A Spanish vineyard has been without irrigation or pesticides for more than 20 years; Its topsoil cover now has more than twice as much organic matter as nearby tilled soil

For more than two decades, the soil between the rows of vines in a Spanish vineyard has remained covered with spontaneous vegetation rather than being repeatedly tilled. This unusual approach was associated with a surprising difference beneath the vines: the soil managed with long-term mulch contained more than twice as much organic matter in its top layer as nearby soil that was tilled conventionally. The finding offers insight into how leaving soil intact and maintaining plant cover could help improve soil health in dry, water-stressed vineyards. The findings come from a 2026 study published in Frontiers in Soil Science, which compared a dryland vineyard in central Spain managed with spontaneous cover crops for more than 20 years with an adjacent vineyard managed using conventional tillage. The researchers examined the physical, chemical and biological characteristics of the soils, including organic matter, porosity, water retention, nutrients and microbial activity.

Two different ways of managing land

The study was carried out near Mota del Cuervo in the province of Cuenca, central Spain. The region has a semi-arid Mediterranean climate, which makes water availability a major challenge for vineyards. According to the study, the farmer claimed to have managed one of the vineyards for more than two decades without irrigation, pesticides or other external inputs. Instead of repeatedly removing vegetation between the vines, the farmer allowed spontaneous plants to grow and maintain ground cover. Vegetation was manually removed only immediately around individual vines.The neighboring vineyard followed a much more conventional approach. Its soil was tilled regularly; The researchers noted that vineyards in the region typically undergo several tillage operations each year to control weeds and keep the soil bare. This created a useful comparison because the two plots were adjacent and had comparable soil conditions. Instead of comparing vineyards from completely different environments, the researchers were able to examine how contrasting management practices were associated with differences in soil properties.

Organic matter doubled

The clearest difference appeared in the amount of organic matter contained in the top layer of soil. The researchers found an average organic matter content of 1.74% in the topsoil under spontaneous cover crops, compared to 0.83% in conventionally tilled soil. This means that the covered soil contained just over twice as much organic matter as the cultivated soil. Organic matter is an important component of healthy soil. It largely comes from the decomposition of plant and animal material and contributes to processes that influence soil structure, nutrient cycling and water behavior.The researchers also found differences in soil structure. At depths of 10 to 30 centimeters, soil under long-term cover crops had a porosity of about 51.2%, compared to 44.0% under tillage. Soil covered with cover crops also showed greater biological activity, with several enzyme activities elevated compared to conventionally managed soil. The results suggest that maintaining vegetation in the soil for long periods can gradually alter the soil environment. Plant roots continually add organic matter, while fallen vegetation decomposes on the surface. At the same time, less soil disturbance can allow soil structure and biological communities to develop with less disturbance.

A possible lesson for dry vineyards

The findings are particularly relevant because vineyards in Mediterranean regions often face a difficult combination of limited rainfall, soil degradation and the need to control vegetation around crops. Conventional tillage can keep vineyard rows visibly bare, but repeated disturbance can also break down soil aggregates and accelerate organic matter loss. Cover crops offer an alternative by keeping vegetation alive in the soil for at least part of the year and reducing the amount of bare soil exposed to wind and water erosion. Previous research has similarly linked soil cover to improvements in soil organic carbon, aggregate stability, and infiltration.However, the study does not suggest that cover crops are automatically suitable for all vineyards. Plants growing among vines can compete with vines for water, especially in dry climates. Recent research in Mediterranean vineyards has found that cover crops can sometimes reduce vine growth in severe drought conditions. This makes the Spanish vineyard studied in Frontiers in Soil Science particularly interesting. It represents a long-standing real-world example of how a farmer maintained spontaneous vegetation without irrigation or pesticides and allowed the soil to develop under relatively low conditions for more than 20 years.Instead of treating every plant growing among the vines as a problem to be eliminated, the system allowed the vegetation to become part of the vineyard’s soil management strategy. According to the researchers, their findings support the idea that long-term spontaneous cover crops can improve soil structure, organic matter and biological functioning in semi-arid vineyards. The results do not prove that the practice will eliminate the need for irrigation everywhere, but they show how maintaining a living ground cover can potentially strengthen the soil’s ability to perform in difficult conditions. For vineyards facing increasing pressure from drought and soil degradation, the lesson is relatively simple: Sometimes, healthier soil can start by disturbing it less and allowing plants to remain.