Key Points
- Drought is one of the main causes in seasonal yield variation. Crop response to drought can be calculated in terms of potential soil moisture deficit (PSMD), the cumulative difference between crop demand and water supply.
- Timing and duration of drought on maize was studied in the rain shelter at Lincoln. The control plot was irrigated weekly. Droughts of different duration were created in early, mid and late season by with-holding irrigation.
- The critical deficit, the point of PSMD beyond which yield is lost, was 100 mm for early drought and 160 mm for mid season drought, a difference thought to be due to rooting depth. The late drought starting in February and March was not severe enough to affect yield.
- Maize yields declined by 11 kg/ha (grain) and 22 kg DM/ha (silage) per mm of PSMD beyond the critical deficit.
- If irrigating to avoid yield loss to drought stress, growers should keep PSMD above the critical deficit. Once yield loss has occurred, it cannot be regained.