Table 3. This table shows estimated crop yield declines at particular soil or irrigation water conductivities.
ECe is a measurement on the extract from a saturated soil paste. ECw is the conductivity of irrigation water with yield declines based on an estimated 15–20% leaching fraction. These data are always presented as guidelines, not definitive limits, and are for modern crop varieties. Given the range of tolerance within a given crop type, see squashes, it is possible that varieties used by Chacoan farmers were less susceptible than modern varieties largely grown in wetter climates. Data, except for sunflower, is from [81]. Amaranthus, found to be part of diets at Salmon Ruin and Antelope House, is considered a tolerant plant to salinity [82]. Chenopodium, Amaranthus, and Asteraceae were found to be significant diet contributions [82], and each is considered a halophytic, or salt adapted, plant.
| Yield Decline Percentage | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 0% | 10% | 25% | 50% | 100% | ||||||
| Crop | ECe | ECw | ECe | ECw | ECe | ECw | ECe | ECw | ECe | ECw |
| Corn (Zea Maize)1 [81] | 1.7 | 1.1 | 2.5 | 1.7 | 3.8 | 2.5 | 5.9 | 3.9 | 10 | 6.7 |
| Sunflower (Helianthus annuus L.)2 [83] | 4.8 | / | 6.8 | / | 9.8 | / | 14.8 | / | 24.8 | / |
| Squash, scallop (Cucurbita pepo melopepo) [81] | 3.2 | 2.1 | 3.8 | 2.6 | 4.8 | 3.2 | 6.3 | 4.2 | 9.4 | 6.3 |
| Squash, zucchini (Cucurbita pepo melopepo) [81] | 4.7 | 3.1 | 5.8 | 3.8 | 7.4 | 4.9 | 10 | 6.7 | 15 | 10 |
| Bean (Phaseo lus vulgaris) [81] | 1 | 0.7 | 1.5 | 1 | 2.3 | 1.5 | 3.6 | 2.4 | 6.3 | 4.2 |
1This is for sweet corn or grain corn. For forage corn, it is given as 1.8 with a decrease of 7.5% per 1 dS/m increase, not the 12% presented here.
2Based on the initial threshold and 5% seed yield reduction per unit dS/m increase.