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PROPOSED
MEASURES: CROP & LIVESTOCK YIELD AND CROPLAND PRODUCTIVITY
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Crop yields
(tons per acre) of major crops, specifically corn, soybeans, wheat,
sorghum, hay, potatoes, and cotton, as a measure of how much energy
is converted from sunlight and made available for human and animal use,
and as a measure of how intensely and efficiently farmland is used.
The efficiency and intensity of use affects how much land is needed
to produce a given amount of food.
(Fig. 1)
Calories and
protein produced per acre of harvested land, as a measure of nutritional
output of major crops and thus their usefulness to the human diet. This
measure would track improvements or declines in the amount of usable
food value per acre. (Fig. 2)
Amount of feed
used per pound of meat or milk produced, as a measure of how efficiently
plants are converted to usable animal products. This is a key determinant
of the amount of usable meat and milk produced per acre of cropland.
(Fig. 3)
Satellite measurements
of cropland productivity (conversion of sunlight to plant material)
as a means of locating large-scale changes in cropland condition. (Fig.
4)
Yields of major
crops have increased steadily over the past 50 years.
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Calories
and Protein
per Harvested Acre (2)
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Source:
USDA, National Agricultural Statistics Service
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Source:
USDA, National Agricultural Statistics Service: Loomis & Connor,
1992
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Starch,
protein, and oil are the major chemical constituents of crops; the
proportions of these components vary among crops. Differences in
yield and chemical makeup result in significant variations in nutritional
productivity.
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| Product
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Feed
Type |
Feed
Requirement (Pounds of feed required per pound of meat/milk
produced)
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| Beef
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Hay/silage |
12-13 |
| Corn/silage
(50% grain) |
7.5-9.0 |
| Corn(100%
grain) |
5.0-7.0 |
| Pork
|
Grain |
2.7-3.8 |
| Poultry
|
Grain |
1.8-2.5 |
| Milk
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Grain
+ concentrates |
0.35-0.5 |
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Source:
Oak Ridge National Laboratory & Auburn University
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Some
animals can live almost entirely on plant materials that people
cannot eat, such as hay or corn silage, whereas others are fed considerable
amounts of grain. The amount of meat produced from a pound of feed
varies by feed type, animal species, and animal growth conditions. |
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This image
shows changes over 10 years in the normalized difference vegetation
index (NDVI), a satellite-derived measure of plant growth. Dark
areas exhibited a trend toward more growth, whereas lighter areas
grew less. Most areas showed no significant trend. |
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Source:
USGS, EROS Data Center
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STATUS
OF DATA & OTHER NOTES
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Information
on calories and protein per harvested acre of cropland is based
on yield data (as provided in Graphic 1, Major Crop Yields) and
general characteristics of individual crops. Future reports may
incorporate updated crop characteristics, in order to identify
significant trends in protein and calorie content, if such data
are available.
Information
on conversion of plant material to meat and milk is tentative.
Future reports may address changes in the amount of feed required
to produce different meat products, if appropriate data are available.
We did not
select a specific measure for overall cropland productivity. The
normalized difference vegetation index (NDVI) presented here is
a key candidate for additional consideration.
Please see
the Technical
Notes for additional information.
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