Crop yield is based on <b>soil fertility</b>. If a farm has 50% soil fertility it will only have a 50% yield of products. Crops consume fertility as they grow but fertility is also naturally replenished over time (an empty farm would eventually reach 100% fertility).
Põllukultuuride saagikuse aluseks on pinnase <b>viljakus</b>. Kui farmis on 50% viljakust, saab ta ainult 50% saagist. Põllukultuurid tarbivad kasvades viljakust, kuid viljakus täieneb aja jooksul ka loomulikult (tühi talu saavutaks lõpuks 100% viljakuse).