planted to their final spacing, thereby improving space use efficiency and productivities [107]. Thus edi-
ble biomass productivities of ~20 g m^2 day^1 and conversion rates of ~0.5 g mol^1 appear achievable
with careful horticultural techniques and CO 2 enrichment.
By using the potato productivities of ~20 g m^2 day^1 (Table 3) and a tuber caloric value of about
3.7 kcal g^1 [10], this productivity would equate to about 75 kcal m^2 day^1. To provide a conservative
requirement of 3000 kcal person^1 day^1 would then require about 40 m^2 per person (3000 kcal person^1
day^1 /75 kcal m^2 day^1 ). Doing a similar calculation but using the higher productivities achieved with
wheat suggests that area requirements could be reduced to ~15 m^2 per person, assuming the high irradi-
ances could be provided [21,31,47]. Although these estimates consider only caloric yield of the crops, the
results suggest that much of the food production could be met with reasonably small areas, provided the
lighting energy is available (Figure 4). Alternatively, if high light cannot be provided, more growing area
934 WHEELER ET AL.
TABLE 3 Productivities of Some Crops Grown in NASA’s Biomass Production Chambera
Radiation Radiation Edible
use use biomass,
Edible Total efficiency efficiency optimized
PARb biomass biomass (edible) (total) spacingc
Crop (mol m^2 day^1 ) (g m^2 day^1 ) (g m^2 day^1 ) (g mol^1 ) (g mol^1 ) (g m^2 day^1 )
Wheat 57.5 12.6 31.6 0.22 0.55 —
Soybean 36.9 6.0 15.7 0.16 0.43 6.7
Potato 42.2 18.4 27.2 0.44 0.64 20.3
Lettuce 16.8 7.1 7.7 0.42 0.46 11.0
Tomato 38.6 9.8 19.6 0.25 0.51 11.1
aPlants grown in 20 m (^2) area in closed chamber with CO 2 enriched to 1000 to 1200 mol mol (^1).
bPARphotosynthetically active radiation. Total PAR varied between crops depending on photoperiod requirements and
types of lamps used.
cEstimated yield if 10 days were eliminated from growth cycle by using transplanted seedlings. Transplanting of wheat
seedlings would be impractical.
Figure 4 Crop caloric yield and crop area requirement to sustain one person as a function of total photosyn-
thetically active radiation (PAR) provided to plants.