CAN Fertilizer Explained

Urea or CAN? That is the real question behind most searches for CAN fertilizer, and the answer turns on your soil, your rainfall and how carefully you apply. CAN is calcium ammonium nitrate, usually 26 or 27 percent nitrogen with about 8 percent calcium, and it is stocked across Uganda as a top dressing. It holds onto its nitrogen where urea gives some away to the air.

On notation: compound fertilizer bags print their nutrient ratio as numbers joined by dashes, and the ratios below appear with colons in their place, so 17:17:17, which sits better on a narrow screen. CAN carries no such ratio. It has one headline number, the nitrogen percentage, and a calcium figure underneath it.

What CAN Fertilizer Is and What Is in the Granule

CAN is not a single compound. It is a blend: roughly 70 to 80 percent ammonium nitrate mixed with 20 to 30 percent calcium carbonate, which is limestone, sometimes with a little calcium nitrate as well. Each granule carries two different things a crop wants and one thing the soil wants.

That composition explains almost everything about how CAN behaves. The ammonium nitrate supplies nitrogen in two forms at once: nitrate, which a root takes up immediately, and ammonium, which the soil holds onto and releases over the following weeks. So you get a quick response and a continuing one from the same handful of granules.

The limestone in the blend is what stops CAN pushing soil pH down the way a pure ammonium product does, and it is also where the calcium comes from. Fertilizer grade CAN spans roughly 21 to 27 percent nitrogen depending on the manufacturer, with about 8 percent calcium. The grade sold across East Africa is 26 percent nitrogen, and 27 percent grades turn up too. Read the bag rather than assuming, because the number changes what you should apply.

Turn the percentage into something useful. A 50 kg bag of CAN at 26 percent nitrogen holds 13 kg of nitrogen. Write that down, because every fertilizer recommendation you will be given is in kilograms of nitrogen while every bag is sold in kilograms of product.

Urea or CAN: How to Decide on a Ugandan Farm

Start with the arithmetic, because it is the part most conversations skip. Urea is 46 percent nitrogen, so a 50 kg bag holds 23 kg of nitrogen. CAN at 26 percent holds 13 kg in the same size bag. To deliver the same amount of nitrogen you need about 1.8 bags of CAN for every bag of urea, which means nearly twice the weight to carry, nearly twice the labour to spread, and nearly twice the bags to buy.

That is the case for urea, and it is a strong one. The case for CAN is that the nitrogen you buy actually reaches the crop. Urea spread on the surface and left uncovered can lose a large share of its nitrogen to the air as ammonia gas within days, and Ugandan temperatures sit permanently in the band where that loss runs fastest. CAN does not do this in any meaningful quantity. A bag of CAN that holds 13 kg of nitrogen delivers close to 13 kg. A bag of urea that holds 23 kg might deliver 23, or might deliver 16, depending entirely on what you did in the hour after you spread it.

Which reframes the question. It is not urea against CAN. It is urea applied properly against CAN. Urea worked into the soil or covered with a scrape of earth beats CAN on nitrogen per shilling and per kilo carried, comfortably. Urea broadcast on a dry surface and left there does not. If you will do the covering, buy urea. If you will not, or if the field is too big and the labour too short to cover every granule, CAN is the product that forgives you.

Two other things tip it. On soil that already tests acid, CAN is the gentler choice and urea makes a real problem slightly worse each season. And where rain is unpredictable, CAN lets you apply when it suits you rather than gambling on a forecast. Our page on how urea works and how its nitrogen escapes covers the loss mechanism in full, and it is worth reading before you settle this.

Why CAN Fertilizer Holds Its Nitrogen When Urea Does Not

The difference is not a matter of quality or of one product being better made. It is a difference in chemistry, and once you see it the rest follows.

Urea has to be converted before a plant can use it. Soil contains an enzyme called urease, and when urea meets moisture that enzyme breaks it down, raising the pH of the little pocket of soil solution around each granule as it does so. Above about pH 7.5 in that pocket, the nitrogen converts to ammonia gas and leaves. That conversion step is the gap urea's nitrogen escapes through.

CAN has no such step. The nitrate half is already in the form a root absorbs, so there is nothing to convert and nothing to lose. The ammonium half is held on soil exchange sites and nitrified gradually, underground, where the ammonia has nowhere to go. There is no urea for urease to act on, so the alkaline pocket never forms. Volatilisation loss from CAN is described in the technical literature as negligible, and the practical consequence is the one that matters on a farm: timing becomes flexible.

That flexibility is worth more in Uganda than the literature suggests, because the literature was mostly written for places where a farmer has a tractor, a spreader and a plough and can incorporate fertilizer the same afternoon. A smallholder applying by hand across two acres cannot always cover every granule the day it goes on, and cannot always predict the rain. CAN removes that whole class of loss from the calculation.

CAN does have its own loss route, and it is worth naming. Nitrate does not bind to soil, so heavy rain after application leaches it downward past the roots. That is a different failure from volatilisation and it is managed differently: split the dose rather than applying everything at once, and avoid applying immediately ahead of a downpour.

The Calcium in CAN and What It Does for Crops and Soil

About 8 percent of a CAN bag is calcium, and it arrives as a free extra rather than as the reason you bought the bag. Whether it is worth anything depends on your crop.

Calcium builds cell walls, and the crops that show calcium shortage most visibly are the ones where a firm wall matters commercially. Blossom end rot in tomatoes and peppers is a calcium related disorder, often triggered by uneven watering rather than by an outright soil deficiency. Bitter pit in apples, tip burn in cabbage and lettuce, and soft fruit that will not travel to market are all in the same family. A grower of fruiting vegetables who top dresses with CAN gets a small, steady calcium supply through the season alongside the nitrogen.

For a maize or bean crop the calcium is close to irrelevant as a nutrient. Cereals rarely run short of calcium in a way that limits yield. What the calcium does on those fields is work on the soil rather than the plant, which is the next section.

One thing the calcium in CAN does not do is replace liming. The quantity is far too small. If a soil test says your land needs lime, it needs lime, applied at the rate the test calls for, and a CAN programme will not substitute for it.

CAN Fertilizer on Acidic Ugandan Soils

This is where CAN stops being a convenience and starts being an agronomic decision.

Every nitrogen fertilizer that supplies ammonium acidifies soil, because soil bacteria convert the ammonium to nitrate and that conversion releases acidity. Ammonium sulphate does it fastest. Urea sits in the middle. CAN does it least of the three, for two reasons at once: only part of its nitrogen is ammonium, and the granule carries calcium carbonate, which is limestone, and limestone neutralises acid. Under steady use CAN is described as not acidifying soil at all, which is why it is the nitrogen source recommended for acid land.

Uganda's problem is the starting point. Maize wants a soil pH of 6.0 to 7.0 on MAAIF's own figures, and a large share of Ugandan cropland tests below that band, worst on the old weathered profiles and on gardens worked for two or three generations with nothing put back. On that kind of land the penalty compounds: the crop struggles directly, the phosphorus you apply locks onto clay and iron instead of feeding the plant, aluminium becomes available enough to damage roots, and bean nodulation fails.

So on a plot that tests acid, switching the nitrogen source from urea to CAN is a real intervention rather than a preference. It will not reverse existing acidity, and nothing short of lime will. What it does is stop you adding to the problem twice a season, every season, while you sort the lime out.

MAAIF's order of operations repays following. Sample first. Apply lime to whatever figure the result returns. Leave it three months at least, so the reaction has run before a seed goes in. Fertilize last. Liming and planting in the same week wastes the lime. Read our page on soil testing before any fertilizer goes on for how sampling works and what the pH result actually tells you.

CAN Top Dressing Timing and Rates Per Acre

CAN is a top dressing product. It goes onto a crop that is already growing, not into a planting hole, because it supplies no phosphorus and a seedling's first need is phosphorus. Planting day belongs to DAP or to a compound.

On timing, regional East African guidance for maize puts the first dressing at two to three weeks after planting or once the crop is around 45 cm tall, which is roughly knee high. In higher rainfall areas the dose is split, with the first part around six weeks after sowing and the second ten to fifteen days later or just before tasseling. In drier areas a single application is common. Placement is a ring or a line about 15 cm out from the plant, then covered with soil. That is regional guidance rather than a Ugandan recommendation, so treat it as the pattern and let your own crop and rainfall adjust it.

On rates, be careful whose number you take. Ugandan evidence splits into two camps that land almost five times apart, and the split is instructive rather than embarrassing.

One camp works backwards from what the crop takes out. Total the nitrogen a heavy maize crop hauls away in cob and trash, then add the annual bleed from Ugandan soils regardless of cropping, and the replacement figure is large: somewhere around 70 kg of nitrogen an acre if you are chasing a high yield. Converted into CAN at 13 kg of nitrogen a bag, that is more than five bags an acre. Nobody farms that way here, and the reason is not ignorance.

The other camp works forwards from field trials. Ugandan maize response work across a spread of sites and seasons found the nitrogen rate that actually maximised a farmer's profit sat at 45 kg per hectare at best and 24 kg per hectare at worst, which is one to one and a half bags of CAN an acre. Nitrogen clearly worked in those trials, lifting mean yield by something like 120 percent above the unfertilized plots, off a base around 1.8 tonnes a hectare. What did not follow was a licence to keep adding.

The gap between the two is the gap between what a crop could eat and what your wallet should feed it. Crossing it takes one number, and no soil laboratory can supply it: what a kilogram of fertilizer costs you set against what a kilogram of grain earns you. Across that trial work the optimal rate slid from 45 to 24 kg per hectare as the ratio climbed from 10 to 30. Put plainly, price out a bag of fertilizer against a bag of maize on the day you are buying. A wide gap between them means the profitable rate is low and extra bags will cost you money you never get back. A narrow gap means you can push towards the agronomic figure. The ratio moves every season, which is why no page can hand you a settled rate.

There is a practical wrinkle for anyone buying CAN in Uganda. The Uganda Fertilizer Use Optimizer, whose sheets are drawn up region by region from Ugandan trial data for the use of extension staff, deals only in DAP and urea. It does not carry CAN at all, which tells you something about which products the trial work was built around. So a Ugandan farmer who prefers CAN has to convert. The conversion is straightforward: take the urea rate the sheets give, multiply by about 1.8, and you have the CAN weight that delivers the same nitrogen. For maize in Central Uganda, whose top sheet asks for 43 kg per acre of urea placed in a band at the second weeding, that works out at roughly 75 kg per acre of CAN, or a bag and a half. At the lower spending tiers, where the sheets give 10 to 15 kg per acre of urea, the CAN equivalent is 18 to 27 kg per acre, well under half a bag.

You will also see a single dressing of 50 to 100 kg of CAN an acre quoted for low rainfall areas. That figure comes from Kenyan extension practice rather than from Ugandan work, and its upper end sits above anything Uganda's own optimiser recommends, so weigh it accordingly. Feed whatever recommendation you settle on into the fertilizer requirement calculator to get bags for your own acreage, and see the maize fertilizer application guide for how the dressings sit inside a whole season.

Crops and Soils Where CAN Is the Better Choice

Maize is where most Ugandan CAN goes, as the top dressing after a DAP planting. On acid land and on plots where covering the granules is not realistic, it is the sounder choice, for all that it carries less nitrogen per bag.

Vegetables are the crops where CAN wins on more than nitrogen behaviour. Tomato, pepper and cabbage growers get the calcium, and a vegetable plot is usually irrigated and intensively managed, so multiple small dressings through the season fit the crop anyway. Nitrate nitrogen suits a crop you are harvesting continuously, because the response is quick.

Coffee and bananas both sit on long cropped land where calcium has been walking off the farm inside harvested produce for years. CAN in a coffee or banana programme supplies nitrogen for leaf and berry growth without pushing the soil further acid, which matters on plantations that have had nitrogen applied for decades. Our coffee fertilizer guide and the cabbage fertilizer schedule set out crop by crop programmes.

Where CAN is the wrong buy: legumes, which fix their own nitrogen and do not want a heavy nitrogen dressing at all, and any situation where the deciding constraint is how much weight you can move. A farmer three hours from the nearest input shop carrying fertilizer on a boda has a good reason to prefer the concentrated product and to commit to covering it.

Reading a CAN Fertilizer Bag Before You Buy

Two numbers on a CAN bag change what you should apply, so read them rather than assuming. The nitrogen percentage is either 26 or 27 in most of what is sold here, but grades down to 21 percent exist and the difference between 21 and 27 is a quarter of the nitrogen you think you are buying. The calcium figure is usually printed underneath.

Quality is worth a careful word, because CAN has the weakest Ugandan evidence base of the common fertilizers. Market assessment work in Ugandan input shops tested ten CAN samples and found total nitrogen out of compliance in four of them, with the shortfall averaging around one percent of the declared figure. The same report says plainly that ten samples are not enough to make a strong statement about CAN nitrogen content in Uganda, and that the sample sizes were also too small to say anything about the calcium. So the honest reading is that CAN in Uganda has not been tested enough to clear it or condemn it, which is a reason to buy from a dealer with a reputation rather than a reason to avoid the product.

What you can check yourself: weight on a scale, since 10 percent of 50 kg bags weighed in Ugandan markets were short by more than the half kilogram tolerance. The bag construction, since loose seams turned up in 42 percent of bags examined and a loose seam lets moisture in. Whether the granules pour freely or sit in lumps. And whether the label's declared nutrients agree with the breakdown printed below them, because Ugandan inspectors have found bags where the two contradicted each other outright.

Storage and Safe Handling of CAN Fertilizer

CAN pulls moisture out of the air readily, and Ugandan store conditions are exactly wrong for it. Market surveys measured median relative humidity inside Ugandan fertilizer stores at 55 percent, and several fertilizers start drinking water vapour out of the air from that point upward once it gets past 30 degrees. Add tall stacks, found in 22 percent of stores, and concrete floors without pallets, found in 38 percent, and you have a product slowly turning into a block.

So keep CAN raised on timber or pallets, clear of the wall, beneath sound roofing, in short piles, and tie the mouth of an opened sack shut. Buy for the season rather than for the year. A caked bag can be broken up and used, but the granule size becomes uneven and hand spreading gets less accurate, which matters more than it sounds when you are applying a ring around each plant.

As for handling it, CAN is a concentrated salt and skin does not enjoy it. Gloves for hand placement, which is how almost every gram of it goes on in Uganda, and a wash before eating. Anything that lands in an eye needs clean water at once. Breaking up a hardened sack throws dust that catches in the airways, so take the job outdoors and keep the wind at your back. Keep granules clear of wet foliage and out of the growing point of a young plant, where a strong salt against soft tissue will leave a burn.

Then the separation rules, which are worth taking seriously rather than nodding at. CAN near a feed store is a hazard to livestock if a bag splits. Seed tins belong elsewhere too. Children and unlocked stores do not mix. Nobody sleeps where the fertilizer is kept. Empty sacks get destroyed rather than reused for food or water. Pesticides get their own shelf.

One further point specific to this product family. CAN is built around ammonium nitrate, and ammonium nitrate in concentrated form is regulated in many countries because of how it behaves in a fire. The calcium carbonate blended into CAN is there partly to make it safer, and agricultural grade CAN is sold and handled routinely worldwide. What that history means for a farmer is simple and worth honouring: keep it away from fuel, oil, and anything that burns, store it in its own space rather than beside the paraffin, and do not keep more of it than you are going to use.

Frequently Asked Questions About CAN Fertilizer

Is CAN better than urea for maize in Uganda? It depends on two things. If your soil tests acid, or if you broadcast by hand and cannot cover the granules, CAN is the better buy even with less nitrogen per bag. If you will work the fertilizer into the soil or time it to rain, urea delivers more nitrogen for the same money and weight. Urea applied properly beats CAN; urea left on the surface does not.

Can CAN be used at planting instead of DAP? No. There is no phosphate in a CAN bag, and phosphate is precisely what a two week old seedling is hunting for while it lays down the roots that will carry it through the season. Using CAN at planting leaves the phosphorus gap open and puts nitrogen in before the crop can use much of it. Use a phosphate source at planting and CAN as the top dressing afterwards.

Does CAN replace lime on acid soil? It does not. The calcium carbonate in a CAN bag is a small fraction of what liming a hectare requires. What CAN does is stop you adding fresh acidity each season the way urea and ammonium sulphate do. If a soil test calls for lime, apply lime at the rate the test gives, at least three months before planting, and use CAN alongside that rather than instead of it.

How many bags of CAN equal one bag of urea? About 1.8 bags. Urea at 46 percent nitrogen puts 23 kg of nitrogen in a 50 kg bag; CAN at 26 percent puts about 13 kg in the same bag. So two bags of CAN deliver slightly more nitrogen than one bag of urea. That arithmetic is the reason to work in kilograms of nitrogen rather than in bags whenever you are comparing the two.

Can CAN be used on vegetables and coffee? Yes, and these are the crops where it fits best. Vegetables benefit from the calcium along with the nitrogen, and a crop being harvested continuously suits the quick response you get from nitrate nitrogen. Coffee takes CAN in the dressings timed to flowering and berry filling. Keep granules off wet leaves and out of the growing point either way.

Is CAN safe to store at home? With ordinary care, yes. Keep it dry, off the floor, stacked low, out of reach of children, away from animal feed and seed, and out of any room where people sleep. Because it is built around ammonium nitrate, keep it away from fuel, oil and anything flammable, store it in its own space, and hold no more than you plan to use. Nothing about a farm quantity of agricultural CAN is exotic; it just wants a sensible corner.

Is CAN more expensive than urea? Per bag the two are usually closer than the nitrogen difference would suggest, which means per kilogram of nitrogen CAN works out dearer, since a bag of it carries around 13 kg of nitrogen against urea's 23 kg. The comparison that matters is cost per kilogram of nitrogen delivered to the crop, not cost per bag, and that calculation changes once you account for the nitrogen uncovered urea loses to the air. Prices move week to week with the exchange rate, freight and the season, and they differ between Kampala and upcountry, so look up what fertilizer is selling for in Uganda now and run the figures yourself.

Settle the urea against CAN question once for your own soil and rainfall and it will hold for several seasons. Buying is the bit to revisit each time, because the nitrogen percentage on the bag is not always the one you expect and the price of the same 50 kg varies between dealers, seasons and distances. Find out who is selling fertilizer within reach of your farm, glance over what the product is going for beforehand, and insist on a weighing. The farm inputs hub holds the companion guides, among them the overview of every fertilizer type used in Uganda and the guide to NPK compounds.