One of the following two approaches is generally employed to assess fertilizer consumption potential:-
derivation from food production target to meet the nutritional needs of the population, i.e. the output or end-use approach.
calculation on basis of area under each major crop and recommended level of fertilisation of each crop, i.e. the input approach.
The output method is useful to determine the long-term potential for fertilizer. These projections are not of relevance to manufacturing or marketing companies, nor to wholesalers. What these firms need is a long-term demand forecast (as distinct from potential) as a guide for their investment decisions. The response ratio assumed for the purpose of projecting fertilizer consumption can vary from one agro-climatic region to another due to differences in soil, management practices, irrigation available, etc.
Although the potential determined by this method is based on several subjective assessments, the approach can be adopted by planning ministries for developing long-term policies and plans. While it is of limited use as a forecast of effective fertilizer demand, the exercise is useful in that it recognises the importance of fertilizer use efficiency in increasing food production.
The procedure under the output method is relatively simple and does not involve complex mathematical tools. The basic data for applying it is available in most countries and consists of:
population - likely growth rate;
nutritional standard in terms of foodgrain per capita - present, ideal and desirable;
current foodgrain production;
gross area under foodgrain as a percentage of total gross area;
area under irrigation as a percentage of total net area;
likely increase in area under irrigation, as this is significant for assessing the effect of multiple cropping in the newly irrigated areas;
ratio of N, P & K usage - present, ideal ratio based on cropping pattern and realistic intermediary ratio/s;
ratio of use of different fertilizer types - expressed as percentages;
potential increase in food production on account of non-fertilizer factors.
The following steps are involved in the assessment of potential by the output method:
the period for which the assessment is made should vary from five to ten years.
based on forecast population growth rates the population for each year is calculated.
the current nutritional standard, adjusted for a realistic improvement if the current nutritional standard is poor, is arrived at.
applying the per capita nutritional requirement to the projected population, food requirements for each year are calculated.
subtracting the current food production from the above, the incremental production needed each year is determined.
a part of this incremental production can result from factors other than fertilizer, eg. extended irrigation, better seed varieties, improved cropping practices, etc. This is estimated by experts and deducted from the incremental production for each year to ascertain the net incremental production required from fertilizer application.
based on the ratio of yield response to fertilizer, i.e. the number of kgs. of foodgrain per kg. of N, P or K (this can also be reckoned collectively for all the three nutrients) the quantity of each nutrient of N, P and K is determined. In the latter case, the quantity of individual nutrients is derived by applying the current ratio of nutrient consumption or, if it is in serious imbalance, by a realistic improvement to the N P K ratio. The incremental quantity of nutrients is added to current consumption.
from the total N, P and K quantities thus arrived at, fertilizer types and their potential demand can be calculated. A practical way of doing this is to apply the ratio in which different fertilizer types are currently consumed and allocating the balance of any individual nutrient to the fertilizer type which is the main carrier of that nutrient.
to arrive at the total fertilizer potential, we still have to estimate the quantity of fertilizer consumed by non-food crops. This must be based on factors such as world market prices for commodities, recent plantings and planting intentions.
We now have the potential fertilizer consumption, year by year, by fertilizer type. The population growth rate, the per capita food requirement, the non-fertilizer increase in food production and yield response ratio are all assumptions or, at best, values determined by expert opinion. The projected potential is correct only to the extent that these assumptions are reliable.
The input method assesses potential by using the desirable nutrient dosage for each major crop and the area under each. The resultant food production may still be inadequate to feed the growing population at the desired nutritional standard but it is useful to know the deficit. The output approach focuses attention on need and the input approach on capability.
The following steps are involved in the assessment of potential by the input method.
the total gross cropped area is taken as the basis. Where there is more than one crop in a year this should be taken into account in assessing the gross cropped area, e.g. 100 ha of land which grows two crops annually represents a gross area of 200 ha.
allowance is made for likely increase in irrigated area and the consequent increase in the gross cropped area and the total area is apportioned among major crops in the existing proportion.
the recommended N P K application as established by fertilizer trials and soil analysis for each crop in each major agricultural zone is listed.
the area under each crop in each major zone is multiplied by the recommended N P K application rate per hectare to determine potential fertilizer consumption.
for conversion of N P K into fertilizer types the same procedure is followed as under the output method.
a refinement is to apply to each major crop a graduated increase in current fertilizer application, moving towards the recommended dosage. This is realistic as current low application levels in many countries are unlikely to change significantly over a short period.
The limitations of the input method are:-
data on actual area under different crops is not easily available and, therefore, projection of crop areas into the future presents serious problems.
the recommended dosage varies with crops and soil types, introducing another difficult element in the calculation.
there is hardly any information available on actual fertilizer application on different crops in different areas. Even if this is determined by sample surveys, the information obtained cannot be relied upon.
the fertilizer dosage per hectare as a basis of evaluating the potential ignores the impact of other factors on fertilizer consumption.
adoption of recommended rates by all farmers would lead to levels of crop production far in excess of demand.
This method is not really a forecast but a visualisation of the possible future potential, useful mainly to agricultural departments as a yardstick to measure progress in relation to fertilizer adoption. In actual practice, all farmers do not use fertilizers and those applying fertilizers rarely adopt the recommended rate. The gap between the current fertilizer application and the projected potential under this method provides the basis for a development programme to encourage farmers to use fertilizer and to persuade present users to follow the recommended rate. District assessment of potential on this basis is useful for marketing organisations as a measure of potential to allocate development efforts and resources.