The Strawberry Newsletter

February 2019


Get your strawberries off to a strong start this spring

It is well known that calcium (Ca) supports root development and crop establishment, including the growth of young leaves, buds and crown expansion. It also plays a key role in maintaining the physiological stability of plant tissue ensuring good plant structure and health. For example, Ca builds strong cell walls and is vital to cell membrane integrity and permeability. In addition, Ca helps improve the plant’s tolerance to diseases and environmental stresses such as salinity, promoting active, stress-free growth. Calcium applications help maintain good soil structure to improve water infiltration, aeration and reducing crusting of the soil.

While most Ca is found in the leaves, petioles, crown and roots, the small amount that gets into the fruit is critical for good berry structure and shelf life. Although the inner fruit and distal parts of the fruit contain little Ca, the relatively high concentrations found in the fruit margins are particularly important for their effects on fruit quality. If the product does not successfully endure the period between harvest and sale, we will have failed even though we have done a superb job of growing the crop in the field.

Most efficient way to apply Ca

It is important to apply Ca where the root growth is most intensive and to stimulate root growth in order to achieve an optimum nutrient uptake. Because Ca is not phloem mobile, root tips have to meet their Ca demand by direct uptake from the external soil solution. Due to the high Ca demand of growing roots, a large amount of Ca is accumulated in the root after it has been taken up and is not translocated to the shoot. Most Ca is transported to the leaves via the transpiration system and cannot be transferred from the leaf to the developing fruit. As a consequence, strawberry fruit may suffer from Ca insufficiency or deficiency as only small amounts are taken up by new growth or the fruit.

Calcium nitrate fertilizers are effective at supplying soluble Ca and trials show that they can be applied through fertigation or foliar sprays to help reduce environmental stresses such as salinity or sodicity. Fertigation and foliar applications which cover the fruit provide a regular supply over the growth of the crop and are the most effective means of raising Ca levels in the berry.  

Regular Ca supply throughout the production cycle ensures that Ca required for fruit integrity will find its way into the fruit also boosting yields. Trials show that Ca increases fruit firmness and prolongs shipping quality. Calcium also minimizes cell leakage and tissue senescence through supporting membrane structures and also disease suppression.

YaraLiva CN-9 treated strawberries on the left, untreated on the right. 

Strawberries with YaraLiva CN-9 nutrition program have longer storage and shelf life than the standard grower program. We will explore these findings in more detail in the following newsletter.

Facing challenges

Cation competition

Even with sufficient Ca supply to the roots, Ca deficiency can occur due to excessive concentrations of competing cations (Mg, K, NH4), or oversupply of nitrogen in general. Achieving the correct balance of K:Ca:Mg is important at different stages of growth (read previous issue). It is important to maintain high Ca concentrations to ensure that this nutrient is not limiting, or physical fruit quality can be compromised. Where salinity or sodicity are an issue, use of Ca can help to mitigate these effects. In trials, adding extra Ca in a saline situations has been shown to help reduce cellular breakdown and leakage, improving growth and yield.


We normally see an increase of Ca deficiencies into the winter months along coastal California. The cool, overcast conditions limit root water uptake and thus calcium uptake. Limited transpiration leads to poor Ca uptake by the roots. As a result roots become short, stubby and dark. Petiole necrosis, flower stem lesions and tip burn increase with decreasing Ca uptake. Adequate calcium supply to the fruit is a particular issue when excessive heat or cold reduces transpiration. Berry quality will suffer as a direct consequence. Fruits that are low in Ca are prone to rots and shortened shelf life.

A good way to supply the plant’s nutritional demand for Ca is by using foliar fertilization, reducing the need for root uptake. Calcium is immobile within the plant, making foliar applications ideal for situations where soil application is not possible or impractical. Pre-harvest foliar applications which cover the fruit are an effective means of raising calcium levels in the berry for subsequent harvest.

While there is no substitute for a sound soil fertility program, there are many occasions when applying foliar nutrients is a much more efficient and effective way to meet the crop’s needs at critical development periods. Yara has a complete lineup of foliar nutrition products to supply any mineral nutrient requirement your strawberry crop may need. YaraVita CALTRAC provides an abundant amount of available 23.8% Ca, making it an ideal choice to overcome Ca deficiencies. The YaraVita foliar sprays are developed to target the leaf or fruit, to work fast and to effectively overcome crop deficiencies. Each YaraVita foliar product is formulated from consistently high quality nutrient compounds with co-formulates, such as wetters, stickers and absorption aids, to control and enhance performance.

  For more information, contact your local Yara agronomist:

Eddie Muro
Sales Agronomist, Central Coastal California
Yara North America


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