Crop substitution

America. The author describes some of these consequences of operations such as the ongoing Plan Colombia, including threats to the biodiversity of the Amazon, one of the world s richest ecosystems, and health threats from the herbicides used. Coca eradication efforts also threaten the survival of cultural groups and violate norms of human rights. An alternative strategy, crop substitution, has some promise but can cause economic problems when highly profitable crops are replaced by less remunerative ones. 

X 10 Btu/short ton), the solar energy trapped in 17.9 x 10 t of biomass, or about 8 x 10 t of biomass carbon, would be equivalent to the world s fossil fuel consumption in 1990 of 286 x 10 J. It is estimated that 77 x 10 t of carbon, or 171 x 10 t of biomass equivalent, most of it wild and not controlled, is fixed on the earth each year. Biomass should therefore be considered as a raw material for conversion to large suppHes of renewable substitute fossil fuels. Under controlled conditions dedicated biomass crops could be grown specifically for energy appHcations. 

Table 2. Potential Substitute Natural Gas in United States from Biomass at Different Crop Yields...

Sodium is an indispensable element for some crops (notably sugar beet), can partially substitute for potassium in several crops, contributes to neutralising soil and subsoil acidity, and has a positive effect on soil phosphoms solubiUty. Sodium is an essential nutrient for cattle, and sodium appHcation to soil increases its content in pastures. Sodium nitrate is particularly effective as a nitrogen source for sugar beet, vegetable crops, tobacco, and cotton (qv), and for any crop in acid soils. 

Jojoba is a desert crop that gives a small bean containing about 50% of a wax, a fatty acid ester with a fatty alcohol. The only other large source of such a wax is sperm whale oil, traditionally used in fine lubricants (see Lubrication and lubricants). Because the sperm whale is an endangered species, relatively Httle sperm whale oil is available and there is a large market for a substitute. Jojoba oil has been found to be usable for most of these appHcations. The jojoba oil is obtained by simply pressing the nut followed by conventional refining. Some jojoba oil is used in cosmetics (qv). 

The number of reports about hemicelluloses that have been covered by this review indicates the significantly increased importance of all types of hemicelluloses as plant constituents and isolated polymers during the last decade. Attention has been paid not only to known hemicelluloses but also to the primary structure, physicochemical, physical, and various functional properties of hemicelluloses isolated from hitherto uninvestigated plants. The efforts to exploit a variety of plant as potential sources of hemicelluloses were pointed out particularly for agricultural crops, wood wastes, as well as for by-products of pulp and rayon fiber technologies. Many studies were devoted to characterize seed-storage hemicelluloses from plants that have been traditionally applied in food and medicine of many underdeveloped countries to find substitutes for imported commercial food giuns. 

Future studies must focus on those specific agricultural technologies that have contributed to the increased use of pesticides during the past 40 years, and why crop losses to pests continue to Increase. Research needs not only to identify the detrimental technologies, but, more Important, develop ecologically sound practices that farmers can use as profitable substitutes (15). 

Some oil crops can be grown to provide a substitute for petroleum. 

Seeds of lettuce and other species have frequently been used to bioassay for the allelopathic activity of plant exudates (17.18.19). As with the use of cell suspensions, there are certain advantages and disadvantages to this methodology. The experimental simplicity, small amounts of material required and short time frame are certainly attractive qualities. However, species used in such bioassays quite often do not represent the actual target species under consideration. This is especially true when terrestrial crop species are substituted for weeds of aquatic systems. Nevertheless, information obtained from such experiments are often valuable when used in conjunction with results of other assays. 

Sri Lanka (Ceylon) was an important coffee-growing country until a leaf disease decimated crop production. In the 1880s, tea cultivation was substituted for that of coffee, and Sri Lanka has been another of the world s major tea producers ever since.7... 

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