Little analysis for N and P nutrient optimization in RDWC hydroponic system

[martani]

Hi guys,
we are just starting with this new project pointing towards the determination of optimal P and N concentrations in the nutrient solution during the flowering stage for a high CBD selection Charlotte Web, grown in RDWC systems (Alien). The experiment will be performed in a 15m^2 containing 6 6-pot RDWC systems, equipped with chiller and UV-C lamp to sterilize the solution. For the entire experiment we are going to perform 2 cycles of 6 treatments each.

Here are some photos of the rooting system: to obtain 36 uniform rooted clones we took 120 cuttings on the 21st of January from 1yr old mother plants and we put them in the rooting system with 40L of demineralized water-based solutions containing 4mL/L of CANNA Rhizotonic, 1 mL/L of Purolyt and phosphoric acid as a pH- until pH=5,6 was reached (for pH and EC readings we use HM-200 HydroMaster). The solution was completely replaced after 2 weeks: rooting times are longer than expected, almost surely due to too low temperatures in the rooting chamber, which range from 10°C at night to a maximum of 18°C (we have a temperature control system, but it's not powerful enough to reach the desired temperature).

PS: we apologize in advance for the huge amount of data we are going to upload, but this thread is meant as a sort of grow/study diary. Since it is our first time with an hydroponic system we'll love to read any comment and/or advice from you. It's going to be hard, but we have high expectations from this project

 

[martani]

Hi guys!!
here we are with some news: the clones started rooting at an acceptable rate (25 new clones rooted in the last 3 days) but, as you can see we are now struggling with some nutrient deficiencies. We tried to give intermittent watering to the rooting clones and it seemed to work fairly well, although we've not been as constant with the timing, mostly because we weren't confident enough to leave them the whole weekend without checking their health status. As for the nutrients we are now adding some vegetative compound fertilizer from Terra Aquatica, hoping in good results. We also added Terra Aquatica's micronutrient solution for soft water, dosage as recommended (0.2mL/L). By next monday we are going to choose the most uniform rooted clones and to put them in the vegetative NFT system, in which they'll stay for 7 days before being put in the flowering room.

Here we leave some pics

 

[martani]

Hi guys, these are pics from the 28th of February (we didn't have much time to upload news here). We transfered 46 clones (36 clones directly in the RDWC mesh-pots, the remaining 10 in the mesh-pots delivered with the NFT system so that we could have some replacement) in the NFT system and they stayed there for 7 days. We put Terra Aquatica nutrients (veg and microelements for soft water) up to 1.05-1.1 mS of EC. We also added phosphoric acid to lower the pH until 5.6-5.8 was reached. We added 1mL/L of Purolyt (hypoclorose anion, obtained through an electrolitic process) to ensure solution sterility.
As you can see the roots were healthy and stretched a lot compared to the previous week. While transferring the clones in the NFT system we cut the roots approximately at 20cm from the stalk, to ensure uniformity and to prevent breakings while pouring the expanded clay (which we thoroughly washed 3 times to reduce the amount of powder accumulation in the system).

 

[martani]

Hi guys, these are pics from 7-03-22: we transferred the plants in the RDWC system and started the flowering phase (and the true experiment). In the first pic you can see the NFT system with the 46 plants just before topping and pruning. Most of the deficiencies seemed to be resolved, with the exception of 1 plant in the 36 mesh-pots which appeared excessively chlorotic (you can see it in a dedicated pic uploaded with this post) and which we substituted with another plant (dedicated pic also for this one). We proceeded with topping, in order to reach an height between 13 and 17 cm for each plant and we removed the bottom branches until only 6 axillary shoots remained (the second and third pic are of a representative plant, before and after topping and pruning, metre for scale).
In the meantime we filled the RDWC systems with 100L of Renverse Osmosis water (EC=0.03 mS) and dissolved different amounts of nutrients (CaNO3, NH4NO3, KCO3, H3PO4, MgSO3 and microelements) according to the experimental design (we'll make a dedicated post in the next days about the amounts of nutrients tested). EC varied between 1.4mS and 2.2mS. We adjusted the pH with citric acid up to a value of 5.6-5.8 was reached, waiting approximately 10 minutes between adding the acid and measuring the pH (you'll find out that probably it is way too short).
We then transferred the plant to the RDWC system positioning them randomically, paying attention only to evenly distribute the plants still presenting chlorosis symptoms between the 6 RDWC systems. You can see the final result in the last pics (sorry for the reddish nuance, but we didn't set the camera yet for the new LED lamps).
We also added some pics to show you our setup: you can see the inspection pit, with the two pumps, one sending water to the chiller, the other sending water through the system. In line with the chiller we mounted an UV-C lamp to ensure solution sterility and, we thought, to avoid adding chlorinated products to fight microrganism proliferation.
Air is also sterilized with an UV-C lamp; there's no air change, therefore we provided added CO2, controlled by our trollmaster control unit, which controls also temperature and humidity. The settings are: [CO2]=1100ppm; T should vary between 21 and 24 degrees (we wanted different temperatures between day and night, but the setup doesn't allow it) and air humidity is monitored by the control unit, but is kept between 40% and 60% by a dehumidifier.
That's all for this post, new updates coming soon!

 

[martani]

The files were too heavy, so we had to split them into two posts. These pics are from 7-03-22 too, as in the post above

 

[can'tfindmyway]

and then??