Can you imagine a world with no fertilizer?
Wednesday, February 2, 2011
Agriculture without fertilizer is already a reality in many developing countries. What would it be like if it happened here?
by KEITH REID
Some of you may watched the various programs on television based on "what if" scenarios of various calamities and the dire outcomes from these. Most of these programs are pretty far-fetched, but it did spark a thought in my mind about just what would happen if suddenly there were no mineral fertilizers available for agriculture.
This thought has already been in the news with regards to peak phosphorus and, while reserves of most minerals are adequate for several centuries at least, it is good to remember that all resources are finite. Agriculture without fertilizer is also a reality already in many developing nations, due to a lack of money or infrastructure.
So what would happen to agricultural production? And what could we do to compensate?
Some fertilizer companies would have you believe that crop yields would immediately collapse if we didn't apply fertilizer, but this is a considerable exaggeration.
The impact on legume crops would be barely noticeable, except in those fields where levels of phosphorus or potassium were already low. Cereals, corn and other crops in the grass family, on the other hand, would see a significant yield decrease from a lack of nitrogen. This does not mean zero yield; most crops would likely yield 60-80 per cent of their fertilized yield. But, considering that our reserves of grains are generally less than 10 per cent of annual usage, this will be enough to trigger huge increases in food prices.
Longer term, grain yields would start to decline as nutrients in the soil were depleted.
The rate of this depletion will depend on the size of the fertility stores, as well as on the capacity of the soil to hang on to nutrients. Some will become poor enough that even the weeds won't grow, returning to the original vegetation of the bogs and fens where the plants adapted to catch insects so they could extract the nutrients from their decaying bodies.
As we adapt to a zero-fertilizer economy, the first major changes will be to increase nitrogen supply for crops, since that will be where the largest immediate impact will be. Unlike the other nutrients, we do have biological methods of increasing N supply since the amount of N in the atmosphere is virtually inexhaustible, even though it is not useful to crops until it is converted to ammonium or nitrate.
Legumes will become a much larger part of the rotation, both because they don't need added nitrogen and because some of the N they fix can be used by following crops.
Forage legumes generally leave a much larger reserve of N in the soil than grain legumes, but they may be grown as feed for livestock or simply as a green cover between grain crops. Either way, fewer acres of cereals and corn will be grown.
Livestock manure and human waste will be very carefully managed to retain as many nutrients as possible from the time of excretion to the time the nutrients are taken up by plants. Fresh manures will be favoured over composts to avoid the nitrogen losses during the composting process, and judicious rates will be carefully applied and immediately incorporated into the soil.
These changes will go a long way towards ensuring that an adequate, albeit reduced supply of N is available for crop production, but it does not address the export of phosphorus and potassium from the land with the harvest of each crop.
Current systems involve the long-distance transport of nutrients, in the form of fertilizer, feed or food products but, as nutrient deficiencies begin to appear, these extensive nutrient cycles will begin to contract. The first stage will be to re-integrate livestock production into the crop-producing areas, so that the minerals in the manure can be recycled back to the land more effectively.
Eventually, as soil fertility continues to decline (although at a much slower rate), these cycles will need to contract further to return the minerals which have gone into food back to the land. Otherwise, crop productivity will decline to the rate that the natural weathering of soil minerals can supply the nutrients needed for plant growth and yield.
I have described an orderly and logical adaptation of our farming system to cope with the end of fertilizer, but this would be happening against a backdrop of food riots, collapsing economies and perhaps outright war.
The sad reality is that the impacts on agriculture, and on human civilization, would be much, much worse than the best case scenario I have presented. Wise management of nutrients today is one way we can ensure this never comes to pass in the future. BF
Keith Reid is soil fertility specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs, based in Stratford. Email: keith.reid@ontario.ca