Is the landowner required to pay zakat on the 10% received from agricultural produce, or is the full zakat due from the farmer on his share?

If your share of grains reaches the zakat threshold (nisab), you are obligated to pay zakat on it. If the entire crop was paid zakat on before you received your share, that is sufficient. However, if you took your share and the farmer only paid zakat on his share, then you must pay zakat on your share if it reached the nisab, because you own it at the time zakat becomes due, which is when the grains harden. The nisab for grains is three hundred sa's according to the Prophetic sa'.