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Crops & feedstuffs

According to Pimentel et al. (1974), 15 crops supply about 90% of the world’s food (presumably in addition to animal products), and occupy about 75% of the total tilled land area. These comprise cereals and other grains (rice, wheat, maize, sorghum, millet, rye, and barley), root crops (cassava, potato, sweet potato), legumes (soybeans, peanuts) and tree crops (banana, coconut). All of these crops contribute to the feed base available for animal production to some degree, but the main crops from this list that are used for livestock feeding (Hendy et al., 1995; Table 1) are maize (52% of concentrates), barley (19%), wheat (19%), sorghum (5%), and soybeans, plus a variety of agro-industrial byproducts (10%). Of course, the primary feed base for ruminants consists of grasses and other forages. As feed comprises the major cost in all livestock production systems, any accounting of energy costs must begin with crops and other feeds.

Table 1. Global concentrate feed resources (1990-92)
 
Commodity
Kton/year
%
Cereals 600,516 66.8
Brans 118,946 13.2
Oilseeds 13,463 1.5
Oilmeals and cakes 119,263 13.3
Roots and tubers (90% DM basis) 47,003 5.2
Total   100.0

Source: Hendy et al. (1995).

Pimentel (1980b) compiled the most comprehensive data set regarding the fossil energy costs of crop and livestock production systems. In that and other publications, Pimentel and others have argued that intensification of maize production between 1945 and 1975 has reached the point of diminishing returns, and that further increases in inputs will yield progressively smaller improvements in productivity. Smil et al. (1983) examined the assumptions used by Pimentel (1980) and revised their estimates. That report concluded that the earlier estimates of efficiency were too low, but agreed with the decline over time. The present analysis indicates that the reason for declining energy ratios is not reduced efficiency but rather the non-zero intercept (Figure 1). Of course, very low energy inputs (e.g, no fertilization) may not be agronomically or economically sustainable

Figure 1. Changes in energy efficiency of corn production in the US between 1945 and 1975. Solid line indicates full regression line, dashed line indicates line with no intercept. Source: Pimentel, 1980a.Moreover, comparison of energy ratios (J output/J input) showed that human or animal-powered systems in use in some developing countries were more efficient than the mechanized, high-input systems used in developed countries (Pimentel, 1980ab). As pointed out by Fluck (1980), use of energy ratios is suspect, since there is little substitutability among fuel and food forms of energy. In this report, energy efficiency will be expressed as kg product/J input. The data on inputs to crop production given by Pimentel (1980b) were re-evaluated and revised to reflect changes in tillage and fertilization practices, and to account for multiple outputs from cropping systems. The resulting changes in energy costs due to changing cultural practices were small, and the original estimates were retained. Differences in accounting for multiple outputs, however, can produce large discrepancies in the embodied energy of main crops, crop residues and processing byproducts (Table 2; NAS, 1983). Model users may select which value to use in a particular situation. Davulis and Frick (1977) assigned all input energy to the main product, so that only the energy required for processing was allocated to byproducts. Embodied energy in feedstuffs were tabulated using values from Davulis and Frick (1977) as well as from Pimentel (1980b) and other sources. These values are summarized in Table 3. Fossil energy embodied in feeds represents the single largest cost in all animal production systems, therefore the values assigned to feeds are critical to the final analysis. Wherever possible, local data should be used.

Table 2. Crop byproducts
 
 
Residue
Crop
Type
 x Main product
Rice
straw
 1.22
Wheat
straw
 1.00
Maize
stover
 2.00
Sorghum
stover
 2.00
Barley
straw
 1.00
Oats
straw
 1.00
Cotton
trash
 3.00
 
cotton seeds
 .25
Soybean
trash
 1.00

From: Parikh and Syed (1988).Table 3. Embodied energy (MJ× kg-1) of various feed ingredients
 
Ingredients
Production
Transport
Processing
Total
Alfalfa hay - - - 1.59 
Animal fat -  -  10.92  10.92 
Barley 3.74  0.07  -  3.81 
Brewer's dried grains -  -  11.62  11.62 
Cane molasses -  -  5.81  5.81 
Cereal grains - average - - - 4.72 
Cottonseed oil meal -  -  1.29  1.29 
Distiller's dried grains -  - 11.62  11.62 
Dried beet pulp -  -  12.12  12.12 
Dried citrus pulp -  -  12.12  12.12 
Dried whey -  -  53.22  53.22 
Hay - - - 2.77 
Limestone - - - -
Maize gluten meal -  -  12.46  12.46 
Maize grain 4.22  0.08  0.82  5.13 
Maize silage - - - 2.33 
Meat & bone meal -  -  8.60  8.60 
Oats 2.63  0.12  -  2.75 
Rice bran -  -  0.32  0.32 
Salt + minerals - - - 0.38 
Sorghum 5.80  0.07  -  5.87 
Soybean oil meal 4.41  0.09  1.11  5.61 
Soybeans - whole - - - 5.90 
Urea -  -  29.01  29.01 
Wheat 3.96  0.07  - - 4.03 
Wheat bran -  -  0.32  0.32 
Wheat middlings -  -  0.32  0.32 

Sources: Davulis & Frick (1977); Pimentel (1980b).

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