I will have to admit I am not a big fan of soil testing.  Over the years, numerous articles have been written in this country stating the results would vary with the lab used.  With higher fertilizer prices I am rethinking my lackluster approach to the matter. 

The testing we have done have always shown very consistantly high levels of K. Soybeans and alfalfa both use alot of K, so where we have not applied any supplemental K over the years because of the high level shown on the soil tests, one would expect the level to fall off, but it never does.  I have noticed a few fields that show consistant but lower levels of P without additional P being added, the numbers stay constant.  The lab shows it to be available, but can that really be right?  I am going to test my corn ground soon, and believe it will probably show adequate levels of P and K.  We have always put P on the ground that will be planted to corn.  My gut feeling is that the corn will need it no matter what the test shows.  So, what do you guys think??  Do you believe the soil test, or go with your gut feeling that since the levels never change, it must actually be unavailable to the plant?

They are crap. I only get them done to show the various people who come to assess us for certification.

Our clay soils lock all the nutrients up anyway, so having a Mg index of 6+ means nothing if the plant cant access it. Certainly we suffer from loads of potash but not enough phosphate. OSR only leaves a high residual N because they plant is so poor at utilising it that half of what you sling on is wasted, and will probably now be running into the ditches if this rain continues.

I did a story in Crops magazine a couple of years ago comparing how soil mineral nitrogen results from the same sample varied between different labs - and there were certainly some interesting results!

Cores were taken (by an agronomist) at 0-30cm and 30-60cm from 2 fields - one heavy clay, another sandy loam. Samples were sent to 4 labs (NRM, Direct Labs, Lancrop Labs and Hill Court Research). When the results came back, on the heavier field (wheat after set-aside), the SMN analysis for the total of the 2 cores (0-60cm) varied from 63-132kg N/ha. For the light land, results ranged from 42-78kg N/ha. Which was closest to the truth is anyone's guess...

This opened a whole can of worms around how samples were taken in field, stored, transported, sub-sampled at the lab and analysed. You may take a bag full of soil from the field, but if the lab only selects a 40g sub-sample for analysis, there's a pretty good chance it might not be representative of the rest!

The main conclusion was to use sampling as a guide only and take unexpectedly high or low results with a very large pinch of salt!

Paul (FW arable)

Residual nitrogen is a load of rubbish anyway - we are supposed to take into account what there is to begin with in the soil, and assume it can be 100% utilised. If this is the case, there ought be none left the following year. Putting fert on is an economic consideration - you can apply 300kg of N in splits and the right conditions and it will be used. You can put half that on and watch it wash away in bad weather.

KI K/F  I opened a thread on here a few weeks ago on FERT WHAT FOR,no one responded,you are right many soils,have enougth P FOR A FEW LIFE TIMES,and puting more on is largely a waste of money,as it is locked up very quickly,hence your results.We work on makeing what we have!!in the soil come more avaible to the plant.Then have the soil tested for plant avaible nutients.P/K indics are a pointless test.Last year i am told that lorrys had to pull out of the que to let my wheat in first,i know it sounds a bit bassar,all our potatoes have long been sold out,in a year when imports are takeing a big chunk of the trade,so it cant all be wrong,i do still use N and some P/K for pots but a lot less than befor,so much so that we have non to buy this year.I DONT WONT TO SAY TO MUCH AS WE DO PAY FOR ADVICE,test the odd representative field,for plant avaible nutients.  I ENJOY READING YOUR COMMENTS FROM KANSAS.      JOHN.