When several of the sweet pepper plants at Zwingrow in Honselersdijk (Westland, the Netherlands) were found to be growing more slowly than the rest, the nursery decided to have an uptake analysis performed. An uptake analysis gives the grower a detailed picture of the actual uptake of nutrients by the plant. After all, as field researcher Ruud Kaarsemaker says, the drainage and drip values often don’t give a clear enough picture on their own.
It was in May that Zwingrow saw the first signs that the crop was ‘unhappy’. Cultivation manager Bart van der Valk noticed several plants across the crop that were not growing as vigorously as the others. They were wilting under high solar radiation and had brown, thickened roots. These plants were less dense, thinner and shorter than the others, prompting the growers to look into what could be going wrong. Were the systems still working properly or had something gone wrong with the nutrient tank schedules or the watering strategy? The grower couldn’t quite put his finger on it and called in Groen Agro Control of Delfgauw to help.
This research organisation was already sampling the nursery’s irrigation and drainage water on a weekly basis and, after visiting the site and talking to the growers, they recommended an uptake analysis. The analysis was carried out retrospectively to obtain a picture of the development of the nutrient uptake that led to the imbalance in the crop.
A glance at the graphs illustrates what this analysis is about. The lines show the calculated uptake of all main and trace elements per week. The results are based on the concentrations in the irrigation and drainage water, the drainage percentage, watering volumes and a calculated estimate of the dry matter produced based on the amount of light and the CO2 concentration achieved. Another line in the graphs indicates the concentrations in the slab. Comparing the crop uptake with the slab concentrations and the ratios of the various nutrients provides additional information on the crop’s nutrient status.
The Zwingrow values showed that overall nutritional uptake was already very low in early April. Kaarsemaker: “When uptake is low, it is especially important to ensure the nutrients are properly balanced. But these sweet pepper plants were taking up much less potassium than other cations at the time. Potassium is important for opening and closing the stomata: if the stomata don’t close properly, the plants can wilt. Potassium is also needed for transporting sugars. A potassium deficiency can therefore result in insufficient transport of sugars to the root system.”
Iron, boron and zinc deficiency
The analysis also revealed that the values of at least three nutrients were well outside the desirable bandwidth. “The graphs show a distinct boron, iron and zinc deficiency. Low uptake of these nutrients fits in well with the picture of a weak plant. An iron deficiency will cause the young leaves at the top of the plant to turn yellow, a zinc deficiency causes yellow discoloration between the veins, and low boron uptake results in distorted, brittle leaves, weak plants and a brittle crop.”
The sweet pepper growers were surprised. These trace elements were present in the drainage water in sufficient quantities and in the right proportions during the period analysed. And you wouldn’t expect there to be an uptake deficiency if the parameters are correct. “Clearly the plants were not being stimulated enough to take up the nutrients,” cultivation manager Bart van der Valk says. So he significantly increased the irrigation volume – by 50% – but to his surprise, he found that the drainage values remained the same. That made it clear that something else was going on. Van de Valk also realised that from then on, he would need to start looking at the drainage and drip values from a different perspective. Uptake analysis has been a permanent fixture at this nursery ever since.
Combination of factors
Kaarsemaker: “As we know, the conditions for optimum growth are complex and a healthy plant is the sum of various factors. Nutrition is just one of those. We don’t yet fully understand what effect all the elements the sweet pepper needs have, but we can spot anomalies in the uptake pattern. What led to these phenomena at this nursery were most likely a combination of high plant load, too little watering and imbalanced nutrition. We could probably have avoided some of the problems by optimising our plant nutrition in good time. It’s so important to keep a constant eye on nutrient uptake.”
This realisation is gradually taking root among greenhouse growers as they discover that this analysis method allows them to steer their crops more precisely. The result: better quality, higher production, more vigorous plants and possibly even savings on fertilisers and water discharge. Kaarsemaker is seeing growing demand for the calculation tool, particularly among tomato and sweet pepper growers. They have a good understanding of their water flows and can therefore make excellent use of the analysis data.
A lot is already known about tomatoes, and for the past year Groen Agro Control has been working more intensively with sweet peppers, a slower crop. The more data they can collect, including from new varieties, the more accurately the results can be interpreted. After all, all the information about the growth phases and plant stages of each crop type is used. That makes an uptake analysis in ornamentals a particular challenge, Kaarsemaker says. “We are doing them with plants such as rose and gerbera. Growers of these flowers often grow several different varieties and have plants of various ages in the same part of the greenhouse. That makes things complicated.”
The adjusted nutrient strategy at Zwingrow is working. The cultivation manager was concerned that the weaker plants may have been permanently damaged, but even they have been visibly improving. More importantly, no new problems have arisen: the healthy plants are staying healthy. So the damage caused by the imbalance has remained limited. From now on, the grower will be allowing enough time to check the uptake graphs once a week and is hoping that this will avoid any problems in the future. However, he realises that not everyone is falling over themselves to get hold of a tool like this. It costs money and it’s also difficult to prove that it will help increase yields.
Kaarsemaker is also coming up against resistance. “Nurseries prefer to stick to the traditional method. They sample the drip and drainage water and decide how much to fertilise based on the target values in the slab. That’s fine as long as everything stays ‘average’, in other words if the plant and root system are healthy and the climate is right. But as soon as a plant starts taking up less for whatever reason, an imbalance can occur. An uptake analysis enables you to keep on top of things and intervene as soon as there is the slightest anomaly. That way you can prevent problems from escalating.”
An uptake analysis gives growers an accurate picture of which elements the plant is actually taking up, enabling them to fine tune the nutrient solution to the plant’s needs. The values from drip and drainage samples alone are sometimes not enough, as sweet pepper nursery Zwingrow discovered. The calculation tool highlights even the smallest anomaly and prompts the grower to take action in good time.
Text: Jojanneke Rodenburg. Images: Jos Bezemer.
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