Intense cropping, imbalanced use of plant nutrients and absolutely no use of organics.

Growing crops not supported by the natural resources. Forgetting crops as per adoption and distribution. 

Principles of crop ecology to be considered, forgetting immediate short term benefits. 

Involvement agriculturarists at grass root levels. 

PRA is must for long term planning. 

Policy makers to understand technologies /technologiss.

Please follow the following links and the attachment for answer to your queries.

http://www.biologydiscussion.com/soil/what-are-the-main-causes-of-soil-degradation/7276

http://www.sciencedirect.com/science/article/pii/S1658077X13000088

http://www.doityourself.com/stry/fertilizer-restoring-soil-fertility#b

http://www.vellag.com/index.php/articles/methods-of-maintaining-soil-fertility/

https://quizlet.com/7107427/ways-to-preservemaintainrestore-soil-fertility-flash-cards/

The main cause of soil fertility decline is inadequate rains, lower org carbon and soil compaction. All these factors are inter related and ultimately affecting the soil heath in toto.

There could be many , but I am emphasizing the most prominent ones , endorsing the response of Dr Mahapatra.

* Non-implementation of Land Capability -based Land Use Planning .

* Poor synthesis from the relation between soil suitability criteria and crop requirement criteria.

*  Non-implementation of crop planning  as per agro-ecological regions/sub-regions.

* Lesser emphasis on periodical  evaluation of soil health/quality.

* There is no robustness in prediction model with required dynamism to be able to timely diagnose any potential deterioration in soil health or water table or lack of sustainability of a given cropping sequence in a given agro-ecological region or sub-region. We need a kind networking system .

Thanku Dr  Anoop Kumar Srivastava ji.

My another response  would be , when you fail to assess the nutrient budget of your farm precisely in the light of input -ouput ratio..

Niche area crops needs reinforced along with balanced approach of crop/resource management practices to be done for restoring fertility and soil health. 

Take example of rice in punjab. News says record production of rice. But if you refer to research articles, destruction of soil fertility and other natural resources are maximum. 

Here is an excellent piece of work about nutrient budgeting...

Soil fertility decline does not  get the same public attention as that of drought, pests  and disease outbreak, since it is a gradual process  that are associated with catastrophic feature and mass starvation and hence farmers and policy makers are unable to perceive it. Changes in soil fertility level should be mostly  found best monitored to provide early caveat to identify the problem areas..

Dear Dr. Sukhvir Kaur,

hereunder is my first response to your question.

Soil fertility decline: Soil fertility decline occurs when the quantities of nutrients removed from the soil in harvested products exceed the quantities of nutrients being applied. In this situation, the nutrient requirements of the crop are met from soil reserves until these reserves cannot meet crop demands. This results in a reduction of plant growth and yield.

Contributing factors: Nutrients may be removed from the soil by: growing crops, soil erosion and leaching. Nitrogen can also be lost from the soil as a gas by the process of denitrification.

Effects: Organic matter plays a key role in maintaining soil fertility. It holds nitrogen and sulfur in organic forms and other essential nutrients such as potassium and calcium. The loss of organic matter mainly occurs through continuous cropping with stubble (removal or burning, and is accelerated by frequent tillage.  In all agricultural systems, nutrients are removed over time in harvested products, such as grain. Off-site losses of nutrients can also occur through soil erosion, runoff, leaching and burning of crop residues.

Fertiliser use: The usual management response to nutrient removal or loss is to apply fertiliser. Significant areas of cultivated land in tropical countries are now unable to produce economic crop yields and high protein grains without the use of fertilisers.

Nutrient stratification: In some rain-fed cropping systems such as grains, minimum/zero tillage with stubble retention has resulted in nutrient stratification (particularly phosphorus and potassium) in the surface soil (0–10cm).

Subsoil depletion: Limited in-season rainfall often causes crops to meet their water (and nutrient) requirements from the subsoil. This has resulted in subsoil depletion of nutrients even though the surface soil may have adequate levels due to redistribution via crop residues.

Management of soil fertility decline: Fertility management aims to maintain soil organic matter, soil structure, soil nutrient status and satisfactory soil pH. This can be achieved in cropping systems by:

• including pasture phases and leguminous crops
• including the addition of soil amendments or fertilisers
• employing a reduced tillage system
• retaining crop residues on site.

However, managing nutrient stratification in reduced till/stubble retained systems may require strategic tillage to redistribute surface soil nutrients into the subsoil and/or deeper placement of phosphorus and potassium fertilisers.

Hope you find this input interesting and useful.

Detail answer given by Dr. Kundu, appreciable. Fertility of the soil was inherent with the soil formation processes with in a given set of climatic conditions. Intensive Cropping, forgetting input :output and considering maximum productivity with out supplementing the essential nutrients as per need has resulted maximum break down of the soil organic matter, deteriorating all the soil physical, chemical and biological properties and hence soil fertility in long run.

Balance fertilization with with addition of organics is the need of the hour along with diversified crops, and specifically legumes in system are most important considerations.

Any crops, Cropping Systems detrimental to soil health needs replacement as evidenced from most of the long term experiments, and rice - wheat in particular 

Another important issue would be to  develop and implement evaluation and monitoring system of  soil fertility soil fertility evaluation based on different crops or cropping system or in  farming system mode..?