These people who are worried about catastrophic global food production losses caused by a dip in fertilizer supply have obliviously never been on a farm. If you have a one season drop of 30% in fertilizer usage there will only be a slight drop in production. Why's this you may ask? Mainly because the relationship between fertilizer and production is non-linear.
The best way to explain this, in a way that most could relate to, is it to give example scenarios of a man's physical fitness/health that correspond to a farmer crop's health:

Scenario 1:
Today, I could go to just about any amateur male league of a team sport played on a field (eg: hockey, soccer, league, AFL, etc.) and find some young men who can run 100 meters in under 12.5 seconds (ie:they average greater than 28.8km/h over 100m). Now the fastest person *ever* is Usain Bolt, who ran it in 9.58seconds (37.58km/h). Compare this in absolute terms: a fit amateur who doesn't even specialize in sprinting can sprint 100m at three quarters of the speed that the fastest ever can. ie. Usain Bolt is not 10 times faster, not 5 times faster, not 2 times faster, not even 1 and a half faster, but merely a bit more than 1 and a quarter times faster than amateurs.

NOW HERE'S THE IMPORTANT POINT: I seems that Usain Bolt is not that much faster than amateurs and indeed he isn't in absolute terms. HOWEVER, for the fit amateur to go from within about 25% to within 1% of Usain Bolt's speed it's going to take an massive, incredible effort (it might even be impossible due to genetics). That's because, for each percent point in gain of speed it requires more and more effort than the last percentage point. Continually increasing the training effort is giving them less and less reward. Eventually, they may even start to over-train and start running slower. The important point here is that overall, the relationship between training and speed is non-linear!

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And it is the same with fertilizer, a farmer can add more and more fertilizer, but they get less and less of an increase in production by doing so. In economics this is known as "diminishing returns". Eventually, they may even add too much and it goes the other way in that they start poisoning their crop and reduce yields. In economics these are "negative returns". The farmer strives to maintain the health of their soil so that they farm at the point of the cross-over from diminishing returns to negative returns.
This is part of the reason why if we have a 30% decrease in fertilizer we don't get a massive drop in food production. That missing fertilizer that the farmer would have applied would have given way less of an increase in production than the first 30% they applied (just like a professional running athlete where the last 30% percent in training only slightly improves their speed when compared to the first 30% of training).

Scenario 2:
But also there is more to the story due to the response dynamics of healthy soil. Again this is best illustrated by an human's fitness example:
I, myself, am a mid-fifties years old Australian male and I typically run on my treadmill for exercise for about 45mins three times a week. Part of my usual treadmill routine includes a 5km jog which takes me between 20-to-22 mins (times varies because effort applied depends on how I feel at the time). I do this quite consistently throughout most of the year. However, in December where in live it starts to get very, very muggy. Running in these conditions, at my age, is really draining and hard to do. So for about two months, mid December to mid February, I don't do any running or other deliberate exercise, only incidental exercise like mowing the lawn.

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NOW HERE'S THE IMPORTANT POINT: even after a two months break, when I return to my treadmill I can pickup quite close to where I left off. eg. the 5km jog component of my routine maybe takes only a minute more than normal. This is because my baseline fitness takes time for it to decay, it doesn't drop to nothing as soon as I stop regular exercise.

It is similar with a farmers field. In general, if their soil is currently healthy then if they don't give it much care for just the next season it doesn't affect production much, because it takes time for its baseline health to decay. In particular, if the Strait of Hormuz is closed only for a season and the farmers can't apply as much fertilizer as normal it won't do much to production because of the residual background health of the soil that still persists.
However, obviously if a farmer completely neglects to manage their soil's health for multiple seasons then it will cause considerable production loss, potentially causing irreparable damage (just like me: if I started smoking, drinking heavy and sat in front of the TV all day then after a few years of this I will shorten my life span).