A Viability Bound for Farm-Saved Maize Seed: Months Above Sowing Quality for Five Storage Methods, and the Moisture or Temperature Each Method Would Need

A farmer who saves maize seed from one harvest to the next planting, or holds it across a failed season, needs to know how long the lot stays worth sowing. This paper computes that period from stated assumptions, using Harrington's rules of thumb — the viability period halves for each percentage point of added seed moisture and for each 5.6 °C of added storage temperature — inside a probit viability model for maize starting at 96% germination, with a reference deterioration scale of 60 months at 10% moisture and 20 °C, under a repeating cycle of a six-month hot season and a six-month cool season. Of five storage methods a farmer actually has, an open gourd or basket in the house (13.5% moisture and 32 °C in the hot season, 12.0% and 24 °C in the cool season) stays at or above 85% germination for only 0.86 months and reaches the 50% floor in 2.10 months. Ash-covered seed lasts 4.85 months above 85% and 16.78 months above 50%; a sealed tin lasts 8.32 and 24.36 months; a sealed plastic bottle in a cool pit lasts 55.10 and 136.45 months; and a clay pot with desiccant lasts longest, at 60.93 months above 85% and 148.22 months above 50% — about 70.8 times the open basket's life at sowing quality. To hold 85% for a full 12 months, the open basket's seed would have to be dried to a uniform 9.77% moisture at its house temperatures, or its temperature lowered by 16.71 °C at its present moisture; the sealed tin needs only a 0.26-point further drying, to 10.24%. The study is simulated, not measured: the ranking and the size of the gaps follow from the stated rules, while the absolute month counts rest on the stated reference scale and should be re-run with local values.