The application of lime and gypsum to a sodic soil significantly has increased yields in the 3 years prior to 2003 (ie. 2000, 2001 & 2002).
Severe drought conditions in 2003 saw a reverse trend of the untreated plot yielding significantly higher any lime or gypsum treatments.

Background

Long-term soil amelioration trial sites have been established at the Gunning Gap CWFS regional sites. These long-term sites are being monitored over five years. Below is a summary of the first 4 years' results at the sodic soil site.

METHODS

Location: Gunning Gap

Cooperator: Mark Judson

TRIAL HISTORY:

Date spread: 16 May 2000 (treatment rates, commencement of trial)

20 March 2002 (3.5 t/ha lime on the Albrecht plots)

Lime and Gypsum source: Bagged agricultural lime and gypsum

Sowing: 2000 - 2nd June, 45 kg/ha Janz, 85 kg/ha DAP

2001 - 17th May, 25 kg/ha Tilga, 85 kg/ha DAP

2002 - 29th June, 50 kg/ha Tilga, 85 kg/ha DAP

2003 - 19th July, 50 kg/ha Tilga, 75 kg/ha DAP

TRIAL DESIGN:

This trial is based on a randomised block design with six treatments consisting of one nil treatment, four lime rates (2 t/ha, Albrecht recommendation, 6 t/ha & 8 t/ha) and one gypsum treatment (4 t/ha). The Albrecht plot was treated with 4t/ha of lime in 2000 and 3.5t/ha of lime in 2002 (as per the Albrecht recommendation). The treatments are replicated twice.

Rainfall 2003

RESULTS

Soil Test Summary:

YIELD AND ECONOMIC RESULTS:

Table 1. Sodic soil amelioration trial results 2000 to 2003

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

DISCUSSION

Soil Test Comments

Soil samples were collected at the beginning of the trial in May 2000. The sample was split, with half being sent to the Incitec soil lab and the other half being sent to the Perry soil lab (USA) for a full Albrecht analysis and interpretation.

The Albrecht interpretation stated that very low calcium (Ca) and excess magnesium (Mg) were the major limiting factors, with a total lime deficiency of 10.8 t/ha. As a result, the Albrecht interpretation recommended that lime at a rate of 4 t/ha be applied in the first year (2000) and then re-tested to fine tune further lime applications. 3 kg/ha of zinc sulphate was also included in the Albrecht recommendation. The zinc (Zn) sulphate was not applied and no Zn deficiency symptoms appeared in the crop at any stage. Extensive Zn trials in the NSW CW district have not shown convincing responses to Zn fertiliser in wheat.

The Albrecht plot was retested in the second year (2001) as recommended and sent to the Perry soil lab (USA) for another full Albrecht analysis and interpretation. The second interpretation following the 4t/ha lime application stated excessive Mg and Na, and very low Ca were still the major limiting factors, with a total lime deficiency of 3.5t/ha. As a result in 2002, 3.5 t/ha of lime was added to the 4 t/ha lime treatments as recommended by the Albrecht interpretation.

A fourth soil test was conducted in May 2003 on the Albrecht plot and sent to the Incitec Pivot soil lab. Top soil and sub soil samples were taken. The results from this test suggested that the lime was having the desired effect of reducing exchangeable Na (ie sodicity) and increasing the Ca:Mg ratio. However, these test results highlighted that the sub soil was still very sodic (13.9% exch. Na).

Yield and Economic Response Comments The lime and gypsum treatments provided significant yield advantages in 2001 and 2002. No yield effect was seen in 2000. It is thought that the late application of lime and gypsum in 2000 (ie only 2 weeks before sowing) was responsible for the lack of response in that year, with ameliorants needing more time to react in the soil. Visually, the gypsum treatment has looked the best treatment. It was the highest yield plot in both 2001 and 2002. The effect of the gypsum on the soil can be visually seen, as attested by those who have attended the Gunning Gap Regional Site field days in recent years.

Severe drought conditions in 2003 resulted in yield penalties with all lime and gypsum treatments. Grain protein levels of over 19% in some plots indicate that moisture stress was severe during the grain fill period. Protein levels in the high rates of lime treatments (ie 6 and 8t/ha) were significantly higher than the nil treatment.

It is thought that the lime and gypsum treatments encouraged better plant root and foliage growth during the winter and early spring. Severe conditions in September, made these plots more susceptible to moisture stress and "haying off".

An economic analysis shows that only the 2 t/ha of lime treatment has repaid the cost of soil amelioration treatment. However, this economic analysis has been greatly influenced by the low yields received during the 2002 and 2003 seasons. Continuation of the trial over the next year will provide further economic and yield response data.

Please note a mistake was made in last year's results. The cost of the extra 3.5t/ha lime on the Albrecht plot was incorrectly added to the 4t/ha Gypsum treatment. Table 1 and 2 above represent the correct economic figures.

Acknowledgments

Mark Judson (Trial Cooperator); Greg Gibson and Tim McNee (Technical Assistance); Sharon Taylor and Helen Nicol (Statistical Analysis); Catherine Evans (Editing); Central West Farming Systems, Grain Growers Association and GRDC (Funding).