Cleanliness is next to holiness

19 September 2017

Contamination from weeds in rice seed used for sowing can occur from field to field, farm to farm and from one region or country to another. Contaminated rice seed results in the international spread of weeds, can have devastating financial implications for smallholder farmers and depreciates local and global food security.  

New research sprouting from the University of Sydney is quantifying the extent of weed seed contamination, and assessing farmer knowledge and practices relating to reducing weed seed contamination. Our researchers are identifying the problem, giving local farmers the resources to solve the problem and working to lift the profitability of agricultural enterprises in a developing nation.

Associate Professor Daniel Tan from the School of Life and Environmental Sciences and Sydney Institute of Agriculture is a co-author of this new study published in Weed Research: An International Journal of Weed Biology, Ecology and Vegetation Management. This survey was led by Dr Bob Martin with support from Dr Srean Pao and Mr Ratha Rien of the University of Battambang, Cambodia

“The research is central to the rice growing communities in the Cambodian provinces of Battambang and Takeo,” said Associate Professor Daniel Tan.

“Our interest in this area stems from a development agriculture perspective. We want to work in conjunction with the smallholder farmers in Cambodia to deliver a better product which is suitable for international trade, and we want to see these communities thrive financially.

“It is common practice for farmers to keep their seed from season to season to sow. In fact farm-kept seed for sowing accounted for 88% of sown seed in Battambang, and 89% in Takeo,” said Dr Bob Martin, also from the School of Life and Environmental Sciences and Sydney Institute of Agriculture.

But retaining seed for the next season might have an impact on the quality and quantity of rice produced.

“Seeds of 41 different weed species from 13 different plant families were found in the farmers’ freshly harvested paddy samples.

“Failure to manage weeds at critical periods can result in yield losses of more than 50% and it is not just the presence of weed plants during cultivation that is a problem; weed seeds can contaminate the rice grain at harvest resulting in a lower rice selling price or even worse, product rejection at rice mills with consequent negative financial impacts on farmers.”

But weed management is not a simple task. A number of weed species with very small seeds, for example, Fimbristylis spp. Ludwigia octovalvis and Linderniaantipoda, were found in the paddy samples. The spikes, spikelets, capsules or pods remain largely intact and are close to the size and weight of a rice spikelet.

“The priority for our farmers is to improve seed hygiene. We are assisting farmers to further improve their seed purification techniques and to caution them to inspect seed before purchasing from neighbours, seed producers and seed companies in the absence of the implementation of seed certification regulations.

“The key finding in this study was that farmers could reduce the weed seed content by 60% in seed kept for sowing compared with freshly harvested paddy and it appears that this was achieved by careful selection of seed to keep for sowing, combined with employing basic seed cleaning techniques such as winnowing and flotation. 

“This study emphasised the importance of weed control in general, the control of seed-set in the crop and effective cleaning of seed for sowing.

“We also discovered that many farmers were incorrectly identifying weed species, so the management techniques applied were not necessarily working.”

Hence, the research team came up with the plan to develop WeedID, a mobile phone app that contains a photo dictionary of the most common weeds in northwest Cambodian rice fields at different stages of growth. The app has images of seeds, seedlings, mature plants and flowers that will all help to identify the weeds which are devastating Cambodian farmers’ rice crops.

“The WeedID app also contains links to specific management information and details the most appropriate way to manage the weed,” Daniel said.

The app is already being used in the provinces included in this research project.

“The University of Sydney takes its role in lifting communities out of poverty very seriously and this research is just one small step to improve the situation for farmers in one region.

“For Battambang, based on the average selling price of $216 t-1, the value of kept seed is approximately $0.25 kg-1 after adding the cost of cleaning by the farmer. The current cost of seed producer seed is up to $0.75 kg-1.

“It makes financial sense to keep seed as farmers have done, but improving the knowledge of weed species, employing seed hygiene techniques and weed management throughout the growth stages of rice production will improve the product and profitability.”

This research was supported by BASF South East Asia Pte. Ltd., Singapore, the Australian Centre for International Agricultural Research (ACIAR) and the University of Battambang.