Deeper look at soil chemistry

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GroundCover™ Issue: 116 | 04 May 2015 | Author: Clarisa Collis

Western Australian grower Brad Jones examines the subsoil constraints to crop productivity exposed by soil pits on his property, about 184 kilometres east of Perth.

PHOTO: Evan Collis

Growers are increasingly complementing the expertise of agronomists with that of soil consultants to better understand how their soils function at depth

With a shared interest in soil health and its constraints to crop productivity, three growers discuss their efforts to deal more holistically with both topsoil and subsoil constraints on properties in the southern and western grains regions.

Soil consultant Michael Eyres, from Injekta Field Systems, examines the soil profile inside soil pits to help identify constraints to crop productivity in the topsoil and subsoil on growers’ properties across the country.

PHOTO: Clarisa Collis

Fine-tuning their nutrient-management tactics for different soil types, Pete and Mel Kitschke from South Australia, Brad and Kate Jones from Western Australia, and Leeton and Katrina Ryan from Victoria are applying a range of nutrients at low rates in a ‘prescription mix’.

Guiding this is soil and plant tissue analysis combined with firsthand insights into the composition and structure of variable soils by digging multiple soil pits on each different soil type.

Exposing the soil profile to a depth between 40 and 150 centimetres, the soil pits allow growers to observe the soils’ many layers (or horizons) and how they may influence the nutrient availability and moisture uptake needed for crop growth.

Encouraging the growers to excavate pits to help better understand how variables in the soil might influence potential and actual yields are soil consultants Michael Eyres and Ed Scott, from SA-based soils advisory company Injekta Field Systems.

Drawing on a preliminary assessment of different soil types gleaned from the soil pits, plus an additional soil structural stability assessment and plant tissue testing, Michael and Ed determine the nutrients required from the evident production constraints.

The nutrients applied mostly address ‘deficiencies and inefficiencies’ in regard to the many primary, secondary and trace elements needed for healthy crop (and root) growth.

Michael says “nutrient inefficiency” is not a familiar term in Australian cropping, yet can help growers better understand what they are dealing with: “You can measure and address a nutrient deficiency, such as copper, but there can be other factors stopping the element in the soil from efficiently responding in relation to plant uptake,” he says.

“For example, in Pete Kitschke’s case, when the soils on his property wet up they have a high potassium solution value – and potassium, in volume, can override the uptake of copper at critical points in a plant’s life cycle. It’s an example of how certain nutrients can interfere with other nutrients. So you need to understand your soil’s particular chemistry to ensure that nutrient deficiencies are treated effectively.”

Michael and Ed are also keen to dispel the notion of liquid versus granular fertilisers, saying liquids were not intended to replace granular products: “They are meant to be used to improve the efficiency of granular fertilisers – a point appreciated in other countries, but that seems to have been misunderstood here.”

In their work with growers in SA, Victoria and WA, Michael and Ed adjust the prescribed nutrient mixes from year to year depending on the findings of soil and plant tissue testing against the background of the previous season’s crop sequence, specific cultivars, grain yield and quality.

“It is often just subtle changes, but bear in mind that you only need a six to seven per cent lift in yields to double profitability in dryland cropping,” Michael says.

SA growers Pete and Mel Kitschke believe that bringing a soil consultancy into their farm business team seven years ago has helped lift the productivity of their grain crops by about 10 per cent, on average.

To achieve this, the Kitschkes have significantly changed their approach to nutrient management.

Liquid approach

In 2008, the couple, who crop 2300 hectares with Pete’s parents, Peter and Mary, 10 kilometres west of Jamestown, SA, implemented a liquid fertiliser system to complement their granular fertiliser applications.

In the same year, they also started using a much wider range of nutrients at low rates, combined with soil conditioners, in liquid and granular applications tailored to their variable soils, which include clay loams and red-brown soils.

This strategy complemented the family’s conventional nutrient regime that involved applying high rates of nitrogen and phosphorus as granular fertiliser.

Pete says that in the past three years the liquid nutrient blend containing specific trace elements to optimise soil performance has increased crop yields up to 15 per cent on their red-brown soils.

“Our new approach to nutrient management has helped to maximise the amount of soil available for the growth of each plant, increasing water use efficiency and, in turn, soil use efficiency.

“We’d previously spent 15 years trying to improve the top few inches of our soil,” Pete says. He says it was not until they started digging soil pits that they were able to identify, and subsequently address, their main constraint to crop productivity.

Examining the soils’ composition and structure inside 1.5-metre deep soil pits, they found that a dispersive layer of clay in the topsoil, as opposed to the subsoil, posed a barrier to grains productivity on 80 per cent of their soils.

Pete says the soil pits (now totalling 18 across the farm) have also allowed them to obtain horizontal, instead of vertical, soil samples.

Horizonal soil sampling has improved the accuracy of their soil testing because it has allowed them to analyse each layer or horizon of soil in isolation, he says. In contrast, standard soil sampling tends to mix the soil layers together, resulting in a skewed picture of a soil’s composition and characteristics.

The Kitschkes’ new knowledge of the topsoil constraints affecting their farm business profitability led to the use of liquid fertiliser applications. Applying nutrients as liquids means they can use them in-furrow to help correct issues with soil pH and electrical conductivity, and they can also be combined with fungicides for cereal crops and freeze-dried inoculants for legume crops.

Their liquid applications, which mostly include zinc, sulfur, calcium, copper, manganese and magnesium, are used in combination with granular fertiliser applications of nitrogen and phosphorus.

Pete says the transition to liquid applications saw them invest $20,000 in modifying their seeder, which they trialled for three years. Seeing gradual cost benefits over this time, they further invested in a new seeder equipped for applying both liquid and granular fertilisers.

He says the ability to use liquid and granular fertilisers is an important aspect of their nutrient program because it has allowed them to increase yields while spending roughly the same amount on inputs.

Their expenditure on liquid nutrient applications is about $25/ha. To offset this cost they have reduced their granular fertiliser rates by about 20 per cent.

On-farm trials

WA growers Brad and Kate Jones say applying a soil-specific blend of liquid nutrients for the past three years has increased the family’s overall farm business profitability by more than 10 per cent.

Brad says this profit lift is consistent with the 2012 findings of on-farm trials across 800ha of their 11,000ha property at Tammin, about 184km east of Perth, which led them to use liquid fertiliser applications across their entire cropping program in 2013. In 2013 and 2014, further trials showed that the liquid nutrient mix tailored to their variable subsoil constraints had increased wheat net margins by more than 20 per cent.

Brad says the increased profitability mostly stems from the wide range of nutrients applied at low rates, targeting specific subsoil constraints on each of their soil types.

In contrast with the Kitschke family’s approach, the Joneses are applying a different combination of nutrients on each of their soil types (whereas the Kitschkes are applying just one combination of nutrients to suit all their soil types).

Typically, the Jones family’s liquid applications contain nitrogen, phosphorus, potassium, sulfur, magnesium, copper, zinc, manganese, cobalt, molybdenum, boron and iron.

Brad says soil test analysis, including microbial DNA testing, following harvest each year has shown that the nutritional variety in their liquid applications has corrected a range of nutrient deficiencies.

The result, he says, is an overall improvement in soil health.

Meanwhile, regular plant tissue testing has shown that the nutritional variety in their fertiliser program has also provided a “more balanced diet” for their wheat, barley, canola, field peas and oaten hay.

Brad says that, together, the benefits in terms of improved soil and crop health have helped buffer their grains operation against seasonal risks and climate variability.

He says their crops now need to yield as little as 0.7 tonnes/ha for their farm business to break even, down from 1.3t/ha before they started applying the liquid nutrient mix to their entire crop area in 2013.

Another cost-benefit of the advice received from a soil consultant is that it has seen them switch to a liquid fertiliser system, which Brad estimates has improved the efficiency of their seeding operations by about 17 per cent.

He says it was “distribution issues” when applying low nutrient rates as granular fertiliser that led them to invest $20,000 in modifying their seeder bar to apply liquid fertilisers.

The hole truth

Victorian grower Leeton Ryan excavates a soil pit to help better understand constraints to grains productivity in the variable soils across his family’s property at Manangatang.

PHOTO: Clarisa Collis

For Victorian grower Leeton Ryan, who farms with his wife Katrina and his parents Kevin and Trudy, getting to know the soils across their 5500ha-property at Manangatang is part of a lifelong strategy to secure and optimise grains productivity.

“I plan to do this for the rest of my life, so I need to understand the soils that support our grains operation and start replacing the range of nutrients that decades of cropping have taken out,” Leeton says.

With this in mind, in 2010 Leeton excavated 18 soil pits representing each soil type on his family’s property to help shed light on the composition and structure of their soils at depth and how these factors influence crop growth.

“You don’t kick goals, unless you dig holes,” Leeton says of the soils pits that have helped the Ryans better understand specific subsoil constraints in consultation with Michael Eyres.

He says the 1.5m-deep soil pits allowed them to identify problems with moisture infiltrating at depth into the sandy loams over 80 per cent of their property as the main constraint to farm productivity.

Like the Kitschke and Jones families, this new insight has spurred the Ryans to address the issue with liquid applications containing a wider range of nutrients, plus soil conditioners and wetting agents.

To apply this “prescription mix”, the family invested $35,000 in a liquid fertiliser system, including a tank for use in paddocks.

Leeton says the cost-benefits of their outlay have shown in the overall improvement in their cropping performance. For the past three seasons, their wheat and barley have yielded up to 20 per cent more grain, he says.

Apart from adding to their farm business gross margins, the yield increase has also provided “insurance against seasonal risks”.

“Healthier soils have meant healthier crops that are able to use water more efficiently in dry seasonal conditions,” he says.

Testifying to their improved soil health, Leeton says regular soil and plant tissue testing has indicated that their liquid fertiliser mix has corrected all the nutrient deficiencies identified through early soil analysis, apart from magnesium.

In response to this finding, they have adjusted their nutrient formula to include higher rates of magnesium, but have continued to apply other major and minor nutrients at the same low rates to help maintain soil health.