Reusing soil (tomatoes) - informational observations
Last fall, when I went to empty my 18 gallon containers of 5:1:1 soil into the compost pile I found that over 3-4 years of use, the sun had destroyed the structural integrity of the rim of the tubs I was using to the degree that when I tried to lift the tubs the handles & rims were breaking. My option then, was to leave the tubs in place with the soil exposed to the weather over the winter in an attempt to get another year out of the set-up, or replace the tubs & soil. I felt confident in my ability to gauge water needs, so decided to turn it into something of an experiment.
In late May, I pulled the weeds in the tubs & used a trowel to turn the old soil over, stripped the bottom leaves off the sets and planted the sets deep. As the plants grew, I stripped the lower leaves and back-filled the containers with fresh 5:1:1 until they were filled, the old soil being 5:1:1 that was a year old at planting time. I ended up adding about 1/4 of the container's total volume as new soil.
The results weren't awful, but there were notable differences between last years results in fresh soil and this years in the soil that underwent a growth cycle of use and a winter's worth of composting. I would estimate this years plants to be about half the size in terms of o/a vegetative mass, and the yields to be about 2/3 of what I had last year. I'm currently getting some typical dieback of just the lower foliage, but the vines continue to bloom & set fruit. If I had no basis for comparison, I think I'd be perfectly happy with both the condition/appearance of the foliage as well as the yields. In fact, since I have more tomatoes than I need or can eat from the 6 plants I have, I'd call my decision a good one, even though it's clear I left a fair amount of potential lying on the table.
To be fair, it's also possible that the intense heat we suffered for several weeks in late Jul through mid-Aug had some impact on the outcome, but I tend to think not so much because the foliage never seemed to suffer. Still, I'm prevented from making any sweeping conclusions based on how things went down. I just thought there might be some interest, even though all I have is a strong suspicion the difference was primarily related to the reduction in the % of air the soil was capable of holding, in spite even of the care I took in watering.