Rambler hit the nail on the head. If you are taking more off of your field than you are adding back, you are literally mineing your soil of nutrients. Nutrients in the soil are boundup with other nutrients, in all sort of combinations, due to their cationic (+) and anionic (-) charges. While some of the biological soil amendments will work on and loosen up those bonds, they seldom will work for more than two or three years and then crop production will decrease, even when adding more of the biological suppliments. It doesnt matter if its a compost tea or someother biological stimulant, if you keep removing available nutrients, sooner or later, you will endup with all the easy nutrients gone and nothing left but the stuff that is tiedup into unsoluible forms. The first signs of trouble will be loss of productivity, then the soil will start becoming hard and compacted, will lose organic matter and humis, and then water retention capabilities. All of this spells doom for optimal crop production. While I aint a big fan of chemical petroleum based fertilizers, and believe that their are other alternatives in wasted organic residues, only you can decide how you wish to manage your fields and your crops. Which ever method you choose to use, at least replace to the soil what is taken off. Soil test your fields and find out what is missing and develop a fertilizer strategy that will produce your crop and maintain (or improve),the fertility levels at the same time. A proper soil test will tell you how much of the fish emulson you need to apply for your crop and then you can decide from there which is the cheaper alternative.