Sunday, July 8, 2012

Do You Know What The "Soil Nutrient Cycle" Is?

Today in a show on television called “Asar”, Mr. Amir Khan rightly upheld my point that it's better to eat slightly damaged or slightly infected fruits instead of eating totally shiny and infection-free fruits and vegetables and government representatives promised to check the contents of pesticides in the fruits and vegetables at a point before they are supplied to retailers in Delhi. 

A good lab equipped with capillary GLC with FID detectors could detect pesticide contents in fruits and vegetables (even less than 1 ppm) and I know from my experience that Delhi University South Campus and some of the colleges in this area, like Shri Venkatesh College of DU  Zoology Department, have the capacity and capability to do so.  However, what made me write this article was a mention by one of the persons in the debate that in Dehradun one restaurant has been opened which will provide “organic food only.”

In my last blog, I noted that all food that we eat is “organic food” but plants produce it from inorganic components and 'organic' farming is not to provide organic food to the plants but to improve the soil conditions. Unfortunately, not much emphasis is given to soil science and soil technology as is given to recombinant DNA technology, but soil has a perspective and plant nutrition is a complex topic that needs to be understood.  

Soil, a heterogeneous mass, consists of three major components: a solid phase, a liquid phase and a gaseous phase. All three phases specifically influence the supply of nutrients to plant roots. The solid phase is the main nutrient reservoir.  The inorganic particles of this phase contain cationic nutrients such as K, Na, Ca, Mg, Fe, Mn, Zn, and Cu while the organic particles form the main reserve of N and to a lesser extent Pand S (Mengel and Kirkby 2001).  

Organic fertilizers stabilize the soil, lower the pH value ( make it acidic while salinity makes soil alkaline and unproductive) and at the most provide some N, P and S upon decomposition. Soil types, environmental conditions such as O2 supply and temperature have important role to play in decomposition of organic  matter. 

Thus the organic Carbon mainly accumulates in the upper crust of the soil. Long term application of FYM increases soil carbon. Rothmsted field trials have proved that microbial biomass which comprises of living and dead biomass of soil bacteria and fungi make significant part of organic component Plant growth is better in neutral or slightly acidic soil . The liquid phase of the soil solution facilitates nutrient transport in the soil e.g. for the transport of nutrients from various parts of the bulk soil to plant roots. Nutrients transported in the liquid phase are mainly present in ionic form , but O2 and CO2 are also dissolved in the soil solution. The gaseous phase of the soil mediates the gaseous exchange which occurs between the numerous living organism of the soil ( plant roots, bacteria, fungi, animals ) and the atmosphere. 

This process results in the supply of living soil organisms with 02 and the removal of CO2 produced by respiration from the soil atmosphere. Plant roots also respire and take 02 and release C02 like any other living organism. In  plant species living symbiotically with N2 -fixing bacteria the N2 supply to the root nodules is also mediated by the soil atmosphere. Mineral nutrient behaviour in the soil is closely dependent on nutrient interactions between solid, liquid and gaseous phases. These interactions influence the accessibility of mineral nutrients to the plants. Mineral soil composition are rather stable and changes occur mainly over geological time spans. However the organic soil component is characterized by steady turnover and by an input and decomposition of organic matter . 

Supply of FYM has to be given each year afresh. Input of organic matter basically originates from photosynthetic organisms mainly higher plants or indirectly from cow dung which is also partly digested organic matter synthesized by plants. This organic manure or organic matter or organic Carbon in the soil serves as food for microbes, fungi and bacteria and under aerobic soil conditions decomposition is indicated by the release of C02. 

A part of organic matter is easily decomposable such as amino acids, organic ions and structural carbohydrates like sugars and polysaccharides as well as proteins can be rapidly decomposed by micro organisms. However cellulose, hemi-cellulose and lignin are difficult to decompose. 

The soil with its mineral composition and organic contents provide substratum for the plant growth which is regulated by  interaction of environment and genetics of the plant determines its ultimate growth response. All food what we eat is organic but what is advertised as "organic food" must be specified before its charged a higher price to customers in Europe. 

I am grateful to Professor Dr. Mengel, a very senior Professor Emeritus of Institut fur Pflanzenernaerhung der Justus Liebig Universitat, for gifting me the latest edition of his book during my visit. I made use of this book to provide some of the authentic information quoted here. I am also thankful to Professor Dr Sven Schubert and Alexander von Humboldt Foundation for supporting my studies in plant nutrition and metabolism. 

And thanks to Mr. Amir Khan, an actor, for generating interest among the people. Times have changed and society needs an actor to tell them facts and not a scientist, but if scientific facts are well understood and conveyed by an actor, it's a service to the society. Perhaps that is the way nowadays for science popularisation.  I wish one day the issues of deforestation and biodiversity loss will get attention, and message to preserve them shall go to society via Mr. Amir Khan's show. -  Ashwani Kumar, Science 2.0 

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