Cultivable vs. arable
In Spanish, both 'cultivable' and 'arable' pertain to land suitable for cultivation. Their usage and meaning can often overlap, however, they also hold subtle differences in certain contexts.
Cultivable
'Cultivable' refers to a land that can be used to grow crops. It doesn't necessarily highlight the quality of the land but more on its potential for cultivation.
Este terreno es cultivable, pero necesita más riego para ser productivo.
(This land is cultivable, but it needs more irrigation to be productive.)
A pesar de la ubicación montañosa, esta zona es altamente cultivable.
(Despite the mountainous location, this area is highly cultivable.)
Arable
'Arable' carries a more specific connotation in Spanish. This word not only means that the land can be cultivated but also implies it is currently suited or ready for successful farming – whether due to its fertility, property of soil or weather conditions.
Debemos buscar tierras arables para asegurar una buena cosecha.
(We must look for arable lands to ensure a good harvest.)
Gracias al sistema de riego, el desierto ahora es tierra arable.
(Thanks to the irrigation system, the desert is now arable land.)
Summary
'Cultivable' and 'arable' may seem interchangeable as they both denote a piece of land's potential for crop production. However, 'arable' carries a more explicit connotation of readiness - it is not just theoretically farm-able, but more so currently prepped and conducive for successful plantation.