Soil Systems Farm

Organic weed control

Weed management in organic pastures is one of the biggest challenges facing farmers today. Whether it be hay, broadacre livestock or dairy production, the decision to invest time or money into strategies can significantly turn your business around. Here are some thoughts on how to approach this challenge during difficult financial times that may have other benefits like increased production and increased water use efficiencies.

 

Broadacre livestock with native pastures – outcompeting the weeds with good grazing
 on a low budget

Whether you are a small or large producer, the key to increasing cash flow is converting dry matter (or feed quality) into kilos of meat. For example, depending on the land you have, 6-10kg Dry Matter (DM) produces 1kg beef. Your target should therefore be to produce as much high quality feed (DM) as possible. If your farm is primarily made up of native species, grazing management will play the most important role in increasing profitability and reducing weeds. Over grazing will lead to reduced pasture root systems, pasture dieback and the creeping in of unwanted weeds (especially woody weeds over time). Carefully monitored grazing (like cell grazing) leads to larger pasture roots, better infiltration rates, soil carbon buildup, even development of the pasture, less weeds due to crowding out by healthy pastures and reduced costs of production – hence increased profitability. When finances are tight and the banks are pressing for payments, the tendency is to always put a few more stock on the property. Try to resist this as it will lead to more weeds and heartache. Instead, take some time out and plan a new grazing strategy.

In the photo below (Photo 1) I have captured the stark difference between a good cell grazing farmer and a set grazing farmer in Uralla, NSW. Note the even colour, lack of weeds and body of feed on the RHS due to cell grazing. Nutrients from the manures are evenly spread compared to set grazing (in this case overgrazed) where nutrients tend to concentrate at the top of hills in sheep camps and bare patches with weeds can be seen. These sheep camps over time tend to get weedy. The only short term solution is sowing down the sheep camp to an introduced pasture, manual removal or use kikuyu cuttings. I have used kikuyu successfully on sheep camps in the high country, Victoria. This cell grazing farmer was very innovative indeed. Not only did he increase his carrying capacity in his superfine flock from 1 to 4 sheep per acre using cell grazing but he also managed to use cell grazing to completely stop gully erosion in a fenced off gully. The periodic grazing returns valuable carbon to the soil and builds up valuable feeder roots that bind the soil particles together. The fenced off gully excluded from cell grazing still had an active gully.

 

Photo 1 Cell grazing versus set grazing – photo by Soil Systems Australia

 

Hay and dairy production – investing in a healthy diverse pasture
In an article titled “Weed Management in Organic Agriculture – are we addressing the right issues?”, Barberi outlines that there are a number of issues that could be addressed when tackling weed control. Some of these include alleopathy (chemical released by one plant that effects the next generation like lab lab and desmodium), mechanical weed control, thermal control, bio weed control, nutrition, timing of sowing and rotations.

A few illustrated points
The first issue is most of the varieties used in hay and dairy pasture production are introduced species from the northern hemisphere. As the soils there were developed during the last ice age, the mineral and organic matter content is much higher than here in Australia. It therefore follows that if you wish to grow these species in depleted Australian soils (especially marginal soils) you will need to focus on building both soil carbon and mineral levels together. If you deplete these old soils weeds will proliferate and take hold as nature abhors a bare patch of earth. For Lucerne producers, weeds can be controlled using flame weeders and the use of lucerne points. However if you wish to increase the yields of each cut from 2.5t to 7.5t/ha (and hence outcompete the weeds), priority must be put on correct nutrition. We have seen this with eliminating crow foot in kikuyu as discussed in the Australian Organic Producer Winter 2011.

Photo 2 – Lucerne points used to clean up weedy paddock – photo by Soil Systems Australia

The other important issue is providing a diverse range of species in both the pasture and hay mix. In Photo 2 you can see the healthy coat of a Romanian dairy cow in the middle of summer. On this hot 42 degree celcius day, the cows were feeding on a Mediterranean pasture made up of over 32 different legume and grass varieties. With no grain supplements these cows were still milking 20 litres per day.

Photo 3 – Diverse pastures the key in Romania – photo by Soil Systems Australia

 

The last issue is the symbiotic role of legumes and grasses together. The mixture of the legume and grasses stimulates the plants production of root exudates that feeds the surrounding microbes in the rhizosphere. This improves feed quality (more dry matter DM), amino acid amounts and increases the metabolisable energy in the feed. In Photo 3 you can see a healthy oats and vetch hay paddock two days after a grazing. This pasture paddock was prepared with on-farm compost together with nutrients. The additional efforts of preparing an on-farm compost as opposed to buying in a “certified allowable input” are outweighed by the productive outcomes in the field. Note there are no weed issues.

 

Photo 4 – Quality oats and vetch hay outcompetes weeds- photo by Soil Systems Australia

 

Adam Willson is the Director of Soil Systems Australia
www.soilsystems.com.au

 

Further reading

Cell Grazing – the first 10 years in Australia – Terry McCosker RCS, Tropical Grasslands 2000 – Vol 34, 207-218

 

Organic Insights December 2004

 

“Weed Management in Organic Agriculture – are we addressing the right issues?” – P Barberi, European Weed Research Society Weed Research 2002 Vol 42, 177–193

 

Organic Weed Control – Adam Willson – Australian Organic Producer Winter 2011.

 

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