The important role of sludge in increasing global crop production


Earthworms, in particular, are important ecosystem engineers that influence plant growth.  (Image Courtesy – Canva)
Earthworms, in particular, are important ecosystem engineers that influence plant growth. (Image Courtesy – Canva)

Agriculture has undergone significant changes over the past century, primarily through improved crop varieties, increased use of agrochemicals, and agricultural intensification through mechanized farming.

These changes have contributed to feeding the growing global population. However, they have also come at a considerable environmental cost, including loss of biodiversity, water and air pollution, and contributions to climate change.

As the world’s food demand continues to increase, it has become increasingly important to find sustainable agricultural practices that minimize these negative impacts.

An important aspect of sustainable agriculture is soil management and overall soil health. Soil biological communities, in particular, have the potential to support food production and provide various ecosystem services.

Earthworms, as important ecological engineers, influence plant growth by influencing their soil composition, water retention, organic matter cycling, and nutrient availability. They also facilitate the production of plant growth-promoting hormones and enhance the immune response of crops against common soil pathogens.

Despite being recognized as indicators of healthy soils, the precise contribution of earthworms and other beneficial soil organisms to global agricultural production is poorly understood. This knowledge gap is critical to the development of modern agro-environmental practices and policies.

Estimating the effects of sludge

To estimate the contribution of sludge to crop yield, a study analyzed the responses of sludge abundance, soil properties, crop yield, and sludge yield from existing literature. The results show that earthworms play an important role in global crop production, with their effects varying by crop type.

For major cereal crops such as maize, rice, wheat and barley, earthworms are estimated to contribute about 6.5% of global production. This translates to over 140 million metric tons of grain annually.

In the case of legumes, such as soybeans, dry beans, peas, garbanzos, lentils, alfalfa, clover, their share was less than 2.3 percent of the world total, which is equivalent to 16 million metric tons. The difference in effect between cereals and legumes can be attributed to the greater influence of earthworms on cereal growth due to mineralization of organic nitrogen in the soil, which is more beneficial to cereals.

Regional effects of sludge

The effects of sludge on crop production are not uniform in all regions. The most significant relative effect in this study was found in sub-Saharan Africa, where earthworms contribute about 10% of total grain production and 3.2% of legume production. Latin America and the Caribbean also benefit significantly, with legumes contributing about 8% of grain and 3.1% of legume production.

These regional variations are influenced by soil characteristics, such as low pH and high clay content, which increase the benefits of sludge in the global south. In Europe and East/Southeast Asia, where the abundance of earthworms is high, their impact on grain yield is estimated at 7.4%.

However, in areas with low silt abundance, high fertilizer use, and less favorable soil properties, the contribution of silt to crop production is less pronounced.

Identify sources of uncertainty

The study acknowledges potential sources of error in its estimates. Most of the studies included in the analysis depend on simple mesocosms with controlled sludge density, which may not fully capture the long-term benefits of sludge under realistic conditions.

Furthermore, the analysis assumed simple additive effects of vegetation and environmental factors, without considering potential interactions between these drivers.

There was also sampling bias in the data used to estimate snail abundance, with most data points being from Europe and eastern North America. This bias may lead to underrepresented mud contributions in underrepresented regions, such as sub-Saharan Africa.

Therefore, there is a possibility that the global mud map used in the study underestimates both mud diversity and abundance in these regions.

This study is the first to quantify the contribution of sludge to global agricultural production. While earthworms were found to have a significant effect, it is important to recognize that other soil biota may play an equally important role. The study does not advocate introducing the sludge to areas where they do not exist naturally, as this could have negative ecological consequences.

Instead, it emphasizes the need for continued research and development of agroecological practices that enhance all soil biological communities, including mud, to support a range of ecosystem services. These practices are critical to the long-term sustainability and resilience of agriculture in a world where demand for food continues to grow, and environmental concerns are paramount.

First Published: 28 Sep 2023, 09:53 IST


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