Energy Use In Grain And Legume Production
Below: a crop of oats.
Plants are an extremely important source of calories, protein, and other major nutrients. In fact, plant foods provide about three-quarters of the calories and proteins consumed by humans.
Cereal grains have always been the predominant source of human food, for several reasons: they can be cultivated under a wide range of climate and environmental conditions (e.g. temperature, moisture levels, soil types, etc.); they yield large quantities of nutrients per unit of land area; cereals also have a relatively low moisture content (13 to 25 %) at harvest and hence can be transported more efficiently than potatoes, for example, which are about 80 % water. Cereals' low moisture content facilitates storage for long periods of time with minimal storage facilities. Finally, most cereal grains sustain less damage from pests and disease than other crops.
Legumes (e.g. soybeans, peas, lentils, peanuts, etc.) are also very important plant foods and complete cereal grains diet very well. They average a high protein content from 20 to 30 percent (dry cereal grains average only 9 percent protein.) Legumes also have a high content in lysine, an essential amino acid, which is lacking in cereals, and are excellent plant sources of iron and thiamine. Legumes also extract nitrogen from the air and transfer it into the soil through their root system in a form usable by other crops. Nitrogen is one of the three basic nutrients used by plants - nitrogen for tissue growth, phosphorus for root development and potassium for reproduction - and the ability of legumes to provide the element for other crops is an important aspect of managing soil conservation.
Grain and legume production are relatively efficient systems where energy input and yields depend considerably on the method of production. Cereals or legumes can be produced using human power, animal power or full mechanization and the energy efficiency for the main grain and legume productions will now be examined.
Grain production
Corn production
Human and animal power are widely used for corn production, especially in developing countries, and are very energy-consuming. For example, in Mexico, corn production by a single person using swidden or cut/burn agricultural technology requires about 1,140 hours (143 days) of labor, the total energy input from human labor being 17,245 kJ per day. When animal power is used, such as ox power in Mexico, the human labor investment is reduced from 1,140 hours to 380 hours. Under these farming conditions, 1 hour of oxen power replaces nearly 4 hours of human power. Assuming that an ox consumes 83,710 kJ per day in forage and grain and that a human still consumes 17,245 kJ per day at hard work, growing corn using animal power requires more energy input than growing corn by hand, but gives more free time to the farmer to pursue other activities.
Yields of corn produced by hand or with animal power in Mexico are significantly lower than yields produced by mechanization in Canada, for example, but the reason is not related to the type of power used. The lower yields can be attributed to reduced use of pesticides and fertilizers, to the lack of hybrid (high-yielding) varieties and to poorer soils on which crops are grown.
The energy analysis in mechanized agriculture is different from labor-intensive agriculture. Of course, the total input of human power is very low, but this is balanced by the significant use of fossil fuel energy required to run the machines. In the US, in 1990, fossil fuel energy inputs averaged about 43.9 million kJ/ha of corn, the equivalent of about 1,050 liters of gasoline, resulting in an output/input ratio of 2.5:1. Compared with the output/input ratio of 11:1 for corn hand produced in Mexico, it can be observed that the former is actually more efficient in terms of energy consumed.
Wheat production
Below: a crop of wheat.
More people eat wheat than any other cereal grain, making it the single most important cereal crop grown in the world. As with corn production, wheat is produced using energy sources ranging from human and animal power to heavy machinery. Energy inputs and yields vary with each system, influencing the ultimate output:input ratio.
In India, in the Uttar Pradesh region, human and bullock power are used for wheat production. A total energy input of about 11.7 million kJ/ha is required to attain a wheat yield of 11.3 million kJ/ha of food energy, for an output:input ratio of 0.96:1. This ratio means that the wheat energy produced is less than the energy expended. However, this ratio is misleading since the largest energy inputs are for the two bullocks needed to cultivate the land: these bullocks consume primarily grasses that cannot be used for human consumption. They are in fact a type of food conversion system, converting grass energy into wheat energy through the livestock's labor in the wheat fields. If the bullock input is removed from the analysis, however, the output:input ratio increases to 5:1, which is a more realistic representation of this production system.
In the United States, wheat production, with the use of heavy machinery and fertilizers, requires large amounts of fossil fuel energy. So, even if yields are greatly increased, the efficiency ratio is still relatively low: overall, 10.9 million kJ/ha energy input is needed to produce 24.3 million kJ/ha of wheat energy, giving a 2.2:1 ratio.
Legume production
Soybeans
Soybeans are the single most important protein crop in the world. About two-thirds of all soybeans produced are grown in the United States, Brazil and China. In the US, most of the soybeans are processed for oil, as well as the cake and meal fed to livestock. Relatively little is used as human food.In the United States, the output:input ratio is relatively better than for grain production. Production inputs being of 7.5 million kJ/ha while the average soybean energy is 31.8 million kJ/ha. The energy ratio is then 4.2:1. The main inputs are for herbicides, seeds and manufacturing of the machinery.
An advantage of legumes over other types of crops is than they need less nitrogen, saving energy used for fertilizers. For example, soybeans need only one-tenth of the nitrogen required to grow corn. Legumes obtain nitrogen from the atmosphere, where it is present is great quantities, through their symbiotic relationship (to be glossarized) with microbes in the soil.
Energy used in Livestock Production | Energy Use In Fruit And Vegetable Production