Water Deficit Timing Effects on Yield Components in Maize

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Abstract
This study was designed to determine the interval of sensitivity of maize (Zea mays L.) yield components to moisture stress, and to evaluate that interval using estimates of plant available water (PAW). Individual maize plants were grown in containers in a glasshouse. For each treatment, water was withheld until the accumulated water use in well‐watered control containers was 20 L, approximately twice the PAW in each container. Containers were well watered at all other times. Containers were weighed to determine water use rates and to estimate PAW. Moisture stress was assumed initiated when water use rates declined below the average for well‐watered containers. The interval when kernel number was sensitive to moisture stress began 2 to 7 d after silking and ended 16 to 22 d after silking. Stress initiated prior to silking but relieved within 2 d after silking did not reduce kernel number, kernel weight, or plant yield. The fewest number of kernels, 45% of the control, occurred for stress during the 7‐d period after silking. Kernel weight was reduced by stress during the grain filling period, and the lowest weight, 51% of the control, occurred for stress 12 to 16 d after silking. Water use rates in treatment plant containers were compared to estimates of the soil moisture stress index (SMI) determined as the percentage of PAW in the containers. Water use rates declined when SMI declined below thresholds of between 0.20 and 0.30. These thresholds were similar to those reported for other crops. Thus, this analysis demonstrated that parameters based on PAW can be useful for evaluating the timing of moisture stress on maize yield components.