First of all Astaria has the exact same loading practises as any other country. It's a first world nation with strict safety regulations. However...
How to put it...
This post is contradicts canon facts about Astaria, facts that I've made abundantly clear. Hell it ignores facts that you, yes you Shep, have yourself used to argue with Stas earlier on!
That fact is as follows: 135 ships handle all cargo with Astaria, those ships are all owned by Astarians. In short this could not possibly be a foreign ship. You yourself accepted this. Steve accepted this too, though he argued that there'd be foreign ships around Velaria. Truth be told none of you objected to the idea that all Astarian trade was handled by 135 ships.
More on the implications of that number later on.
So having cleared up the fact that there are no foreign ships in Astarian harbours the question is how big would an Astarian bulk freighter be? Well earlier on during the Shroom Viking incident I went on record as to the size of the
largest Astarian oil tankers, so that's approximately the size of an Astarian bulk freighter. Larger ships are modern container vessels.
Of course that could still be a respectable boom right? It could be an Astarian ship headed from a foreign port to an Astarian harbour? Sure it could, but it wouldn't be carrying fertilizer.
The reason for this, and Skimmer and others can vouch for this, is that Astarian foreign trade is government trade. Private enterprises are not involved, aside from the odd smuggler and rogue trader, and he is not about to come home with a cargo of fertilizer. Basically Astarian trade is barter, cotton, tobacco, gold, silver, and diamonds to San Dorado and the IRT, in return for machine goods, electronics, high level advisers, and so forth. With Japanistan I agreed to supply concrete in return for Japanistani goods, specifically Bulwark Against Imperialism anti-cruise missile defences.
Ah yes, concrete, or cement rather, a bulk cargo, a bulk cargo that is manufactured in South Velaria (limestone and such, natch). So in return for a certain bulk cargo Astaria would be getting weapons... hum... Three guesses as to whether or not the Astarian regime would prioritize fertilizer or moving as much cement as possibly to Japanistan.
But wait you say, couldn't they buy fertilizer in Japanistan? Maybe, I find it doubtful, Astaria has extensive hydropower and therefore makes its own fertilizer, South Velaria ditto though not so developed. I could see a few ships going to South Velaria with fertilizer, though I doubt it; crops such as rice, grain, and what have you would be more interesting since we're building up supply dumps in case of war.
So in short going by perfectly canon statements, that no one has so far seen fit to contradict, there is no way that any ship foreign or otherwise would be in an Astarian port carrying fertilizer.
However that is not my only argument by far, I have three other arguments that really put the kibosh on the whole idea of a fertilizer shipment.
First any export of fertilizer is out since there's sort of a war footing on, and people want to use the facilities to make munitions, only producing enough fertilizer to supply local farmers (in Astaria or Velaria).
Second any import is out, not only for the reasons mentioned above, but also because the Astarian regime refuses to allow import of anything Astaria can make itself. A prime example of this is the cars, Astarian cars are basically 1970s style crap. They could easily have imported cheap cars from the IRT, but since they
can make an insufficient number of slightly too expensive cars themselves...
Third, and this is the good one. If you did the numbers you would notice that 135 ships of 23K deadweight each isn't enough to handle what the Astarian
domestic trade ought to be. In fact the total Astarian shipping could handle roughly 53% of what their domestic shipping alone ought to be. Think about the implications of this...
Shipping is a luxury, only the most valuable goods can be shipped, bulk goods are right out. Whenever possible local alternatives must be found, or railways be used instead of shipping. New, large, ships are invariably container ships so as to be able to quickly move expensive worthwhile cargoes.
Not much room for bulk freighters there, and when you then consider that what little bulk capacity there is, is now being taken up shipping cement to Japanistan. Well...
And yes all of this is part of a government program to make Astaria less reliant upon shipping, for the simple reason that enemy navies would invariably be able to ruin Astarian shipping at will. It is in fact part of Astarian overall paranoia.
A solution to the current scenario
Since all of the above is canon, no one argued with it when I presented it, or its been cleared with another player, a question arises: Why would the CSR and Shepistan think that a large container ship held fertilizer?
The answer of course is simple, it's only a large container ship by Astarian standards, by most other standards it's a handysize ship. So yeah it could easily be taken for a bulk freighter, it might even be disguised as one. The reason is that even the IRT weapons and electronics manufacturers might be a bit leery of dealing openly with Astaria, so instead of marking the cargo as "Electronics by Tonkin Industries," it's labelled "fertilizer."
It wouldn't be entirely in vain though, I imagine that this attack would cause quite a bit of damage to a valuable military cargo.
Oh by the way from now on we'll be chucking explosives into the water at irregular intervals. Bit costly but worked marvels against the Italian frogmen.