Phosphate what and when ?

[Clever Dic]

Probably a dumb question for some of you but this is not my area.
We are on heavy ragdale type clays , continuous grass reseeded every 2 years all land mapped so really wanting to utilize VR. Most indices are 2 and better but do have an acerage (150 odd ) that is at 1 or less .
My question is what is my best source of phosphate is it TSP ? but does this lock up rapidly and thereby diminish it's efficacy?
When would you apply ? Spring or in the autumn pre drilling ?

Many thanks.

 

[Kevtherev]

Most put it on in the autumn.
@Cab-over Pete @Mounty
Fibrophos or P-Grow

 

[Kevtherev]

Have you tested the PH?

 

[Mounty]

Maintenance P can be applied anytime but to build P levels it is better applied close to the seedbed.
TSP can be locked up quickly on high pH soils so factor this in. P-Grow is 23% P2O5 so double the rate applied compared to TSP. Some useful additional nutrients in the P-Grow for grass but if you are going to apply VR you will only get the additional nutrient benefit where you are applying the P.

 

[ollie989898]

I am a bit confused by the initial question. You intend to reseed the entire 150 acres in the autumn or not?

If you have low P then you need to rectify it now or else suffer the consequences of it throughout this growing season?

Can I also ask, why reseeding every 2 years, although perhaps this is for horse hay or some other particular end use?

 

[Brisel]

Top up P can be applied in any half available form whenever you like. Indices of 1 or less ought to be ASAP and in a more soluble form. TSP is ok but the granule size makes it slow to dissolve. Fibrophos products get some stick for being unavailable but the particle size is much smaller. Do what is best for your system but I'd use a decent dollop of P Grow as the pricing is good relative to TSP or DAP plus you get useful calcium for your clay and lots of other trace elements. The price discount to TSP usually covers the contractor's spreading costs too. Spreaders will travel well on pasture.

If you're applying lots of K as well e.g. 0.12.12 Fibrophos, be aware that you risk staggers (hypomagnasaemia) if applied within a couple of months of grazing or cutting.

 

[willy]

if you are using vari rate through your own spreader, you dont really have an option other than tsp. i would whack it on as soon as you can travel ok.

 

[Brisel]

I have done VR 12.60.0 MAP back when it was much cheaper and the variation was not great. It was in osr & we didn't have yield mapping, so didn't see any visible differences.

There are plenty of Fibrophos spreaders with VR capability.

 

[Oat]

Top up P can be applied in any half available form whenever you like. Indices of 1 or less ought to be ASAP and in a more soluble form. TSP is ok but the granule size makes it slow to dissolve. Fibrophos products get some stick for being unavailable but the particle size is much smaller. Do what is best for your system but I'd use a decent dollop of P Grow as the pricing is good relative to TSP or DAP plus you get useful calcium for your clay and lots of other trace elements. The price discount to TSP usually covers the contractor's spreading costs too. Spreaders will travel well on pasture.

If you're applying lots of K as well e.g. 0.12.12 Fibrophos, be aware that you risk staggers (hypomagnasaemia) if applied within a couple of months of grazing or cutting.

Based upon the Crop Nutrition seminar at Croptec this year, maybe a P index of 1 isn't a serious problem?

 

[yellow belly]

is the low p soil at 1 or 0 what concentration
I farm similar soil and have had no measurable yield penalty for low indexes this was also backed up by some of the latest research that showed that index 1 on that type of land showed no financial benefit from increasing the amount of p added

if you are grass based and access to muck use that also you may be able to get sewage sludge or use fibrophos or calciphos this can be at lower cost per kg of p than tsp and you may get a good deal on spreading out of the arable season

I would also be carefull with the accuracy of soil testing as I have had big variations in analysis taken at different times

one block had index 5 which fell to index 1 in 4 years

I have also had indexes rise from 0 to 1 or 2 without adding big amounts of phosphate

 

[Brisel]

Adding P to soil to get an Olsen index is imprecise for the reasons @yellow belly mentions. Different soils respond differently. One of my best yielding fields had an index of 0 and took a lot of TSP, MAP and DAP to raise that P index to 2 for little improvement in yield. NIAB TAG did some work on optimum P levels & found little difference above 2 but a greater likelihood of yield responses below that though little consistency. @Fromebridge may be able to correct me if I'm wrong on this.

 

[Gong Farmer]

You're right of course, 2 is Ok or even high 1. Application in spring doesn't work until it's worked in with post harvest cultivation. K is more soluble so can get responses to spring application.

 

[tr250]

We use sewage sludge. We find mowing leys rob the p and k but k if easier to put back with muck and we always end up short of p