Off-site movement of  nutrients  , either through erosion of soil  or through  non-synchronization between    fertilizer  requirement and addition  on an annual basis is most important , if we are looking at containment of soil fertility depletion .  Floor management  is another issue , to be effected through combination of cover crops plus contour/terraced planting ..We also need to make  a clear cut distinction between nutrient uptake to nutrient removal..?

Fulfill the demand-supply equations from your land. That will maintain the fertility, besides arresting losses.

you need calculate  the suplply by soil analysis and the demand by plant analisis

I have assumed that (in your case) the erosion does not need civil works to prevent it getting worse. So you can begin right away with building the soil.

Consider the lectures of Dr Elaine Ingham. Many are available on YouTube. Start with https://www.youtube.com/watch?v=xzthQyMaQaQ

I have also posted a research idea to evaluate synergy between vermiculture and biochar. See http://bit.ly/1Nrs63d

We  infact need  a kind of nutrient budgeting , having track on nutrient reserve of the soil in active pool contributing towards the harvesting of crop and the amount added annually to replace the amount of nutrients leaving the system . And , to  do that , there  are many ways of soil fertility management , which i feel is outside the ambit of the discussion . 

Practices like arresting of topsoil erosion by growing cover crops, making of field bunds, contour or terrace farming, application of fertilizers and manures to meet the nutrients need of crop plants grown and removed from the field, and recycling of crop residues to the soil will help in sustenance of soil fertility in the given situation.

Hamzeh: this is one of the most serious global problems facing humanity.

But very difficult to give specific advice, because solutions have to be site-specific. Each locality has particular soil, climate and water issues - added to which are the complex socio-economic restraints on farmers. 

Hence some sort of basic diagnostic is needed to identify the most pressing problems and potential solutions - the attached might be of some help.

5 ways to reduce nitrate leaching from the farm:

1. Plant winter cover or scavenger crop

2. Build soil organic matter using practices such as cover cropping and compost applications

3. Conduct annual soil tests and use organic matter, pH, and micronutrient levels to plan your fertilization strategy

4. Use split applications of nitrogen fertilizers on long-season crops; rely on mineralized nitrogen for short-season crops

5. Manage irrigation carefully

Conservation Agriculture is the solution where it is recommended to adopt a set of soil management practices that minimize the disruption of the soil's structure, composition and natural biodiversity. Besides, it has proven potential to improve crop yields, while improving the long-term environmental and financial sustainability of farming.

Good point Dr Malhotra , its a kind of way forward approach . 

Conservation agriculture(CA) for sure will take care  of any possible depletion in soil fertility . However , systematic information on precision nutrient  management under conservation agriculture in different cropping systems is distinctively lacking , in addition to introduction of site specific nutrient management (SSNM)to capture both spatial and temporal variability in soil fertility to feed the crops at all the growth stages , collectively coined as SSNM-based 4R Nutrient stewwardship in CA. 

While it is, obviously, true that conservation agriculture is beneficial  in terms of erosion control, it is, as such, not a solution for fertility depletion. CA can strongly reduce nutrient losses through erosion (see e.g. Leys et al., 2010) but does, as such, not bring nutrients to the soil (although it may promote retention of the nutrients in the crop residue). It also may have some negative effects on plant growth (e.g. due to the fact that seed emergence is more uneven and diseases are more likely).  Its overall effect on crop yields is therefore very often slightly negative (see Van den Putte et al., 2010, Pittelkow et al., 2015, both attached).

Thus, conservation agriculture can indeed be a good start for sustainable soil management as it stops the soil resource from being depleted. However, increasing the soil's fertility can only be achieved by making sure that the crops growing on that soil receive an adequate nutrient supply: this supply has, in most cases, to come on top of conservation agriculture.

This is, in my view, a very important point. It is obvious that soils in e.g. Africa are often strongly underfertilized (see the figure attached, FAO 2009) and will therefore have low yields. There is only one solution to remedy this and that is to make sure that the nutrient supply is adequate, which will often require the use of mineral fertilizers (as the loss of nutrients through harvesting and leaching cannot be undone by improving nutrient recycling within the farming system alone). We should embrace the simple truth that decent crop yields require decent fertilization and cannot be achieved by any agricultural technique that does provide the vital nutrients to the plants that need them.

Again, the point is not that CA would be bad, on the contrary. The point is that CA will not solve our soil fertility problems: the latter is only possible when we make sure the necessary nutrients are provided.

Kind regards, Gerard Govers

Article Scale effects on runoff and erosion losses from arable land ...

Let me add some facts about nutrient mining  and  Nutrient Audit Models through an excellent paper 9 source : Sheldrick et al ., 2002, a conceptual model for conducting nutrient audits at national , regional and global scales. Nutrient Cycling in Agroecosystems, 62: 61-72).

Mining of nutrients from the soil, particularly in developing countries, is a major problem, causing soil degradation and threatening long-term food production. This paper develops a methodology for carrying out nutrient audits, which includes the calculation of nutrient balances and an evaluation of trends in nutrient depletion/enrichment. Nutrient balances for arable farming are constructed for 197 countries for 1996 and for the world and two specific countries – a developed/enriching country (Japan) and a developing/depleting country (Kenya) for the period 1961 – 1996.

The results indicate that nutrient efficiency is approximately 50% for N, 40% for P, and 75% for K. In some countries in Western Europe and in Japan and the Republic of Korea, with large, mixed farming systems, there is a surplus of N, P, and K. However, in almost all other countries, food production is currently dependent on depleting large quantities of nutrients from soil reserves and this is likely to continue. The world average soil depletion of nutrients in 1996 was estimated to be 12.1 kg N ha−1, 4.5 kg P ha−1, and 20.2 kg K ha−1. The depletion of K is particularly severe and could ultimately lead to a serious loss of crop productivity in several countries. There is an urgent need to investigate this issue further. Analytical tools, such as the nutrient audit model described, can play an important role in assessing the problem, and in developing sustainable nutrient management policies, strategies, and practices.

Hope , you will like it . 

Dear my colleagues,  I appreciate your answers and comments

Let me add another response  with regard to on-going discussion , as  how to put check on annual depletion of soil fertility   , which i find quite interesting ;

Two sustainable, intensified nutrient management concepts, that have been proven successful in famer’s field, are Integrated Soil Fertility Management (ISFM) and Conservation Agriculture (CA). ISFM includes the combined use of mineral fertilizer and organic resources management with the aim to improve agronomic efficiency and crop yields. These components and others (e.g. improved varieties) can be adopted stepwise. CA, on the other hand, is advocated as a package that the farmer should preferably adopt as a whole. Also, CA is stricter than ISFM in regard to the must-have key components, above all minimum tillage and surface residue retention. Even though proven profitable in the long-run, the attractiveness of ISFM and CA is often impaired by smallholders’ limited resources (money, labour) as well as the delayed responsiveness in terms of improved yields. In mixed crop-livestock systems it is primarily the competition for crop residues that vitiate the farmer’s

willingness to adopt. Farmers keeping livestock see little value in leaving residues on top of the soil (CA) or incorporating it into the soil (ISFM). Feeding residues to the animals is considered a much better investment. Research is needed to identify the true value of residues, so as to be able to balance the competing uses. Both, ISFM and CA, intend to move farmers out of subsistence and therefore depend on access to input (credit, fertilizer, herbicides, and modern varieties) and output markets (selling surplus production). They also are knowledge intensive as far as management of residues, fertilizer, herbicides and (zero-tillage) direct seeding of crops is concerned. We believe that the combination of ISFM and CA, which we named ISFM+ — i.e. working towards full adoption of CA but using the step-wise approach of ISFM — allows for easier, smoother and faster adoption, as farmers can implement improved management components at the pace they feel comfortable with.( Source : Profitable and Sustainable Nutrient Management Systemsfor East and Southern African Smallholder Farming Systems– Challenges and Opportunities by Sommers et al ., 2013)

Dear you can use the following remedies.

1. Plant winter cover or scavenger crop

2. Build soil organic matter using practices such as cover cropping and compost applications

3. Conduct annual soil tests and use organic matter, pH, and micro nutrient levels to plan your fertilization strategy

4. Use split applications of nitrogen fertilizers on long-season crops; rely on generalized nitrogen for short-season crops

5. Manage irrigation carefully

Endorsing the valid  points as detailed by Belay , we need to have a robust and dynamic soil test -based fertilizer recommendation model  on a nearly real time basis to keep checks and balances  of soil fertility well within control. ..