Is it possible to estimate the exact quantity of nutrient fixed by biofertilizers during a cropping period. Any standardized methods.
You need to define your meaning of 'fixed'.
If you are referring to nutrient use efficiency it can only be estimated securely by isotopic labeling.
Hi colleague,
I think to determine the fertilizer rate for a particular nutrient, just multiply the rate of the desired nutrient by 100 and divide by the percentage of the nutrient in the fertilizer. If you want to refer the quantity nutrient in the soil, available nutrient method using ammonium acetate-acetic acid can carried out. Hope it help.
Paul, i feel , nutrient fixed by biofertilizers, he means , how much biofertilizers make nutrients available to plants , if i am not wrong..?
You might want to check this articleArticle Nitrogen soil surface balance of organic vs conventional cas...
or others using the GRAFS method.
In a way , are you willing to say , how biofertilizers save on inorganic fertilizers...DearBasavaraj...
Yes sir, Thank you all for your comments
What is the extent of save on inorganic fertilizers by using biofertilizers.
At the most 25 % saving has been reported so far in the literature.However in exceptional legumes having more content og leg-haemoglobin it may be slightly more.Otherwise it is basically a situation specific responde governed primarily by temerature,rainfall pattern,soil flora/fauna and ph level.Same microbe may be doing wonder in one case while in other case it is hard to see any effect at all.So site specific responses in case of microbes do matter a lot.
Amendments of microbial biofertilizers and organic substances reduces requirement of urea and DAP with enhanced nutrient availability and productivity of wheat (Triticum aestivum L.) , Ecological Engineering,Volume 71, October 2014, Pages 432-437
Abstract: Conventional biofertilizers (Azotobacter chroococcum and Bacillus subtilis; CBF), different doses of conventional chemical fertilizers (CCF) i.e. urea [(NH2)2CO,] and di-ammonium phosphate [DAP, (NH4)2HPO4] and combination of CBF and CCF were applied as different sole nutrient sources for the cultivation of wheat (Triticum aestivum L. c.v. PBW-343) in experimental plots of 2.0 × 2.0 M. The lower doses i.e. 1/4 and 1/2 of the recommended dose of CCF along with the CBF separately and in combination of these two were entrapped in an organic matrix (OM) consisting cow-dung, neem (Azadirachta indica) leaf powder and clay soil in ratio of 1:1:1 along with saresh (plant gum of Acacia sp.) as binder (15% w/w of dry mixture of the matrix materials; designated as super granules), were also applied as alternatives to the free/conventional forms of the various fertilizer treatments in the experimental fields. A combination of CCF and CBF increased nutrients availability and productivity of wheat more than the same fertilizers applied alone. The same fertilizers when entrapped in the above mentioned organic matrix further enhanced nutrients availability in soil as well as uptake in plants as measured on 30, 60, 90 and 120 days after sowing (DAS) in terms of nitrate, nitrite and ammonium in rhizospheric soil (0–15 cm) and in plant leaves as well as yield and productivity of wheat. The data indicate that even the lower dose of conventional chemical fertilizers in combination with microbial biofertilizers and organic matrix can be more effective for the enhanced productivity of wheat in sub-tropical agro-climatic conditions of wheat cultivating northern Indian regions.
Please have a look at enclosed PDFs....
Methods used to quantify the amount of nutrient fixed by the biofertilizers
For nitrogen fixers,Acetylene reduction assay or Nitrogen balance method
PSM biofertilizers-Vanabdomolybdate method for a culture broth containing microbe
Hi Basavaraj,
In lucerne crops we measured up to 80% of total N requirements coming from N fixation by Synorhizobium melilotii. As mentioned earlier by Paul, the only way to efficiently measured the amount of N coming from the atmosphere (fixation) is using isotopes. In this case, the proportion of N15 vs N14 differs whether N is coming from the soil or from the atmosphere, thus allowing you to discriminate the proportion of N coming from either source.
N fixation largely depends on biotic (i.e. proper rhizobial strains) and abiotic (i.e. temperature, precipitation, soil moisture) factors.
You should also consider that when you refer to Azospirillum and other P solubilizing bacteria, the amount of fertiliser you actually "save" comes from the soil. Therefore, you are depleting soil reserves of that particular nutrient and, in the long run, you will need to somehow put those nutrients back in the soil.
Hope you find this info helpful.
Cheers,
José
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