By Ruth Vaughan, Msc. Applied Science
As mentioned in the previous newsletter there are no water soluble, non-reactive calcium nitrate alternatives that you can throw into your fertigation recipes as a direct replacement. So here I will list some of the options available for calcium to boost calcium levels.
NOTE FIRSTLY that calcium nitrate brings a huge contribution of nitrates into your fertigation recipe. This is a major essential nutrient and the first thing any grower should do when removing calcium nitrate from their recipe is ensure that the N level is topped up via Ammonium Sulphate, MAP, Potassium Nitrate and Magnesium Nitrate sources. Nitric acid is also a very good source of N, when balanced with lime or bicarbonates. Without the calcium in soluble form the EC in the recipe can come down – it will be balanced by the topdressing. When balancing the nitrogen = bear in mind that ammonium can be very acidifying AND is a cation – so competes with calcium uptake. Ideally you need to apply the Nitrogen in Nitrate form.
There are two types of lime.
- Calcitic lime or agricultural lime should have a Calcium content of >35% and Magnesium content of below 1%
- Dolomitic lime has a Calcium content of 20-24% and a Magnesium content of 10-14%.
Lime comes in dust form and can be hard to measure and messy to apply. It is generally mined in Kenya and therefore cheaper and more easily available than imported limes. The Calcium Carbonate Equivalent (CCE) of a good lime should be >70%. It is determined by quality and the fineness of the lime. The finer the lime, the faster it will react with the soil – releasing Calcium and taking the pH up. Large lumps are every unreactive and have little agricultural value. Quality varies according to the source and subsequent milling – it is good to check the lime quality before you apply it.
Lime is Calcium and Magnesium Carbonate. Lime adds add Calcium and Magnesium to the soil and the carbonate reacts with acids in the soil (like H+) to increase up the soil pH. Lime can be used in acidic soils, the amount required is determined from a complete soil analysis – which takes into account the pH, H+, Ca2+, other cations and soil CEC (heaviness) in a scientific way to balance pH and cations properly.
Applying too much lime is called over-liming and increases the soil pH. At high soil pH many nutrients get locked up and plants start yellowing. The high soil pH can be counteracted with acidic drip water or acidic fertilizers like ammonium sulphate.
Nitric acid is preferred to bring in the extra nitrates that are missing from the calcium nitrate application. Sulphuric acid can work and is cheap, but has two downsides. One it is very dangerous to handle and is not allowed by some certificates. Sulphuric acid brings in excess sulphates that may temporarily tie the calcium up as semi-soluble gypsum. Phosphoric acid can bring in too much phosphates that will tie up calcium and iron.
Lime calcium nitrate reaction:
2HNO3 + CaCO3 —–> Ca(NO3)2 + H2O + CO2
Calcitic lime reacts with nitric acid to produce calcium nitrate, water and carbon dioxide. Amounts depend on the strength of the acid and the quality of the lime.
Generally, standard limes may not react fast enough to supply enough calcium. For hydroponics you need a more readily available calcium source. Soil is more buffered and as long as there is enough calcium in the soil – it is just a matter of regularly replacing plant removals by top dressing.
Granulated micronized limes are more expensive due to the additional processing & they are imported. But they are much easier to measure out and apply & there is less dust. The granules collapse when wet and the micronized lime particles quickly move into root zone and dissolve fast.
So, they deliver calcium faster – but they also change the pH faster. An idea would be to top dress the granules at the calculated rate of weekly calcium application (from your weekly calcium nitrate application per ha). For hydroponics you would apply a smaller rate more often and closely monitor with media and drain analysis until you get a balance.
Closely measure pH and counteract the alkalinity with extra acid and or acidic fertilizers. Always take your water quality into account. High bicarbonate water needs to be neutralized. Granulated limes include Calciprill and Magprill from Omya (Lachlan), G Lime from Amiran, Liquid lime from Dudutech.
Gypsum contains calcium sulphate. It is available locally and relatively in-expensive. It should be tested as the quality varies from source to source. It is only sparingly soluble in water at a rate of about 2.2 g/liter. It does not affect the pH directly but can cause an increase in EC and sulphates.
Normal gypsum is fine for top dressing soils if you have enough calcium in your soil profile and are just topping up the plant removals. There are also micronized and ‘soluble’ gypsum products that will move into solution much faster and would be more suitable for hydroponics. Ezy Flow Gypsum from Dudutech is a micronized liquid gypsum that can be drenched.
Application of lime and gypsum
Solid lime and gypsum products should not be applied via drip – they are very insoluble and will block your irrigation system. They should be sprinkled on the surface between the plants and watered in with a showerhead on a hose. The drip water will then pick them up and move them through the profile. Liquid gypsum and lime products should be applied alone as a drench as the last irrigation of the day.
Calcium ammonium nitrate
Calcium ammonium nitrate (CAN) is not fully soluble and only suitable for top dressing. It is hygroscopic and quickly dissolves in absorbed water from the air, and then can move into the soil/media. Fertilizer grade CAN contains roughly 8% calcium and 21-27% nitrogen. It is less acidifying than ammonium sulphate and brings some calcium into the equation. It tends to have about 13% nitrate and 13% ammonium ions. It should be used sparingly and only after trials in your system. Ammonium ions compete with calcium ion uptake and can cause a rapid soft growth flush.
Other calcium products
Mainstay Calcium – a micro-encapsulated liquid calcium that can be drenched and remains available in the soil solution for a long time – manufactured by Cosmocel, available from Ocean. (20% Calcium) (no sulphates, nitrates, carbonates or chlorides).
ICL have a range of fertilizers suitable for topdressing that contain varying levels of calcium and other nutrients. (Agroleaf Power Calcium 11-5-19+9CaO+2.5MgO+TE, Nutrivant calcium 12-5-27+8CaO+TE, Polysulphate – 17%CaO).
ETG Kynoplus Nafaka 18-38-0+5S+2.3Ca+0.2MgO, Kynoplus Horti 15-9-21+4.75S+2.9Ca+1.5MgO.
There are also a number of drenches that can bring in calcium – Dekompakt 9% Ca(Amiran), Trafos Green Plus 15.2% Ca, (Elgon), Codasol Plus 12.5%Ca (Twiga), Barrier 14.8% Ca (Ocean), Osa Calpower 5%Ca, (Novixa).
Apply calcium drenches as the last cycle of the day to get maximum uptake in your plants.
Calcium Foliar Sprays
There are also many different foliar sprays to boost calcium levels in the plant. Note that calcium moves through the xylem – up the plant, very little is moved in the phloem down to the roots. You always need some calcium in the root zone. Green flower buds and fruit (eg tomatoes) – have less stoma and tend to be at the ends of the stems – concentrate foliar sprays here for better uptake.
Foliar sprays don’t just contain calcium – look at the other ingredients too. Some foliar sprays are designed for 1-2 sprays in an orchard/coffee plantation per season and contain high boron or zinc and are not suitable for weekly spraying. ALWAYS read the label and do a phytotoxicity test first. (OmyaPro calcium is a 35% Ca pure calcium foliar). Calcium foliar sprays must be applied regularly and concentrate on the new growth.
Always consider the whole picture when it comes to nutrient application – add up the irrigation water / fertigated nutrients and topdressing nutrients and keep a balance.
Case Study – 20 ha Roses grown in the soil
Complete soil analysis at planting and addition of scientifically calculated lime and gypsum to balance calcium levels in soil. 500 kg calcium nitrate is used in fertigation daily over 20 ha. The fertigation recipe is adjusted to reduce calcium nitrate by 50%, using potassium nitrate and magnesium nitrate to increase the nitrate levels and lower the sulphate levels in the fertigation program. The balance of N is added as urea. The N:NH3 ratio in fertigation kept below 20% N:NH3. The EC is reduced. The ppm N in the final drip water remains constant.
250 kg/day /20 ha calcium nitrate reduction = 3500 kg/20 ha/ 14 days. ie 175 kg CaNO3 per ha per 2 weeks. (34 kg calcium). This works out as a topdressing of 150kg/ha gypsum (225 Ca) every two weeks, sprinkled on and washed into the soil with showerheads.
Monitor available nutrients with a 1:2 soil analysis every month and leaf nutrients levels with a leaf analysis every two weeks & adjust feeding program until the situation has stabilized.
To source lime / gypsum / calcium fertilizers and foliar feeds please visit http://shambaza.com/
To adjust recipe’s, test soils / hydroponics or leaves please contact us on 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