The land would therefore no longer continue to yield its strength to Kayin. What exactly did that entail?
Ramban: Whether he plowed, dug or planted, he would never achieve what he expected to; He would for example, plant a lot, but only a little would grow 1 . He would arrive at a pile of corn that had consisted of twenty Sa'ah, but find only ten.
The earth would hide as it were , all that was planted in it - measure for measure.
"You shall be a vagrant and a wanderer on the ground". How was this part of the curse regarding the ground mentioned
Rashi: This was a decree prohibiting Kayin from remaining for long in any one location;
Why did Hashem mention the punishment for covering Hevel's blood, but not for murdering him?
Seforno: It was not necessary to mention it, since everybody knows that someone who causes any form of damage earns himself the same punishment. 1
רש"י: אין לך רשות לדור במקום אחד: למה הוסיף רש"י 'אין לך רשות'?
גור אריה: אין הכוונה שלא יוכל להיות במקום אחד בגלל קללת האדמה, אלא מרצונו יגלה בגלל חטאו.