Question on NPK

Farm Questions
1

I hear/see a lot of reference to NPK without actually understanding it much. I was reading the article on precision farming on TNAU website and came across a couple of things I dont understand.

For example, the Precision farming guidelines on cabbage says : “75 % of the total recommended dose of super phosphate i.e. 588.93 kg is applied as basal dose.”

“Fertigation requirement for cabbage F1 hybrid is 200: 125: 150 kg of NPK/ha is applied once in every three days throughout the cropping period.”

My question: So we need 200 kg of Nitrogen, 125 kg of phosphorous and 150 kg of potassium per ha. When they say 75% of the total recommended dose of super phosphate 588.93 kg, What do they mean? What is the 125 kg of phosphorous for, if you are using 588 kgs of super phosphate?? Does it mean you have to use 588 kgs of super phosphate and 125 kgs of phosphorous? What happens to the remaining 25% of the recommended dose?

I would appreciate if any of you guys with a chemical bent of mind can explain more about it.

Thanks

2

On second thoughts, does it mean 200 kg of Nitrogen, 125 kg of phosphorous and 150 kg of potassium to be applied every third day i.e if cabbage grows for 90 days then 200+125+150=475 kgs X 30 times = 14250 kgs??

or is it that 200+125+150 = 475 kgs to be used over the entire growing period of 90 days??

Thanks

3

Hi All,

I am also in the same boat as Arig_exec.

Yes for an “intended to be farmer” with some formal education, it is misleading as one one tends to dissect and get into the roots. But for a rural farmer, it does not matters as he is simply not bothered. I think that is the problem with we guys.

Here is a link which gives some basic info, but again some holes are left out.

sunset.com/garden/garden-bas … 000015144/

Best thing would be for an hands on Guru to explain in simple terms. I for sure know that N-P-K forms some percentage of proportion. Thus a 16:16:8 indicates out of 100 total, 16% is Nitrogen, Again 16% is Phosphorous and 8% is Potash.

Now the question arises, is it pure Nitrogen or as a compound, If so then then its % of pure NPK again becomes negligible. Another confusion is if you see the recommended dosage for some plants crops, then per acre is a few hundred kgs of each. I doubt whether this % of NPK really makes any difference. But seeing the plants under Hydroponics, gives different thoughts. !!

For Banana it is given here at Jain. Every one says Banana is one plant where you can see the difference immediately on NPK application.

jains.com/Tissue/tissueculture2.htm

This 200gm of N, some 70 gm of P and some 300 gm of K per plant in its life cycle to me looks very negligible, A banana plant with its produce weighs around 150 to 200 KG. making me tilt towards Organic methods.

Some recommended NPK for other crops are also a pittance. 100 to 200 KGs per Hectare (2.5 Acres). To apply or not to apply is a big confusion. Because for an hectare this is a small %.

Cowherd a senior and an hands on person, on this forum has very very clearly explained this. In organic methods tons and tons of microbes do this and produce NPK and provide it to plants. So make these microbes thrive in soil by organic methods.

Confusion , confusion and more confusion :-[ !!!.

On other hand, @ my house no NPK but Banana grows without a care for this world. Again at the same place it is surviving ratoon after ratoon… Only thing is what ever organic waste generated @ my house lands at this bananas bottom.

Gurus kindly step in. Both Organic and Inorganic followers kindly pitch in. With collective effort lets clear this confusion forever.

Regards

Murali

4

[quote=agri_exec]
For example, the Precision farming guidelines on cabbage says : “75 % of the total recommended dose of super phosphate i.e. 588.93 kg is applied as basal dose.”
My question: So we need 200 kg of Nitrogen, 125 kg of phosphorous and 150 kg of potassium per ha. When they say 75% of the total recommended dose of super phosphate 588.93 kg, What do they mean? What is the 125 kg of phosphorous for, if you are using 588 kgs of super phosphate?? Does it mean you have to use 588 kgs of super phosphate and 125 kgs of phosphorous? What happens to the remaining 25% of the recommended dose?[/quote]

Let me try with my rusty Agronomy knowledge.
Basal is before planting normally as part of land preparation. Since Phosphorus is not a very mobile nutrient (does not move or leach much) and requires microbial activity to be made available to plants, generally it is recommended to be applied basally so as to reach the root zone.

P requirement is normally expressed as P[sub]2[/sub]O[sub]5[/sub].
Single Super Phosphate (SSP) has 16% P[sub]2[/sub]O[sub]5[/sub]; so the recommended dose of 125 kg P[sub]2[/sub]O[sub]5[/sub]/ha translates to 100*125/16=781.25kg SSP/ha
75% of 781.25kg has to be basal, i.e., 585.9375kg SSP (you have a little typo here?)
The remaining is to be applied later during the crop, the split normally is to avoid wastage due to losses.

That dose is for the entire crop season; fertigation means providing the fertilizer with irrigation (drip etc.) and hence the dose has to be uniformly mixed with the water over the complete irrigation cycles during the cropping period.

5

Chandra,

Thanks a lot for the explanation. So, Its an efficiency thing and not quantity. If i use a P18% SSP then my over all qty goes down and if i use say P8.8% then the qty goes up. Kool. Similarly for nitrogen, if I am using N 20% it will be 100200/20 = 1000 kgs and if N 46% then 100200/46=434.5 kgs/ha. Correct? Same for K?

Thanks

6

Correct. SSP is 16% though.
That said, bear in mind the choice of a fertiliser is based on several other factors, e.g., SSP also supplies Sulphur and Calcium. Non complex fertilisers also contain micronutrients. The form of the nutrients and availability, the reaction and how they affect soil pH, crop specific compatibility of fertilisers are a few of the other factors additional to cost of the nutrient.
Then of course is the bigger organic argument as Murali refers to.

7

Then what is 18:18:0 ?? Does it not mean availability of P2O5 is 18%? Is single super phosphate completely different from Phosphorous? Isnt the application of phosphorus is in fertilizers for its phosphatic use?
I see there are various strengths of SSP at 18%, 8.8% etc. Maybe 16% is the common thing in india?
Why is SSP 16% only?

sorry im confused again :slight_smile:

Thanks

8

Hi Agri_exec,

Go thru this link,

mangalorechemicals.com/produ … p?links=mu

And other products. Some go upto 46% by weight. Yes we are all are confused.

May be this complex formula which is beating us is really the spoil sport the reason why soil is getting depleted by random usage. If it is confusing to us then imagine the village farmer.

Regards

Murali

9

Murali,

Thanks. Thats Only “N” or urea which is easy to deal with. You know how much N you can get from a bag.
Problem is dealing with a combination of all these chemicals with strange ratios.

Thanks

10

Hi,

Look at these two.

mangalorechemicals.com/produ … p?links=sf

mangalorechemicals.com/produ … p?links=fp

3 to 4 ml per liter and the second is 4 to 5 gm per liter. So for an hectare how many liters ? This when compare to the bagged ones there is a lot of variation.

Regards

Murali

11

3-4 ml / lt is for foliar spray only. Think for fertigation it should be based on crop’s requirement. Also, calmax and sulphomex are not as subsitutes for macro nutrients.

12

Hi,

It looks like me, you and chandra are only discussing things here. We had a lot of doubts. Its like 3 blind men describing an elephant. :-[ :-[

Where are all the gurus ?? Surprising that most of the gurus are silent. :'( :'(

Regards

Murali

13

Hi Chandra and Argi_exce,

Found some article which may clear some doubts on calculations. Attached .

Regards

Murali
fertiliser-calculations.pdf (169 KB)

14

18:18:0 does mean 18% P along with 18% N and no K (this is not SSP composition of course).
Most complex fertilizers have a mix of nutrients.

SSP is a compound that contains P in its phosphate form in the range of 16% - 22% P[sub]2[/sub]O[sub]5[/sub] but I think the grade we have is 16%. I suspect you are mixing it up with the 8.8% which is the proportion of P and not P[sub]2[/sub]O[sub]5[/sub]. You also have other superphosphates than ‘single’ which have higher P content but SSP is commonly available.

15

Thanks Chandra, Is it 16-22% P or P205?

16

Hi,

In the attached document concentrations of NPK and other things are fairly explained. Many of my confusions got clarified.

But one thing who decides how much an hectare requires for a particular crop ? Is it the fertilizer manufactures, in that case the dosage would be dubious. Or any research being done at our agri universities ?? any thumb rule which says that each plant requires some minimum dosage of N P K etc ??

Regards

Murali

17

This is based on field research and statistical analysis of response of each plant/variety to different combinations of fertilizers - on various parameters such as dry matter production, yield, oil percentage etc. etc. based on the crop. The recommendation is normally the ‘optimal’ dose. Arguably, the vast majority of research in any university would be around plant nutrition.

The response varies based on a large number of environmental factors (e.g., soil moisture), and is also different for each “variety” (loosely used). For example hybrids generally show a greater response to added fertilizers as compared to traditional varieties.

18

Hi

Looks like its hypothetical. Just like “Action 500” with 500mg of some compound which will cure headache from 18 year old to 99 year old,

I am just wondering what dosage of these NPK is required to produce those amazing brazillian forests or our western ghats. Its truly amazing. Nature at its best.

Another doubt, if NPK is totally avoided, then in Organic Farming how does one come to a requirement ? As many say output exceeds chemical farming from 2nd year onwards. Does any calculations hold good here ?? If left to nature, then nature should produce these NPK in abundance. If so then no need of applying these man made NPK. Confusing isnt it ?? I admit there is some micro link that is missing. If only we find it out, then its a different story all together. !!

Mainly problem arises in monocroping. In nature we hardly find this type of monocropping, one species acres over acres. Can you see ?? Say only banana or teak spread as a main vegetation acres over acres.

It still leaves a lot of gaps !!!

Regards

Murali

19

Hi Murali,

This was exactly the discussion on the farmnest.com/forum/natural-farmi … practical/ topic.
Go revisit it! :wink:

20

Hi Chandra,

I have seen it, it lost steam in between. So this !!

No updates since long, it was really a nice discussion but some how lost steam in between. Many veterans gone cold there.

Regards

Murali