By Ruth Vaughan, Msc. Applied Science
In soil and plant nutrition calcium is King. Calcium Nitrate is the only non-reactive soluble calcium fertilizer suitable for drip feeding fertigated crops, so it goes without saying that calcium nitrate is the sovereign of fertilizers. There are NO realistic, long term alternatives. Sadly, Kenyan (and Ugandan) growers have encountered a glitch in Calcium Nitrate supply. It has been stuck in the ports for some time pending clearing. This has resulted in many farmers running out. There is a knock-on effect of the port bottle necks.
For starters, we can expect a big increase in cost – storing containers in the port is expensive and suppliers have had to pay extra clearing charges. Secondly, a long delay in clearing containers (and the extra costs) have resulted in the following shipments being diverted to other, easier countries. So, in a nutshell, we can expect increased costs and long delays for an indeterminate time. What can our growers do? As already mentioned, there are no direct alternatives to calcium nitrate, so we are going to have to be brave and innovative and move into untested waters…….
Calcium in the soil
Calcium is not called the King of nutrients for nothing. Calcium is very important for soil health, microbial diversity, soil structure, heavy metal protection and countless other soil properties. As a soil amendment, we do have alternatives. Soil growers that are following our soil health program and balancing calcium and pH levels at planting, and annually, have built up adequate calcium levels in their soils, which will hold them in good stead through this crisis. They will be able to “mine” their soil calcium and top it up with topdressing of gypsum / lime or dolomitic lime (depending on the soil test).
Calcium in Hydroponics
Hydroponic growers are not so lucky. At planting growers should load their media with gypsum, lime, calmag to bring up the calcium levels to optimum at the start – but the amount the media can store is very limited and the calcium very quickly (in a matter of days!) runs out. The whole concept behind hydroponics is to be able to have a system of nutrient feeding that can be changed at the drop of a hat…
Calcium in plant nutrition
Calcium is an essential secondary plant nutrient, and typically supplied in nutrient solutions at a rate of 80-240 ppm. Crucial for plants, Calcium prevents various deficiencies and is an essential ingredient of strong cell walls which leads to sturdier crops with increased vitality and storage properties (critical for exported crops that need to reach their destination in good form!).
Calcium is vital to cell wall formation and is deposited as calcium pectate in the cell walls. This means it is not mobile in the plants and cannot be moved from older tissue to younger tissue, it is also needed all the time. Important for all plants – calcium is especially important for roses, tomatoes, peppers, brassicas and cuttings.
Calcium is important for the uptake of other nutrients. It is important for root cell division and cell strength. Low levels of calcium in root tissue make the roots susceptible to soil borne diseases and nematodes. Without root division phosphorous uptake slows down.
Calcium is important for the stability and functioning of cell membranes. When calcium supply slows down – the cell membranes become leaky, and cell division is disrupted – causing twisting and cupping of the newer foliage. Leaky membranes are more susceptible to pre-harvest diseases and post-harvest botrytis. Calcium slows the ageing of cells by protecting them from toxins and ethylene – hence its importance in maintaining quality and shelf life. For cuttings producers – ample calcium levels are vital – not just for shipping, but also in root cell formation for rooting.
Because it is immobile, Calcium deficiency occurs in the newest growth, and includes tip burn in leafy crops, and blossom end rot of tomatoes and capsicum. Softer ‘leaky’ cell membranes are more susceptible to spray damage and heat stress. Calcium deficiency symptoms vary according to plant type, variety, degree of severity of the Calcium deficiency and growing conditions.
At the onset symptoms are difficult to spot, and it is important in this difficult time, to monitor calcium levels with regular leaf analysis. By the time the Calcium deficiency expresses symptoms, cupping of new foliage, pale marginal bands, increased spray damage, diseases and insect pressure, water-soaked areas on stems and leaves and root tips that become jelly like, yield and quality will have been affected beyond repair.
Keep a close eye on your flower vase-lives and vegetable shelf-lives. In is not just the cells on the outside that are affected, Calcium deficiencies affect the inside cells too. Look out for black heart in lettuces, empty cabbages, the inside of flower buds, browning in cut beans, pithy baby corn.
Optimum levels of Calcium in leaves vary from plant to plant, but typically fall in the range of 0.8-2%. The age of the leaves for sampling is important – because it is immobile older leaves will generally not show a deficiency. Hence the need for sampling the youngest most mature leaves for leaf analysis – in roses this would be the 3-4 leaf down on roses showing color. Calcium deficiency can cause loses of > 50%! So, it is important to stay on the ball.
Boosting calcium uptake
Optimizing Calcium nutrition in a crop is not just a matter of dosing correct levels. Calcium uptake is complex and often misunderstood. Soils, media and nutrient solutions generally have sufficient Calcium and many Calcium deficiencies are actually induced deficiencies. Environmental factors, crop factors, solution management, moisture levels and elemental ratios all interact to affect Calcium uptake. Understanding the factor that affect Calcium uptake will help us maximize the limited Calcium we have and will influence our choice of replacement fertilizers.
Calcium uptake is a passive process and Calcium moves into the root and through the plant in water movement driven by the transpiration stream. So, it goes without saying that anything that factors that influence transpiration will affect the uptake of calcium.
- High light levels, lower humidity, warmer climate, air movement, optimum moisture in the root zone, growing out of flush all promote calcium uptake.
- Dry roots, high humidity, thick plant growth, cold weather, low light levels, excess spraying (closed stomata), some silicate and oily products (blocked stomata) reduce calcium uptake.
- Optimum Copper and Potassium are required for xylem strength and translocation efficiency. Low levels induce premature wilting & reduced calcium uptake
- Excess Nitrogen promotes very fast soft growth – inducing Calcium deficiency through wilting and increasing the amount of growth the Calcium needs to satisfy.
- High soil temperatures promote Potassium uptake and reduce Calcium uptake – mulch / cover the soils.
- Flowers and fruits have a lower transpiration rate and will be the first to be affected by Calcium deficiency – hence blossom end rot in tomatoes and peppers.
- Note that if the humidity is too low – the transpiration is high and calcium will be deposited quickly in the lower leaves resulting insufficient levels remaining for the upper.
- In very low humidity, in the hottest part of the day, with dry soils, flooded soils, high salinity, plants can shut down their transpiration by restricting the xylem, closing the stomata and turning their leaves – Zero calcium uptake happens then.
Warm, humid conditions combined with limited airflow and rapid growth are known as ‘calcium stress periods’ and result in tip burn & death of growing points (blind shoots).
Optimize moisture levels
Plants cannot take up water, and therefore Calcium, from dry root zones. EC builds up in dry soils and media. Flooded roots have no oxygen and shut down = no calcium uptake. Optimum moisture = optimum root activity = optimum root activity. If you haven’t got one, get a moisture sensor like Aquacheck, and use it to guide you on your irrigation cycling.
Balance your pH’s
pH has a big effect on calcium availability and uptake. Low pH increases the solubility of metallic cations which depress calcium uptake, in particular, aluminium. High pH and lime induced chlorosis are also associated with calcium deficiencies. The calcium is bound up as an insoluble carbonate (Lime), acidic conditions are required to neutralize the carbonate and release the calcium.
For soil planting do a complete soil analysis at the the start – and the correct addition of lime / dolomitic lime, gypsum or Sulphur will help balance your soil pH and optimize calcium levels. For media, analysis and pre-conditioning of media will balance media pH. Organic media like cocopeat can contain large amounts of sodium and potassium and can absorb large amounts of calcium and nitrogen. This needs to be done pre-planting.
The irrigation water quality, amount of acid and ratio of nutrients all affect the immediate and long-term pH in the root zone.
Balance your EC’s
At low ECs plants struggle to take up any nutrients. High salt levels in the root zone reduce water uptake and calcium uptake. Take extra care in maintaining the optimum EC in the root zone. Note that drip & drain analysis in hydroponics can be misleading with regards to EC levels in media. Monitor EC in the root zone with regular sampling for a 1:1.5 media analysis, or a 1:2 soil analysis.
The measured EC is time and moisture sensitive. Samples should be taken fresh, not dried out, and shipped to the lab as soon as possible and not over the weekend. Sending samples in absorbent bags (eg paper) will suck out the moisture and give a false high reading. EC in the root zone is a balance between EC soil/media, of drip and the water uptake of the plants.
Balance your nutrient levels
Most well-balanced nutrient solutions at the correct EC range contain enough calcium for optimum uptake. Balance is the key here. Copper and potassium deficiencies cause premature wilting, lowered translocation and reduced calcium uptake.
- High sodium & potassium in the root zone compete for uptake with calcium AND translocation of calcium to the growing tips, a common cause of tip burn.
- Calcium and magnesium are opposed in the plant system and have antagonistic interactions. High magnesium competes with calcium and induces phytotoxicity in plants. Magnesium and calcium have a homeostatic balance that need to be maintained for optimum growth.
- High iron and other trace elements, which are also cations, compete with calcium for uptake. (Ditto heavy metals and aluminum…). Keep your iron and trace elements optimum and not too high.
- High bicarbonate levels in irrigation water bind with calcium to form insoluble lime, taking it out of the nutrient solution. These should be neutralized with correct acid dosing.
- High nitrogen causes soft rapid growth.
- The nitrate to ammonium ratio is important. Calcium nitrate is important as a nitrate source especially for hydroponics. It is highly soluble and rapidly taken up by the root system. While a small proportion of ammonium in the root zone helps boost growth in alkaline conditions and in low light and temperature, ammonium is also a cation (NH4+) and significantly aggravates calcium uptake, and should be reduced to zero in hot weather and rapid growth conditions.
- High phosphates can bind with calcium, forming an insoluble precipitate, removing both calcium and phosphorous from the roots’ reach.
- High sulphates combine with calcium to form gypsum – which has a limited solubility.
- Calcium and boron go hand in hand – low or high boron levels have a huge impact on calcium uptake and use!
The health of the root system plays a vital role in calcium uptake. Root diseases, nematodes, water logged roots, anaerobic root zones all restrict calcium uptake. Run regular nematode and root borne disease checks.
To know more about creating healthy soils for your flowers, fruit or vegetables, for help in planning your hydroponics system or manage plant diseases through proper plant nutrition, please contact us at firstname.lastname@example.org.
Till next time,
Ruth Vaughan is the Technical Director at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). Ruth is also a contributing author to Kenya’s leading horticulture magazines such as the HortFresh Journal, HortiNews and Floriculture. Ruth is a great believer in soil health, organic matter, biochar and carbon sequestration as a way to alleviate climate change and increase food security. Loves visiting farmers and seeing all the different farming methods