Soil Requirements

Strawberries have no specific requirements in terms of soil type. Fields and tunnels should be well drained and relatively flat with no frost pockets. Yields are usually slightly higher on heavy soils with a greater water holding capacity. However, light soils warm up faster so that flowering is earlier. In these situations frost protection may be more important. Light or sandy soils do have advantages in that harvest is earlier, helping the grower catch an early market. These soils also have fewer problems with root diseases.

Soils that have previously grown potatoes or other Solanaceous species should be avoided to reduce the risks of Verticillium wilt and Rhizoctonia solani in the strawberry crop. Strawberries that follow grass can also be subject to greater pest attack from grubs, so planting is commonly delayed for a year, giving the grower a better chance of controlling weeds as well.

Strawberries prefer slightly acid soils with a pH value between 5.5 (light soil) to 6.8 (heavy soil). As a result, liming is not common in strawberry production. In soils with a higher organic matter content strawberries can tolerate a slightly lower pH. When the soil pH drops below 5.5, magnesium, calcium, phosphorus and molybdenum availability drops, so supplies need to be maintained. At pH levels above 7.0, zinc, manganese and iron can become deficient (Figure 12).

Salinity

Strawberries are very sensitive to salinity (Figure 13).

All irrigation water contains dissolved mineral salts, but the concentration and composition varies. Water with the highest concentrations will cause the greatest salinity issues. Once the salinity of the irrigation water exceeds an ideal EC level of 0.7mS/cm, yield losses will occur (Table 6) and at much higher ECs, yields are significantly reduced (Figures 14 and 15).

Salinity symptoms are commonly seen as dry and brown leaf margins, brittle leaves, stunted plant growth, or even dead roots and plants. Poor irrigation management can also lead to a build-up of salts around the roots, so it is important to flush these out of this zone.

The salinity level in the root zone is directly related to water quality, fertilizer rate and the depth of irrigation application. It is possible to predict potential yield loss using the following equation derived by Maas and Hoffman (1977):

This is where Y is the relative crop yield (%), ECe is the salinity of the saturated soil extract in dS/m, a is the threshold value for maximum, 100% production, and b is the yield loss per unit increase in salinity.

For strawberries: a = 0.7, b = 33.3, therefore the equation is: Y = 100 – 33.3 (ECe-0.7)

Table 6 details the effects of different levels of soil salinity (ECe) and water salinity (ECw) on percentage crop yield loss. It also provides an indication of the amount of irrigation water required to flush salinity out of the system (LF). It is important to test soils/substrates regularly for levels of soluble salts and to manage irrigation water accordingly.

A high salt content is controlled by leaching using 10-20% more irrigation water than that normally applied. The proportion of water that leaches below the root zone, carrying with it a portion of the accumulated soluble salts is known as leaching factor (LF). The amount and frequency of irrigation should be adjusted to allow sufficient leaching yet at the same time minimizing the risk of excessive soil moisture levels which could cause other problems.

Two types of salt problems exist - those associated with the total salinity and those associated with sodium chloride. Soils may be affected only by salinity or by a combination of both salinity and sodium. Sodium is antagonistic with potassium and calcium. Chloride competes with nitrate. Therefore, levels of Na and Cl in water and fertilizers must be as low as possible.

High concentrations of salts in the soil prevent the plant from absorbing the water, resulting in leaf scorching, wilting and yield loss, and varieties differ in their sensitivity to this salinity (Figure 15).

The effects of specific nutrients on mitigating salinity are dealt with within each individual nutrient section.

For more information on fertigation and salinity, consult the Yara Fertigation Manual.