That depends entirely upon the reason why he is infertile. If it is because he makes no sperm, there is no way to change that. Low sperm count can be fixed only by laboratory work to concentrate the sperm or for in-vitro fertilisation. Other problems can be fixed medically.
Examine his ejaculate under a microscope to see whether there are sperm.
A man can become fertile again if he is infertile through various ways. Medical analysis and improvement in nutrition may resolve the problem gradually.
His ability to produce sperm
Take tonic SSS
Yes
alfalfa
Yes
Men do not stop being fertile, Women stop when they pass though the "menopause".
Orientals are the least sexually active and least fertile. Blacks the most sexually active and most fertile. Whites are intermediate.
Organic matter.
It makes the land more fertile
well by doing the right thing.
ash and lava
ash and lava
makes land around it very fertile
it makes it more fertile.