Biodiversity

In recent decades, intensive use of herbicides has led to degradation of soils with negative impacts on both human health and the environment.

Environmental consequences include:

• Soil erosion;
• Nitrate run-off; 
• Loss of organic matter;
• Biodiversity decline;
• Appearance of herbicide resistant weeds; 
• Groundwater contamination with herbicides. 

All of the above show the need for alternative soil management practices that minimise environmental impact, thus increasing the nutrient value of the soil. 

In this context, the Alentejo Regional Wine Growing Commission aims to encourage members of WASP to implement cover crops, as a recommended sustainable viticulture practice. The cover crop comes as a practical alternative land management practice, providing more sustainable viticulture due to its effects on environmental dynamics.

This ancient technique consists of the development of a permanent or temporary cover soil for all or part of the vineyard lines. Cover crop advantages are multiple:

• Control and / or reduction of soil erosion;
• Improving soil structure;
• Release of useful nutrients for the vines through the decomposition of cover crop constituents;
• Water infiltration allowing for adequate levels of moisture;
• Enhanced mobility for agricultural machinery.

As well as the positive effects it has on the vine, cover crops can also reduce the density of the hedge and thus contribute to a lower incidence of fungi botrytis, commonly known as “bunch rot” and in the improvement of grape maturation.

Cover crops also help to increase the biodiversity of the vineyard ecosystem, particularly with regard to auxiliary organisms (organisms that can contribute to a considerable decrease in pest populations), earthworms and other existing fauna that assist in pest control. 

In order to install cover crops, one should take into account the following factors (amongst others):

• The period immediately after harvest for sowing;
• Preparing the ground to maintain a surface layer with about 6 to 10 cm;
• Controlling phosphorus and potassium levels for optimal fertilisation and soil correction;
• Coating with legumes, which guarantees high fixation rates, contributing to the level of soil fertility. If the soil already has high levels of fertility, the coating may also be made with grass.

 Despite all of the advantages indicated, it is necessary to consider that in the early years (depending on its composition and some fundamental aspects), the cover crop may promote an increase and /or inhibition in vegetative growth and vine vigour.

Among these aspects are:

• The characteristics of the "terroir" (climate, soil, grape variety, rootstock);
• The vine´s initial vigour;
• Vineyard fertilisation;
• All factors influencing the use of water for cover crops and the existing soil fauna and flora.

There are also potential drawbacks as there is a risk of weed pests in drier years, competition from weed species with the vine for water and nutrients, especially in rocky, sandy and "dry" soils. Under such conditions, recovery of the vine root system has been observed after some years.

However, the cover crop is possibly the most sustainable soil management system for the cultivation of vines, offering one of the most practical and cost-effective options to provide the organic matter needed to maintain and improve soil.