It's annoying because the novel is genuinely interesting and introduces a lot interesting historical tidbits. If not for the random biases, prejudices, and propaganda pinging like random rock metal notes in a classic symphony, it would be far far more enjoyable. How in the world an archaeology graduate throw the sins of the British Empire to those Mithra believers? They're not even the same people, and separated by more than a millenia.
How to say this... I know it's fiction but even though he has a broken godhood, he's far from being able to rewrite natural law. In short, if he doesn't expose the soil after tilling it, parasites, fungi, and the sort should affect the plant. He replant the first crops and the next without fertilising them. Even if he uses magic to speed up the growth, it should consume nutrients (that's not being replenished) and shouldn't be able to grow that well.
It's.... original? I would like to give a higher grade but I try to follow his train of thoughts and keep ending up wondering what actually happens and where I am.