At Pinney Purdue (PPAC) 2.67 inches of rain fell July 27 through August 9. The potential evapotranspiration (PET) over the period was 1.68 inches. Estimates for water use by the crops are equal to or just slightly lower than potential evapotranspiration. For tomatoes, estimated water use was 1.68 inches, and for watermelons, 1.52 inches. There were fewer irrigations over this period than in the previous two weeks: 1 in the sensor-based watermelon treatments, 4 in the evapotranspiration (Et)-based treatments for tomato and watermelon, and 7 in the sensor-based treatment for tomatoes. The sensor-based watermelon treatment is allowed to dry to a greater exent than the sensor-based tomato treatment.
The first bell peppers are ready to pick; the earliest tomatoes are at the mature green stage, earliest eggplant are approaching maturity, and earliest watermelon appear full-sized. Younger fruit continue to develop on all plants.
The graph below (Figure 1) shows sensor readings for the unirrigated and the Et-based watermelon beds, along with bars indicating the daily totals of rainfall and irrigation. During the period from July 28 to 31 the decrease in soil moisture during daytime hours is visible in the lines for both beds. Beginning Aug. 1 the soil moisture in unirrigated plots decreased much less quickly. This is likely because the soil had become dry enough at that depth that the watermelon could not easily extract moisture. There may have been moisture deeper in the soil that the plant could use. Rain on Aug. 3 replenished the soil moisture in the unirrigated plots; the irrigation plots also received irrigation before it rained.
Figure 1. Soil moisture measured by electronic sensors at 12 inch depth in watermelon plots irrigated based on evapotranspiration (Et-based) or not irrigated, and daily precipitation and irrigation. Pinney Purdue Ag Center, July 27-Aug. 9, 2022.