvest due to the high number of missing values.
² Means within each column with the same superscript are not significantly different (P=0.05).
³ n.a. = not analysed

Dry matter production was found to differ significantly (P<0.001) between grass species. Distichlis produced significantly more dry matter than Leptochloa and Paspalum (P<0.05). Distichlis and Paspalum both produced more dry matter when irrigated with moderately-saline water than with highly-saline water (P<0.05) (Table 2).

Table 2. Total dry matter production of three grass species irrigated with moderately-saline and highly-saline water.

¹ Treatments means with the same superscript are not significantly different (P=0.05).

• "Solutions for a better environment". Edited by Murray Unkovich and Garry O'Leary. Proceedings of the 11th Australian Agronomy Conference, 2-6 February 2003, Geelong, Victoria.