From Soil to Soilless Vegetable Cultivation
By Dr. Mohyuddin Mirza
It wasn’t that long ago that vegetable growers across Canada worked in the soil. But there were many problems they had to cope with, and researchers soon took note. The result was the development of new media and growing systems.
By Dr. Mohyuddin Mirza
August 2016 – Growing media for greenhouse crops fascinate me because as a greenhouse specialist in the early 1980s, I faced problems with the growing medium in which cucumbers were grown.
It was what I called “Prairie virgin soil” in the Redcliff and Medicine Hat region, along with other areas in Alberta. Cucumber was the major crop with a few tomatoes being grown (Photos 1 and 2). The soil had a low organic matter and growers were not adding peat moss or other amendments to replenish it. At the end of the crop season, growers would add manure, steam the soil and start new crops. Soil was also used as a growing media in many other areas of Canada as well.
But at about this time people noticed that cucumber production per square metre had stagnated. I remember our best production was around 50 cucumbers/sq.m. and it stayed there for a few years. Growers would add some peat moss, straw or sawdust, steam-pasteurize, and plant the next crop.
Photo 3 and the inset photo atop facing page show a later stage crop the 1980s. When the plants were pulled out (inset), growers often found root knot nematodes. Combined with diseases like pythium, this compelled us to develop information on the use of soilless growing media and hydroponics systems. These pictures depict a historical perspective of soil as a growing medium in the 1980s.
I still remember how my first production guide focused on growing cucumbers in soil; the recommendations were developed for the use of insoluble fertilizers. A typical fertilizer program included so many pounds of superphosphate, gypsum and mono-ammonium phosphate rototilled in the soil, with magnesium sulphate applied as needed.
(These pictures depict a historical perspective of soil as a growing medium in the 1980s.)
When nematodes became difficult to control even with the use of steam and chemicals, research efforts started with the development and use of soilless cultivation systems. I thought at that time that nematodes had learned to survive. For example, I found that after steaming there were plants with nematode infection near the greenhouse posts. They later moved towards the middle of the greenhouse when steaming was completed.
INTRODUCTION OF THE CORNELL MIX
This was about the time the Cornell mix was developed. It consisted of peat moss, perlite and vermiculite. Dolomite lime was added to counter the acidity contribution from peat moss. Fritted trace elements were added and in some cases a basic nutrient charge was provided. I believe that was the starting point of modern soilless growing media.
In the early 1980s, we started testing various growing media, including straw bales, sawdust, rockwool and various types of peat-based media. Along with these growing media, better nutrient formulations were developed. The development and availability of soluble fertilizers ranging from calcium nitrate, potassium nitrate, mono-potassium phosphate and magnesium sulphate, along with chelated trace elements, really gave a boost to soilless cultivation.
This was also about the time Dr. Allan Cooper from the U.K. reported on his work with the Nutrient Film Technique (NFT). This involves the use of water with all the necessary nutrients instead of a solid growing medium. There was lot of excitement about this approach to grow plants.
I had very good results when I grew my first crop of cucumbers in wooden troughs lined with plastic. I was excited when we got 80 cucumbers/sq.m. with a 100-day crop, however the development of a massive root mass resulted in crop senescence.
Many growers tried this technique in Alberta and abandoned it after some time. There is still one grower in Alberta who is using this method.
This technique, however, has been widely adopted by lettuce and leaf vegetable producers after some modifications, including the use of floating rafts.
After experimenting with various growing media and learning how to use them, most Alberta growers have settled on coir for cucumbers, tomatoes and peppers. In other parts of Canada growers use rockwool and sawdust.
Here are a few facts growers should be aware of before using their growing media:
- They should know the physical characteristics of the growing medium they are using or planning to use.
As an example, when using coir be familiar with its physical consistency. There are three terms used in this context – coir fibre, coir pith and coir chips/chunks. Coir pith is the most commonly used component in growing mixes. Very fine coir is generally not used for vegetable production. Similarly if peat-based media are used, then one should know the physical characteristics of peat moss, such as its percentage of different types of fibre lengths.
Ask suppliers about water holding capacity, total porosity, air porosity, and cation exchange capacity, and then based on that information, plan your usage accordingly. There are commercial growing media now available with high porosity for rooting, and medium porosity for main production. Once you know these factors, then adjustments can be made with your watering practices. I find one common problem results from growers creating water-logged conditions.
Learn about the supplied nutrient charge. Dolomite lime is used for countering the acidic pH of peat moss. This type of lime provides some calcium and magnesium over a period of time and may also react in two to three weeks to raise the pH. Beside lime, some commercial media contan small amounts of nitrogen from various sources. Knowing about the basic nutrient charge allows growers to adjust their feeding programs.
In a research project, we avoided fertilizing bedding plants for three weeks after transplanting until very early symptoms of nitrogen and phosphorus deficiency showed. The rooting was better in such plants compared to when fertilizing was started immediately after transplanting. Growers can benefit by utilizing the existing nutrient charge.
- There are many fine, newer growing media in the marketplace with different microbes/biologicals added for better root health and disease control. Learn about these additions and manage accordingly.
Growers may have noticed there are growing media with silicon amendments. Take advantage of such microbes for better root health and thus better plants. Silicon is known to provide many plant health benefits. A grower reported much better heat tolerance in tomatoes and an increase in fruit weights.
- Water as a growing medium is now widely used for lettuce, leafy vegetables and salad crops. Learn to manage nutrients and oxygen in water-based systems. Oxygen levels below
4 ppm could hinder root growth. Consider water disinfection systems because the microbial load could increase.
Paying attention to the physical, chemical and biological characteristics of your growing medium will ensure healthy crops and healthy profits.
Dr. Mohyuddin Mirza is an industry consultant. He can be contacted at firstname.lastname@example.org.