While I was at the allotment this morning I noticed quite a few plots had a dusting of white powder on top of them but then others didn't .
Would this be something like blood fish and bone ? If so, I thought that it would be forked in and not just left on top. Is this practise aimed at one particular crop as I thought blood fish and bone was a general fertiliser ?

The white powder would be lime. Blood, fish and bone is a grubby brown/grey colour. There are trains of thought that you don't apply them together on the same ground as they cancel each other out. Why go to the trouble of raking it into the soil, when the rain will come along and do the work for you Cheers, Tony.

Evening Donedigging, i would say it is lime too. Unless there has been a local drugs raid, with the dealers trying to dispose of the evidence.

So saying that, the 1cwt of lime i bought this year has a distinct grey colour.

Thank you Tony, obviously had a very senior moment regarding the rain washing it in
Didn't think of lime...having never used it, that's why I was thinking blood fish and bone, I know I need a new eye test....will book one soon

Dear OH,
Regarding the dealers....they were very particular where they put it amazing

I spread bone meal like this once without raking it in and my neighbour's dog came along and licked most of it up. Birds like it, too. But yes, it will be lime. I'd be interested to see what the pH readings are like on the limed plots. It doesn't usually need to be applied every year, but many old boys get out the lime at the end of every winter regardless, because that's what they've always done. Years of applying lime can make a soil's pH stratospheric unless it's countered by considerable quantities of organic matter. Here in the East Riding most of the soils are on shallow chalk, but many allotmenteers lime anyway without paying heed to a pH test and then wonder why their potatoes are scabby.

On cue, just having read the above postings:
With it being completely still this morning, I spread lime onto the new brassica bed and just a bit on the parsnip patch, the mangetout pea row and the spray chrysanthemum bed. I had checked the pH beforehand and they were on the acid side of neutral. When the lime has been washed in by this week's expected rain, I will take some more readings. For the brassica bed, I usually aim for 7 - 7.5.

Our allotment is divided into three main beds (brassicas, potatoes, peas/broad beans), as well as some smaller side plots but only the brassica bed gets a thorough liming every year.

Hi Monika,
The pH preference for Brassicas is 6.0 to 7.5 so slightly acidic is ideal.
With potatoes the pH preference is 4.5 to 6.0 although they grow very hell here with a natural pH of 7.0 but we do get the occasional outbreak of scab.
Strangely most vegetables pH preference begins around 6.0 so why everybody is so keen to lime beats me.
JB.