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Built For This Country

Built For This Country
Cropping into kikuyu maintains soil carbon

Nuts and bolts

  • Perennial pastures increase soil carbon because they are deep rooted and fibrous systems
  • They utilise summer rainfall to extend the green feed season and stabilise top soil to reduce erosion
  • Cropping into kikuyu pasture allows diversification of income by providing a profitable cash crop which:
    • maintains soil carbon storage
    • improves pasture productively by reinvigorating the kikuyu
    • provides additional grazing opportunity of stubble
  • Cropping into kikuyu gives farmers the ability to be opportunistic and make farming systems more robust against future climate variability.

Ken and Jan Reddington obtained a conditional purchase block in the early 1970’s on the South Coast of WA. Over the past 40 years Ken and Jan have developed the property Malamerup into a productive farm, which they now operate with their son Paul and his wife Alice. They focus mainly on grazing, running sheep for prime lamb production and super fine merino wool, as well as cattle for beef.

As they began to develop the farm, the Reddington’s realised the region’s regular strong winds had the potential to cause significant soil erosion on the property. Approximately 25 per cent of the South Coast region is at high to extreme risk of wind erosion (D. van Gool et al. 2008). Furthermore, a recent study analysing wind erosion data from the 1980s estimates that wind erosion can lead to the loss of approximately three per cent of soil carbon stock in the top 1m of soil  each year (Harper et al.  2009).

To prevent wind erosion, farms should aim for 50 precent ground cover all year round by non-erodible material (gravel, stubble or pasture residue) (Evergraze, 2013). This prompted the Reddingtons to look at various options to stabilise the top soil. The ones available included the adoption of no till practice, land use change, use of tree belts or planting a hardy deep rooted perennial pasture. Eventually a solution was discovered that not only stopped wind erosion, but had a production benefit as well.

 “On the south coast we get out of season rain events, “ Ken Reddington said. ”Probably 25 to 30 percent of our rain is in summer. We get strong wind events too and found that sheep would camp in one area and water in another all leading to “a perfect storm” condition; - if a paddock could blow, it did blow. “ he said.

“We looked at different options to stabilise the top soil. The perennial pasture kikuyu was the one we chose because it was virtually bullet proof. It stabilised the soil and responded to those summer rain events, we got good quality green feed off it and ended the problem of blow.”

Benefits of kikuyu

The suitability and benefits of kikuyu have resulted in many positives for the Reddington’s livestock production and the sustainability of their land.

 “Now that we have kikuyu planted the late summer autumn period is not as stressful as it used to be,” Ken said.

“I would be on tenterhooks wondering when the break of the season was coming and would lose top cover, and my feed before the break arrived, so I would have vulnerable paddocks, and have to lock the stock up and feed lot them.”

“At the moment we know we have cover on the paddocks and we can push them pretty hard without risking wind blow.”

 “In the late summer and autumn you wouldn’t have anything else. I love kikuyu then, especially the way it responds to summer rain. If we get a thunderstorm it becomes electric green, it really bounces out of the ground and you’ll have an inch of kikuyu virtually overnight.  It’s amazing how it responds to summer rain. It’s built for this country or this country’s built for it.”

Benefits of periodically cropping into kikuyu

Although kikuyu proved a great benefit to the farming system, some management issues were discovered which needed addressing, particularly after the kikuyu had been established for around 20 years.

The kikuyu had done an excellent job at stabilising the Reddington’s paddocks and taking advantage of summer rainfall when it occurred. However, in the older paddocks the kikuyu wasn’t growing with such vigour and it was becoming more of a proposition for sheep than cattle.  “The kikuyu had become very dominant and started to choke out certain annual species, especially when they had false breaks the clover would really struggle.” Paul Reddington said.

Ken and Paul noticed that anywhere they had worked or “tickled up” the kikuyu it really responded well.

Paul had the idea of cropping canola into the kikuyu for one to two years.

“Canola has a large tap root so by cropping canola they could use the tap root as a soil aerator as well as using the crop to knock the kikuyu back. It also provided the ability to get a cash flow off it at the same time as controlling the kikuyu.”

By growing kikuyu, the Reddingtons now have a reliable source of feed for their livestock, are able to utilise out of season rainfall, have the ability to grow a cash crop if the conditions are favourable and most importantly, have confidence their paddocks will remain stable throughout the year.

Perennials pasture and soil carbon

Perennial pastures are generally expected to store more soil carbon than annual pasture due to their extensive root system which persists all year round. Soil carbon plays a pivotal role in contributing to the physical, chemical and biological processes of soils and is essential for having a healthy soil. The Reddingtons were interested to see if the soil carbon had increased in the paddocks planted to kikuyu and also if cropping into the kikuyu effected soil carbon stores. South Coast NRM in conjunction with the University of Western Australia conducted research on the Reddingtons farm to find answered to find out more.

Below is a summary of the research trial undertaken on Malamerup.

Trial Aim

To investigate:

  1. soil carbon stores under kikuyu grazing systems compared with an annual grazing system; and
  2. how cropping into a kikuyu pasture affects soil carbon.

What we did

Compared total soil carbon under different farming systems within the same farm:

  1. Annual grazing system
  2. Kikuyu grazing system (15 years)
  3. Crop converted from kikuyu paddock (15 years)

How we did it

Through soil testing that was consistent with the CSIRO’s Soil Carbon Research Program (SCRP) methodology. Randomly distributed 25x25m quadrats were used to sample the soil profile from 0 to 30cm to measure total soil carbon.

What we found

Mean of total carbon

Figure 1. Mean of total carbon (0-30cm) in different farming systems relating to the different types of carbon.

  • Total soil carbon is higher in kikuyu grazing system compared to annual grazing systems.

Cropping for up to two years into a kikuyu grazing system doesn’t change the total soil

Since cropping into the kikuyu we have noticed it comes back looking healthier, more invigorated and with increased production. Incorporating kikuyu into our farming enterprise has been a life saver.” Paul Reddington, Bremer Bay, WA

  • carbon.

Soil carbon fast facts:

  • Provides energy for biological processes for nutrient cycling.
  • Enhances water holding capacity.
  • Improves soil structure and stability through binding soil particles into aggregates.
  • There are three fractions of soil carbon.
    • Particulate carbon is carbon from initial decomposed product of organic matter which includes the plant and root residue.
    • Humus is from decomposition of particulate carbon and is the final product of decaying process.
    • Resistant carbon is a stable form of carbon that is long lived in the soil and cannot be affected by management practices.

Although it hasn’t been an issue on Reddington’s farm in some circumstances kikuyu can overwhelm native plants, particularly around creek lines. Care should be taken to manage kikuyu in these circumstances to maintain the environmental and production benefits that these habitats provide.

Farmer Profile

Name: Ken and Jan Reddington farm with son Paul and his wife Alice Reddington
Location: Bremer Bay
Average Annual Rainfall: 520 mm
Enterprise mix: 80 per cent livestock (sheep and cattle) 20 per cent cropping
Property size: 2000 hectares
Soil Type: Sandy duplex (non wetting)

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