Whether your crop is nearing the end of its cultivation cycle or will grow through the winter, the irrigation strategy is an important steering tool at this time of year.
For plant quality we need to protect root quality. If we over-irrigate, we run the risk of losing root quality and increase the chances of crop losses from fungal diseases, such as Botrytis and Mycosphaerella.
|Photo 1: A water content meter by Grodan.
Within the irrigation strategy, the general rule of thumb still applies – “transpiration then irrigation.” EC management is still important but we can accept higher ECs in the substrate, especially on darker days. Water content meters, such as the Grodan water content meter, can help you judge when to start and how frequently to apply irrigation during the day. It will also provide information as to EC development. (See Photo 1)
TIPS FOR MANAGING SUBSTRATE WC
Before the first irrigation, look for a 1.5 – 2.0 per cent decrease in substrate WC from sunrise. This will ensure the crop is sufficiently active before we apply the first irrigation. This will avoid moments of root pressure.
|Photo 2: Good root health.
At the end of the day, look for a four per cent drop in WC within the first three hours after the last irrigation. This will prevent unwanted moments of root pressure and ensure enough drop in WC overnight.
As light and overall radiation levels will become lower compared to summer conditions, it is too easy to over-irrigate. This is normally seen in high drain amounts. Table 1 presents the suggested drain volume for radiation level.
TIPS FOR MANAGING SUBSTRATE EC
It is important to maintain some drain with the lower amounts of irrigation. Most critical for successful EC control is to achieve the first drain ±two hours after the first cycle, within three to four cycles. In this way, EC will be at its lowest level when radiation is at its highest point and water uptake is most needed.
|Monitor the rootzone regularly.
During the fall and winter period, we should accept higher EC levels for plant balance (over-wintered crops) and fruit quality for those crops nearing the end of the cultivation. EC levels will be higher and water uptake will be lower, ensuring the required amount of nutrients into the plant. Higher EC levels will also help maintain sufficient fruit quality. For suggested EC levels in relation to light levels see Table 2.
Table 2: Indicative substrate EC values (measured at midday) in relation to highest daily light intensity (w/m2)