Winter Oilseed Rape Nitrogen

[MNBVCXZ]

Is there any correlation between high N = high yields? I'm talking of N amounts in excess of 220 kg/n/ha applied in the spring, eg 250 - 300.

 

[Clive]

correlation is between GAI and N

high N rates will benefit some crops but not others - its all depends on biomass / GA! etc


plenty of good research on this in OSR that is pretty accepted and used in practice by many - download one of the GAI applications for your smart phone maybe ?

 

[franklin]

We have found that the GAI tools are pretty good. However the idea of holding off the last N for "as late as you can travel" has not increased yields on this farm. Once the clay warms up the crop grows so fast that there is little difference waiting for it to grow another foot or so than just dolloping it on. We now only hold off for crops with huge canopies, and in this case we can still yield with a much lower rate of N - the additional N doesnt seem to add yield or oils. Consequently crops this year with their fairly small canopy (my fault - really really crappy September for spraying here) I will be putting 100kg N on as soon as I can around Valentines Day, and the balance about a month later. All urea-based fert. If the crop was thicker then I would stick to the same timings but reign back the first split.

 

[MNBVCXZ]

Do that already, however N Max allows large variations. 220 kg/n = 3.5 t/ha + 30 kg/n/ha over 3.5 t/ha?! So you could quite easily be on 280 kg for a 4.5 t/ha crop.
I was just asking does anyone use that amount regularly.

 

[franklin]

Well, I dont.

 

[Feldspar]

Some excellent NIAB data on OSR canopies and optimum amounts of spring N. This year we have very different crops across fields. Will probably vary N between 160 at the low end up to maybe 230-240 at the top end.

 

[i dont belief it]

Always best to try it on your own farm 2 or 3 tramlines at the higher rate I would take samples of the two rates have heard that high rates of N can lower oil content that was a trial putting 350kg/n on don't think it increase the yield that much.

 

[warksfarmer]

Is there any correlation between high N = high yields? I'm talking of N amounts in excess of 220 kg/n/ha applied in the spring, eg 250 - 300.

Yes I think so as we’ve tried reducing N and it just reduces yield ultimately even with good soil N levels. Quite simply the more N we put on the better the yield we get but only up to a certain point obviously. We definitely see a yield response increasing from 250 to 350kg/ha in wheat. We’ve been out of osr for 7 years but back in this year and we’ve not decided how much and when yet but I suspect it’ll be towards 300kg assuming RB209 allows it.

Another thing to think about is your magnesium levels because high Mag can lock up N.

 

[Renaultman]

Yes I think so as we’ve tried reducing N and it just reduces yield ultimately even with good soil N levels. Quite simply the more N we put on the better the yield we get but only up to a certain point obviously. We definitely see a yield response increasing from 250 to 350kg/ha in wheat. We’ve been out of osr for 7 years but back in this year and we’ve not decided how much and when yet but I suspect it’ll be towards 300kg assuming RB209 allows it.

Another thing to think about is your magnesium levels because high Mag can lock up N.

I knew it could lock up K didn't realise it could lock up N too? How would you go about reducing Mg? Lots of Calcium?

 

[warksfarmer]

I knew it could lock up K didn't realise it could lock up N too? How would you go about reducing Mg? Lots of Calcium?

Gypsum but you need loads. We applied it for a few years then retested and were still towards 10 on the index for Mag. So we dropped it as it was wasting money really as we were also unsure about how much sulphur we were getting from it as well. Instead we have concentrated on increasing OM just to make the soils generally healthier. It’s not reducing the Mag or increasing the soil N but the soils are easier to work.

 

[Renaultman]

Gypsum but you need loads. We applied it for a few years then retested and were still towards 10 on the index for Mag. So we dropped it as it was wasting money really as we were also unsure about how much sulphur we were getting from it as well. Instead we have concentrated on increasing OM just to make the souls generally healthier. It’s not reducing the Mag or increasing the soil N but the soils are easier to work.

Thanks, sounds like were on a similar soils. Going to stick with the gypsum, and try and get everything else Ca based. Ie thinking of using Calfphos for any extra phosphate we need after the OM we are applying, in whatever form we can acquire it. Hopefully have some compost lined up too.

 

[warksfarmer]

Thanks, sounds like were on a similar soils. Going to stick with the gypsum, and try and get everything else Ca based. Ie thinking of using Calfphos for any extra phosphate we need after the OM we are applying, in whatever form we can acquire it. Hopefully have some compost lined up too.

Are you applying sulphur as well as the gypsum or just relying on the gypsum? Iirc it was 2t/acre and was about £6/t including spreading but it was a while ago.

 

[Renaultman]

Are you applying sulphur as well as the gypsum or just relying on the gypsum? Iirc it was 2t/acre and was about £6/t including spreading but it was a while ago.

No the sulphur in the gypsum is only a bonus, also getting Sulphur in the Polysulphate and in the Liquid N.

 

[warksfarmer]

No the sulphur in the gypsum is only a bonus, also getting Sulphur in the Polysulphate and in the Liquid N.

Flipping heck you must be right up there sulphur wise then. We only put on 60-70kg/ha of so3 which I’ve questioned really as I’m not sure it’s enough. You must be double that at least doing all that every year?

 

[Brisel]

IIRC there's lots of sulphur in gypsum? Compost, Fibrophos/Kalfos and lime will give plenty of Calcium. CAN is a more expensive way of adding Ca. I have high Ca soils with low Mg, so use kieserite rotationally to supply extra sulphur.

I've always put approx 220 kg/ha N on in the spring with approx 100 kg/ha SO3, and varied the first spring dose in Feb according to canopy size. Whilst big canopies don't always need as much in theory I feel that the higher yield potential justifies a good dose too. Just my opinion & perhaps I'm not being flexible enough.

 

[Feldspar]

IIRC there's lots of sulphur in gypsum? Compost, Fibrophos/Kalfos and lime will give plenty of Calcium. CAN is a more expensive way of adding Ca. I have high Ca soils with low Mg, so use kieserite rotationally to supply extra sulphur.

I've always put approx 220 kg/ha N on in the spring with approx 100 kg/ha SO3, and varied the first spring dose in Feb according to canopy size. Whilst big canopies don't always need as much in theory I feel that the higher yield potential justifies a good dose too. Just my opinion & perhaps I'm not being flexible enough.

NIAB data shows large canopies do not need the N to get over 5 t/ha yields. Maybe put more N if you're aiming for 7t/ha (!), but otherwise perhaps you could cut back. I weighed some m2 last year and we only put 160 kg/ha in the spring on (crop had a fair amount of N in the summer / autumn) and we got about 4.6 t/ha. Did some extra liquid N on one tramline and it didn't stick out like a sore thumb on the yield maps (but we slightly lost where it was in the field so not a totally fair test).

 

[Brisel]

My chalks are 55% efficient on N. Your mineral soils are 60% efficient so that's 11 kg/ha more for me for a start. I did a trial of my own on a few fields by applying the last 40 kg/ha N at the end of April instead of the final dose being a big one at the end of March. The split trial yielded less wit the later dose but I wonder if the dry April/May skewed the result?

There's also a fair bit of historic NIAB TAG data to say that N timings make little difference to yield!

 

[Renaultman]

Flipping heck you must be right up there sulphur wise then. We only put on 60-70kg/ha of so3 which I’ve questioned really as I’m not sure it’s enough. You must be double that at least doing all that every year?

We don't always get the gypsum on before OSR and only aiming for one dressing per rotation that is why I treat it as a bonus. I'm still trying to work out how, how much and when the sulphur is a available from polysulphate and used it for the first time last year, as a replacement for MOP with the Ca and S03 as a bonus.

 

[Feldspar]

My chalks are 55% efficient on N. Your mineral soils are 60% efficient so that's 11 kg/ha more for me for a start. I did a trial of my own on a few fields by applying the last 40 kg/ha N at the end of April instead of the final dose being a big one at the end of March. The split trial yielded less wit the later dose but I wonder if the dry April/May skewed the result?

There's also a fair bit of historic NIAB TAG data to say that N timings make little difference to yield!

Good point on different N efficiency. No mention of accounting for that in NIAB Strategies 3 booklet.

 

[Renaultman]

My chalks are 55% efficient on N. Your mineral soils are 60% efficient so that's 11 kg/ha more for me for a start. I did a trial of my own on a few fields by applying the last 40 kg/ha N at the end of April instead of the final dose being a big one at the end of March. The split trial yielded less wit the later dose but I wonder if the dry April/May skewed the result?

There's also a fair bit of historic NIAB TAG data to say that N timings make little difference to yield!

This is the problem with trials, you never get the same weather two years in a row, before you even think about pest pressures, so what works perfectly one year can be a total disaster next .