Rural Water and Sanitation

Worthy alternative

A new field experiment shows that fertiliser derived from faecal sludge can improve crop yields

The use of biosolids sourced from faecal sludge as organic fertiliser positively influences germination rates and significantly enhances the growth and yield of plants (Photographs: Atun Roy Choudhury)

India has constructed over 100 million household toilets under its Swachh Bharat Mission in recent years. While this has improved the country’s overall sanitation levels, it has thrown open the challenge of handling vast amounts of faecal sludge, the mixture of human excreta and water. One of the solutions lies in separating the solid and liquid components and treating them separately. The liquid can be decontaminated and used for irrigation and toilet flushing. The solid can be composted and pasteurised to make biosolids and used as organic fertiliser.

To understand the potential of faecal sludge as a fertiliser, we recently conducted a field trial in Alair, Telangana. Our experiment, conducted on okra cultivation, shows that the use of biosolids sourced from faecal sludge as organic fertiliser positively influences germination rates and enhances the growth and yield of plants. Biosolid generally contains high concentrations of macro and micronutrients essential for plant growth.

The setup

The trial was conducted by growing okra on two soil beds, one with only red soil that is commonly used for farming in southern India (control bed) and the other with premixed biosolids and red soil in a 1:1 ratio (experimental bed).

Both beds were initially flooded with 80 litres of water, carefully applied to ensure uniform distribution and to avoid water-logging. Next, 16 g or roughly 250 okra seeds were evenly distributed on each bed, ensuring optimal spacing for healthy plant development. The incorporation of biosolids into the experimental bed aimed to provide additional nutrients to the growing okra plants. The biosolids used had a high nutrient content, including a healthy carbon-to-nitrogen ratio of 9.57, a total nitrogen content of 0.93 per cent and a total phosphate content of 1.95 per cent.

To maintain the integrity of the experiment, regular monitoring and care were provided to both soil beds throughout the process. The experiment lasted for 75 days, allowing sufficient time for the okra plants to mature and produce yields. The first yield of okra pods was harvested on the 55th day, followed by two subsequent harvests after an interval of 10 days each. This frequency allowed for the assessment of multiple yields and the observation of any variations in yield over time.

Better yield, quality

The impact of biosolids could be seen throughout the life cycle of the plant. Within just seven days of seeding, the control bed saw 92 saplings. In contrast, the experimental bed recorded as many as 98 saplings, indicating a positive influence of biosolids on the rate of germination. Over the course of the 55 days, okra plants in the experimental bed displayed a significant growth compared to those in the control bed.

The average height of the plants in the experimental bed ranged from 1 to 1.2 m, while those in the control bed ranged from 0.6 to 0.7 m, suggesting positive influence of biosolids on plant vigour and overall growth.

The total okra pod weight from the control bed for the first and second harvests was recorded at 0.519 kg and 0.830 kg, respectively. In contrast, the experimental bed produced substantially higher yields: 1.176 kg and 1.713 kg, respectively.

The application of biosolids also positively affected the quality of the okra pods. The average, maximum and minimum pod lengths were noticeably longer in the experimental bed compared to the control bed.

While further research is required to ascertain the nutrition levels of crops grown with biosolids, the field trials offer an important first step to mainstream the conversation. Fertilisers derived from faecal sludge are not only healthier than their chemical counterparts, but they are also cheaper to produce. While the production cost of chemical fertilisers can be anywhere between Rs 15 and Rs 20 per kg, biosolids, when produced at a large scale, will cost only Rs 5-8 per kg.

Given the success of the Swachh Bharat Mission, particularly in rural India, the untapped potential remains immense.

(Atun Roy Choudhury is with the Cube Bio Energy Private Limited in Hyderabad, Telangana; Neha Singh and Namita Banka are with the Chadwick’s FSM Laboratory in Secunderabad; N Chandana is with the Centre for Emerging Technologies for Sustainable Development, Indian Institute of Technology, Jodhpur, Rajasthan; and Jitesh Lalwani is with the Department of Civil Engineering, Vardhaman College of Engineering in Hyderabad)

This was first published in the 16-31 January, 2024 print edition of Down To Earth

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