It has been observed that the current fertility levels for major nutrients is within a wide range. On the basis of these fertility levels fertiliser recommendations were made. Though there are several precision methods for soil test, target and location specific (SSNM) based recommendations yet most often the routine method is followed. It sometimes gives better result than farmers' practice, sometimes doesn't result much. Are these fertility levels too wider for judging fertiliser recommendation .
I'm not sure that I have completely understand the question. But if you know the ammount of nutrients that your soil has and you know the nutrient necessities of your next crop, then you know if your soil is fertil enough for this crop or if you need extra-fertilization.
Let me clear you Dr. Gabriel. The soil test values have been assigned as low, medium and high within a wide range. Accordingly fertiliser recommendations are prescribed based on these levels. As for example, say for a soil the fertility level range is. 200-300 kg/ha (As medium fertility )forr one nutrient. This range seems to me is quite high and in this casr do you think that the response of fertiliser for fertility levels of 201 kg/ha be same as 299 kg/ha though the recommendation currently used is same for this level.
In this case I think that the recomendation is very broad but also very high. first of all you should know what is the nutrient uptake expected. I.e. around 250-300 kg of N/ha in a corn field. Secondly, if you are in a field with medium fertility (you should know medium respect what) you are probably speaking about no less than 100 kg N/ha plus no less than 50 kg N/ha from organic matter mineralization. Then, the recomendation could be 150 kg N/ha, considering that 50 kg N could be lost as drainage or gasses.
However it is very dificult from here to make a recomendation with these details. Other recomendation that I would try in my farm could be to crop most of the field with medium-upper part of the rage, but another part with the lower and compare, in order to get real information for the next year.
Dear Indranil Das
You have initiated good discussion of practical significance.
What I understand is that the laboratories, agencies or any other providing advisory service to farmers have vested interest except govt organizations if have trained staff and analytical facilities.
Otherwise the matter is very simple. You see nutrient removal by a crop for a targeted yield are available in literature. Soil test simply directs to decide additional fertilizers to obtain a pre-decided yield. Hence the Adviser making recommendation must consider crop type, soil type, rainfall, irrigation water quality, OM status of soils and desired yield.
The terms low, medium and high fertility are meaningless unless referred for any particular nutrients and thus we, the soil scientists, should not use these terms in our writings.
Yes I completely agree with you Dr. Ghafoor. So soil test based fertiliser recommendation should be recasted considering the points you mentioned, though currently fertility levels, crops were considered but other parameters are less considered moreover the fertility level range should be narrowed with few more subdivision based on STCR trials or SSNM trials.
Dr. Abdul Ghafoor pointed out very important fact that should be always in consideration when deciding fertilizer recommendations for a field or locality.
I think the soil lab, probably puts a wide range for nutrient sufficiency as there are so many parameters that influence the decision on whether there are enough of a nutrient in the soil or not.
When we do fertilization recommendations (i.e. narrow the range) we know that soil balance is more important than nutrient levels. You can look at a soil analysis and come to the conclusion that you might have enough of a certain element, when that element is not available due to antagonisms with other elements because of incorrect ratios.
For this reason we do soil balance corrections before making a recommendation. Recommendations are influenced by crop type, crop requirements, key soil ratios, soil nutrient corrections actually made, soil type (As this will influence "normal waste" associate with application), pH and what we think the biology can contribute. The latter will again be influenced by Soil carbon and whether or not a suitable carbon is applied with the fertilizer or not.
Unfortunately, because of this complexity, a good recommendation is more art than science and wisdom comes with experience. For instance we have learned through iterations over years on citrus crops that if we add a certain liquid carbon that we can make substantial but varying cuts to different elements, whilst maintaining leaf analyses within norm. (Even this varies based on whether the soil is alive or stripped of it's biology due to fertilizer an chemical regimes of the past.)
Endorsing the comments from my colleague dr Ghafoor and Dr Nazir , i personally feel , current trend of soil testing has very little to offer , with regard to soil test-based fertilizer recommendation . This is issue , we have debated at length on the same forum earlier also . One of the basic reasons , is the distinctive absence soil test -based fertilizer recommendation with specific crop and with different targeted yields. How can we match the soil test values with the crop nutrient requirement .. this is the biggest issue..an d unless , we solve it , soil test -based fertilizer recommendation will continue to underscore its immense utility..?
Thanks Dr Nazir ,. Unless we have crop specific nutrient diagnostics , we will continue to receive inconsistent response of fertilization , since wrong nutrient diagnosis will lead to inappropriate response. On the other hand , the concept like SSNM is still needed to be tailored to user friendly option in terms of measuring the spatial soil variability within a field and offering a rationale of fertilizer use with regard to specific crop ...
Dr.Nazir,the topic we are discussing is a much debated one.I can only say that in India we have crop specific recommendations for most of the field crops in many states.Now compilations are available state- wise and at country level,even in local languages. Geo-referenced fertility maps for both macro and micronutrients are available for many states.There were attempts in some states to link fertilizer recommendations with soil fertility maps and one can get recommendation for a particular crop in a village .Such system is being followed by Coromandel international in some Southern states.I have seen a live demonstrations to farmers in centrally located villages( information is available at input supplying centers).One can access the fertility maps for both macro ans micronutrients from IISS,Bhopal website.Fertilizer recommendations crop-wise are also available from the site.Our Ministry of Agriculture and Cooperation, Government of India is promoting both geo-referenced soil fertility maps and STCR recommendations for targeted yields of crops in different states. One can use this information for forecasting fertilizer requirement in a particular state.The following sites may consulted for more information.Please see the information mentioned by me under AICRP STCR
www.iiss.nic.in/downloads/recommendations.pdf
www.iiss.nic.in/STCR.html Cropwise recommendations are available in this component of website of IISS.
For me the most important are experience and to know the field (soils and crops settle in them) for choose the best range. In our cases we have specific recommendations for several crops in different states (Venezuela), but there are big spatial variability in tropical soils, so, maps can help us if they are a huge accurate ( very details scale). For this reason I use my expertise in soils of the land that we need to apply fertilizer (chemical or organic).
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