Everyone Lives Downstream: Nutrient flows and influence on Soil Organic Carbon

SOIL HEALTH-II

Subrata Singh* & Shubo Biswas**

‘Everyone lives Downstream’ was the theme of the World Water Day 1999 and it meant to convey that problems/benefits in one part of a watershed, or even in a country abroad, can affect people great distances away. Through this article, we share our preliminary findings on nutrient flows and its impact on downstream farming systems.  

Early in 1997, I (Subrata Singh) witnessed a conflict between two villages - Muktapasi and Sundhikateni (in Dhenkanal district, Odisha) regarding sharing of the stream water coming down the hill from the forests. The villagers were fighting to have the grey water into their fields. The water flowing down the stream was rich in humus and nutrients that was crucial to the productivity of their crops. The water is diverted to either village using temporary stone and mud structures. The communities protected their forests through the year, repaired the feeder channels to get the rain water to their fields and the water harvesting structures they constructed as well as developed rules and regulations for governance of their resources. Several years have passed, fertilisers and alternative nutrients are available as alternatives, but the value for the nutrient rich water continues and the right to use the water is still contested.

In the map above, blue line is the feeder channel flowing into Sundhikateni village and the red channel flows into Muktapasi village. A temporary structure is built to divert the water to the two villages based on requirement.

These are not stray incidents. We see and observe this in most villages adjoining good forest areas, farmers value their forests more for the nutrients and soil moisture regimes they benefit from (than the timber and forest produce that they provide). It's also a fact that the land nearer to the forests are the lands with little or no use of external fertilisers.

Researchers (Cleveland et al. 1999; Jobbágy and Jackson, 2000; Hedin et al. 2009; Cloern et al. 2014) have found, tropical forests and their soil have higher carbon (C) and nitrogen (N) stocks than those in other climate regions because of active photosynthesis and biological N fixation throughout the year. Nutrient cycling is influenced significantly by the species of a forest ecosystem thereby influencing the quantity and quality of litter produced in a forest. When precipitation and the run-off water pass through forest soils, the organic carbon in the soil gradually flows downstream to the adjoining farm lands.

A geospatial analytical tool called Soil Health Explorer has been developed by GreenGood Labs, LLC. It is being used by Foundation for Ecological Security to analyse the information from 80,000+ soil health cards spread over 8 districts in Odisha through the portal. FES and GreenGood Labs, LLC. have been working together to improve our understanding and support decision making for farming interventions involving farmers, extension workers and the government.

We mapped the soil organic carbon data based on the Government of India set criteria of high (>0.75%), medium (0.51 - 0.75%) and low (<0.50%) as green, yellow and red colours to represent the data spatially. We added a coarse layer of drainage to explore the relationship between the land use in the upstream, extent of vegetation and soil health downstream. The spatial representation of soil health data reveals a positive correlation between good vegetation in the uplands and the organic content in the farming lands and vice versa.

The water that flows at the onset of monsoons carry the litter and organic matter from the forest floor to the agricultural lands downstream. The farm lands nearer to the forests are the most benefitted from such organic matter

Most of the stream beds from the hillocks/forests in these districts are used for paddy cultivation, the humus and organic content in the soil are deposited in the lands and thereby contribute to improving soil carbon in the soils. The inflow of soil organic carbon is dependent on the type, diversity and thickness of the vegetation. Contrarily, in case of degraded systems, the soil erosion from the slope gets deposited in the lands leading to reduced soil fertility, thereby lesser soil carbon content.

As an example, the agricultural lands in or adjoining the drainage lines in Angul, where the forests are in better shape show/exhibit netter soil carbon.

The agricultural lands adjoining the drainage lines in Koraput, which are denuded and used for quarrying activities show medium or low soil carbon

Nutrient cycling, an important supporting service contributes 69–89% to the total value of ecosystem services. It tracks movement of nutrients during various biological processes between biotic and abiotic components of the ecosystem (2021, Mehta & Jain). According to Robert Constanza, Nutrient cycling represented the highest valued ecosystem service, at $17 trillion per year. The nutrient cycling ecological services are based on determination of major ecosystem functions like nitrogen fixation and litter decomposition and mineralisation rate, which is the most common ecosystem functions/processes.

There is a growing demand from policy makers and forest managers for spatial estimates on nutrient cycling at local, regional, and national scales (2021 Mehta & Jain). The Soil Health Explorer enables different stakeholders to understand and analyse how the nutrient cycling enables nutrient flows for better soil health downstream as well as suggests how lack of vegetation has serious impacts on the farm lands downstream. This article is aimed to share the preliminary understanding from the spatial representation of the soil health data and it opens up scope for much larger investigation into the issue and establish more concretely the dynamic relationship arising due to the land use in the upstream and the impact on the soil health in the downstream agricultural lands.

* Subrata Singh is the Programme Director at Foundation for Ecological Security and has more than two decades of experience working on issues related to land and water commons, natural resource management, community governance, polycentric governance, and public policy.

** Shubo Biswas is the Founder and CEO of GreenGood Labs, LLC. which works with a vision to co-create solutions with the help of local communities and make them available to the maximum number of people through open designs and free access to education material.