A quiet revolution is taking root in Romania's agricultural fields, where simple cover crops are challenging the dominance of chemical fertilizers.
Imagine a farm where fields never lie bare, where crops work in shifts, and where soil becomes richer with each passing season. This is not a futuristic vision but a return to agriculture's roots through the power of green manure.
In Romania's northwestern region, where Albic Luvisols struggle with acidity and declining fertility, this ancient practice is being rediscovered as a sustainable solution for modern farming. By incorporating specific plants into the soil rather than synthetic chemicals, farmers are embarking on a remarkable journey to restore their land's natural vitality while reducing agriculture's environmental footprint.
Plants create natural fertilizer through nitrogen fixation
Improves soil structure and water retention capacity
Reduces dependence on synthetic fertilizers
Green manure refers to specific crops grown not for harvest, but to be incorporated into the soil while still green or shortly after flowering. These plants, typically legumes like vetch, clover, or cowpea, serve as living fertilizers that offer multiple benefits for degraded soils.
The magic begins with nitrogen fixation. Leguminous green manure plants host beneficial bacteria called rhizobia in their root nodules. These remarkable microorganisms can convert atmospheric nitrogen—which plants cannot use—into forms accessible to plants, essentially creating natural fertilizer factories beneath the soil surface 4 .
When these plants are incorporated into the soil, they continue to serve even in death. As they decompose, they release this stored nitrogen along with other essential nutrients, making them available for subsequent crops. This process simultaneously reduces the need for synthetic fertilizers while improving soil structure and water retention capacity 3 .
For acidic soils like the Albic Luvisols of northwestern Romania, green manure offers particular promise. The decomposition of these plants can help neutralize soil acidity while improving the soil's ability to retain nutrients that would otherwise be lost to leaching .
The organic matter from decomposed green manure also binds soil particles together, creating a more stable environment for plant roots and soil organisms.
Perhaps most importantly, green manure feeds the countless microorganisms that constitute the soil's "digestive system." A teaspoon of healthy soil contains more microbes than there are people on Earth, and these organisms are essential for nutrient cycling, disease suppression, and soil structure formation 1 8 .
Chemical fertilizers can disrupt these delicate communities, while green manure sustains and enhances them.
Recent research conducted in Romania's challenging sandy soils reveals just how powerful green manure can be for soil restoration. Scientists at the Research Development Station for Plant Culture on Sands Dăbuleni implemented a innovative crop rotation system to test green manure's effectiveness .
Between 2020 and 2023, researchers established a rotation of cowpea-rye + cowpea in successive crops for green manure-sorghum grains. The experimental approach was meticulous:
After harvesting the rye crop, initial soil samples were collected to assess baseline fertility
Soil preparation works (ploughing + disking) were performed, followed by sowing of cowpea in successive cultivation
The cowpea was incorporated into the soil as green manure during the pod formation phase, when biomass production peaks
Grain sorghum was sown in a bifactorial experiment with two variables—with and without green manure incorporation, and two different fertilizer levels (N80P80K80 and N150P80K80)
This structured approach allowed researchers to isolate and measure the specific contribution of green manure to soil health and subsequent crop performance.
The findings from this multi-year study demonstrated green manure's dramatic impact on soil quality. Chemical analyses conducted after the sorghum growth cycles revealed significant improvements across multiple parameters when green cowpea manure was incorporated .
| Soil Parameter | Annual Increase | Improvement Context |
|---|---|---|
| Total Nitrogen | 0.17–0.29 g/kg | Enhanced natural fertility |
| Extractable Phosphorus | 9.5–13.33 mg/kg | Improved nutrient availability |
| Exchangeable Potassium | 11.33–24 mg/kg | Better plant nutrient access |
| Organic Carbon | 0.08–0.12 g/kg | Increased soil organic matter |
Beyond these measurable nutrient improvements, the green manure treatment also reduced soil acidity and significantly improved the soil's water holding capacity—a critical benefit for sandy soils prone to drought . Perhaps most notably, the incorporation of cowpea manure allowed for reduced synthetic fertilizer application while maintaining crop productivity, demonstrating that this approach offers both economic and environmental advantages.
The benefits of green manure extend far beyond the nutrient improvements measured in the Romanian study. Research from diverse agricultural systems reveals additional remarkable advantages:
The incorporation of green manure like hairy vetch before planting maize has been shown to significantly improve the subsequent crop's resistance to pests like fall armyworm. Scientists found that plants grown in green manure-amended soils produced more defense-related compounds like DIMBOA, jasmonic acid, and salicylic acid, making them less palatable to pests 5 .
Green manure does more than provide nutrients—it enhances the soil's ability to perform multiple ecological functions simultaneously. Known as ecosystem multifunctionality, this includes nutrient cycling, water regulation, and support of biodiversity. Research shows that green manure improves soil quality precisely by enhancing these interconnected processes 1 .
Green manure application dramatically transforms the soil's biological community. Studies document that incorporating plants like Chinese milk vetch and ryegrass increases microbial biomass carbon by 29.8–72.9% and enhances enzyme activities critical for nutrient cycling 8 .
| Enzyme Type | Function | Change with Green Manure |
|---|---|---|
| β-glucosidase | Carbon cycling | 65.9–172.9% increase |
| Urease | Nitrogen cycling | 35.6–142.6% increase |
| Catalase | Oxidative metabolism | 22.5–55.6% decrease |
Investigating green manure's effects requires specific approaches and measurements. Here are key elements from the researcher's toolkit:
| Tool/Measurement | Function | Application Example |
|---|---|---|
| Soil Enzyme Assays | Measure microbial activity in nutrient cycling | Assessing β-glucosidase and urease activities 8 |
| Microbial Biomass Carbon/Nitrogen | Quantify living microbial component | Tracking soil biological health 1 |
| High-Throughput DNA Sequencing | Profile microbial community structure | Identifying bacterial and fungal shifts 8 |
| Nutrient Analysis | Measure nitrogen, phosphorus, potassium | Determining fertilizer replacement value |
| Soil Organic Carbon Fractions | Assess carbon sequestration potential | Measuring labile vs. stable organic carbon 3 |
The evidence from research on Romania's sandy soils and global studies points to a clear conclusion: green manure represents a powerful, sustainable approach to revitalizing degraded agricultural land. For the Albic Luvisols of northwestern Romania, this practice offers multiple benefits—from countering soil acidity to enhancing fertility and building resilience against drought.
What makes green manure particularly compelling is its ability to address multiple challenges simultaneously. It reduces dependence on synthetic fertilizers while improving soil structure, enhancing water retention, and supporting biodiversity both above and below ground.
As one study demonstrated, the strategic use of green manure can substitute 40% of chemical nitrogen fertilizer without reducing crop yields 4 .
The transition to green manure systems does require new knowledge and approaches—selecting appropriate green manure species for specific soils, timing incorporation correctly, and understanding how to maximize benefits while managing potential limitations.
But the Romanian research and global evidence suggest that this investment in learning returns dividends in the form of more resilient, productive, and sustainable agricultural systems.
As we look to the future of farming in Romania and beyond, green manure offers a path toward reconciling agricultural productivity with environmental stewardship. By working with natural processes rather than against them, farmers can build soils that become more fertile with each passing season—creating a truly sustainable foundation for our food system.