VARUN
PERUMAL

portfolio

Frugal Sensors: Soil Moisture

In collaboration with the Copenhagen Institute of Interaction Design (CIID)

INTRODUCTION

For the majority of the small scale farmers in India, agriculture is still practiced with age old methods, most of them not suitable for the current situation which is dominated by water shortages, high seed prices and demand for yield. Quite often farmers choose appropriate crops for their land, resulting in sub optimal yield and in some cases loss of the entire crop.

Water shortages are becoming more and more rampant in India. More than 60 % of India’s agricultural water usage is from ground water * and with the alarming depletion of the water table. Water is the prime constraint for agricultural development in India.(* 2009, study by The Economist)

In this project we attempt to make a simple device to allow farmers to measure the moisture content of the soil. It is an effort towards developing affordable and relevant agricultural tools developed in a way that is easy to use as well as to manufacture.

APPROACH

The systems consists of a beads made from a hygroscopic polymer which absorbs water and expands. The material is moulded into spherical beads for our use case.

 

 

When the polymer bead absorbs the water in the soil, it grows in size, the reference card (below) is used to asses the amount of water it has absorbed using the size of the bead. The size of the bead is matched to a calibrated chart printed on the card. The most important factor in the entire system is to accurately calibrate the size of the beads with the amount of water/moisture they absorbed. The beads are at an un-shrunken size of 1.4 mm diameter; they grow up to 8mm in diameter depending on the amount of water they absorb.

PROCESS

1. Plant one of the beads into the soil, preferably before the evening at an approximate depth of 3-8 cm’s. The bead is left in the soil overnight for a period of 24 hours; this is to ensure the precipitation that happens at nightfall is taken into account. 
2. After the 24-hour period has elapsed, it would have expanded after absorbing water from the surrounding soil.
3. Then the bead is inserted in to the provided reference card’s holes, one at a time, until the closest fit is found.
4. The corresponding data to the hole is read from the card, thus providing a good estimate of the soil humidity. For example in the picture above, the person can dial the number given (say of the agricultural department, or a co-operative society) and report the water content number. They could then receive counseling over the phone on how to proceed with planting, harvesting etc. for the season.