I have applied round up to a heavly weeded field twice. Once with 17 percent at recomended doseage then with super concentrate at 50 percent .... it seems to do the job but is there a cheaper alternative to round up. Or do they sell the main ingredient by its self. that would be cheaper. Also i have a soy bean and cow pea and want to know is there is a herbicide that i can spray that will kill the weeds and leave everything else alone.