My thoughts on fertilizer

Fertilizer can be broken down into the following parts:

• Nitrogen
• Phosphorous
• Potassium
• Calcium/Magnesium
• Trace or micronutrients
• Biologicals 

Commercial fertilizers in the US are required to list the Nitrogen, Phosphorous and Potassium content. That is, the percent of elemental Nitrogen that is available to the plant (N2 the most common form of nitrogen is NOT available to plants). The percent Phosphorous-equivalent of the phosphate ion (H3PO4). The percent Potassium-equivalent of the potash ion (K2O). These are the Big Three of fertilizers.

Nitrogen: From the perspective of the suppliers, Nitrogen is primarily a way to turn "waste natural gas" into a salable commodity (rather than flaring it off) that is much easier to ship than compressed natural gas. It can either be turned into anhydrous ammonia which is a gas but liquifies at much lower pressures than methane. Or it can be turned into urea which is a solid. Or it can be turned into ammonium nitrate...which is very hard to purchase due to its potential as an explosive.

The United States has the capacity to make lots of "Nitrogen" fertilizers and every bushel of corn requires about one pound of Nitrogen.

Phosphorous: In North Africa, much of the natural gas is converted by way of several chemical steps into DAP, Diammonium phosphate. Morocco is the principal source of phosphorous in the world and Algeria has natural gas. DAP combines Nitrogen and Phosphorous. Shipments of DAP to Indian and China go through the Red Sea but not the Straights of Hormuz. Shipments of DAP to the US go through Straights of Gibraltar.

Potassium: Saskatchewan is notable not only for being harder to spell than Massachusetts but for have very large deposits of Potassium chloride that is economical to mine. Potassium chloride from Saskatchewan is shipped by rail to the US.

The amount of composted manure (upper-left corner of image) required to get 200 bushel/acre corn. Approximately 2-1/2 cubic yards for every 3000 square-feet or 30 cubic yards per acre

Key points: Phosphorous and Potassium are usually well retained by the soil. That is, it can be "banked". Failures due to decreasing soil levels of either of those two elements tends to be slow-motion reduction in yield. One exception to that generalization is if you seed alfalfa and have low potassium...that will be a hard-stop on establishing that crop.

Nitrogen is different. Nitrogen is highly mobile and doesn't "bank" outside of organic matter. If you stop adding Nitrogen to a corn field on a yearly basis, your next harvest will be reduced to 1/3 or 1/2 the first year and 1/3-to-1/4 thereafter. 

Cycling of nutrients

There was a time when most livestock was raised on-farm, very close to where the feed was grown. The manure and the nutrients in the manure, was returned to the fields from which those nutrients originated. Very little additional fertilizer was required to keep the farm productive because relatively small amounts were shipped off the farm.

Corn belt

That model did not scale well. Banks and economists like large farms where machines feed the animals. Grain is easier to mechanize than forage. 

Pig production

Chicken population distribution

 

Cattle per hundred acres

So you can see that the corn fed to hogs and cattle often turns into manure that falls to the ground far from where the nutrients were sucked out of the ground.

At this time, those orphaned nutrients are treated as pollution rather than as a resource. It is not economical, in most cases, to return them to the field they came from. 

This is not an issue of technology. It is an issue of economics: Cost of labor, cost of borrowed money, cost of fuel, cost of fertilizer, cost of building materials, cost of regulatory compliance (EPA).