Creating optimal conditions in the greenhouse

More than a shell

The Merriam-Webster dictionary defines a greenhouse as ‘an enclosed structure used for the cultivation or protection of tender plants.’ Greenhouse structures are a big investment which makes it necessary to ensure that the greenhouse irrigation and fertigation system incorporates the latest technology, is of superb quality, is tailored to the conditions and crop requirements and is managed with expertise.

The irrigation designer, supplier, advisor or installer has a very important role in this regard. He must not only make the producer’s investment worth his while, but also lighten the producer’s load in managing the greenhouse crop.

A wide variety of crops is grown in greenhouses, each with their own demands. But let us consider the agronomy of blueberry production, to truly understand the importance of expert irrigation support and a top-notch greenhouse irrigation and fertigation system. 

Limited root systems

Pieter Burger, Netafim’s agronomist in the SADC region, explains that a complicated factor in blueberry production is that blueberries have a very limited root system. “In greenhouses blueberries are usually grown in 20 to 30 litre containers in growing media with limited water holding capacity. This means that water will have to be applied often and in small quantities. The growing media also has very low buffering capacity.”

This means that nutrients will have to be applied to the plant very accurately in terms of nutrient mix, Ec (electronic conductivity of the nutrient solution), at the right pH and during the correct growth stage of the plant to be able to fulfil the needs of the plant. If it is done correctly, it will enable the plant to produce high quality fruit in abundance. “Even when blueberries are produced in soil, the plants have a very shallow and small root system. The above scenario will prevail, and the same demands will have to be met with regards to the supply of water and nutrients,” he adds.

Precise Management

The complexities discussed here demand a lot of attention to detail and strategic actions from the producer.  The producer has a massive responsibility, including mixing the nutrient solution carefully and monitoring the application of these nutrients continuously to obtain a constant supply of nutrients, at the right ratios, Ec and pH, as well as a very precise supply of water to the plants. This must be done day and night, day after day for the entire growing season.

Pieter explains that the limited water reservoir, created by the limited root zone, demands that the water and nutrient delivery system must be able to cope with very short and frequent pulses of irrigation throughout the day. “The pulse lengths and frequencies must also be adjusted throughout the day. This becomes necessary as the water demand of the plant varies as temperature, humidity, sunshine and other climatic conditions change. This means that we have to open and close valves for a specific block frequently in order to supply in the water and nutrient demands of the specific block of plants.”

Supportive Solutions

The producer and his employees have an important responsibility. Mistakes can be very costly and even fatal to the project or farming enterprise. Luckily, the producer is not at all without support and there are tools to help him manage this burden. Over the past few decades, several solutions have been developed by irrigation and fertigation experts around the world to overcome challenges producers face in the production of specialised crops, such as blueberries. Especially in demanding production areas.

Pieter says that by harnessing automation solutions in the production system, for example, a producer can largely automate the actions that answer the water, nutrient and climatic (in controlled greenhouse systems) demands of the crop during all the production phases.

“Nutrients can be mixed into the irrigation water at the correct ratios, Ec and pH and will be monitored and adjusted to pre-set programs, set up by the producer. Irrigation pulses can be controlled by the CMT (Crop Management Technology) computer and valves can be opened and closed as determined by the producer. This will leave the producer’s hands free to attend to other problems and planning in the production system. The system can also be set up to send warnings to relevant people if problems arise or if the system operates outside of predetermined parameters.”

Automation products are installed as part of the irrigation system and were developed to cope with the specific hydraulic demands of such a precision production system.

It is not only automation technology that helps the farmer meet the demands of blueberry irrigation. The frequency and short duration of the irrigation pulses put massive hydraulic demands on the delivery system.

The irrigation pulses are so short, that there is no time to refill empty pipes, be they mainlines, submains or driplines. They must be full from the outset.

If the systems fail to cope with this, some plants will get more water and nutrients than others and uniformity of water and nutrient distribution will be compromised. This will impact the yield uniformity and fruit quality. The irrigation equipment and all complementary products must also be able to meet these demands. To achieve this, the drippers in the irrigation block should be CNL (compensating non-leakage). This will prevent the driplines and submains from draining when irrigation is not taking place. Depending on the slopes within the irrigation block, further non-leakage devices may be required. The mainlines too should be non-draining. This is facilitated by check valves and a pressure tank constantly applying pressure to the mainlines when they are not being used for irrigation. Once this is achieved, as soon as the irrigation to a block is opened, all drippers open at the same time. Likewise, when irrigation finishes, all drippers shut-off at the same time (no leakage).

Greenhouse complexities

When you develop a new greenhouse system a host of questions must be answered, and a team of experts must be involved in the process. Fact is, these intricacies become less complicated if we pool expertise from all the relevant fields. It is not only important that the producer involves experts in the process, but that the several experts involved are in sync and share data and knowledge.