By Jacopo Parigiani
Fertilization is probably the highest expense per hectare in the rose industry. The high cost of fungicides and other pesticides for the control of downy mildew and botrytis also has a toll on farm economics. Fertilization in flower farms goes hand in hand with irrigation: every time there is an irrigation event, fertilizer is applied (fertigation), except in those few occasions when the system is flushed with water in order to clean out the drip lines.
But how are farmers managing their irrigation? Surely the amount of water applied is calculated based on the amount of water present in the soil and the amount of water that is absorbed by the plant? Irrigation, however, is not only the management of soil water but it is also, and just as important, the management of soil oxygen. There are three things required by all roots: nutrients, water and oxygen. Any of these missing, then it becomes the limiting factor and the roots will suffer and as a result the plant itself will suffer too.
Saving On Irrigation Water
There is a tendency on Kenyan flower farms to apply a lot of water on a daily basis. Irrigation management is pretty much based on feeling: today it’s very cloudy; I need to give a small amount of water. Today it’s very sunny; I need to give a lot more. Not really very scientific. Not very precise either.
Other ways farm managers check whether it’s time to irrigate, is by rolling up their sleeves, digging into the soil and “feeling” the wetness of the soil. This is actually a great way to assess soil moisture. A soil at optimal moisture content, at field capacity, is easily identified by touch. There are various problems with this technique though.
- How many times in a day can the farm manager check the soil for moisture?
- How many different locations per greenhouse can the farm manager check daily?
- How many different soil depths per location can the farm manager check with this method?
It’s easy to see that the farm manager will never have the time to do this more than once per greenhouse, unless someone is specifically employed. It’s also easy to see that in order to “cover more area” the soil depth which will be checked will only be the first 20cm. Which as it happens is actually the layer most exposed to the atmosphere due to the way flower beds are constructed and thus the layer that dries quickest. This technique, however great, is not sustainable.
The Cons of Over-Irrigating
Actually, throughout Kenya farms (and probably even beyond Kenya) there is a tendency to over-irrigate.
- The negative effects of over irrigation are numerous. For one, when applying water above the water holding capacity of the soil, the water, with its nutrients dissolved in it, leaches straight through the soil. Think of it as pouring water in a glass that is already full to the brim: it cannot hold anymore water. It is exactly the same. Both fertilizer and water are wasted through deep water leaching and, moreover, they end up back in the water table polluting downstream water sources.
- Too much water in the soil porosity displaces the oxygen from the pores creating an anaerobic environment in the root zone, meaning that roots get starved for oxygen. The roots will therefore tend to concentrate where there is oxygen, close to the surface.
- Oxygen is not only required by roots but by worms and other beneficial aerobic soil fauna which are also suffocated by the anaerobic conditions created by saturation.
- The “need” of farm managers to irrigate each and every greenhouse everyday means that irrigation goes on from morning till dawn. Greenhouses that are irrigated in the late afternoon do not have enough time to dry (transpiration stops at night) meaning that, at night, through evaporation there is a build up of atmospheric humidity right above the soil surface, creating the ideal conditions for fungal infections: downy mildew and botrytis.
- Not to mention the negative effects that the weight of water (or a wet soil) has on the sub soil: compaction.
The negative effects of over irrigation are many and costly. Over the past two years we at Cropnuts have been installing Aquacheck soil moisture probes in flower farms across Kenya with incredible results. The Aquacheck probes provide continuous soil moisture data down to 60cm and more. They are installed permanently in the ground in a location that best represent the greenhouse. They record soil moisture data and automatically upload it to an online software that can be accessed by phone, tablet or computer anywhere with an available internet connection. Aquacheck has given farm managers the ability to “feel” the soil moisture instantaneously and continuously from the comfort of their desk.
With over 20 farms across Kenya using Aquacheck we have realized that irrigation is quickly changing from the simple switching on and off of a button dictated by cloud cover, to a real art form of manipulating irrigation volumes and timings variably not only from farm to farm but from greenhouse to greenhouse. Aquacheck has provided the soil with a voice that can tell farm managers the exact quantity of water they require and down to what depth.
Aquacheck has reduced fertilizer use by 30%. Leaching is no longer an issue, meaning that there is no more wasting of fertilizers nor of water. The irrigation systems are no longer stressed meaning that irrigation can finish before 12:00 giving the greenhouse enough time to dry so as to reduce incidents of botrytis and downy. In one farm the reduction of fungal disease incidents has been by 80%. The great thing of all these benefits is that the plants are now healthier, producing more and bigger stems.
Irrigation management is not only about managing water. It is the management of water, oxygen, fertilizer and also pests and disease.
After two years in southern Tanzania planting trees and sequestering carbon from the atmosphere, Jacopo returned to his country of adoption and joined Cropnuts back in October 2012 to dig the Kenyan soils and conserve her waters. A graduate from Wageningen University (the Netherlands) in Land and Water Management, he has extensive expertise in irrigation management and precision agriculture (PA) technologies. The times he is in the office, you can find him crunching numbers, making colourful variable rate fertilizer prescription maps and feeding lots of data to a smoking computer!