First, looking at the P & K….

Penn State uses crop removal numbers for corn silage to be 7-4-8 (N-P2O5-K20) per ton corn silage.  So, 31 tons corn silage removes 217 lbs N – 124 lbs P2O5 – 248 lbs K2O.

Liquid dairy manure.  Penn State book value is 28-13-25 (Total N – P2O5-K2O) per 1000 gallons. 

So, 10,000 gallons liquid dairy manure supplies 280- 130-250 (Total N- P2O5-K2O).

So, based on these numbers you are supplying breakeven amounts of P2O5 and K2O to meet your corn silage needs.  For one year.  And you are applying manure every other year.   I can see why you are soil K levels are low, and, frankly, I don’t see your P levels to be high either.  If you believe there is carryover of the P & K from the manure application to cover the following crop, it just isn’t there.   Your manure is meeting P & K needs for your corn crop, and that is about it.

I don’t know what values you have/use for manure nutrients and crop removal, but that is what I use.

Second… you say you are using clover and radishes in your cover crop after wheat.  I wonder if you would benefit from having a cover crop with more Total dry matter produced.  I wonder if having something like in a mixture of: sorghum-sudangrass (or just sudangrass), plus maybe some Sunn Hemp, or maybe try berseem clover in the mixture as well.   It’s just a thought I had.  The goal is to maximize DM to help increase Soil O.M. levels.  It probably won’t have as much nitrogen produced for your sugar beet crop – you may need to add extra nitrogen.  ???

Someone may say it’s a crazy idea..... Maybe......  I’m just tossing it out.  ??