SpeedChisel

Recent thinking now calls for far greater incorporation of lime applications into the subsoil in order for growing crops to reap the benefits that lime offers. Especially in the case where widespread adoption of minimum-till farming has led to pH stratification in high-rainfall zones.

Research has shown that farmers who are simply applying lime to the soil’s surface and hoping it dissolves down into the soil could be missing a trick as the soil subsurface does not always have access to the applied lime. And even when farmers use a Speedtiller^® to incorporate lime beyond the surface, they are only mixing it down to a depth of around 125mm. With soils now showing an acid throttle of approximately 150mm, it has now become apparent that there is the need to work the lime deeper into the subsurface to 250mm to really benefit the roots that grow to these depths.

Getting to the root of acid issues

If farmers are only testing the acid levels of surface soils, or the subsurface to a depth of 100mm, they are not getting an accurate indication of the conditions which seedling roots are experiencing. Helen Burns, DPI Development Officer-Pastures, based at the Wagga Wagga Agricultural Institute, is a scientist who has been studying the issue for several years, in particular on the root development of acid-sensitive pulses. She is an advocate for strategic tillage to help address the issue of acid soils. The research project she has been working on is showing that the applied lime to the soil’s surface may not be working as effectively as farmers think it is. This is because traditional zero to 100mm soil tests to check pH levels and guide lime requirements has been the accepted norm, however, Ms Burns points out that as farming practices have changed so much over many decades, farmers should be testing pH levels at deeper depths.

“The guidelines currently used for liming programs were developed at a time when traditional cultivation incorporated the lime to a depth of about ten cm,” she said. “It’s time to review liming programs, as not only have tillage practices changed, but we are also using more nitrogen fertiliser and exporting more product, which in combination, result in higher rates of acidification and pH stratification. There is elevated pH on the surface, and if you take a nought to ten cm soil test a pH (CaCl) of 5.2, for example, appears to be suitable for the acid-sensitive pulses. But when we sampled at five cm intervals, in this case, we found we have the lime concentrated in the shallow surface layer (pH of 6.0) with a drop down to an acid pH of 4.4 at the five to ten cm levels.”

Ms Burns continues, “Our recommendation is if you are wanting a rapid solution in cropping paddocks, you really should be incorporating the lime into the acidic subsurface because lime moves very slowly. Also, from the results so far, perhaps the rates we are using are not high enough to counter acidification rates of our current production systems.”

The research also highlighted the lack of comprehensive paddock records needed to capture change in pH within the subsurface 50mm to 200mm layers or the effectiveness of lime applied over the past two decades.

“It is a ‘wake-up’ call,” Ms Burns concludes. “Farmers don’t have adequate records, even though some are now on their second or third lime application, but nobody has been doing a sequence of soil tests actually monitoring how their lime programs have been working.”

The research recommended, where the subsurface is too acidic, to apply adequate rates of fine-grade, high-quality lime and preferably incorporate the lime deeper into the soil subsurface where it is also needed at least 12 months before sowing.

Identifying the need to go deeper

To help address the significant issue of subsoil acidity, K-Line Ag has been developing a new machine that is ideal for deeper tillage applications, such as incorporating lime to greater depths, as it combines a Chisel disc and a Speedtiller^®. Introducing the SpeedChisel which has just been released by K-Line Ag after rigorous testing to ensure it does the job right the first time.

To be one of the first to find out more about K-Line Ag’s new SpeedChisel machine, please contact your nearest local dealer. They are ready and waiting to talk to you about all the benefits of our newest addition to the K-Line family of Australian designed and made equipment, with the needs of Australian farmers in mind.

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Crop stubble is defined as “the straw and crown of plants left on the soil surface after harvest. Stubble also includes straw and chaff discharged from the harvester (header). It is also known as ‘residue’ or ‘trash’.”

In surface-retained and standing stubble systems, wetter-than-usual conditions are conducive to an increase in residue production. With nitrogen and water required to break down the crop stubble and residue, this can tie up much of the available nitrogen in the soil.

The result is that incoming crops may be starved of the nutrient support required to achieve optimal growth.

Riverine Plains Inc.’s Stubble Management Guidelines No.3 document ^[1] says “nitrogen tie-up” is directly related to stubble retention due to a temporary nitrogen lag during early crop growth stages, as microbes ‘borrow’ soil nitrogen to break down the stubble from the previous crop. “This may leave the current crop short on available nitrogen during the initial stages of plant growth if adequate fertiliser nitrogen is not supplied.”

Figures from the Grains Research and Development Corporation ^[2] back this up. Field trials conducted over many years indicate that without direct action to address nitrogen tie-up, wheat yields may be impacted by up to 0.3t/ha to 0.4t/ha.

A proactive, two-pronged strategy

It’s a clear and present danger in the wake of one of the wettest Spring seasons on record in many regions. But a proactive strategy can help to maintain soil viability and mitigate many of the adverse impacts of nitrogen depletion.

The first action in a two-pronged approach is to incorporate and size up the stubble, to speed up its breakdown. When done at the earliest opportunity, this allows the stubble to move from immobilisation to mineralisation before the next crop is sown.

The key is to utilise tillage machinery that’s designed to manage heavy loads at fast pace, with excellent incorporation ability.

A good example is K-Line’s Speedtiller^®, a high-performing, dual purpose disc-tillage machine. Because it’s able to penetrate the soil at the ideal depth, it promotes better incorporation by chopping up the residue and feeding it back into the soil where it is more easily broken down.

Another benefit of the Speedtiller^® is that it lifts the soil to reduce compaction, and simultaneously levels the field, leaving a well-prepared seedbed in just one pass.

Its heavy-duty construction, built-for-Australia engineering and no-nonsense operation makes the Speedtiller^® the ideal tool to take advantage of the shorter windows of opportunity in volatile weather conditions.

The result is that the incoming above-ground crop has access to the nutrients it needs to thrive – sunlight energy (carbon), water and warm temperatures. Below the ground, crop roots and microbes continue to feed on the available nitrogen and carbon stored in the soil, rather than immobilising the nitrogen to help break down stubble residue.

From tie-up to top-up

However, maintaining the appropriate nitrogen content in soil can still be an issue. It’s now conventional wisdom that retention of crop residue is superior to burning stubble, because it helps to prevent soil erosion and retain moisture in the soil, in addition to averting air pollution.

Agriculture Victoria’s discussion paper Managing Stubble ^[3] says that during the last 25 years, conservation farming has continued to evolve.

“There is now less burning, less soil cultivation and increased retention of crop stubble. This trend has been driven by the need to maximise water use and protect soils from erosion, in an era of increasing climate variability.”

One upside of burning residue was that the practice could leave significant nitrogen stored in the topsoil ready to assist the incoming crop. Instead, retaining stubble risks depleting that precious store and requires careful management and compensatory measures.

Studies undertaken by the GRDC suggest that nitrogen tie-up is more likely to occur in-season, rather than during the summer fallow, meaning that waning nitrogen levels may not be picked up in pre-sowing soil mineral measurements.

“Yield penalties for retained residues were significant, but confined to successive cereal crops, and could be reduced by reducing the stubble load or by applying more nitrogen ( approximately 5kg nitrogen per t/ha of cereal residue) and applying it earlier to the following crop,” the GRDC says in its 2018 paper, The effects of stubble on nitrogen tie-up and supply ^[2].

“Deep placement of the nitrogen improved nitrogen capture by crops irrespective of stubble management, but was especially effective in stubble-retained situations.”

Therefore, the second recommended angle of attack for combatting nitrogen tie-up is to have a good, heavy-duty spreader at the ready, for efficient dispersal of nitrogen fertiliser.

This could take place during incorporation, to feed the sub-soil microbial growth and speed up its turnover, freeing more nitrogen for uptake by the incoming crop. More nitrogen can be added at sowing, and can be deep-banded to separate the nitrogen from the higher microbe population in the surface soil, to give the crop an advantage.

This dual approach can help overcome the impacts of nitrogen tie-up, the GRDC says. “In summary, nitrogen tie-up is an easily managed issue for growers with suitable attention to the management of stubble and nitrogen fertiliser.”