Soil nitrogen test

[cowboysupper]

Hi all, looking for some guidance on lab based soil nitrogen testing, something I'll admit to knowing little about.

We're running a biogas plant growing grass silage and wholecrop as our main feedstocks. Ultimately we have digestate available in the autumn to spread prior to sowing winter crop. Approximately 3000g was applied in late September ahead of winter rye. This is a higher rate than we would like but was a necessity on this occasion to help make sure we had enough winter storage and wet conditions restricted appropriate land to spread.

Our digestate is rather potent. Regular analysis shows available nutirent per 1000g as typically 30-35 units of N, 8-10 units of P and 80 units of K. This is great for growing grass and spring crops with very little chemical fert but admittedly N rich for autumn applications. But we are where we are at the minute.

I've had a look at RB209 in terms of doing the field assessment for SNS but given the level of organic manure that went on in the autumn I'm wondering should we be considering a lab based approach for trying to calculate what is still available in the soil? Can any of you more knowledgeable growers provide any guidance on the pro's and con's of soil nitrogen testing, which type of test is best, when is the best time to do it? We'll not be applying any N until March so we have a bit of time work with.

 

[deleted user 837354]

I presume you have been applying digestate to the land in this way for several years?

You can do a nitrogen soil test but in your situation I would be more inclined to drive the crop manually- working by eye.

When you apply organic manures, solid or liquid you aren't just applying raw nitrates, though there will be some in it. Most if not all of these products contain a slew of nitrogen in a variety of forms- some you will detect readily now. Others will be made available when the bacteria in the soil release it when the soil warms in spring. Others still may be available in maybe 6 months or even 12 months. This is the beauty of them- they drip feed the crop over time.

You can take some nitrogen samples as a guide to caliberate yourself but if your digestate is as potent as that you may not need much bagged product at all. Infact there will be people putting a dose of digestate on crops if it ever dries up in spring.

People will rightly assume that growing crops with perhaps only 50 units of N is madness and flies in the face of all textbook thinking but I have done it a few times and how many people put the full amount on maize- a crop that will provide the same biomass as your rye.

Put your soil to work and experiment a little on a small area I would.

 

[Brisel]

For soil with regular doses of digestate, a soil N test is a good idea IMO. I'm a bit cynical about the value of the figures but where high doses of high N fertilisers have been used it's going to give you a good guide. Don't forget to allow for the crop/grass biomass in your calculations too.

Soil Mineral Nitrogen (SMN) - Anglian Soil

Soil Mineral Nitrogen (SMN) usually has a bigger effect on crop growth, yields and quality than any other nutrient. Nitrogen can be supplied from the soil, atmosphere, organic manures and crop residue as well as from fertilisers. Nitrogen can be lost by leaching, ammonia volatilisation and...

www.angliansoil.co.uk

Other providers of soil testing are available

 

[cowboysupper]

I presume you have been applying digestate to the land in this way for several years?

You can do a nitrogen soil test but in your situation I would be more inclined to drive the crop manually- working by eye.

When you apply organic manures, solid or liquid you aren't just applying raw nitrates, though there will be some in it. Most if not all of these products contain a slew of nitrogen in a variety of forms- some you will detect readily now. Others will be made available when the bacteria in the soil release it when the soil warms in spring. Others still may be available in maybe 6 months or even 12 months. This is the beauty of them- they drip feed the crop over time.

You can take some nitrogen samples as a guide to caliberate yourself but if your digestate is as potent as that you may not need much bagged product at all. Infact there will be people putting a dose of digestate on crops if it ever dries up in spring.

People will rightly assume that growing crops with perhaps only 50 units of N is madness and flies in the face of all textbook thinking but I have done it a few times and how many people put the full amount on maize- a crop that will provide the same biomass as your rye.

Put your soil to work and experiment a little on a small area I would.

Yes we generally spread approx 2000g prior to autumn drilling so this ground will have had regular applications.

I wouldn’t mind taking the SMN sample just a a guide to help aid a trial in the field.

We’re in a high rainfall area (circa 900mm). Can we take the sample at this time of year or are we better waiting for drier conditions and warmer soil?

 

[teslacoils]

Best to do smn before you want to apply any n. Where we have historically applied digestate we don't tend to find a lot in year two.

 

[teslacoils]

Got my tests due back soon. But how to quantify nitrogen taken up from the cover crop, and how much will be available next season if destroyed in march?

 

[mo!]

I was at a meeting about N last week, YARA were there and basically said that soil nitrogen testing was so inaccurate as to make it worthless. It made me smile as they run the labs that do the testing. Their preference was leaf testing, which of course they can sell you the gadget to do...

 

[cricketandcrops]

I was at a meeting about N last week, YARA were there and basically said that soil nitrogen testing was so inaccurate as to make it worthless. It made me smile as they run the labs that do the testing. Their preference was leaf testing, which of course they can sell you the gadget to do...

Incorrect Yara don’t run the labs that do the SMN test

 

[teslacoils]

Incorrect Yara don’t run the labs that do the SMN test

Maybe that's why they were slagging it off then. I'm mainly checking to see if on land with high applications of slurry and muck, if the idea that a percentage is released in year two is true or not. If muck / digestate is supposed to give a slug of N in year two, but my soil N in February is the same a land that hasn't had it, then that makes a big difference in my nitrogen paperwork.

 

[cricketandcrops]

That’s why I’ve never been a fan and yes J work for Yara but wasn’t a fan long before I joined.

I have used the N-Tester for a number of years (and all lend mine out to agronomists each spring) and it is ideal for you scenario.

 

[mo!]

Incorrect Yara don’t run the labs that do the SMN test

Apologies, I thought Lancrop did them.

 

[cricketandcrops]

Maybe that's why they were slagging it off then. I'm mainly checking to see if on land with high applications of slurry and muck, if the idea that a percentage is released in year two is true or not. If muck / digestate is supposed to give a slug of N in year two, but my soil N in February is the same a land that hasn't had it, then that makes a big difference in my nitrogen paperwork.

Quite happy to visit and go through N-Tester and I also have some very good real N-Sensor data that shows that a good amount of N is released 18 months after application, Just send me a direct message and happy to pop over as not a million miles away

 

[teslacoils]

Quite happy to visit and go through N-Tester and I also have some very good real N-Sensor data that shows that a good amount of N is released 18 months after application, Just send me a direct message and happy to pop over as not a million miles away

Cheers. My dilemma, if you'd call it that, is that our spring cereals normally go in in April. So we normally put all the N in the seedbed as urea or liquid then a pass of digestate. However, the field has a history of digestate and currently a healthy crop of volunteer winter barley. Last year's soil N test showed we could (and did) reduce n by 100kg/ha.

Crop will be oats and I'm keen to keep them stood up!

 

[d williams]

Cheers. My dilemma, if you'd call it that, is that our spring cereals normally go in in April. So we normally put all the N in the seedbed as urea or liquid then a pass of digestate. However, the field has a history of digestate and currently a healthy crop of volunteer winter barley. Last year's soil N test showed we could (and did) reduce n by 100kg/ha.

Crop will be oats and I'm keen to keep them stood up!

Bit of urea in with seed33% wait for tramlines to appear assesses then digestate

 

[Brisel]

Got my tests due back soon. But how to quantify nitrogen taken up from the cover crop, and how much will be available next season if destroyed in march?

Use the cut and weigh 1m2 of biomass recommended by NIAB TAG for osr canopy management/GAI. What that won’t tell you is what that will do for the following crop N. Personally, I’d ignore it as the contribution won’t be much and it’s slow release.

 

[cricketandcrops]

Cheers. My dilemma, if you'd call it that, is that our spring cereals normally go in in April. So we normally put all the N in the seedbed as urea or liquid then a pass of digestate. However, the field has a history of digestate and currently a healthy crop of volunteer winter barley. Last year's soil N test showed we could (and did) reduce n by 100kg/ha.

Crop will be oats and I'm keen to keep them stood up!

Tricky one, as our two bits of kit won’t work with oats, and yes very easy to get wrong and they go flat in the floor!!!

This is an interesting read but doesn’t give you an answer http://randd.defra.gov.uk/Document.aspx?Document=NT1508_7773_FRA.pdf however does suggest a w barley cover can take up 20-50 kg/ha N, however doesn’t say how much is then realised for the next crop

You could download the Irix app from the App Store and use it to take a reading of GAI which should give you a N uptake figure but again won’t actually say how much stored N the cover crop will release

SMN testing is so variable, with my agronomy hat on we stopped doing it because it gave more questions than answers!!

 

[teslacoils]

Yes, the lit suggested around 50kg from the cover, so I'm going to count it as 20kg. Soil N may not be wonderful but I'd be cross to do nothing then it all go flat. At least I have some more info to get my decision wrong with.

 

[cricketandcrops]

Yes, the lit suggested around 50kg from the cover, so I'm going to count it as 20kg. Soil N may not be wonderful but I'd be cross to do nothing then it all go flat. At least I have some more info to get my decision wrong with.

I would suggest also having a go with the app (it’s free) I had a go on some winter wheat on Saturday and seemed to work OK, gives you a N uptake figure......unlike OSR where it gives a recommendation

I like your last comment......the best decision is the correct one, the second best is the wrong one. but at least you make one

 

[teslacoils]

Thoughts?

 

[cricketandcrops]

Thoughts?

Is it hybrid??? If not would you consider taking it harvest? That is a serious amount of N uptake.....so it has taken up some of the organic n applied for sure.....question is how much would it now release when stored......you would assume (although you never should) that SMN will now return low with that amount of uptake