Dear Prithwiraj

It is possible to produce high yield by N fertilisation. However, much of the commercial N fertilisers (e.g. urea) is produced by using substantial amount of fossil fuel energy. Given there has been global move to cut down fossil fuel as an energy source to reduce GHGs (greenhouse gases) emissions, it is sustainable to rely on solar energy to synthesise NH3 from atmospheric N2 from symbiotic process to produce food from pulses. In many tropical nations, solar energy is not a limiting factor (CO2 is available in plentiful nowadays) to produce plant carbohydrate except for water which can be limiting even with fertiliser-N application.

If you still wish to provide external source of N for plant uptake without taxing plant energy, there may be other sources such as readily mineralisable compost or organic manure.

Kind regards

Selva

Dear Dr. Selva, thank you for your comments. I understand the environmental concerns. But the question is if a considerable increase in yield is possible or not through N fertilization or not.

In India, we are trying hard to increase the pulse productivity. Relying upon the biological N fixation imparts too many boundations on the system viz. Soil ph, moisture content, Mo content, higher P fertilization etc.

I think, if the alternate is possible, then the energy concern can also be judicially managed. @selva selvarajah

The more fertiliser N you apply the less symbiotic N may be acquired

The question is not about the sustainability or environmental issues. The question is only about the possibility. Majority of the cultivated crops can't fix N. But for the sake of environmental pollution, no one is going to switch totally upon the biological fixation to save the energy. In a country, where a lot of foreign exchange is required to import a huge amount of pulses to maintain its food sufficiency, it is important to explore diverse possibilities.

Take the example of French Bean. It cant fix N but grows well on supplementary N. Addressing the problems in BNF is a big issue and in last 50 years we were unable to increase the productivity to the satisfactory level.

So the question is only that, if there is any possibility to enhance yield by supplementary N fertilization instead of dependence upon BNF or not.

Dear Prithwiraj

Whether one uses or N fertiliser or symbiotic N fixation, soil moisture & pH and P fertilisation are critical except for Mo requirements. Whilst you can obtain good yield response with increasing fertiliser-N applications in theory, the price of N fertiliser has to be factored into estimating profit, without which pulse farming could become an academic exercise.

Some papers argue increasing fertiliser-N use in association with P does not necessarily result in increasing pulse yield (e.g.

https://saskpulse.com/files/newsletters/Lentil_Response_to_N_fertilizer_or_high_soil_N.pdf).

Some argue biofertiliser approach provides better yield than mineral fertiliser-N application (e.g. Bangladesh J. Agril. Res. 40(3): 501-506, September 2015).

If fertiliser-N use is compelling, starter-N application may be more beneficial (e.g. Agronomy 2018, 8, 120; doi:10.3390/agronomy8070120).

There is convincing evidence on the benefit of BNF (biological N fixation) in grain and forage legume production without compromising yield (e.g.

Article A Comparative Nitrogen Balance and Productivity Analysis of ...

When considering crop rotation, fertiliser-N use becomes more complex (e.g.

Article Tropical Legume Crop Rotation and Nitrogen Fertilizer Effect...

Even if you wish to ignore energy use and the above factors, there is also compelling evidence on heavy nitrate leaching from high fertiliser-N use, even when split dosing.

Kind regards

Selva

I think you could do some filed experiment to assess the effect of N fertilizer on the yield of pulse. In theory, N fertilizer could inrease the yield owing to save photosynthates, but the effects of fertilizers will be affected by some factors, such as water supply, soil pH and availablity of other elements etc.

Linquan Wang Thanks for your words. Currently I am not having any grant for the experiment concerned. But I think that some one can do the same and enlighten us about the applicability of the theoretical concept.

Physiologically, inherently low yielding pulses such as Lentil are unable to benefit from excessive N fertiliser application. Judging by many papers it could be argued under rain-fed conditions (with P not limiting), maximum grain yield with high protein can be achieved with low applications such as 20-25 kg N/ha/year.

Excess applications such as 50 or 60 kg N/ha could lower the grain yield with no change in protein content hence it could be concluded that high fertiliser-N application can result in fertiliser wastage and less profit.

Please see some examples of N fertiliser rate vs yield:

Niri HH, Tobeh A, Gholipouri A, Mostafaei H, Jamaati-eSomarin S (2010). Effect of nitrogen and phosphorous rates on fertilizer use efficiency in lentil. World Appl Sci J 9:1043- 1046 (I have already referred to this paper in my previous response)

AND

http://www.notulaebotanicae.ro/index.php/nbha/article/viewFile/6373/6461

Kind regards

Selva

Selva Selvarajah

Thanks Dr. Selva for your informative comments. After studying the mentioned literature, it is quite sure, that the excess amount of nitrogen can't be used by the lentil under dry land situation due to moisture stress. And we all know the nitrogen actually responds under the irrigated/moisture non limiting conditions. Even if we look for the N recommendation for cereals too in dryland condition, it is quite low than irrigated ones as the crops don't respond to excess N. My concern was actually for the high input optimum situations to boost productivity.

I appreciate your enthusiasm in N fertiliser & irrigation effects on pulses and I hope I am not dowsing it with my comments Prithwiraj. My comments are aimed to make any new pulse research projects effective from the outset.

Unlike cereals, pulses are very sensitive to increased soil moisture levels which could result in lower yields. Like most crops pulses will perform better under irrigated conditions but this depends on the extent of the seasonal rainfall or soil moisture availability.

An example of increased irrigation effects can be seen in

http://www.agr.gc.ca/resources/prod/doc/pfra-arap/csidc-crdi/pdf/lentil-lentille_eng.pdf.

Detailed studies also showed irrigation having little or no effect in some seasons and even decreased yields with irrigation -

https://researcharchive.lincoln.ac.nz/bitstream/handle/10182/2736/mckenzie_phd_oa.pdf?sequence=6.

On occasions where irrigation effects were pronounced, fertiliser-N effects were not prominent -

https://researcharchive.lincoln.ac.nz/bitstream/handle/10182/1126/Kang_MAgSc.pdf?sequence=3.

Kind regards

Selva

@selva selvarajah

Thank you for your concern sir. Your comments are really informative. About irrigation, there is plenty of references that optimum irrigation and drainage condition enhances the yield of legumes. May be the variying response is caused due different agroclimates. I am not going into that. And I also agree with you that N application has a -ve relation with pulse yield in general. But the question is why. Most of the literature says that it is due to

a. non fuctional nodules or less/no nodule formation under high fertility condition

b. Excessive vegetative growth

Still a clearer view is required. Even no nodule formation is taking place, why there are instances of reduced yield? Are legumes unable to uptake soil nitrogen?

If it is mostly due to excessive growth, it can be controlled with the thoughtful N scheduling. I don't have the perfect answers to this questions. If you can explain it to me, it will be highly helpful.

Thanks & Regards,

Prithwiraj

Hi Prithwiraj

Nodule formation in Pulses normally are sensitive to medium to high concentration of the nitrogen in the filed, However, even for optimal symbiosis certain level of nitrogen in required. Based on my experience 2mM of KNO3 is very useful for plant growth and nodule formation. in this concentration plant growth properly with higher yield in compare with non treated plants. Lets to forget the biological process governed by plants to balance photosynthesis functionality and symbiosis or...these are very complex circumstances and almost unknown !!

Hello Maryam,

Thanks for your comments. In my opinion, unknown or less understood areas pose the greatest possibilities. That's why I have put the question on RG to discuss with knowledgeable persons. Its really new fact to me that even optimum nodulation needs inorganic N source.

For this I can suggest to test dosage of the N resource and check for nodulation efficiency, photosynthesis functionality and yield simultaneously . Definitely you can find an optimal point, though finding underlying mechanism needs long term efforts but interesting!

Good luck

What are the possibility to explore non symbiotic N fixation in pulses?

@Maryam Seifi Kalhor

Thank you for your suggestion.

Sachin Kanta Rautaray

Thank you Dr. Rautaray for your views.

Sachin has correctly summed up the limitations with pulse yields. The good news, however, is most pulses are dryland crops which can perform relatively better without irrigation. The increase in yield by maximising BNF or fertiliser-N addition or irrigation may not be very high in typically low yielding pulses. For example, if all factors remain ideal lentil yield could be maximised between 1-2 t/ha and that of soybean could be double. Compared to the above, other non-pulse grain crops such as wheat yield could be maximised in excess of 10 t/ha.

For the above reasons, inherently low yielding crops such as lentil will require smaller amount of N fertiliser for seed production. Low yielding lentil also fixes lower BNF (e.g. 50 kg/ha) compared to relatively high producing pulse such as soybean (e.g. 150 kg/ha) under optimal conditions. As identified low yielding pulses can also be sensitive to typical irrigation cycles.

As Sachin had correctly articulated, the most effective way of increasing pulse yields is by varietal improvement/plant breeding.

By being persistent in your questioning you have been able to bring out many useful information on pulse yields Prithwiraj!

That was a really helpful and healthy discussion indeed. Thanks everyone for your valuable comments.