Ancient printing method informs development of low-cost soil sensor

To this end, Dr Andrew Ward from Strathclyde University’s Department of Civil and Environmental Engineering is leading an EPSRC-funded project that will use discarded everyday items to build sensors for use on Kenyan smallholdings and beyond.

According to the US Agency for International development, the agriculture sector accounts for around 33 per cent of Kenya's GDP and employs over 40 per cent of the total population and 70 per cent of the rural population.

The sector is dominated by smallholder production on farms of between 0.2 and 3ha, which are said to account for account for 78 per cent of total agricultural production.

Despite its importance to the Kenyan economy, a large proportion of the population is food insecure, a situation exacerbated by land parcels shrinking because of population growth; farmers being pushed into dryer, lower quality areas of land that are vulnerable to drought; and conflicts resulting from competition for land.

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To address food insecurity will require an increase in agricultural productivity and a key factor to making the improvement is soil fertility.

According to Dr Ward, this requires measurement tools that can be used by farmers to understand the spatial changes in nutrient concentration within a field, and how these vary over time.

However, no technology currently exists that allows this to be carried out at very low cost.

The project, carried out in conjunction with colleagues from the Glasgow School of Art and Kenyatta University in Nairobi, will develop a low-cost sensor that farmers can use to determine nitrate and phosphate, which are soil macro-nutrients.

Dr Ward explained woodblock printing allows the creation of lots of copies of the same pattern and that natural materials such as egg, linseed oil and plant starch have previously been used as printing inks.

“Instead of using these to print artwork, we plan to use them to make very low cost, biodegradable single use sensors that, in conjunction with a cheap meter, can measure the concentration of soil nutrients,” said Dr Ward. “We want to see if we can make a sensor using only resources that are available local to the farm; could we use yesterday’s newspaper, some egg yolk as a binder, carbon black and some plant-based proteins to produce the sensors?”

The meter in the sensor – acting like a blood glucose meter - would require a small power source like a battery to run, but this would last over a long period of time, Dr Ward added.

The project, funded by International Science Partnerships Fund through the EPSRC, will develop a proof-of-concept device for testing in Kenya. A long-term aim is to deliver the solution to farmers as a ‘factory in a box’ containing the tools needed for sensor manufacture, or as an information pack that shows how to gather the resources required and print sensors.