Plants are renewable resources. Can plant resources support increasing population in the future? Will we have sufficient plant diversity to choose new crops or to improve present day ones?
Over half the world's population is inadequately fed. The average American consumes about 5 pounds of grain per day. About 80% of this is fed to animals. In many underdeveloped countries, individuals consume about 1 pound of grain daily, mostly directly.
The problem is complex. There is already enough food produced to feed everyone. Our farming methods are not applicable in most of the world.

Better crops
Yields can be improved greatly in many cases by selection of better cultivars. There is resistance to change in cultivars by farmers. Another problem is the loss of "land races" and hence genetic variation however.
See the diagram on page 465. Changes in human population and food production.
The major problem is that all this so far has just barely kept pace with human population growth.

The Green Revolution
Wheat varieties were selected that could grow well in humid tropics. They were widely planted in India. For several years, production increased markedly and India even began exporting wheat. Then the population increase caught up. Now India is back in the importing category again.
A similar thing happened with rice. Shorter cultivars of rice that matured more rapidly permitting the farmers to grow more crops per year were developed. Most tropical crop plants are relatively unselected and probably yields could be improved dramatically. Will all this solve the problem?
See figure page 459.

Genetic variability
People are gradually depending on fewer and fewer crops. Further, they are cultivating fewer and fewer types of these crops. Wild forms are, in many cases, even eradicated to prevent them from crossing with the cultivated forms.
Almost all our hybrid corns come from selections made by one family in the 1840's and 1850's in the U.S. Almost all hard red wheat comes from a hybrid cross made in Canada about 1900.
Pima cotton was selected from a single plant of a cultivar developed in Egypt in 1910. The same is true for many other crop plants. All of these things can lead to disastrous problems with monocultures. This happened with the southern leaf blight of corn in the early 1970's.

Gene banks
Gene banks have been established for many of the major crops. However, many tropical crops are still not included. The quality of preservation in these gene banks also varies widely. We are just now learning how to preserve and maintain seeds for long periods of time. The seeds must periodically be taken out and grown. Care must be given to prevent any hybridization with nearby similar plants.

New ways of making plant variation
Many of these involve plant tissue culture. This is especially useful for plants that are reproduced vegetatively. Somatic mutations may be created. Protoplast fusion can also be used. Genetic engineering.

Expanding agriculture
Agriculture can possibly be expanded into areas that are presently too cold, too dry, too saline etc. Some crop plants already have been grown in many cases and may well be adaptable. Knowledge of minor crops may be useful in this regard. But the areas to be used will be changed and in some cases destroyed. As tropical forests are destroyed, many species will be lost.
This shows where the potential sources of arable lands. We have no idea what the long term effects of forest destruction are, but they don't look positive.

Dependence on fossil fuels
Although our system of farming appears to work well, we are heavily dependent on fossil fuels (petroleum, natural gas and coal) to make fertilizer, drive tractors etc. We put six times more energy into farming than we get out.
More energy efficient methods of agriculture will almost certainly have to be developed. Some crops require much less energy input than others. This has recently led to reduced tillage agriculture, which has its own set of problems.
There are also problems with over use of pesticides and herbicides. Many of these will have to be resolved in the future. Naturally occurring compounds may provide a partial solution. Biological control will almost certainly become more important.

Uses of plants as chemical precursors
General fractionation of plant material for precursors -- use of plants as source of botanochemicals. Biomass is the total quantity of organic material produced.

Fuel uses
Methane: Biomass can be fermented anaerobically to produce methane. Methane is easy to transport and use. The systems for delivery are already largely in place. Ultimately, all come from CO2 fixation by plants or solar energy. Cellulose is probably the most abundant organic compound. Lignins are also very common. When dried, straw or wood has only about half the energy content of oil. Sewage and animal wastes can also be fermented to product methane.
Some of the limits are the cost and land area requirements to grow the crops. Many schemes of this type produce less energy than they consume. Energy farming of this type is never likely to be successful in most of Europe and the U.S.
Methanol: Destructive distillation of wood and many other plant materials produces methanol. Methane can be converted by steam reforming into methanol. Methanol can be added to gasoline or used directly.
Ethanol: This is the most common approach. In countries like Brazil, it's fairly favorable. The cost and land area to grow the crops is a major limitation. Starch or sugar is converted by yeast into ethanol. The scheme is not new. Ethanol was first used as a fuel in 1894. Gasohol was first marketed in about 1936 (8-10% ethanol). Almost all U.S. gasoline contains about 5% in any case.
In Brazil, in 1973, they began to do in big way. They have abundant cassava and sugar cane. Hydrolysis of wood, bagasse, straw, paper, cotton, to sugar is a major problem. This can be done by acid hydrolysis under pressure or cellulase enzymes. Sugar cane is one of the most efficient plants. The materials are already collected, but not all are used.
Generally alcohol is two to four times more expensive than gasoline. They tried: to improve sugar cane yields, to improve alcohol production, and to improve the yeast. Brazil has about everything going for it: lots of land, no oil, adverse balance of payments, rural unemployment problems, and good climate.

Seed oils for fuel
These are already similar to diesel fuels in many of their properties. They can probably be used without major work except for economics. They will work in basically unaltered diesel engines, but gums and waxes must be removed. Antioxidants must be added to prevent polymerization. Mixing about 50:50 with diesel fuel improves the properties quite a lot, but viscosity is still a problem.
Some farmers already using these because they can make them at home. Sunflower oil is the most popular. About 15-20% of the crop is needed to provide energy to grow the next crop. Sunflower oil costs about two times more than diesel fuel. Peanut oil is also usable. Soybean oil works, but they are grown on more valuable farm land and compete directly with corn and wheat.
Oils can also be isolated from algae and fungi in culture, but the costs of culture are usually too high to permit this to be a good alternative. As much as 70-80% of many Candida species are oil.

Petroleum from plants
Melvin Calvin has worked with Euphorbia lathyrus (Euphorbiaceae). This makes about 4 barrels of petroleum like stuff per acre. Chinese tallow tree (Sapium sebiferum, Euphorbiaceae) grows well in low marginal areas in the southeastern U.S. and yields about 12 barrels per acre.
Sunflower, soybean, and similar crops yield about 1 barrel per acre. Crambe, peanut, safflower all yield about 2 barrels per acre. African oil palm yields about 7-10 barrels per acre.

The petroleum like residues from plants can serve as chemical precursors much in the same way as petroleum. Oil seeds probably serve as the best substitute for petroleum in this regard. They are already used to make plastics, polymers, industrial chemicals etc.
For example, ricinoleic acid from castor beans is used to make nylon. Ricinoleic acid is converted to an 11-carbon precursor which is made into nylon in France. Erucic acid is made into plasticizers and lubricants as well as nylon 13/3. Jojoba oil is made into a lubricant.
Epoxy fatty acids from Stokesia laevis are used to make plasticizers. To make botanochemicals, the plant is grown, harvested, processed, fractionated, and used for many things. Euphorbia lathyrus is cut and dried. The plant material is then ground and extracted. The residue is about 20% protein.
Part may be used for paper and part is burned as fuel. The oil fraction is a source of hydrocarbons, fats and resins. The fats are hydrolyzed to yield fatty acids. The 4 barrels per acre are low in sulfur and cost about $30 per barrel.

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Revised April 2005

© David S. Seigler, Integrative Biology 363, Plants and Their Uses, Department of Plant Biology, 265 Morrill Hall, 505 S. Goodwin Ave., University of Illinois, Urbana, Illinois 61801, USA. 217-333-7577.