In rice-rice cropping system, their number will greatly be reduced or even may disappear

If we apply inorganic fertilizer at a rate at which plants can tolerate and utilize, there will always be an appreciable rhizosphere microbial population that can thrive under those conditions.  Rhizosphere microbial population is extremely resilient and transient.  They can adapt.  Transformations of many forms of nutrients (e.g. NH4+ and NO3-, whether they derive from chemical fertilizer or organic fertilizer) are microbial mediated.

If we apply very high rates of chemical fertilizer, microbes will die… and plants will die too.

Dear J C Biswas, If we look at Nitrogen and Phosphorus the use of chemical fertilizers are generally associated with decreased activity of Rhizobium and mycorrhizal fungi. The answer is probably a little different however when other nutrients that limiting are applied some beneficials may increase in population and activity. The take all fungus which is root and stalk pathogen of small grains can stimulate oxidation of Manganese and reduce some beneficials just because it eliminates the root court. The role of Manganese amendment is to strengthen the resistance of the plant which would prolong healthy root systems which favor a healthy root microflora I suspect. In the case of Phosphorus amendment the root tip pathogenic action would better able to show compensation and again I believe the positive microflora might be prospered. I think the sole of Silicon and Calcium would also be similar as the plant resistance and structure is toughed by these elements the role of positive microflora in the plant would be more conclusive In a quite a few plant diseases the judicious use of Calcium and/or Silicon can give disease response superior to many synthetic fungicides by their effects on plant metabolism and structure. Whether talking about organic amendment or fertilization the understanding of balanced nutrition is important and often lost in a search for a silver bullet.

Dr Biswas , I have my observations somewhat different . As long as chemical fertilizers are applied in balanced quantity , they will continue to trigger the microbial buildup  in soil , since these microbes are very strong sink for nutrients being applied through conventional chemical fertilizers. Microbes from soil will never disappear, irrespective of management practices being followed. Even , if there is a soil contaminated with heavy metals , do you feel , microbes will disappear , certain microbes will surely reduce , but still some of the rhizocompetent microbes will always thrive in soil to keep soil microbially alive , extent of liveliness may vary.  And  same philosophy  stands out for the soils having extremes of either soil acidity or soil salinity .

Just imagine for a time being ,  if there is no microbes in the soil , don't you  feel ,  soil will behave like an ash ?

Dr. Anup,

Thanks for your comments. What we have found at BRRI is that bacterial population reduces greatly with chemical fertilizers alone and after 20-30 cm soil depth there is none; but with organic ammended soil- plenty of microbes.

Thanks Dr. Paul Reed for your valuable information.

Dr. Susantha,

Thanks for you comments. The fact is that microbes need quality carbon, otherwise fatal for them.

Thanks Dr Biswas for your   valuable feedback . It could be possibility under rice-rice cropping sequence , but in other cultivated crops , reduction in microbial load of rhizophere soil to nil population seems unlikely , unless there is some abnormal disturbances in soil environment . What about the crop yield   , do you find any reduction in yield  and associated fertilizer response ?

Dr. Anoop,

Thanks. It is with rice-rice system. No straw residue was allowed- yield stagnation with chemical fertilizers alone, but not with poultry manure and cow dung treated plots.

If we talk about diazotrophs than certainly the chemical fertilizers specifically N will affect N fixation mechanism by activating autoregulated negative feedback and hampering nitrogenase activity. The numbers of microbes may also affected due to slow division and multiplication.  

dramatic decline ....

Chemical fertilizer will effect the microbial population, because chemical fertilizer can,t fulfill the requirements of microbes like carbon as microbes needs carbon for their growth, survival, maintenance and reproduction. Beside this pH of the soil will be adversely affected and which leads to poor microbial population. 

Association between plant and microbes, e.g. in a symbiotic relationship, ids very cost effective for the plant because a process like nitrogen fixation is highly energy demand process. Therefore adding chemical fertilizers to the soil make the life less expensive, in terms of chemical energy production to support itself and associated microbes. Therefore, it will prevent from reproduction of microbes and their population in the soil will start to decline unless they could stay alive as saprophytes in soil.

Gradually soil microbes  population will decrease to alarming level

Dear colleagues, interesting discussion..In India we have a net work project on biological nitrogen fixation and biodiversity under ICAR located in IISS,Bhopal.Studies conducted in that project showed that the Microbial activity is not affected if Fertilizers are applied at recommended level.Even pesticides if applied at recommended doses may not drastically reduce the Microbial population or their activity.One should not think that balanced fertilization reduces the availabilty of carbon source to microbes. The good crop growth in balanced fertilized plots produces a lot of root exudates,returns to soil of lot of rootsand stubles .In long term experiments conducted in India NPK application not only maintained organic matter status in soil but also showed some increase.If nutrients like N and P are adequate or high  there may be some decrease in the population temporarily of N fixing or P solubilizing organisms but they may not disappear from soil system as mentioned by Dr.Hepperly. I endorse the views of Dr.Susantha.

What is balanced fertilization , irrespective of source ( organic or inorganic) , and I am sure , you cannot strike a balance between different nutrients when you  are exclusively relying on organic sources, especially when you aim your  nutrient doses on N-equivalent basis.So as long as , fertilizer application is balanced , I don't think , soil microbial count will display so much decline in counts to use terms like warning signal to soil fertility management . As far as having organic matter for soil microbes  is concerned  , it is abundantly presented after the harvesting of crop ( For example , significant amount of plant  biomass is not harvested under rice -wheat system ) plus the root exudates. Lets not be so averse to chemical fertilizers . But , I admit , there is a need to strike a balance between  two distinct nutrient sources . This I said it earlier  and stick to it,  even now .

Dear Doctor Srivastava, the meta analysis of wheat and mycorrhizal impact would suggest that nutrient levels of pH, soil organic matter, amf activity, P content, N content and Zn content are all related to highly productive wheat capacity.

Since the studies at Rodale clearly show the capacity of providing Nitrogen through legume components of a mixed farming system is potential of optimal yields and quality. I believe the altering effects of fertilizer N cannot be defended based on environmental, energetic and economic impacts.

Instead getting the P content reasonable, supplying adequate Zn and assuring the pH is near optimum with optimize the staff of life wheat bread.

In North America the availability of high competitive yields in biological based organic systems compared to monocultures based on inputs combine with the capacity of certified organic farmers of getting premium on commodity prices which exceed 40% of the commodity price.

Since inputs are lessened and yield upheld the economics of these systems can outstrip the conventional alternative.

Exactly Dr Hepperly , these are all ways to provide  adjustments in soil environment , soil pH being on one the most pre-dominant soil properties  dictating the nutrient availability  , use legumes in crop rotation ,or have any cropping system that could sustain the possible off-site movement of nutrients , all part of soil management  . And such soil fertility  management/ replenishing  annual , nutrient removal  may en-route balanced fertilization  using chemical fertilizers . The population of soil microbes  will not go down to any alarming count .There are many schools of thoughts of crop raising ,  Dr Hepperly , but their ultimate aim is the same and nothing should be obtained at the cost of either soil health or environment health . Hope,  you  find these statements comfortable.   

Dr.Hepperly, it is good if we can exploit organic manures and biological systems for supplementing nutrients and reduce  fertilizer nutrient consumption. In India to produce 260 million tonnes of food grains we are applying around 26-28 million tonnes of NPand K.The uptake of nutrients by crops may be around 35-36millon tonnes.Application of all  organic manures(350milliontonnes) supply around 7 million tonnes of nutrients. We are currently manufacturing and using around 50 thousand tonnes of Biofertilizers. May be around 40% of Biofertilizers are P solubilizing organisms.I have not seen the nutrient contribution of application of Biofertilizers. I have also no data on how much is the contribution of native beneficial microorganisms to nutrient fixation and release in field cropped area.I can presume that the organic manures and Biofertilizers can supply at least 25% of the nutrients requirement of crops and rest 75% need to be provided by Fertilizers.

According to Grand View Research  on Biofertilizers Market Analysis,    current global biofertilizers market is estimated at 536 million US dollars. Nitrogen fixing was the largest product segment , accounting for over 75%of global revenue followed by phosphate solubilizers , the second largest segment accounting for 15% of global revenue in 2014. Seed treatment was the largest application method and accounted for over 65%of the market followed by soil treatment . North American biofertilizers market was the largest regional industry followed by Europe, and together accounted for over 54%of the global revenue  followed by Asia  Pacific accounted for over 15% of the revenue. So , this is one sector coming up very strongly to take off some of the imposing burdens  on use of chemical fertilizers. Therefore , we need to develop a nice synergy between the two sources, so distinctly different to one another,  with regard to their mode of action .  

Dr Biswas and other colleagues, I have two very intriguing points to raise. One , very often,  we call carbon sequestration by plants , nothing but increased photosynthesis getting translated into elevated yield. Soil microbes will be doubly benefitted by such elevated yield through improved allocation of metabolites from root to shoot and vice-versa . And number two , what is the most appropriate time  for soil microbial evaluation ?.  Shall we stick to  particular season regardless of crop phenology or stick to particular crop stage , or evaluate the soil soon after crop harvesting which I feel,  is not the right time?

Dear Doctor Anoop Kumar Srivastava, A great error of the early ideas on Carbon sequestration has been the idea that maximizing photosynthesis in the agricultural system increases necessarily the sequestration in the soil.  This is just not the case ....it does not work that way. The missing ingredient is not the Photosynthesis but the net equation Photosynthesis minus respiration which is the net Photosynthesis or system gain. 

An optimized sequestration may be more related to reducing respiration than increasing Photosynthesis and the changes in soil Carbon and Nitrogen can reflect the net reaction over time as net Photosynthesis which increases the soil Bank account.

In the net regard of Photosynthesis look to mycorrhizae their main effect on the agricultural system is probably the reduced respiration rate. In mycorrhizae the production of glomalin favors sequestration because of its low respiration effect. 

Major effect of Rodale Farming System trial greatly increased mycorrhizae and greater ability to sequester carbon.  Mycorrhizal association favors soil investments over the above ground plant allocation all very important from a Carbon sequestration perspective.

Finally,  I agree with you that crop stages are extremely important and single point analysis is insufficient to understand the dynamics of nutritional status and needs. Indeed for best analysis we need to track things not once in any single season but continuously over years. A generation ago this idea would be fanciful but with burgeoning technological capacity when it comes to data and analysis the sky is the limit.

It is a brave new world and people wonder if cognizant machines will over throw the human species. If so look out because I am going be a technology user and not be technological victim. 

When it comes to the soil everything is done through microbes and they have no brains at all,l yet they sense and obey the jobs which are needed to be done and they do them and That's intelligence. Some thoughts.

i wish to put two points here for discussion

·         Long-term use of chemical fertilizer can change the soil pH, upset beneficial microbial ecosystems.

·         When large amounts of nitrogen are applied in the field , the plant literally slows or shuts down the nitrogen fixation process. It is easier and less energy consuming for the plant to absorb nitrogen from the soil than to fix it from the air or may be rhizobium  activity slows down  

regards

Dear Naveen Kaira, Yes the soil acidity is prevalent and real and Kudos to this acknowledgement of its importance.

Yes, the use of ammoniated Nitrogen fertilizer is  about one half of the energy utilized in Maize production on a typical conventional farm in North America. This same ammoniated fertilizer give a liming equivalent for its neutralization of about 1 mton/ha per year which is normal practice in a state like Pennsylvania. These are costly practices and the issues they leave are seldom addressed but more likely represent unseen festering issues.

Moreover, the cost of Rhizobium biological Nitrogen is one that the plant pays without any consequence to the yield of the alfalfa plant fertilizing. With a plant like Alfalfa adding nitrogen does not raise its productivity only increases cost of its production.In addition, a production of alfalfa can produce all the Nitrogen needs for a subsequent Maize crop without any negative consequence on the Maize and with an economic return on the alfalfa.  As such the heart of a sustainable crop system should emphasize the role of  legumes in crop rotation. Finally, rotation with the legume not only reduces the fertility requirements but increases the soil organic matter which leads to a greater ability to avoid drought the single biggest limitation to rainfed agriculture.

I agree that getting the pH of soil into the right limits and targeting the organic matter optimization will work together with rotation including legumes and correcting toxicities and deficiencies along with organic amendment. Together these practices result in multiplying the life force of the soil and this is related to greater sustainability productivity and environmental as well as economic results over the long run.

Unfortunately the high input based farming methods has strayed from these tried and true principles. Luckily we can restore the damage with the practices elaborated. This regenerative approach represents both a challenge and opportunity for this and future generations.

Mixed farming using diversified rotations and having integrated livestock is a pattern of regenerating our farms rather than mining them. I suggest we need to return to many of the tried and true agricultural practices and use the best of modern tools to make them even better without compromising sustainability or the environment which we depend.

Some thoughts.

Dr Hepperly and Kalra , all said and done about the utility of organic manures , legume crops in crop rotation and biofertilizers , let us first admit ,  such practices are very slow to respond  and above all,  commercial  farmers  do not usually like  deferring   their time tested crop rotation , unless there is some colossal decline in crop productivity  or soil fertility/health to the extent , soils stopped responding to fertilizers. At the same time,  accepting the importance of  long term use of chemical fertilizers , let us reach a concensus to develop a kind of synthesis derived out of tripartite relation between these four distinct   sources . There top foodgrain producing countries who use maximum chemical fertilizers , their  mode and monitoring  methods of balanced fertilization is phenomenal . That's the prime reason , they sustain their productivity , better than rest .

Dr Hepperly & Kalra. In New Zealand we have been able to get dairy farmers to change the way they grow the grass which they graze their cows on. They normally apply urea every 20 days onto pastures the cows have just grazed. Now they apply fertilisers and biological products that stimulate the biology in the soil.

We have been able to measure this by using the scientific method developed by Dr E Ingram, Orgeon. The soil food web counts the bacteria and Fungi in the soil and monitors the results over a 12 month period.

We have seen the Fungi increase 20 times from very low levels. This was due to chemical fertilisers being applied to the dairy farmer over the last 10 years.

Now the pastures have more clover in them and the cows are producing more milk with the farmer spending less money - making more profit.

It is great to read you comments above to further understand how we have achieved these results. Look forward to further comments.

Graeme excellent feedback , I also advocate the same opinion against the conventional wrong notion that inorganic fertilizers reduce the microbial load of the soil. As long as fertilization is neither suboptimum nor overdose , the inorganic fertilizers will remain main stay of modern day agriculture . at the same time , there is second opinion that we need to exploit upon the relationship between microbes and fertilization . regardless of crops grown .Soil microbial world play as a scavenger or strong sink to applied nutrients to eventually release them in a more assimilable  mobile form .   

thanks Graeme and Anoop for nice comments, i agree with you, regards