You can, but then you have to transport the product to the farm to use it.

And, of course, practically all the Haber-Bosch equipment is not on renewables, and will not be for a long time. It is better for now to displace it until carbon taxes can be used to force conversion.

Solar power gathering above cropland also increases yield by reducing water and heat stress. So even after they convert, you will still be better off with this.