Restoring Soil Health with Green Manure

With support from the Dutch Ministry of Agriculture, Nature and Food Quality, EWS-KT is undertaking a multifaceted project called Improving Soil Health, Food Security, Nutrition, Incomes, and Soil Fertility in India and Uganda Through Use of Green Manures. The green manure project seeks to identify viable alternatives to inorganic fertilizers for smallholder farmers.

Green manuring—the practice of incorporating green plant material into the soil—is a climate-smart way to enrich the land. A natural amendment, green manure enhances soil health by adding organic matter and important nutrients like nitrogen.

Advancing Green Manuring in India and Uganda

In both India and Uganda, intensive agriculture has depleted soil nutrients, and improper use of inorganic fertilizers and pesticides has further degraded the land. Restoring soil health through regenerative agricultural techniques like green manuring helps to build sustainable farms that can support increased food production.

The 2-year Improving Soil Health green manure project has multiple objectives. One goal is to train farmers in green manuring and encourage them to adopt this natural technique through demonstration plots showcasing its benefits. Another goal is to gain knowledge through action research, which will inform future recommendations to farmers. This research, implemented in collaboration with longtime technical partner Wageningen University & Research (WUR), will also advance global understanding of green manuring.

How Does Green Manure Work?

Green manure cover crops, which are usually legumes, are cut at the early- to mid-flowering stage (40–45 days after sowing), chopped into small pieces, and mixed directly into the soil.

After the green manure is incorporated into the soil, it begins to decompose. This process releases nitrogen, making this essential nutrient available to the farmer’s future vegetable crops. It also raises the soil pH from an acidic state to an optimal range, improving vegetable plants’ nutrient uptake and contributing to higher yields. Green manure further improves soil fertility by increasing the percentage of organic matter, which results in better water retention, better aeration for root development, and more microorganisms and micronutrients.

Practicing green manure techniques also reduces weed growth. While growing, the cover crop suppresses weeds by competing for nutrients, water, and space. Then, since green manure crops are cut down before maturity, weeds that have sprouted alongside them will also be incorporated into the soil before they have a chance to go to seed.

Action Research

To determine the most effective green manure crops for improving soil health in different regions, several cover crops are being grown as part of action research at EWS-KT learning farms in India and Uganda. The green manure crops’ impact on the amended soil is then recorded and compared.

After new vegetable crops are grown in the amended soil, WUR and EWS-KT are also analyzing the difference in growth attributable to the various types of green manure used. In addition, EWS-KT and WUR are taking measurements in the fields of farmers who are implementing green manure practices, in order to quantify the benefits of this approach under regular field conditions.

Focus on India

The Improving Soil Health green manure project in India is being implemented in Assam and Odisha. These two states have different soil conditions—sandy loam in Assam and clay loam in Odisha—and different farmer practices.

Smallholder farmers in Odisha tend to use a lot of inorganic fertilizer. This is costly, and fertilizer can be difficult to procure during the growing season due to high demand. In addition, if the fertilizer is not the right kind, or is not applied at the right time or in the right dose, it can damage crops and further degrade the land. Based on action research conducted so far, utilizing green manure can allow farmers to reduce their use of commercial fertilizer with no significant impact on yield.

In contrast to farmers in Odisha, those in Assam tend to produce crops more naturally, with limited inorganic fertilizer and pesticide. Green manuring is therefore well aligned with their farming methods, and it is a suitable practice for increasing organic content and enhancing the water-holding capacity of the sandy soil in Assam. Initial action research found that green manure was also effective at raising the soil pH from 5.0 to 6.0, placing it within the target pH range (5.5 to 6.5) for vegetable production.

Focus on Uganda

The Improving Soil Health green manure project in Uganda is also implemented in two different regions: Terego district in West Nile and Lira district in the Northern region. Farmers in the West Nile region have been growing tobacco for decades, whereas the Northern region has a history of cotton cultivation. Both of these crops have left the soil totally depleted of the nutrients needed by plants, forcing farmers to rely on inorganic fertilizer.

Farmers here traditionally grow green manure crops like cowpea and adzuki bean for home consumption. With increasing awareness of green manuring as a sustainable soil health restoration practice, a few farmers are now primarily growing these crops for soil incorporation. Other farmers are continuing to harvest these crops as usual but are now incorporating the crop residue into the soil after harvest.

In Terego, initial action research noted a beneficial increase in the soil pH. In West Nile, green manure was found to reduce the prevalence of root-knot nematodes, which are particularly damaging to okra plants in the region.

Lower Costs, Healthier Soil

Reflecting on the green manure technique he was using to improve his farm’s soil, one farmer in Lira, Uganda, remarked, “Surely you have to feed the soil to feed you.”

By using green manure, farmers can sustainably improve the health of their soil, while also saving money on fertilizer. In addition to the Improving Soil Health project in India and Uganda, EWS-KT has green manure initiatives in Ghana and Cambodia, and field teams in countries such as Nigeria are also encouraging farmers to adopt this climate-smart practice.