How is corn zakat paid if it is milled green with its leaves?

Zakat is not obligatory on corn until its kernels harden. If it is milled before that, there is no zakat on it. However, if it is milled after its kernels have hardened, then zakat is obligatory. The amount of zakat is calculated by estimating (kharṣ) the crop, then giving a tenth or half of it if it reaches the niṣāb. Some scholars have permitted the estimation (kharṣ) of grains out of necessity. But if estimation is not permitted (which is more cautious), then one must wait until the corn is harvested and its zakat is paid. It is forbidden to dispose of the crop after its kernels have hardened, except after paying the zakat.