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Abstract

Whereas the use of gypsum for the amelioration of sodic soils under dryland and

irrigated agricultural systems has been relatively well studied, experiments investigating lime

as a sodicity ameliorant have shown little success. This lack of success, and the use of lime as

a pH buffer, has caused it to be largely disregarded as useful for sodicity amelioration. Thus,

due to the extensive evidence for gypsum use as a sodicity ameliorant and the general

disregard of lime as an ameliorant, lime/gypsum combinations have only been given cursory

consideration, especially under irrigation. This study is principally concerned with addressing

the efficacy of lime and gypsum use for amelioration of sodic soils in the Lachlan and

Macquarie Valleys of NSW. However, there is an apparent lack of knowledge encompassing

the issue of sodicity and perhaps soil health in general. For this reason, it was necessary to

undertake an investigation into landholders’ soil health management education and the

impediments associated with implementing a soil health program in the Lachlan and

Macquarie Valleys.In order to assess the efficacy of lime and gypsum use for sodicity amelioration, four

field-based experimental sites were obtained, two in the Lachlan Valley (near Hillston, NSW)

and two in the Macquarie Valley (one near Trangie, NSW, and the other near Warren, NSW).

The soils form the Lachlan Valley were described as a Brown Vertosol and a Red Dermosol,

with pH 8.0–9.0, electrolyte concentration (EC) ranging from 0.30 to 3.50 dS.m-1 and

exchangeable sodium percentage (ESP) between 10 and 38%. The soils from the Maquarie

Valley were described as a Brown Vertosol and a Brown Dermosol, with pH 6.5–8.0, EC

ranging from 0.20 to 0.30 dS.m-1 and ESP between 6 and 12%. Full-field, replicated

experimental-strips were treated with L0G0 (Lime 0 t.ha-1 and Gypsum 0 t.ha-1), L2.5G0,

L0G2.5, L2.5G2.5, L2.5G5, L5G2.5 and L5G5 at each site. Due to insufficient rainfall and

unsecured irrigation water, only the Lachlan Valley soils were subject to irrigation; the

Macquarie Valley soils were subject to a dryland agricultural system.The study of the dryland agricultural system shows, through pH/EC relationships, that

EC is maintained at higher levels than the control where lime is applied, or where gypsum is

applied alone after 2.5 years. Furthermore, the increases in EC due to lime generally result in

a significant relationship between EC and aggregate stability. There is possibility of a

synergistic ameliorative effect between lime and gypsum on soil sodicity levels, although this

is not directly measured.

For the irrigated agricultural system, it is observed that gypsum is the primary means of

amelioration through Ca2+ exchange after 6 months, although these effects did not persist to2.5 years. The EC effect of gypsum is not observed after 6 months or 2.5 years post-gypsum

application and approximately 12.85 ML.ha-1 of infiltrating irrigation-water/rain. The results

of this work show that the use of lime and gypsum in combination and alone is not necessarily

viable for broadacre irrigated agriculture on two Lachlan Valley soils with pH >8.0.As it is apparent that the rate of gypsum dissolution is too high under the irrigated

system studied, gypsum was combined with chicken manure/wheat straw compost (CMWSC)

in order to investigate the potential of creating a slow release source of calcium (Ca2+). A

leaching column experiment was conducted using a Brown Vertosol treated with C0G0

(CWMSC 0 t.ha-1, gypsum 5 t.ha-1), C0G5, C5G0, C5G5, C144G0, and C144G5. Columns

were irrigated every two weeks for 14 weeks (6.5 ML.ha-1 of irrigation water in total). The

application of gypsum alone was shown to be comparable to the C5G5 treated soil, although

the C5G5 treated soil retained more Ca2+ and leached less Ca2+. Rapid decrease in soil

electrolyte level was evident in all treated soils. The results of this study indicate that gypsumenhanced

CMWSC is more effective in ameliorating sodicity than the use of gypsum alone,

due to a greater retention of exchangeable Ca2+.Despite mounting scientific evidence for the credibility of certain soil health

management strategies such as those in this work, farmers remain hesitant to implement

structured management plans and strategies. Hence, an investigation of the proportion of

Lachlan and Macquarie Valley landholders who implement a structured soil health program

was undertaken with focus on the impediments associated with the adoption of such

programs. Non-parametric analysis of a mail-based survey supported with content analysis of

landholder comments, suggests that the overall attitude towards soil health management is

positive, although soil health management programs are often inconsistent, unstructured, or

ad-hoc. Landholder knowledge of sodicity was found to be low, although landholders’ do not

believe that education is an impediment to program adoption. This research highlights that

ongoing communication between landholders, agronomists, extension agencies and scientists

is shown to be vital in the adoption of soil health management programs. While the initial

investment in soil health management is perceived as an impediment, landholders indicate

that production longevity and long-term financial gain are achievable.