Irrigation Strawberry dry-down

Irrigation in strawberries seems to be one of the hardest issues. If i ask growers i work with 90% of them will mention this as so.

In my last post on LinkedIn, i had a poll about the dry down for strawberries overnight. Interesting to see 640 impressions, but just 16 votes. An indication for the fact that good irrigation is hard working?

But first, what is dry down? Dry down is the difference in moisture content between the frist irrigation in the morning and the last one of the previous day. In the schedule aboveyou can see the level at the irrigation of the previous day and the level at irrigation of the current day (between the red lines in the graph above).

Interesting to see the answers also: no one voted for 4-6%. Although i didn’t mention the substrate in this poll. I ment to ask for organic substrates like coir or peat.

Most of the answers where on the 9-11%. For Rockwool where dry down is a known concept, i do think 9-11% makes sense. For coir i see 4-6% as the optimum. Reasons:
– Rockwool 9-11%:
* Strawberry is a plant that really likes air / oxygen in the rooting zone. The best soils are still the coarse sandy soils. The best substrates those with a lot of oxygen/air in the rooting zone. The oxygen content in Rockwool is essential lower as in most coir i see. A period with more oxygen in the rooting zone is essential for good root growth. A higher dry down can help therefore.
– Coir / Organic substrates 4-6%:
* Several items are directly related to this percentage:
** Tip burn (or calcium deficiency in the young leafs / flowers)
about more then 90% of the tip-burn i see is not related to fertilizer recipe but to climate. Calcium is passiv taken up by the plant with the sap flow (xylem). This means, Calcium is transported to those places where evaporation is taken place. Only in case of rootpressure it gets everywhere.
Low moisturecontent in the evening means low root pressure and thus higher risk on tip-burn.

** Root health and fluctuation in moisture content. Strawberry generally grow better if the fluctuation in moisture content is not too big. Periods with relative wett substrate seems to influence both rooting as well as browning of the roots, probably because of oxygen deficiency.
** EC / drainage. Strawberry have an optimum EC range from about 1,3-2,0. In case of low drain percentages the EC increases causing mainly yield and quality issues. In case of high dry-down more irrigation water is needed for remoisturing and less time on the day remains for drainage. This can be seen in quite strong increase of drain EC in case of high dry down levels.

LAI = Leaf Area Index

Those experiences bring me to the following numbers:
– optimum drip EC: 1,3-2,0
– optimum drain EC: 1,5-2,0
– optimum dry down:
– coir: 4-6%
– rockwool: 9-11%
-optimum drain percentages:

Important to know, that these numbes are quite general, but differ for individual situations. Irrigation is not easy, it is subject for at least a days discussion if not for a week.

One of the most important basics is, that strawberries don’t handle big fluctuations very well. Both in EC as in Moisture content. They almost always lead to quality issues and sometimes to growth issues.

This means very practicle, that if i have a too high EC, i don’t advice to flush it suddenly, but decrease it steadily, slowely. The same for moisture content, if it is too low, don’t suddenly increase the moisture content.

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