This trial is another long-term soil amelioration trial established at the Gunning Gap CWFS regional site. Below is a summary of the last four years of results.

METHODS

LOCATION: Gunning Gap

COOPERATOR: Graham Coombs

TRIAL HISTORY:

Date spread: 16 May 2000

Lime source: Bagged agricultural lime

SOWING:

2000 - 6th June, 45 kg/ha Dollarbird, 75 kg/ha DAP

2001 - 7th June, 45 kg/ha Diamondbird, 80 kg/ha DAP

2002 - 7th June, 45 kg/ha Janz, 80 kg/ha DAP, 42 units Big N (28th April)

2003 - 25th July, 40 kg/ha Tilga, 70 kg/ha DAP (undersown with pasture)

TRIAL DESIGN:

This trial is based on a randomised block design with four treatments consisting of a nil and three lime rates (1.5, 3.0 and 4.5 t/ha) with two replicates.

Rainfall (2003)

RESULTS

Soil Test Summary:

Soil Test Summary: Incitec (May 2000)

YIELD AND ECONOMIC RESULTS:Table 1. Acid soil amelioration trial results 2000 to 2003

Table 2. Economic analysis of Acid soil amelioration trial results 2000 to 2003

DISCUSSION

This site was affected by rhizoctonia root rot in 2000. The root rot combined with a period of severe moisture stress in late September accounted for the poor yield in that year and may have reduced any potential responses to lime

The trial site was deep cultivated just prior to sowing in 2001. The yield results improved greatly in 2001, with trends toward higher yields with higher lime rates, however no significant responses to lime were recorded.

Yields were very low in 2002 due to drought conditions. However a significant yield response was recorded in the 4.5 t/ha lime treatment. Although, response to lime in the 1.5 t/ha and 3 t/ha treatments was still not apparent.

It has been suggested that the low magnesium (Mg) levels at this site maybe limited the response to increasing soil pH. A Mg level of 0.29 meq/100g is considered low, but not critical. Fenton and Conyers (2002) state that Mg deficiency has been recorded in seedling crops and pastures where there was less than 0.2 meq/100g exchangeable Mg in the top 10cm of soil. Mg deficiency is rare in established crops and pastures because the subsoil usually contains an ample supply of Mg which is accessed when the roots develop. In soils with low Mg, Dolomitic lime is often recommended over normal lime. No obvious Mg deficiency symptoms have been observed in this trial site.

Research from NSW Agriculture at Wagga Wagga and Condobolin has shown that in general lime applications do not provide significant yield responses unless the aluminium (Al) saturation % is >5% (Evans personal communication, 2004). Aluminium becomes toxic to plants at levels >5%. Since this soil has an Al saturation % of 1.6, it should not be expected that significant yield increases will occur with the use of lime.

The economic analysis indicates that the application of lime has not had any positive net benefit ($/ha). This economic result is expected as yield responses to lime have not been significant over the past 4 years, except in 2002 in the 4.5 t/ha treatment. As a result of this significant response in the 4.5 t/ha treatment the net benefit figure has moved towards the black

This trial site was sown to pasture in 2003. The pasture will be observed for signs of response to lime.

References

Fenton, G. and Conyers, M. (2002). Interpreting soil tests for calcium, magnesium and Ca:Mg ratios. Acid Soil Action. Leaflet No 7.

Acknowledgments

Graham Coombs (trial co-operator); Greg Gibson and Tim McNee (technical assistance); Sharon Taylor (statistical analysis); Catherine Evans (Editing); Central West Farming Systems, Grain Growers Association and GRDC (funding).