We are using existing literature and beginning trials to zero in on the best protocol for growing sweet potatoes with simplified hydroponics.
Depth of Substrate
We experimented with depths of substrate 24". 18", 12" and 6" deep in containers.
In these trials, there was no difference in the 24" depth and 18". These trials show that 24" is not necessary for depth. Also literature search recommends a 12" depth for plowing in soil because a deeper depth makes sweet potatoes grow long and skinny.
This next year we will trial 18", 15", 12" and 6" to recommend an optimum depth for sweet potatoes.
Looking at this from the sweet potato point of view, roots dangling down from the green plant above will then swell into sweet potatoes. The swelling vegetables are often near each other and push out together. The swelling of the roots occurs in about 8 weeks from planting in soil.
A plant roots appear to grow from three to eight swollen sweet potatoes.
Type of Substrate
After the swelling sweet potatoes start to grow, they appear to want a substrate that is not too soft or not too hard. This would recommend a sand mix with either coco fiber or rice hulls or perhaps sawdust.
Fair Play Missouri trials used a mix of 1/3 sand, 1/3 coco fiber and 1/3 perlite. This substrate worked well in all trials at all depths.
Colombia trials used tire growers.
The tire growers were filled with a substrate of 30% poor soil, 30% grey river sand, 30% rice hull and 10% compost from home residues.
Colombia had excellent productivity, harvesting sweet potatoes in 95 days. Each grower produced 8 sweet potatoes of about 3 pounds each, or 24 pounds sweet potato per grower.
Type of Container
Fair Play Trials used both plastic tub containers and fabric Grow Bags. The grow bags should allow for gas exchange from the roots, with roots requiring to breathe in oxygen and breathe out carbon dioxide. In theory the Grow bags should
produce better than the plastic containers.
The early trials were inconclusive, partly because the grow bags were placed right next to each other, reducing the surface to air area.
New trials this winter and next summer will test the grow bags in a spacing that allows for complete air flow around the entire substrate container.
Even with the trials this summer being inconclusive the grow bags show a slight increase in root growth (10%).
Grow bags show great promise for this technology as the gas exchange of roots could be a limiting factor to sweet potato production. Thay also are useful in emergency kits because they can be folded up and shipped in small spaces.
Trials in Fair Play and Colombia used only a Grow nutrients on the sweet potatoes without switching to root.
Under normal root production the vegetable is changed to Root nutrient after the green growth is firmly established (about 8 weeks). In this first year, only Grow was used partly to see if any growth could be obtained with a one nutrient system.
Both trials had excellent growth with only Grow.
Beginning trials are established using root nutrient for the production of seedlings. This trial involves six different formulas and all are working well. All six will be tried with sweet potato this next summer in Fair Play in full production.
Sweet potato type
USDA nutrient database claims that a sweet potato has 1.6% protein, but this value changes according to type.
Sweet potatoes come in all sorts of colors. There are between 5000 and 10,000 types known. Of these the purple fleshed Okinawa sweet potato can average between 4 and 10% protein. This is an important difference in food value for people in hunger.
USDA also lists sweet potato has highest value of vitamin A of all vegetables. This is true for the orange fleshed varieties, and not the white varieties.
Fair Play trials used two orange fleshed varieties, a beauregard sweet potato purchased as seedlings from Walmart (Bonnie Bell) and a local variety provided by a well meaning neighbor. The Walmart variety was attacked by insects, but the local variety had no insect problem.
In the variety trials, the beauregard sweet potaoes under insect attack averaged 6 pounds per square meter while the local variety averaged 20 pounds per square meter. This seemed to be due to insect attack on beauregard.
In Colombia a local variety produced excellent results.
In experiments around the world it is advised to trial local varieties as well as commercial types. Variety is going to make a huge difference.
For next year Fair Play is going to trial Okinawa sweet potatoes and more local varieties.
The past efforts of simplified hydroponics to end hunger have been hampered by the lack of a steady supply of a staple food. This breakthrough could be an
important step in ending hunger. Any people or group willing to help us establish this protocol would be greatly appreciated.
As 30,000 people die of hunger every day, your efforts could help us see if our technology can reduce or end this terrible condition.
November 7, 2016
© 2016 Institute for Simplified Hydroponics