Soil management in walnut orchards is often treated in the same way as in orchards of other fruit species.

In practice, however, walnut trees have a number of specific characteristics that require a different approach, especially when it comes to soil cultivation, grass cover and competition for water.

The experience of Alexei Micu, owner of MICU&CO SRL, which manages more than 30 hectares of organic walnut and plum orchards, shows that some practices commonly used in other orchards are not always suitable for walnut plantations.

The orchard includes both local varieties and varieties of foreign origin, but adaptation to climate conditions remains decisive.

Walnut trees respond differently to soil cultivation

“In a walnut orchard, soil cultivation needs to be approached more carefully. In the first years, when the trees need support to develop, it is important to give them a competitive advantage, including through mechanical cultivation. But after this period, the approach has to change,” explains Alexei Micu.

According to him, during the first 3–4 years after planting, soil cultivation remains necessary to reduce weed competition and support the development of the root system.

Later, intensive interventions no longer bring the same benefits, while reducing them helps stabilize the soil structure.

“Starting from the fifth year, we moved to grass cover, initially using an alternating system, on every second row, and later to full grass cover.”

Sensitivity to competition for water

One aspect that directly influences walnut tree development is competition for water, especially in the case of intercropping or unsuitable species in the ground cover.

“We had situations where alfalfa was growing between the rows. It consumes a lot of water, and this was immediately visible. Walnut trees with this type of ground cover stopped developing compared to the others,” says Alexei Micu.

Although walnut trees develop a taproot that can reach 3–4 metres in depth, the active absorption zone remains in the upper 60–80 cm of soil.

Under drought conditions, plants with high water consumption can visibly affect tree growth. For this reason, alfalfa is not recommended in walnut orchards, not even in the first years.

Fine root growth reaches its peak in May and June, and under water deficit conditions, these roots explore deeper soil layers.

At the same time, roots need well-aerated soil, while excess water or compaction reduces oxygen levels and quickly leads to tree weakening.

Soil compaction in the orchard

Soil compaction is considered one of the factors that limits the productivity of walnut orchards. In compacted soils, the root system changes: roots become thicker but fewer in number, and the absorption surface decreases.

At the same time, compact layers located at shallow depths can limit tree development, especially during dry periods.

Under these conditions, technical recommendations focus on avoiding work on wet soil and reducing the pressure exerted by machinery in order to maintain soil porosity and aeration.

In practice, however, the situation depends greatly on how the soil is managed.

In the orchard of MICU&CO SRL, where the spaces between rows are covered with grass, soil compaction has not appeared visibly, despite repeated machinery passes.

“We have not observed soil compaction, even though we have been driving on the same track for years. On the contrary, the soil seems to recover better,” says the farmer.

Ground cover reduces the direct impact of machinery and contributes, through the root system and biological activity, to maintaining soil structure.

Over time, a more stable system is formed, one that absorbs pressure better and preserves porosity more effectively.

Ground cover and the balance between protection and competition

In walnut orchards, the ground cover does not develop uniformly and differs clearly from that found in other orchards.

“In the walnut orchard, we generally have fewer weeds under the tree crowns,” Micu notes.

This is explained by the allelopathic effect specific to walnut trees.

The plant produces juglone, a substance found in leaves, roots and bark, which limits the development of other species. Its concentration is higher near the trunk and decreases towards the outer part of the crown.

In areas where more light enters, vegetation develops normally, while periodic mowing becomes the main maintenance operation.

Grass cover in walnut orchards: natural or artificial?

In the farm’s practice, natural grass cover has proven more stable over time.

“We also tried sown mixtures, but over time we noticed that natural grass cover adapts better. The species establish themselves naturally, and those that withstand the orchard conditions remain,” explains Micu.

The ground cover is dominated by spontaneous grasses, clover and other local legumes, as well as species such as dandelion. This mixture contributes to the formation of a stable plant layer, adapted to the soil and climate conditions.

“A balance is created. You no longer depend so much on the exact moment when you intervene,” says the farmer.

Advantages of natural grass cover:

better adaptation to local conditions, without the need for reseeding;

balanced water consumption compared to some sown mixtures;

stabilization of soil structure;

reduction of water evaporation and soil-level temperature;

increased biodiversity, including beneficial insects.

Limitations of artificial grass cover

In the case of artificial grass cover, results depend largely on the choice of species and on management practices.

“With artificial grass cover, when and what you sow matters a lot. If you do not choose correctly, you may end up with more competition and losses than benefits,” explains Micu.

In general, grasses such as fescue or ryegrass are recommended, with the possible addition of dwarf white clover for nitrogen input.

These species establish well and help stabilize the soil, but they can create competition for water if not managed properly, especially during dry periods.

Among the disadvantages observed are:

dependence on the timing of sowing and subsequent interventions;

higher risk of excessive water consumption;

need for additional maintenance operations;

higher costs.

This article was developed by the Agricultural and Rural Advisory Centre (CCAR) within the PROGRESS project, funded by the Government of Germany and implemented by the consortium of organizations led by Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH, in partnership with European Business Association (EBA) Moldova, IEF, OECD and RECC.