Best practice liming

WHY IS THIS PROJECT IMPORTANT

Acid soils have long been a major constraint to crop and pasture production in northeast Victoria. The reacidification of previously limed soils and pH stratification are also becoming increasingly important issues for the region’s grain farmers.

This project aims to increase awareness of the speed of acidification and stratification of soils in the region, as well as the tools available to assist management decisions.

In short: This project addresses acid soil challenges in northeast Victoria by showcasing different liming practices in a field trial. It compares various treatments to inform economic and agronomic decisions, aiming to boost awareness and management strategies for improved soil health and crop productivity.

Background

Acidity levels in topsoil and sub-surface layers are increasing across the southern region of Australia and are a key constraint to productivity.

Applying lime to address increasing acidity is often the first input to be dropped when cash flow is limited due to its high cost. Additionally, the development of acidity can be masked where an acid throttle (a layer of low pH that restricts movement of nutrients and roots past it) exists in a stratified layer. This is often overlooked in lab analysis of 0-10 cm mixed soil samples. Often growers do not recognise the gradual decline in fertility and do not apply lime until the problem is already established.

With the low solubility of lime and its relative immobility, top-dressed lime can take ten or more years to significantly increase subsoil pH below 10 cm. Soils that have not been adequately maintained with lime applications, to counter the increasing rate of acidification, need a management solution to increase subsoil pH, as well as having a faster return on investment and increase in crop productivity.

The placement of the lime in the soil plays a significant role in the lime’s ability to neutralise acidity when it exists at depth due to the need to establish contact for the acid base reaction to occur. The quality of the lime is another factor contributing to its effectiveness in neutralising soil acidity, specifically its neutralising value.

Effective Neutralising Value (ENV) describes a chemical property of the lime based on its calcium carbonate equivalence (CCE) to neutralise acid, which can vary greatly between lime sources.  The lime’s fineness also has a significant impact on its ability to neutralise acid, with finer products having a higher surface area, and therefore greater contact with soil particles to improve its efficacy. A higher ENV  lime is generally more expensive, so ensuring maximum value from higher ENV lime through effective placement in the soils is of great significance to farmers.

Project focus

The project involves the establishment of a replicated lime treatment field trial at Lilliput, Victoria, to demonstrate best practice liming practices and how the incorporation of top-dressed lime can improve its distribution down the soil profile and lessen the impacts of soil acidity on subsequent crops.

The trial was established in early 2022 and is comparing the performance of subsequent crops under different treatments. The demonstration aims to show the difference between coarse and fine limes, as well as the impact of incorporation methods. Treatments include:

• Nil-lime
• Nil-lime with incorporation only
• Lime applied at 1.2t/ha
• Lime applied at 5t/ha deep incorporated
• Lime applied at 5t/ha shallow incorporation
• Lime applied at 8.5t/ha with deep incorporation (NB deep-incorporation was done using a Horsch Tiger and shallow-incorporation with a speed tiller).

These results will then be used to inform an economic analysis of the treatment options, while intensive soil sampling will also help to understand differences in nutrient availability, pH and soil organic carbon between treatments.

The project also involves a demonstration trial of the impact of different lime types and sources, including an elemental sulphur treatment to accelerate acidification and give an indication of the future effects if lime was not applied.

Project outcomes

Best practice liming to address sub-soil acidity

Aim

To demonstrate best practice liming strategies and a field demonstration of the impacts of lime quality.

Objectives

A replicated field trial was established to demonstrate best practice liming strategies, as well as a field demonstration to show the impacts of lime quality per annum, over two years. The site is demonstrating different incorporation methods, evaluating the impact of different lime types/sources, and extending findings, including comparisons of the economic and agronomic returns using the Acid Soils SA calculator tools.

Extension efforts are focused on raising grower awareness on the speed of acidification and stratification of soils in this region. 

It is pertinent for growers to evaluate the most practical and economical methods for managing soil pH and paddock variability in soil types. This forms part of the demonstration, where achieving the best overall benefit on variable soil types is being examined. ‘Nil’ treatments, where no lime is applied, are designed to showcase the cost of complacency toward addressing pH in the short and long term.

Is it hoped that by the end of the project in December 2023, growers and advisers in northeast Victoria will have an improved understanding of the state of topsoil and subsoil acidity, the limitations to crop profitability it causes, and finally, an improved knowledge of the agronomic and economic benefits of different lime sources, lime quality and incorporation methods.

Table 1 Treatments for the trial

Method

After consultation with a steering committee made up of growers and researchers, a number of treatments were agreed as provided in Table 1.

An intense soil sampling regime was completed in February 2022 across every replicate, to baseline and characterise the whole site, understand current pH levels, and ensure the proposed incorporation methods were appropriate. It was calculated that the rates of lime used would be:

• Lime to target pH 5.2 – 1.2 t/ha
• High rate to 5.8 – 5.0 t/ha
• High rate to depth – 8.5 t/ha

Lime was applied on 16 February 2022 ,with the incorporation completed on 17 February 2022. A Horcsh Tiger was used for the deep incorporation, with calibration to ensure that the depth of the lime was kept above 20cm. A speed tiller was run over both incorporated treatments to ensure a smooth surface for ease of sowing. Once the treatments were established, the host sowed and managed the trial site in line with management practices of the remainder of the paddock.

The site was sown to canola on 14 April 2022 with 70 kg/ha MAP. There was 250 kg/ha of urea applied and 100 kg of GranAm® (ammonium sulphate) during the season.

GreenSeeker measurements were taken on 21 July and on 2 August to assess differences in growth between plots. 

Harvest was not carried out by a plot header for the trial site, due to inundation of the site by water, which prevented collection of yield data. Despite significant waterlogging, the host farmer harvested the site with the remainder of the paddock.

Results

Early data suggests high rates of lime with incorporation is an effective tool to improve lime placement and ameliorate subsurface acidity, with pH results presented in Figure 2 . Aluminium and CEC were also measured but are not displayed.

Figure 2a pH results for nil applied lime with no incorporation treatment

Figure 2b Nil applied lime with shallow disc incorporation

Figure 2c 1.2 t/ha lime with incorporation by sowing

Figure 2d 5 t/ha applied lime with incorporation by sowing

Figure 2e 5 t/ha applied lime with incorporation by shallow disc

Figure 2f 5 t/ha applied lime with deep incorporation 

Figure 2g 8.5 t/ha applied lime with deep incorporation 

Slugs caused significant damage to the whole paddock in 2022, despite the site being baited twice. Anecdotally, it appeared that plots that had incorporation and lime treatments were less affected by slug damage, and damage was higher where lime wasn’t incorporated. This however, was not able to be quantified. Figure 3 shows the poor and patchy emergence of one of the plots following slug attack.

Figure 3 Slug damage at the Lilliput site.

The region experienced a large rainfall event in January, with the site receiving around 150 mm. There was a total of 1150mm for the year and 538mm GSR (growing season rainfall, May-Oct). October had a large rainfall event, which caused the canola to lodge in patches, or die.

Due to the condition of the crop, harvest was not able to be carried out by a plot header for the trial site, which disappointingly, resulted in no trial yield data (Figure 4). Despite the crop being black and on the ground, the host farmer harvested the site with the remainder of the paddock.

Figure 4 Trial site in mid-October, 2022, showing areas of poorly established, lodged or rotting canola.

Discussion

Riverine Plains hosted a paddock walk shortly after soil amelioration had been completed. A dig stick and visual observation were used to confirm that the incorporated lime had moved to the required depths.

The areas eaten by slugs were re-sown in an attempt to improve crop cover and trial uniformity, mimicking local grower practice for patchy establishment/slug damage. Re-sown sections were able to compensate for the poor establishment later in the season.

Due to the site experiencing extensive waterlogging there were concerns waterlogging effects would confound trial results, and that the effects from amelioration treatments may not be able to be inferred from yield and soil test results. However, preliminary analysis of the soil test results in 2023,  indicated treatment effects were present, despite waterlogging of the site.

Acknowledgements

This research trial is funded by Grains Research and Development Corporation (GRDC). The authors would like to thank the Spence family for hosting the site. We would like to thank AgriSci Pty Ltd for assisting in the data collection and maintenance of the site.

Authors: Jane McInnes, Riverine Plains; Dr Cassandra Schefe, AgriSci Pty Ltd.