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A key component of increasing agricultural productivity while reducing Green House Gas (GHG) emissions and achieving ‘more for less’ in future is to ensure that when fertilizers are applied that they are used as efficiently as possible by crops.

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Not only does this give the best economic return on investment (ROI) from the applied fertilizer but it also reduces nutrient losses into the environment from both leaching into ground-water, as well as from volatilisation of GHG’s, particularly ammonia and nitrous oxide, from soils.

In recent years the International Fertilizer Industry Association (IFA) along with the International Plant Nutrition Institute (IPNI) have begun to introduce the concept of ‘4R’ Nutrient Stewardship.

This is targeted at assisting farmers, wherever they may be, in the development of Fertilizer Best Management Practices (FBMP’s) using the “4R’s” of applying the Right fertilizer; at the Right rate; in the Right place; and at the Right time; in an environmentally, socially and economically sustainable manner appropriate to their locality.


The over-riding objective of the ‘4R’ Nutrient Stewardship program is to improve Nutrient Use Efficiency (NUE) by maximising crop yield for every unit of fertilizer applied.

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Nutrient Use Efficiency (NUE) can be measured by two relatively simple methods; the most commonly used is the ‘Out-input’ ratio which measures the N taken off by the crop compared to the amount of N fertilizer applied; though the ‘Partial factor productivity’ method is easier to appreciate as it measures the crop yield per hectare (grain in this case) for each kilogram (kg) of N applied.

Both of these are considered rather simplistic but they do enable a basic understanding of the principles of NUE and it’s use in determining the effectiveness and/or environmental foot-print of applied fertilizers.

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Where insufficient fertilizer N is applied to meet a crop’s requirements then the soil becomes depleted leading to ‘nutrient mining’ and if this continues then soil degradation occurs with eventual loss from agricultural production altogether.

As mentioned earlier, it is regrettable that in some countries, particularly Africa, soil ‘mining’ and degradation has occurred and continue to do so at an alarming rate every year. For this reason NUE must not exceed an ‘Output-input’ ratio above 100% for an extended period.

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On the other hand if fertilizer N applications regularly exceed a crop’s requirements then the ‘un-used’ amounts either remain in the soil leading to their ‘volatilisation’ as GHG’s or ‘leakage’ into ground-water.

To ensure that fertilizer N applications provide adequate crop nutrition as well as contribute to maintaining a healthy level of soil fertility, NUE should remain in an ‘Output-input’ ratio range between 70 and 90%.

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So maintaining NUE in the range between an ‘Output-input’ ratio of 70 and 90% ensures that both the crop and soil’s nutrient requirements are maintained in a sustainable manner for maximum agricultural productivity with the minimum environmental impact and helping to assure the important ‘more for less’ principle for a growing planet!

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That by keeping NUE in the optimum range can really give ‘more for less’ has been demonstrated by researchers in the UK for wheat production as shown in the adjacent chart.

Application of fertilizer N between 120 and 190 kilograms per hectare (kg/ha), with an average of 160 kg/ha, resulted in the maximum yield of wheat grain of 10 tonnes per hectare (t/ha).







On the face of it this yield might be assumed to have the maximum environmental impact but by calculating the overall GHG balances, particularly by taking into account the extra land that would be necessary to produce this amount of wheat grain from much lower yields per hectare, then the optimum fertilizer N application actually has the least environmental impact or, as expressed in the chart, lowest carbon footprint.

Safe-guarding the security of pristine land, such as forests, heathlands and wetlands, and the wonderful bio-diversity it supports, through ‘sustainable intensification’ (increasing crop yields per hectare) on the farmland already in production is a founding objective of Furthermore by encouraging evidence-based interaction and exchange of ideas the intention is to develop and build strong scientific and technically relevant knowledge platforms for the creation and implementation of Fertilizer Best Management Practices (FBMP’s) using the seminal principles of ‘4R’ Nutrient Stewardship to achieve ‘more with less’.


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A recent publication from the International Fertilizer Industry Association (IFA) describing a global framework for the application of ‘4R’ Nutrient Stewardship places the optimisation of NUE as a central component for increasing agricultural productivity while minimising GHG’s in future giving ‘more for less’.








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