Filippo – [00:01.000 - 00:28.840]
Welcome again, everybody, to HaifaStream Greenhouse Plant Nutrition podcast made by the Haifa Modern Greenhouse Task Force. This is Filippo from Italy, and I'm here with my colleague, Ronald Valke, from the Netherlands. You may know him already from his last podcast on this series about clogged drippers. Ronald, please.
Ronald - [00:30.040 - 01:16.340]
Thank you very much to have me here, Filippo. My name is Ronald Valke. I'm from Holland. I'm going to explain to you about how to water your plants. First of all, I want to come back on the podcast that I did earlier on how to keep your drippers clean. You already mentioned it, Filippo. It's very important also if we talk about watering your plants and water content, that your drippers are working like they should be. So I suggest that if you didn't listen to my podcast about keeping your drippers clean, please go to the podcast and listen to it, because drippers that are blocked are difficult, make it very difficult for you to steer your plants.
Filippo - [01:17.880 - 01:25.780]
Yeah. And so we were speaking on how to bring, uniformly, the water to the substrate.
Ronald - [01:26.940 - 01:43.220]
Yeah that's absolutely important. If you – if each plant get the same amount of water, then it's easy to steer the plants. If one plant become very wet and the other becomes very dry because the drippers are not performing the same, then it's almost impossible to steer your greenhouse completely.
Filippo - [01:44.620 - 02:09.260]
Yeah. After we bring the water in a good way, we must know how to properly manage the water content in the substrate. Okay, this is the topic for today. How to do it? What should be the measure and the numbers we have to take into account?
Ronald - [02:10.740 - 03:23.120]
Yeah, the water content is absolutely very important. If the water content – if you have too little water in the slabs or too much water in the slabs, then the plants are not performing like they should do. To measure the water content, there are two ways to do that. You can work with sensors, and I see it more and more because it's more accurate, but you can also do it with a scale. The figures I give you is always based on the electronic measurements on the sensors. I think most of the advisors talk about the water content based on the sensors. So it's very important to know what you're doing. That's the reason that I'm going to explain the difference between water content with sensors or with a scale. First of all, the general rule is that the water content should be around 65%. That's in general for most crops. Of course, there are exceptions. For instance, in sweet pepper, they need a higher water content because they need more water available. So that's a difference, but the general is 65%.
Filippo - [03:24.680 - 03:38.540]
Okay, so you speak about 65% of total water content, and we have to know how to calculate the 100%. So where do we start?
Ronald - [03:39.400 - 04:29.100]
To calculate the water content, you can calculate the slabs, and you need to know the size of the slabs. The most commonly used slab is1.20 meter by 20 centimeters by 7.5 centimeters high. If you make this calculation, then you get a volume of 18 liters water content. But the same you need to do for the block. The block is the part where the plant is growing in the beginning. Most of the time they're 15 by 10 centimeters and 6.5 high. There are three blocks on the slab. So if you also calculate this, it's 2.9 liter. So that gives a total volume of 20.9 liters water.
Filippo - [04:31.500 - 04:31.665]
Okay.
Ronald - [04:31.900 - 04:33.244]
So the 20.9 liter is 100%.
Filippo - [04:34.280 - 04:34.411]
Okay.
Ronald - [04:34.890 - 04:46.200]
If you talk about 50% water content, it's 10.45 liters. So with the 65% that we advise, it's around 12, 12 and a half liters, something like that.
Filippo - [04:48.560 - 04:58.680]
So if we use the scale, okay, how do we deal with it?
Ronald - [04:59.460 - 05:03.080]
Yeah, the difference with a scale is that it's depending how do you measure 100%.
Filippo - [05:06.020 - 05:06.264]
Okay.
Ronald - [05:06.650 - 05:50.320]
Some people are measuring it and say the saturation point is 100%, but if you go to the saturation point of the slabs, put it on 100%, if you do it with an electronic measurement, with a sensor, you see that it's only 60 to 75% water content. So there is a big difference, that you think that it's 100%, now it's only 60 to 75%. So for there, it's very important to know, where are we talking about? Also, I think the saturation point can change during the day. It's not a fixed number, what makes it difficult to steer.
Filippo - [05:53.320 - 06:31.640]
Yeah, so like you said, if we speak about saturation point from the scale point of view, so 100%, the electronic sensor, the electronic measurement will say to us that that is not the 100%, but only the 60 to 75% water content. So, again, really important when we speak together, when you give information, to give also the way we calculate this information, if with electronic measurement or only by putting the saturation – the slab.
Ronald - [06:32.700 - 06:56.940]
Yeah. Well, there is a better way to also work with scales in a good way. If you take the weight of the completely filled slabs, including the blocks, or 50% of the blocks, you need to calculate 50% of the blocks, and you take that total weight and you set that as 100%, then it's equal to electronic measurements.
Filippo - [00:06:57.840 - 06:58.158]
Okay.
Ronald - [06:58.460 - 07:00.580]
So if you do it like that, then everything is fixed.
Filippo - [07:01.260 - 07:15.820]
Okay, so with these little tricks, not considering only the slab, but also the 50% of the volume of the blocks, we can have really the 100% water content that the electronic measurement is giving us.
Ronald - [07:16.160 - 07:17.960]
Yes, that's right. Then it's completely comparable.
Filippo - [07:18.520 - 07:35.370]
Yeah, perfect. So we bring water to the slabs, of course, to bring water to plant, but to bring fresh water. So we want also our plants to drainage.
Ronald - [07:36.780 - 08:05.580]
Yeah, absolutely. You absolutely need to get some drainage, to flush out the unneeded elements. But also there are some root root exudates, what can be a kind of poison for the plants. You need to flush it out. If you're not recirculating, I understand that you don't want to flush out too much because you're throwing away water and fertilizers. But the minimum you should do is 10%.
Filippo - [08:06.820 - 08:11.480]
Yeah, and so how we can check if we have enough drainage?
Ronald - [08:14.280 - 08:55.000]
There are different ways to check it, to measure it. First of all, you can see the EC level in the slabs. If the EC level is going up too high, let's just say that you didn't have enough water, you didn't have enough drainage. You especially see that when there was a lot of sunshine. Plant is like we are. When it's sunny, we want to drink more and eat less. If a plant drinks more, EC level is going up because EC is eating. So if you see that the EC level is going up, it means that you give too much water, or too less water. Or water with a too high EC. You can do two things.
Filippo - [08:55.460 - 08:54.991]
Of course.
Ronald - [08:55.760 - 09:00.000]
Lower the EC if there's dripping water in that case, but also you need to create some drainage.
Filippo - [09:00.360 - 09:01.352]
Yeah, of course.
Ronald - [09:02.320 - 09:32.000]
The second measurement that you have is the sodium level in the slabs. It's difficult to measure it every day, but if you send water samples to the laboratory, you see your sodium level. In general, we say, don't go above 8 millimoles per liter sodium, where for those who talk in ppm, 180 ppm is the maximum sodium level you can allow. We know that above you get damage, visible damage.
Filippo - [09:33.120 - 09:33.333]
Yeah.
Ronald - [09:33.400 - 09:45.280]
What means that below, we think that you also get already damage. Damage is one of the things is that you get less calcium uptake. For instance, in tomatoes, if you have less calcium uptake, they become more sensitive for blossom-end rot.
Filippo - 09:45.580 - 09:46.467]
Yeah, for example.
Ronald - [09:47.400 - 09:59.680]
So we always try to keep the sodium level as low as possible. But for sure, if you go above these numbers, above these 8 millimoles or 180 ppm, you need to flush more. Absolutely.
Filippo - [10:01.460 - 10:25.700]
Of course, regarding sodium, fertilizer play a role. So we know that in some fertilizer, or in general, in fertilizer, we also bring sodium sometimes. So we have some possibilities by choosing a different type of fertilizer to reduce this accumulation of sodium.
Ronald - [10:26.220 - 11:34.680]
Yeah, absolutely. In the area I'm responsible for, all the growers are recirculating. It's in the law. They need to do it. They all use the Multi-K Reci from us. Multi-K Reci is our potassium nitrate with a guaranteed low sodium level. And if you compare it to other products on the market, it's 10 to 20 times less sodium in the product compared to the others. And this really, you see it in the figures. I can tell you a story that I was at a grower. He was, for a short period not recirculating, but he changed the drainage percentage based on the sodium level. So if the sodium level was too high, he started drainage more. And he changed to the Multi-K Reci, and he saw that the sodium level was not going to be too high anymore. So he said, yeah, now I'm only drain it to get some fresh water inside and to get some other things out. But for the sodium, it was not necessary anymore. So this is a big advantage. So yeah, very important to look to your fertilizers. And if you don't know if there's sodium in, just ask your supplier.
Filippo - [11:35.500 - 11:37.664]
Yeah, okay.
Ronald - [11:41.240 - 12:27.180]
Yeah. Then there is a third thing, also very important, if you see unbalance in your elements. So if you get your analysis report from the laboratory and you see, for instance, that the potassium level is very low and the calcium level is very high. We see that very often happening in the beginning of the swelling of the tomato fruits. The first tomatoes on the plant, when they start swelling, then you see that they absorb a lot of potassium. And if you didn't change your fertilizer recipe in advance, then you see that your potassium level in the slabs can go down to 1 millimole, so that's around 39 ppm, what is way too low.
Filippo - [12:29.360 - 12:29.628]
Yeah.
Ronald - [12:29.720 - 12:33.260]
Then the only thing that you could do is increase your drainage just –
Filippo - [12:34.020 - 12:34.389]
To refresh the –
Ronald - [00:12:35.720 - 12:36.018]
Refresh more.
Filippo - [12:36.270 - 12:36.562]
– the solution.
Ronald - [12:37.110 - 12:52.040]
To make more available. It's not a good idea directly to change your fertilizer recipe at that moment to increase the potassium nitrate in the fertilizer recipe because then you are running behind. You need to stay in advance.
Filippo - [12:52.530 - 12:52.625]
Yeah.
Ronald - [12:52.880 - 13:02.860]
It's better to do it already in the start when you know that the fruit start swelling, give already some extra potassium, but if you're too late, then just increase your drainage percentage.
Filippo - [13:04.240 - 14:06.700]
So, like we were saying before, we must anticipate the necessity of the plant, let's say, to avoid running behind. And if we have to run behind, because sometimes it can happen, we have a lot of things to take into account, so something always, let's say, forgot. But in that case, we do not have to react directly by adding more potassium nitrate, but starting from refreshing the solution in the slab, so starting by having more drainage. Yeah. So when you were speaking about the drainage in general for greenhouse, but you are, like you were saying, you work in the Netherlands and in countries where recirculation is a must. Okay? So the drainage change when you work in recirculation?
Ronald - [14:07.420 - 14:27.340]
Yeah, in recirculation, of course, you reuse the water and fertilizer again. So cost factor is not an issue anymore. So there we go to around 25% drainage during the day, up to 30%, and then we are on the safe side.
Filippo - [14:27.980 - 14:40.820]
Okay. So we said we need to refresh the water in the slab. How do we increase this refreshing in the slabs?
Ronald - [14:42.160 - 15:38.420]
It's very important to do that in the right way. I see a lot of mistakes, and finally, you don't get then what you want to gain. First, you need to calculate, again, the volume of your substrate. We already did it earlier. I'm not going to over the figures again. But in the calculation I showed you earlier, we came to 20.9 liter substrate. If you work with three drippers, you have three plants, one dripper per plant. Then we say, okay, that's seven liter substrate per dripper. To refresh and to give enough water for the seven liter, you need to give 25 cc each dripping time per liter substrate. So this means in this calculation, seven liters times 25 cc. Each dripping time, you give 175 cc per dripper.
Filippo - [15:39.160 - 15:39.367]
Okay.
Ronald - [15:39.810 - 16:15.120]
There are also some growers who have two drippers per plant. Still three plants on the slab, two drippers on the plant. So no change in the volume of the substrate, only the double amount of drippers. What means that the amount of cc's should be divided by two. Calculation, the 20.9 liters, of course, stay the same, but you have six drippers, so you divide it by six. Gives 3.5 liter, and 3.5 liter per dripper times 25 cc is 87 cc per dripper.
Filippo - [16:15.500 - 16:16.127]
Per time.
Ronald - [16:16.450 - 16:20.860]
But in total, it's the same amount of water per slab.
Filippo - [16:21.260 - 16:24.370]
Yeah, we only divide it by a higher amount of drippers.
Ronald - [16:24.980 - 16:25.510]
That's right. Yeah.
Filippo - [16:26.240 - 16:50.160]
So we started from the calculation of the volume of the substrate, and we gave the numbers. So for a standard stonewool slab plus the three blocks of the plants, we are speaking almost about 20.9, 21 liter of total substrate. Then we know that we have a certain amount of drippers for the slab, for the plant.
Ronald - [16:50.570 - 16:50.705]
Yes.
Filippo - [16:50.950 - 17:10.500]
So we can have three or we can have six. But at the end of the day, what we want to know, what we want to give is 25 cc per liter of substrate. So these are the features, the numbers we should take into consideration when each time we water. Okay.
Ronald - [17:11.030 – 17:11.247]
Yeah.
Filippo - [17:11.300 - 17:17.840]
So this is really important. By, let's say, we are speaking about stonewool.
Ronald - [17:18.860 - 17:58.240]
Yeah, that's one remark that I want to make. With this kind of figures, this information I give is based on stonewool. The biggest part in the market in my area is is working with stonewool. If you work with a different substrate, we see that wood fiber (indistinct) is coming slowly, but you don't see it so much, but it's coming, then the figures are different. So then it's better to talk to your producer of your slabs and ask him, okay, I know this information about stonewool. What about when I work with your slabs? How do I need to measure these? Because it can be that you need to refresh more or less.
Filippo - [18:00.000 - 18:05.900]
Depending on the features of the substrate, we need to change our watering.
Ronald - [18:08.660 - 18:08.922]
Absolutely. Yeah.
Filippo - [18:09.210 - 18:28.740]
Let's say sometimes we see that growers increase the amount of water per dripping time. Okay? But we see that in general, the effect, what they take out is not what they (indistinct)
Ronald - [18:30.000 - 18:51.040]
That's right. It's a big mistake. I see that it happens a lot of times, that you want to create more drainage, to refresh your water in your slabs more, and then you increase the amount of CCs per dripping time. The only thing that you're doing, you're flushing your dripping water directly to your drainage.
Filippo - [18:51.820 - 18:51.933]
Yeah.
Ronald - [18:52.260 - 19:17.520]
Because it's one straight line from the dropper to the bottom of your slab and going out. So that's not the way that you can refresh your slabs completely. Best way is not to increase the CCs, but increase the amount of times that you give water so you're watering more times. Then you get a better refreshment in the total slab. Finally, you get what you want.
Filippo - [19:19.700 - 19:43.520]
Okay. We spoke on how to refresh, but at the end of the day, when the season, let's say, start and when we are working in fall, in winter, in spring or in summer, we have the change, the climate change, the light change. When we have to start and when we have to stop watering?
Ronald - [19:47.480 - 21:27.600]
Yeah, start watering, in principle, we all say, don't start watering earlier than one hour after the sun goes up. It counts for the wintertime, counts for the summertime. The same as when you stop watering, you stop at least one hour before the sun goes down. After this one hour, we still want to have 250 joules of light, because this 250 joules of light is enough to consume this water. We don't want to water after midnight. That's a golden rule. If you water after midnight, you can get serious damage on your crops. So don't water after midnight. If you see that your water content is going to be too low after you stop watering, you can give one extra time water between the sundown and midnight, in between somewhere. During the night, we accept that the water content in the slabs is decreasing by 7% to 15%. That's a general number, but that's okay. You can play with this. If you go down to – if you decrease the water content more than in a higher number, the reaction from the plant is that it becomes more generative. It's an EC effect. If your water content goes down, EC level in the slab is going up, and with a higher EC, you get more generative growth.
Ronald - [21:29.200 - 21:39.430]
Also, the other the other way around. If you decrease – if your decrease of the water content is lower, you can get more vegetative growth.
Filippo - [21:40.120 - 21:40.546]
Okay.
Ronald - [21:40.800 - 22:05.230]
And you can play with this. It's not that you can completely steer your plant with it, because also the fertilizer recipe is very important in this. For more generative growth, I think everybody knows that you need to give more nitrogen. Nitrogen is growth. If you want to have less – no, I'm making a mistake.
Filippo - [22:06.820 - 22:07.396]
Yeah, you want to –
Ronald - [22:07.370 - 22:10.960]
Yeah, I mixed it up. More vegetative growth, then you –
Filippo - [22:14.240 - 22:34.520]
Yeah, if we want more vegetative, we usually increase the nitrogen, the nitrate. While with the generative, we usually reduce the nitrate and increase the sulfate. Let's say that the watering and the fertilizer we are using our two component of our driving for the plants.
Ronald - [22:34.930 - 22:36.960]
You're completely right. I was a little bit mixed up.
Filippo - [22:37.270 - 22:37.626]
No problem.
Ronald - [22:37.840 - 22:57.980]
You're completely right. Nitrogen gives more vegetative growth. So if you increase your nitrogen level, you get more vegetative growth. The other way around, if you want to have more generative growth, you increase your sulfur level, and you can also change a part of the nitrogen to chloride.
Filippo - [22:59.340 - 22:59.543]
Okay.
Ronald - [22:59.780 - 23:13.890]
But that's limited and depending on the crop, because not every crop is reacting on chloride same, like, for instance, a tomato or a sweet pepper plant. So that's the better way to control vegetative or generative growth.
Filippo - [23:15.220 - 23:26.280]
Okay. So we spoke on why to refresh, when to start watering, but how much we should water on a day.
Ronald - [23:28.360 - 23:52.320]
It's difficult to say, of course, because I don't know if you talk about summertime with high radiation or wintertime. So that makes a big difference. But the general rule is that we want to have drain within one and a half to two hours. So after you start watering, within one and a half to two hours, we need to see the first drain. If we don't see drain in one and a half to two hours, you give too less water.
Filippo - [23:53.440 - 23:53.855]
Okay.
Ronald - [23:53.980 - 23:57.040]
You give not enough times water.
Filippo - [23:58.100 - 23:58.413]
Yeah.
Ronald - [23:58.470 - 24:23.660]
Very important. Then after you got drain, we're going to look to the water content. Every time the water content drops by 2%, we start watering again. So we're watering, then everything is fine. When it drops 2%, the water content, we start watering again, and again, and again, and again. You can imagine that in winter time, that's maybe five, six times a day. In the summertime, it can be 20, 30 times a day.
Filippo - [24:24.280 - 25:01.880]
Okay. So we had a complete look into the watering, how to do it, why to do it, when to start, when to stop, based mainly on water content. There is another parameter we can have a look to water, to decide how to water. Before you were speaking, of course, the watering management change depending on the season, and you were speaking about light. So this is another parameter that counts a lot?
Ronald - [25:02.480 - 25:16.920]
Yeah, there is a possibility to steer the amount of water also on the light sum. So depending on the amount of joules that you get, you can also say, okay, if I have this amount of joules, I give some extra water.
Filippo - [25:17.660 - 25:17.859]
Yeah.
Ronald - [25:18.230 - 25:29.120]
So you measure it on the 2% drop of your water content, and on top of it, if you see that you have a very high amount of joules on light, you give one or two times extra water.
Filippo - [25:30.000 - 25:30.246]
Okay.
Ronald - [25:30.420 - 25:34.860]
There are some ideas to do that. It's difficult to say what's the best way.
Filippo - [25:35.340 - 25:35.540]
Yeah.
Ronald - [25:35.750 - 25:37.360]
I think both are okay.
Filippo - [25:37.920 - 25:43.160]
Of course, at the end of the day, we are looking to the same problem in two different way.
Ronald - [25:43.780 - 25:44.363]
Absolutely. Yeah.
Filippo - [25:45.260 - 26:19.530]
It's the same, but with different vision. Okay, Ronald, thanks again for sharing your knowledge, your experience. It was a pleasure. We thank all the listeners of the podcast. So subscribe to HaifaStream, and we will update you with a new episode. If you have any kind of question regarding this podcast, please write to us, and we will be more than happy to reply to you.
Ronald - [26:20.280 - 26:21.400]
Absolutely. Thank you very much, Filippo.
Filippo - [26:21.500 - 26:21.700]
Bye.
Ronald - [26:21.800 - 26:22.610]
Bye-bye.
