Respected Sir, Yes as you mentioned that irrigation water has a potential to reduce the fertilizer requirement, but many a times higher doses of fertilizers are also required to mitigate the ill effect of irrigation water if the he water is saline and/or sodic. One have to consider that too during utilization of these poor quality ground waters. Regards

Canal or well water may be checked for soluble K before they are used for supplemental irrigation to the crops. Similarly for nitrate N. In N-W IGP areas  canal or well water  may be a good source  of these two nutrients.

You will need regular sampling and analysis of the major elements in the irrigation water a well as information as to what are the ideal amounts of these elements for growing each crop on your soil.  The latter is determined by experimentation with different doses of elements in your fertilizer application on sample plots.  You need to watch the total soluble salts (usually measured by electrical conductivity) and also be aware of the salinity limits for each crop.  Remember, when you apply irrigation water, a significant amount evaporates leaving the dissolved salts behind in the soil.  These must be flushed out into drainage ditches or the soil will become too saline to grow crops, as happened to the Sumerians in Iraq.  Also check the trace element content of both soil and irrigation water.  Selenium is a common problem for crops in arid lands.

We calculate contribution of essential macro nutrients supplied by irrigation water, according to water concentration and irrigation volume.

Kg N / ha= NO3- x Vr x 22.6 x F / 105

where NO3-= water nitrate concentration (mg/L)

Vr= irrigation volume

22.6 % N in nitrate molecule

F: efficiency factor between 0.6 - 0.9

Kg MgO / ha = xMg2+ x Vr x 1.66  x F1 x F2 /105

where MgO-= water magnessium concentration (mg/L)

Vr= irrigation volume

1.66 % Mg in MgO

F1: irrigation efficiency factor between 0.6 - 0.9

F2: Mg insolubilization factor, values between 0.4 and 0.6

Based on the nutrient requirement of a particular crop, all  essential soluble nutrients can be applied at different growth stage. Yes, irrigation water may improve the balance and and efficiency of nutrients in the soil. But what is  not perhaps clear for me is that is it proved that irrigation water has the potential to reduce the fertilizer requirement of crops? Because, as water is not a limiting factor in irrigated crops, yield potential is generally higher than rain-fed ones. This means that the amount of fertilizer required for irrigated crops is higher than that of rain-fed ones to express  their full potential (e.g. genetic potential). For example, the N requirement  of irrigated maize is higher than the rain-fed one. I think, more elaboration may be required in relation to this.

I see some good answers from specialist. The irrigation water of canals depends upon the lands of areas from which it is passing and the additions/disposals (cities, industry, floods) made to rivers. The groundwater constituents depend upon aquifers from which it is coming. Normally, both type of water are high in Na, Ca, Mg, SO4, Cl, CO3 and HCO3, with nominal K and NO3. So, these waters can meet partially requirements of secondary and micronutrients but no major contribution is expected for macronutrients. However, these nutrients keep accumulating if rains  are not too high. The long term use may change the scene. Therefore, long-term studies are required to give an exact answer. Mere water analysis will be much useful to tell about the net amount accumulated with time span.      

I endorse Dr. Nazir's views on long term effect.

Yes, Dilip! Long-term investigations can tell us something conclusively.

Subba Rao Sir, Thank you very much for raising this issue; and of course all answers given by renowned Scientists and especially, Dilip Pal sir. 

I have worked in a canal command in Odisha; used canal (Dam) water for irrigation to post-rainy seasons crops like onion, maize, tomato, and sunflower;  of course canal water was used in conjunction with dug well water i.e., ground water. From nutrient source point of view, for my case in Kuanria canal command, there was very less amount of N: nitrite-N 0.006-0.08 ppm, nitrate-N 0.06-0.62 ppm, ammonia-N 0.01-0.3 ppm. It was measured in the month of March 2014; As others have opined, I feel, it should be measured frequently and temporally for both surface water and ground water. After knowing the contribution from irrigation water, it is required to calculate the fertilizer requirement for an irrigated crop under a specified soil and fertility level. 

KG Mandal

I thank  all the colleagues for inputs given so far.I have come across a few references pertaining to contribution of river and well waters  to K nutrition.For some locations it was considerable and others it was small in India. Even in rain- fed areas ,limited  number of well water  irrigations contributed  to K nutrition .Apart from nitrate, sulphate also may be present in considerable amounts in well waters or ground waters.I think the silt and clay brought  by river waters  may also add nutrients. As pointed out by colleagues, long term effect of irrigation water may be studied for salt build up,nutrient additions and also improvement /deterioration in soil physical properties.

Yes Suba Rao, The silt and clay  brought by canal water is also very important, especially with reference to K. Consideration of physical properties when the water is sodic is also of prime importance. 

If irrigation water makes a significant contribution to the nutrient requirement of a well-grown irrigated crop, then it begs the question of why the nutrient concentration of the water is so high, unless of course it is nutrient-rich effluent.  For example, does high concentration of N in groundwater point to over-use of N-fertilizer in the agricultural system, or is it pollution from latrines close to the shallow well?  If river or canal water is nutrient-rich, does this also indicate over-use of fertilizer, or is it soil erosion that needs to be managed? And if irrigation water is nutrient rich, is it also high in salts, the sources of which need to be traced and possibly managed?

Dr.Cornish, high amounts of nitrate nitrogen(not beyond critical limit of 10 ppm N) in well waters in India are detected in a few pockets in intensively cultivated areas in a few  districts.High nitrates are found in some saline waters and also in wells in village periphery where manure pits or heaps are located .Sulphate-S and K occur in some well waters geologically,not received through fertilizer application.River waters also carry variable amounts K along with silt and clay.

Mind that these are site specific reports and must be considered for those areas but cannot be taken as general indications.

As regards soil nitrogen content, the soils across the semi-arid steppes and parkland of Mongolia show high amounts of ammonium nitrogen resulting from the millennia of herding herding animals in the area.  There is insufficient precipitation to leach out the nitrogen excreted by the animals.  Furthermore, some of the dominant plants are legumes the fix nitrogen, e. g., Prosopis and Alhagi spp.

Dr.Nazir you are correct ,they are site specific.Dr.Harris, it is interesting information.

In a comprehensive study contribution of  diverse water sources to nutrition of several crops was worked out.Irrigation water contributed significantly to micronutrient nutrition also.Please go through the following publication.

Srinivasarao,Ch et.al.2012 Contribution of nutrients through critical irrigation from diverse water sources in selected watersheds of semi-arid  tropical India. Indian J.Dryland Agric. Res & Dev ,27,58-69.Download available on Research gate.

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It may vary

Depends where you look.

In large groundwater irrigated oases in Inner Mongolia and in NCP aquafers under Beijing NO3 levels of between 80 and 200 mg/L were measured over an interval of about 10 years (1090-2005). In some instances the N content of irrigations applied exceeded the crop N requirement.

The orrigin of the N was agricultural leachate orriginating from manufactured fertiliser.. At the perimeter of oases NO3 declined sharply and at sampling points further out the level was typically below 15mg/L. 

Yes, such type of variations are local and must be considered under this scenario. That is why it recommended that before starting a use of any canal or groundwater at a local point, a detailed analysis must be determined and recommendations be obtained from local experts. It will help a lot to address the local variations and prevailing conditions. 

There are pollutants as well that are added in canal water

See

https://www.researchgate.net/publication/277523516_Assessment_and_Identification_of_the_Quality_Gradients_of_Canal_Water_used_by_Lahore_Pakistan_Residents_in_Summer

https://www.researchgate.net/publication/277438049_Assessment_and_Identification_of_the_Quality_Gradients_of_Canal_Water_used_by_Lahore_Pakistan_Residents_in_Summer

Article Assessment and Identification of the Quality Gradients of Ca...

Article Assessment and Identification of the Quality Gradients of Ca...

Mr.Masood,thank you for your response.I will go through the publications you attached.

I thank all the followers and participants of the discussion and also very large number of viewers of this question.The topic is very important and the participants have given excellent views on the current status , the need for more information and also the need  for long term studies from plant nutrition point of view (contribution of different nutrients from irrigation) and also the development of salinity/ sodicity under continuous irrigation.

Yes, you are right Dr. Subba Rao, salinity/sodicity are the fields still need investigation.