Grains Research and Development

Date: 04.11.2013

Subsoil manuring drives up HRZ profits

Author: Deanna Lush

Subsoil manuring

Pros: 

  • crop yields are increased;
  • rainfall capture and use can be improved;
  • effects are long-lasting – four years or sometimes more; and
  • savings can be made on nitrogen fertiliser. 

Cons:

  • costs are high at more than $1000 per hectare;
  • access to manure from local sources can be variable;
  • freight can be costly if manure has to be transported great distances; and
  • specialised broadacre machinery is required for application.

While subsoil manuring has long been known to bolster crop yields, its hefty price tag has left many grain growers wondering how to make it pay and hesitant to seriously consider it over a large area.

But new GRDC-funded research has demonstrated the practice to be highly productive and profitable – in fact, potentially quite lucrative. Trials in Victoria’s high-rainfall zone (HRZ) show it can deliver a return on investment of $400 to $500 per hectare per year.

Subsoil manuring encourages deeper root development through incorporation of high rates of organic matter into the upper layers of clay subsoils.

These dense subsoils otherwise constrain crop yields throughout Victoria’s HRZ because tightly packed clay particles give very little pore space for air to move to roots or for water to infiltrate down the soil profile.

These soils are often waterlogged early and late in the growing season because roots cannot grow into the dense clay and are restricted to the upper layers of the profile. Plants can become water-stressed in dry finishes and yield only one-third of their potential.

The trial

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Research finds answers to yield-limiting subsoil: Deep placement of brown manure proves an effective treatment for heavy clay subsoils on this Victorian grain property.

A four-year trial was conducted by La Trobe University and the Victorian Department of Environment and Primary Industries (DEPI) at two sites – Penshurst and Derrinallum in Victoria – from 2009 to 2012.

The trial built on previous work by the university and Yaloak Estate, at Ballan in Victoria. Researchers had been investigating ways to overcome an impenetrable sodic clay layer 20 to 30 centimetres below the surface, which was constraining crop roots and yield potential.

They started deep-ripping to break open soils and then looked at placing different products at depth, such as coarse sand, high rates of gypsum, lucerne pellets and dynamic lifters as a high nitrogen source, and, finally, chicken manure. It was high in nutrients, readily available and became the centre of the four-year trial.

Victorian DEPI’s Dr Renick Peries from Geelong was part of the trial, which involved deep placement of poultry litter at two rates – 20 tonnes/ha and 10t/ha – as well as comparing this with a deep fertiliser treatment and a combination of fertiliser and manure. Manure was applied once in 2009 and the benefits measured in subsequent seasons.

Soil water in the top 100cm was tracked and major yield gains resulted from the soil’s improved ability to capture and store significantly greater volumes of water.

The technology

The manure was placed at depth by a machine Yaloak developed. It involved a six-metre bar and an air suction system to take manure from a trailer and deliver it via a series of hoses down into a ‘sowing’ boot, like an airseeder. It covers about 0.5ha per hour and is likely to be redeveloped to increase the speed.

The machine enabled the trial to evaluate the technology on a broadacre scale. Yaloak manured 100ha in February and March this year to conduct a commercial trial growing wheat and canola with results expected after harvest.

Yield gains

Yield increases in the trial ranged from 2 to 5t/ha in wheat and 1 to 2t/ha in canola, at the full manure application rate and where a successful crop was established (see Table 1).

“Yield gains were greater in years with a dry finish,” Dr Peries says. “This was attributed to the extra plant available water in the subsoil that could be extracted by crop plants.

“Measurements at one site found that plant available water in the 40 to 100cm subsoil layer more than doubled from 60 millimetres up to 138mm after subsoil manuring.

“This capture and deep storage of additional rainfall occurred in summer and early winter. Changes to soil physical properties led to improved infiltration and storage of soil water in manured plots, which means higher water use efficiency and summer fallow efficiency.”

Dr Peries says yield increases were smaller in wet springs, and were attributed mainly to extra nutrient supply from the manure.

“The benefits from subsoil manuring appear to be long-lasting because the manuring process was undertaken in 2009 but large yield increases in wheat and canola occurred in 2012 – the fourth successive crop.”

TABLE 1 Yield comparisons at Penhurst and Derrinallum from 2009–12 (t/ha)

Treatment
Penshurst Derrinallum Penshurst
Derrinallum
Penshurst
Derrinallum
Penshurst
Derrinallum
2009
wheat
2009
wheat
2010
canola
2010
N/A*
2011
wheat
2011
wheat
2012
canola
2012
canola
Commercial crop 4.8 5.0 0.8 N/A 6.8 5.0 2.3 6.3
Deep-ripped only 4.5 6.4 1.2 N/A 7.4 5.5 2.0 6.9
Subsoil manuring – 20t/ha 7.6 9.8 2.0 N/A 11.3 7.4 4.3 10.4
Inorganic only (DAP/urea) 6.0 7.1 1.3 N/A 7.7 7.3 1.9 7.9
Half inorganic/ half manure 5.7 8.8 1.2 N/A 6.8 7.1 3.2 8.8
 *Severe waterlogging at the Derrinallum site in 2010 gave inconclusive results.

Is it profitable?

The total estimated cost of manuring at the 20t/ha rate was $1345/ha at Penshurst and $1244/ha at Derrinallum (see Table 2).

These costs included purchase, freight, handling and labour for manure, which totalled $905/ha and $804/ha respectively. The balance was for machinery, operating and labour associated with its incorporation.

Despite the steep upfront costs, the size of yield response and its continuation over time proved the practice to be very profitable. 

Preliminary results show that at the 20t/ha rate, investment return exceeded $500/ha at Penshurst and $400/ha at Derrinallum each year for four years. This is an annuity that means the returns are in addition to the standard eight per cent per year investment return that would be expected from such an investment of capital.

It was slightly lower at Derrinallum because of waterlogging and crop failure in the second year after manuring.

Using the half rate of manure (10t/ha) halved the cost at both sites and reduced yields. But the operation was still profitable with an annual investment return of more than $300/ha at both sites.

Dr Peries says the trial has uncovered some answers but has also raised more questions, such as access to on-farm soil amendments and the ability to compost crop stubble on-farm, reliance on animal manures and the need to reduce upfront costs.

He says more research is needed on the optimum combinations of products and rates, the duration of the treatment, which land is best to treat and how to best incorporate the subsoil amendments.

TABLE 2 Yield increases versus the estimated extra costs and benefits from 20t/ha subsoil manuring
  Penshurst Derrinallum
2009
wheat
2010
canola
2011
wheat
2012
canola
2009
wheat
2010
canola
2011
wheat
2012
canola
Yield increase (t/ha) 2.8 1.2 4.5 2.0 4.8 0.0 2.4 4.1
Extra costs ($/ha) 1398 27 67 39 1310 0 43 64
Extra benefits ($/ha) 830 789 1184 1100 1359 66 715 1086
Net benefit ($/ha) –568 764 1201 1061 49 66 672 1022

More information:

Dr Renick Peries,
0419 576 811,
renick.peries@depi.vic.gov.au

Next:

Trials demonstrate manuring without the risk

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 Trial shows commercial hybrids deliver higher returns

GRDC Project Code ULA00008

Region South