Monitoring the effects of rapid onset of drought on non-irrigated maize with agronomic data and climate-based drought indices

The 2003 growing season at Mead, NE began with moist and relatively cool conditions that persisted through most of June. During this moist phase of the season, soil water and parameters such as evapotranspiration (ET) and gross primary productivity (GPP) were nearly identical between a rainfed maize site (RMS) and an irrigated maize site (IMS). A drying phase began in late June, causing decline in soil water at RMS and the necessity of irrigation treatments at IMS. The drying phase turned into a “stressed” phase by early August, as only 10 mm of precipitation fell in a 40-day period between mid-July and late August. Conditions at RMS began to deteriorate even more rapidly after maize entered the critical reproductive stage, as the depletion of soil water led to (implied) reductions in stomatal conductance, which led to significant reductions in ET and GPP, compared to the well-watered IMS. Two drought indices, the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI), were utilized to show the effectiveness of short-term indices at detecting flash drought versus field measurements. Results showed that both the 1-month SPI and the 1-month SPEI were quite sensitive to the onset of the flash drought and closely followed the decline in soil water and other biophysical parameters at RMS relative to IMS. Significant precipitation returned and led to some recharge prior to harvest but was far too late to be of any help to the maize at RMS, as the yield difference of 6.3 Mg/ha between RMS and IMS revealed the detrimental effects of a rapid onset of drought during the critical reproductive stage of maize.