Problem to be solved: to provide a water absorbent resin having a small environmental impact even if the reduction of water absorption and water retention performance due to the contact with the calcium component is reduced, and substantially no nitrogen component is contained, and the decomposition occurs in the soil, and the water absorbent resin is used as agricultural constituent Providing water retaining material.Solution: a water absorbent resin having substantially the same ratio XB \/ XA of the pure water absorption coefficient XA before contact with the aqueous solution containing calcium ions corresponding to a hardness of 20 GPG, and a pure water absorption coefficient XB after the contact is 0.1 or more.No selection【課題】 カルシウム成分との接触に伴う吸水・保水性能の低下が軽減され、かつ実質的に窒素成分を含まず、土壌中で分解が起きた場合でも環境への影響が小さい吸水性樹脂、および該吸水性樹脂を構成成分とする農業用保水材を提供すること。【解決手段】 実質的に窒素成分を含まず、かつ硬度20gpg相当のカルシウムイオンを含む水性液との接触前の純水吸水倍率Xaと、接触後の純水吸水倍率Xbの比Xb/Xaが0.1以上である、吸水性樹脂。【選択図】なし
