The big question this week was why are the tomato leaves turning purple on the underside? I think the answer was/is phosphorous deficiency which was very surprising. I’m growing in pure compost, watered with hydroponic tomato fertilizer. How could there possibly be lacking nutrients?
The first part of the equation is: Bacterial or algal growth in the fertilizer reservoirs. I had this problem before in an algae experiment, where after mixing F2 algal fertilizer a bunch of sedimentation happened. I fixed that by using two peristaltic pumps to add part A and part B separately, each part along being insufficient for growth. I don’t have that option here because the two parts of this solution have all the necessary nutrients alone, and I had a separate reservoir for each plant. The bacteria also had made clogs in the dripper hose so not all the drippers were working.
I needed to fix the problem asap, so sadly now I will not be able to measure the amount of water used by each plant. I took apart all the blumats and drippers, washed them in bleach solution. I then used new (opaque) hose and set up one dripper per plant. I am now mixing a new bucket of fertilizer each morning, and pumping it directly onto the plants over the course of an hour. There is lots of runoff, but I siphon that out of the sump. I’m using 3 liters for the 6 plants right now. Near the southmost plant the tensiometer read about 2 kPa while watering, and about 10 kPa right before the watering starts the next day. I may switch to a gravity feed since that will lower the flow rate, and allow for better soil absorption. I purge the lines with water after each fertilizer dose.
So far, this seems to be working. Purple color is receding and lots of new growth without purple. Generally quite a bit of runoff, 2.6 l recovered out of 3 l added today. But I think the experiment can still continue. Or “trial” sorry, this technically isn’t an experiment because I don’t have a error analysis / statistical test setup before hand. I want to compare with the mathematical tomato yield model, and get some good plant scans to see how tomatoes capture light from the side.
I also put a new cover on the trial greenhouse with inflated double wall. That was the first time I’d done a double layer, and I think it went ok. Hard to get it tight, as usual, and the cold weather doesn’t help. Our ultimate goal is to make an inflatable greenhouse cover where you can just unroll and inflate. I now think that’d be a pretty easy sell to anyone who’s had to mess with installing a traditional double layer. I have the PAR sensors setup inside and out collecting data to use with the ray tracing validation.
If anyone reading this knows of an importer of PATI lux greenhouse plastic in Canada or USA, let me know! I settled for MUTI this time and I can see that it’s not nearly as good. Diffusion is too high for my purposes.
Plant scanning is coming along ok, I may run into trouble where I cannot move the scanner around the plants well because there is not enough clearance between plants. Were I to repeat, I’d have each plant in a movable pot so I could take them in and out of the growth chamber. The orientation rig works, but I’ve found a ribbon of magenta on the soil surface works
Sun Aquasystems 