Therefore, there is room for large improvement. I have several comments. The world has been fed rather adequately recently, and the result has been downward pressure on agricultural prices. The lowered payoff for fertilizer noted above is a consequence of that. If more demand increases prices, increased fertilization will be profitable and so will other ways of increasing production that are regarded as too expensive at present.
More irrigation is another example.
Very large scale water projects may again become cost-effective. Maybe the countries that need increased yields would find it to their advantage to fund the international agricultural research institutes. Genetic engineering has only begun to pay off. Probably continuing present methods of improvement can get us up to American standard of living for a population of up to 15 billion. Should population expand much beyond that, fundamentally new technologies may be required.