That's not how math works. They wouldn't need to produce 1% more 30 countires would need to produce 1% of world production in addition to their current produce. In other words the countries producing the other 70% each would need to 42+% more to make up the missing 30%.

Percent math doesn't work that way. Every country should produce an additional 1% of the whole world total. Very different from 1% of what they usually do, which is a fragment of the total.

They'd need to produce 1% more grain as compared to the world's output, not their own output. This could be a significant increase.

The problem is that Russia and Ukraine make up significant amounts of nitrogen fertilizer production.