Table 3–4. Selected indicators of sustainability for agroecosystems, and the indicator values for the conventional and agroforestry farms described in Table 3–5.
| Indicator | Definition | Value indicating high sustainability | Value indicating low sustainability | Conventional farm | Agroforestry farm |
|---|---|---|---|---|---|
| Harvest a | weight of harvested crops and livestock, kg ha−1 (lb acre−1) dry weight | 7,952 (7,100) | 0 | 3,805 (3,397) | 3,923 (3,503) |
| Cultural energy input b | total non‐solar energy inputs, MJ ha−1 (MJ acre−1) | 0 | 59,259 (24,000) | 17,264 (6,992) | 14,091 (5,707) |
| Energy output/input c | ratio of energy in harvested crops to cultural energy inputs | 5 | <1 | 3.9 | 4.5 |
| Energy capture efficiency d | energy in harvested crops as proportion of growing season PAR,% | 1.0 | 0 | 0.38 | 0.35 |
| Water use efficiency e | harvested biomass divided by AET (g m−1 mm−1) | 1.15 | 0 | 0.61 | 0.61 |
| Imported fertilizer f | N + P, kg ha−1 (lb acre−1) | 0 | 151 (135) | 44 (39) | 26 (23) |
| N losses g | losses through erosion and leaching), kg ha−1 (lb acre−1) | 0 | 45 (40) | 28 (25) | 20 (18) |
| Soil erosion h | wind + water, Mg ha−1 (tons acre−1) | 0 | 11 (8) | 11 (5) | 7.8 (2.5) |
| N balance i | N inputs/N outputs | 1 | <0.8 or >1.2 | 0.6 | 0.64 |
| P balance j | P inputs/P outputs | 1 | <0.8 or >1.2 | 0.7 | 0.46 |
| Crop diversity k | no. of crops per farm | 12 | 1 | 2 | 7 |
| Hired labor l | h ha−1 (h acre−1) | 0 | 5 (2) | 1 (0.4) | 5 (2) |
| Net income m | US$ ha−1 (US$ acre−1) | 235 (95) | 89 (36) | 99 (40) | 249 (101) |
| Capital borrowing n | debt/variable income | 0 | 1 | 0.63 | 0.46 |
| Farmer knowledge o | total skills and knowledge held by farm family | high | low | medium | high |
a High value is dry weight of grain from Nebraska irrigated corn (9406 kg ha−1 (150 bu A−1)).
b The value indicating low sustainability is the energy input per hectare to produce irrigated corn in Nebraska (Pimentel, 1980).