the best preservative i ever used was NH3 , anhydrous ammonia. i installed a 250 gallon tank on the hesston 4800 baler above the bale chamber and used a continental flow control to meter it through a line that was orificed down just before the spray bar i made. as the crop ran over the pickup and was in the stuffer chamber the nh3 was sprayed up into the crop. the recommended rate was approx 1.5-2 % by weight dry matter. that meant for a 2200 lb bale around 18 lb of nh3 product was used. the benefit was incredible, it preserved the crop, allowed higher moisture baling, increased the protein value, palatability was enhanced, vermin repelled, and spoilage virually eliminated.. i also injected some round and square bales with a probe i made after they were baled and on the ground, it worked ok but was not quite as effective.. you could install different tanks elsewhere depending on your application and room. the spray bar i made was from a steel brake line with a removeable fitting on the end for cleaning, and had 5 holes drilled in it spaced to cover the area and was clamped to the bottom of the chute with weld on tabs, if i remember the holes were about 7/64 inch, and the orifice at the inlet to the steel tube was 7/32. the idea of the orifice was to create backpressure and maintain liquid delivery to the spray bar as well as provide more accurate metering. it works, the cattle loved the feed better than any other available, and the results were superb. when baling green feed barley crop at 35% moisture it literally made silage in the bale. even the young calves loved it, kinda like a mollasses flavor/ or like a plug of old style tobacco. sweet and savory, with all kinds of benefits for your operation...
