Phosphorus fertilizer is commonly applied to soils in crop production as diammonium phosphate (DAP). To decrease ammonium addition to the environment, triple super phosphate (TSP) is being considered as a DAP replacement. This study was undertaken to compare the response of maize plants to soil fertilization with TSP vs. DAP under well-watered conditions, under soil-drying conditions, and root hydraulic conductance. It was found for well-watered conditions in a controlled environment that there was no difference in plant growth between DAP to TSP treatments. In soil dry-down experiments, however, the initiation of the decrease in transpiration rate was unexpectedly quite different between DAP and TSP treatments. The soil water content threshold for initiation of decrease in transpiration rate with DAP treatment (average fraction transpirable soil water for two experiments = 0.285) was consistent with common observations, but the threshold associated with TSP treatment occurred at an unusually high soil water content (average fraction transpirable soil water for two experiments = 0.545). The higher threshold with TSP resulted in an extended period of soil water use, i.e. soil water conservation. Soil water conservation resulting from the TSP treatment was associated with a 27% greater shoot mass accumulation following a 4-wk re-watering period after the water-deficit treatment than measured with the DAP treatment. The high threshold for decrease in transpiration resulting from TSP was consistent with measured lower root hydraulic conductance as compared to DAP treatment. The unexpected discovery of TSP-induced initiation of transpiration rate decrease at high soil water content is consistent with greater crop drought resilience.