土 and 砂: handling soil and sand
Read ground materials and the states in which they enter or remain on something.
Digging or adding soil
土 (つち) means soil. 「土を掘りました」 means digging soil.
「鉢に土を入れました」 says soil was put in a pot. It does not reverse the direction into putting the pot in soil.
Referring to sand
砂 (すな) means sand. 「靴の中に砂が入りました」 says sand got inside a shoe.
「砂で山を作りました」 means making a mountain shape from sand. Do not inflate it into creating an actual landform.
Material versus condition
「土が乾いています」 describes dry soil. The material noun 土 does not itself mean a dry condition.
「砂を全部出したつもりでしたが、少し残っていました」 says the speaker thought all the sand was removed, but some remained. Separate belief from result.
What moved in 「鉢に土を入れました」?
Show the answer and why
The soil. The pot is its destination.