The Chizkuni 22:6 explains that taking the mother bird with its young ones would be cruel. He also lists cooking a kid in the milk of its mother,and slaughtering a mother with its calf on the same day. All these examples he lists as something that is cruel ,but then he lists netai rivai (bringing up fruit to Jerusalem in its 4th year of growth or redeeming it on a coin) as cruel. How is netai revai included as something which may be cruel?
Text of Chizkuni:
לא תקח האם על הבנים לפי שהוא דרך אכזריות ורעבתנות וכן גדי בחלב אמו וכן אותו ואת בנו וכן נטע רבעי.