Effect of soil salinity on growth of irrigated plantation Eucalyptus in south-eastern Australia

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Abstract

Management of salinity may include establishing trees in saline areas to enhance discharge and may enable productive use of saline land. Field studies of the performance of trees in saline conditions are generally confined to the initial years after planting, and little quantitative data are available on the relationship between the growth rates of eucalypt species to soil salinity in field conditions at later ages (e.g. 10 years). In this study, the growth of irrigated Eucalyptus globulus, E. grandis and E. camaldulensis is examined in relation to soil salinity measured using an electromagnetic induction device (EM38).

The EM38 was found to be an effective tool in determining survival and growth responses of three Eucalyptus species to levels of soil salinity. Differences in measured tree survival, stand volume and leaf area index were correlated with soil salinity. Of the three species, E. globulus performed best in terms of survival and volume growth to age 10 years under slight to moderate salinity conditions, while E. camaldulensis performed best under moderate to severe soil salinity. The ranking of these species for salinity tolerance is consistent with pot trials and younger field trials.

This study highlighted the high spatial variability associated with soil salinity, and studies relating the growth of trees in the field should best be analysed on an areal or stand basis, thereby accounting for variability of salt stored in the soil, and reducing the influence of inter-tree competition on growth–salinity relationships. These results have implications for site selection and management of eucalypts in saline areas.

Highlights

► Growth of three irrigated plantation Eucalyptus species is examined in relation to soil salinity. ► Differences in survival, stand volume and leaf area index were correlated with soil salinity. ► Ranking of species for salinity tolerance is consistent with pot trials and younger field trials. ► Studies of trees in the field should best be analysed on an areal or stand basis. ► These results have implications for site selection and management of eucalypts in saline areas.

Introduction

Soil salinisation is a significant and increasing problem in many areas of Australia. The estimated area of agricultural land in southern Australia affected to some extent by saline scalds, saline seeps, irrigated saline soil and shallow saline groundwater is over 5.2 million ha, and is expected to reach nearly 11 million ha by 2050 (National Land and Water Resources Audit, 2001).

Revegetation of recharge areas with deep rooted perennials, including trees, is recognised as the preferred way to reduce secondary salinity induced by land clearing for agriculture. However, if trees can be sustainably grown in saline (discharge) areas, they offer a means of productively using degraded land of little alternative value, for economic benefit (Marcar and Crawford, 2004), as well as contributing to site rehabilitation and reducing salt loads to streams (Schofield et al., 1989). The low opportunity cost of agriculture on salt affected land may make tree growing more economic than on non-saline land, even if growth rates are reduced somewhat by salinity.

The salt tolerance of particular species is a crucial factor in its success in providing environmental and economic benefits when grown under saline conditions (Dale and Dieters, 2007). A challenge in using vegetation for salinity control lies in the development of plantations with sufficiently tolerant species that provide commercial products as well as environmental benefits (Bartle et al., 2007).

Prospective species are often studied as juveniles (up to 1 year old) in glasshouse conditions. However, results from controlled glasshouse experiments may not be directly transferrable to the field, where there may be substantial confounding temporal and spatial variation in salinity (Niknam and McComb, 2000). Zohar et al. (2010) argue that, when screening eucalypt seed sources for use on saline lands, it is critical to quantify the relationship between salinity and a measure of tree productivity under field conditions.

Field studies of the performance of trees in saline conditions are generally confined to the first few years after planting. Inferences drawn from such trials with young trees should be applied to field growing trees with caution (Arndt et al., 2000, Callister et al., 2008) and performance and characteristics of trees in the field must be assessed. It cannot be assumed that growth rates observed in the first few years will continue as root zone water and salt conditions change as the trees develop. There are few data to quantify the relationship between the growth rates of eucalypt species to soil salinity in field conditions at later ages (e.g. 10 years). Compared with annual crops, it is difficult to evaluate the growth response of eucalypts to soil salinity because these may be affected by dormant periods, changes in climate from year to year, and temporal and spatial changes in the soil salinity profile.

This study examined the growth of Eucalyptus camaldulensis, E. globulus and E. grandis at Timmering, in northern Victoria, as affected by soil salinity resulting from differences in irrigation water salinity. We investigated whether growth rates can be related to the distribution of salinity in the soil, and quantified the effect of soil salinity on the growth of each species.

Section snippets

Methods

The study was undertaken in a field experiment comparing growth of Eucalyptus spp. irrigated with low salinity or high salinity water. The experiment was established under the Trees for Profit program for investigating potentially commercial options for tree growing to achieve land and water care benefits (TFPRC, 1992, Bren et al., 1993, Baker et al., 1994, Baker et al., 2005, Stackpole et al., 1995).

ECe and calibration of EM38

Soil salinity (ECe) varied with depth in the 13 calibration profiles from 1 to 12 dS m−1 (Fig. 1) and the average to 150 cm depth varied from 2.0 to 8.3 dS m−1. Linear regressions for EM38H and EM38V ECa measurements with ECe are presented (for individual depth intervals and averaged across more than one depth interval) in Table 1. EM38H and EM38V were similar in their ability to predict ECe for depth intervals to 60–90 cm, while EM38V was a better predictor for depth intervals 90–120 cm and below.

Effect of salinity on tree survival and growth

Salt tolerance of plants in field conditions may vary significantly with many environmental factors such as soil fertility, soil physical conditions, irrigation method, distribution of salt in the root zone, and climate; with plant factors such as growth stage and variety (Kozlowski, 1997); and with management. In the present study, the range in soil salinity and in tree growth were sufficient to allow comparisons between species. While the range of salinity was large enough across the plots to

Conclusions

Differences in tree survival and stand volume measured for E. camaldulensis, E. globulus and E. grandis were correlated with soil salinity measured using an EM38. Of the three species, E. globulus performed best in term of survival and volume growth to age 10 years under slight to moderate salinity conditions, and E. camaldulensis performed best under moderate to severe salinity conditions. Soil salinity is spatially highly variable, and long term growth effects are best analysed on a stand

Acknowledgements

Funding for this study was provided by the Victorian Department of Sustainability and Environment, the Victorian Department of Primary Industries, and the Cooperative Research Centre for Plant-Based Management of Dryland Salinity. The authors are grateful to D. Chessum who kindly allowed access to the plantation and maintained and applied water to the plantation. A number of people contributed to the design, establishment, maintenance and monitoring of the field study. The authors particularly

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