Key points

• Know what is happening to depth in the soil
• Grow varieties adapted to soil type and landscape
• Deep placement of ameliorants has the potential to improve yield and revenue in dry seasons

A financial review shows improved returns may be available for grain growers with sodic dispersive subsoils.

The approaches reviewed included growing varieties known to yield better in subsoils confirmed to be sodic and dispersive, and ameliorating these subsoils with various amendments.

The review, by consultants Peter and Hazel McInerney of 3D-Ag based at Wagga Wagga, New South Wales, explored the returns likely to be generated by growing Scepter, and ameliorating the subsoil with either organic amendments alone or organic amendments with gypsum and additional nutrients.

It uses costs likely to be charged for the hire of a machine capable of placing ameliorants to a depth of 30 to 40 centimetres. This machinery is currently under development by a grower in southern NSW and his commercial engineering partner.

Variety comparison

From 2015 to 2017, NSW Department of Primary Industries (DPI) researcher Dr Ehsan Tavakkoli led a variety screening trial at Rand, NSW, with GRDC co-investment.

Mr McInerney says the trial showed spectacular results, with Mace averaging 5.5 tonnes a hectare over the three years – almost 0.7t/ha more than other varieties in the trial.

“In 2018, Australian Grain Technologies donated one tonne of Scepter, a variety that is genetically similar to Mace, for the collaborating grower to try as a comparison. One tonne of Beckom was bought to include in the comparison,” he says.

“Both varieties performed well and were incorporated into the farm program in 2019. In the dry 2019 season, Scepter was harvested, while Beckom was ‘salvaged’ as silage and hay.”

Given the season in 2019, Mr McInerney says, both varieties were successful in producing revenue for the growers’ business, with Scepter returning $1078/ha and Beckom returning $1077/ha, after deducting contracting costs for silage and hay-making, and the estimated loss of nutrients by product removal.

“In 2020, both varieties did well, although Scepter returned $1838/ha and was clearly more profitable than Beckom, which returned $1593/ha,” he says. “While Scepter outperformed Beckom at this site, Beckom is still an excellent variety.”

Mr McInerney says making the most of available information, plus small-scale on-farm comparative trials to identify superior varieties, is an obvious and low-cost means of optimising productive potential and profit.

Amelioration comparison

From 2017 to 2020, the site at Rand, NSW, hosted subsoil amelioration experiments. The experiments were led by NSW DPI’s Dr Tavakkoli, with GRDC co-investment.

Dr Tavakkoli’s experiments showed placing organic and inorganic treatments into the subsoil improved the chemical and physical properties of hostile subsoils, which increased grain yields by 20 to 53 per cent over four successive years.

Out of the 12 different amendments explored in the research, Peter and Hazel McInerney reviewed five treatments:

• Treatment 1: Deep pea straw plus gypsum plus nitrogen, phosphorus and potassium;
• Treatment 2: Deep ripping;
• Treatment 3: Deep placement of pelletised wheat straw;
• Treatment 4: Deep placement of gypsum; and
• Treatment 5: Deep placement of pea straw.

In viewing the data, Mr McInerney says, consideration needs to be given to crop type and seasonal conditions.

“In terms of rainfall, 2017 was a decile five or median year, 2018 and 2019 were both decile one years – or in the lowest 10 per cent of annual rainfall records for Walbundrie since 1880 – while 2020 was a decile seven year,” he says.

“Figure 1 shows the percentage yield change from the control treatment in 2017 through to 2020. Figure 2 shows the dollar per hectare impact over the same sequence of years and crops. The prices are those the grower actually received in the year concerned.”

Figure 1: Percentage of grain yield change of each treatment.

Notes: Treatment 1 = Deep pea straw plus gypsum plus nitrogen, phosphorus and potassium; Treatment 2 = Deep ripping; Treatment 3 = Deep placement of pelletised wheat straw; Treatment 4 = Deep placement of gypsum; and Treatment 5 =  Deep placement of pea straw. Source: Peter and Hazel McInerney, 3D Ag, 2021.

Analysis results

Of note among the research outcomes, Mr McInerney says, are strong positive yield responses (see Figure 1) in decile one seasons (2018 and 2019), which ultimately translates to an enormous financial benefit to a farm business’s bottom line (see Figure 2).

Figure 2: The financial impact of each treatment.

Notes: Treatment 1 = Deep pea straw plus gypsum plus nitrogen, phosphorus and potassium; Treatment 2 = Deep ripping; Treatment 3 = Deep placement of pelletised wheat straw; Treatment 4 = Deep placement of gypsum; and Treatment 5 =  Deep placement of pea straw. Source: Peter and Hazel McInerney, 3D Ag, 2021.

Treatment 1

“Deep straw plus gypsum plus nitrogen, phosphorus and potassium, showed outstanding results in the first three years of the trial and a solid performance in the high-yielding decile seven year of 2020,” he says.

“Although this treatment ranked the best on a dollar basis, these results may not be easy to replicate on a commercial basis.”

Treatment 2

Mr McInerney says deep ripping was included in the review because it is still practiced by some growers, although most evidence points to it being ineffective in sodic soils.

“It does, however, still have a place in removing compaction, which highlights the need to ensure a thorough understanding of the physical and chemical properties of a soil to depth, before deciding on a course of remediation,” he says.

“At the sodic Rand site, deep ripping showed a negative response in the first two seasons and every dollar lost hurts the bottom line, particularly in a tough decile one season such as 2018. Accordingly, deep ripping ranked last of the five treatments reviewed.”

Treatment 3

When it comes to deep placement of pelletised wheat straw, Mr McInerney says this ameliorant has potential.

“In Figure 2, this treatment shows the dollar/ha trend line increasing in each of the four seasons of data available, however, overall, it is ranked fourth of the five treatments.”

Treatment 4

Mr McInerney says deep-placed gypsum is included in the analysis because it is commercially available and is used successfully in surface amelioration, in appropriate soil types.

“At the Rand site the deep gypsum produced good yield increases, at least initially,” he says. “It is ranked third out of the five treatments.”

Treatment 5

Deep placed pea straw ranked second and while peas are not grown on all farms, Mr McInerney says other pulse crop residue may be substituted.

“For example, in the case of the grower collaborator, faba bean stubble is likely to be used,” he says. “Pellets of pulse residue, as with cereal stubble, are promising by virtue of their availability and relative simplicity to prepare and use.”

Financial impacts

Table 1 shows four years of yield data from the NSW DPI trial at Rand, derived by averaging the results of four replicates. The financial outcomes (price per tonne) are based on the grain price achieved by the cooperating grower for the year concerned.

Table 1: Yield and grain prices over the four years of the trial.

Source: Peter and Hazel McInerney, 3D Ag, 2021.

Mr McInerney says calculations based on the information in Table 1 show that in the decile one season of 2018, Treatment 1 yielded 53 per cent higher than the control treatment.

“In dollars, this means the control treatment generated $616/ha, while Treatment 1 generated $948/ha,” he says.

“For such a severe drought year, many would consider $616/ha to be a good result; however, $948/ha is a profit worthy of any year.”

Mr McInerney says resilience to drought is something most growers are trying to achieve, and this work shows some promising results.

“While the revenue increases look promising, the cost of achieving them can be significant and growers with sodic soil should undertake on-farm investigations and trial work before committing their whole program.”

He says this is because the costs associated with implementing Treatment 1 include:

• about $250/ha to contract the machine developed by the cooperating grower and his engineer colleague for deep placement of ameliorants;
• $50/t to produce pelletised straw. At a rate of 10t/ha, the cost is about $700/ha; and
• about $200/ha to add gypsum, nitrogen, phosphorus and potassium.

Mr McInerney says if the pelletised material is harvest residue from the same paddock, then all that is happening is that the residue is being used in a more effective way, and the opportunity cost is zero.

Modelled results

To determine what might happen at the farm scale, Mr McInerney says the paddock adjacent to the trial site was used to model two treatments from the trial: Treatment 1 and Treatment 5, using the growers’ actual rotation.

“The growers’ actual yields for the paddock are considered as the ‘control’, then using the percentage increase achieved by the respective treatment and relevant year in the trial, the ‘new’ yield potential is generated,” he says. “The grain prices used are the actual prices achieved by the grower.”

For Treatment 1, he says the modelled revenue showed a positive return to the grower and a cumulative additional revenue stream of $1663 over four years, with outstanding results in 2018 and 2019, which were the driest years.

“The cost of blending and applying pea straw, gypsum and additional nitrogen, phosphorus and potassium would be about $900/ha, producing a net benefit of $770 over the four years,” he says. “However, it is unclear how easily this treatment could be undertaken and additional equipment and/or time might add to the cost.”

For Treatment 5, he says deep placement of pelletised straw alone should be easier to apply.

“This treatment produced a cumulative benefit of $1207 over the four years,” he says. “The projected cost is about $700/ha, producing a gross surplus of $507/ha.”

While only four years of trial data have been collected, Mr McInerney expects yield benefits to continue for several years into the future, making deep soil amelioration financially viable on responsive soils.

Mr McInerney said Dr Tavakkoli was continuing his research at Rand and Grogan to better establish the financial longevity of the deep placed amendments.

More information: Peter McInerney, 0428 317 746, peter@3D-Ag.com.au