S M Samiul Islam , Jerry Mount, Ibrahim Demir

Corn and soybeans are pivotal crops in the U.S. agricultural landscape, providing essential vitamins and oils. These two crops dominate approximately 90% of crop production in Iowa. However, their yields are significantly impacted by recurrent drought conditions. A prolonged deficiency in soil moisture characterizes agricultural drought due to sustained precipitation shortfalls. This study aims to quantify widely utilized drought indicators and ascertain their relationships with corn and soybean yields from 2000 to 2022 to identify each crop's most reliable drought indices. The analysis encompasses meteorological and satellite-derived indices alongside crop yield data from the U.S. Department of Agriculture's National Agricultural Statistics Service (NASS). Indices evaluated in this study include the Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI), Palmer Drought Severity Index (PDSI), Evaporative Demand Drought Index (EDDI), Crop Moisture Index (CMI), and Normalized Difference Vegetation Index (NDVI). Our results demonstrate a positive correlation between soybean yields and long-term moisture indices such as SPI-6, SPI-12, SPEI-6, and SPEI-12, indicating these indices' potential utility in forecasting soybean productivity. Conversely, corn yields exhibit fewer regular patterns and are negatively correlated with EDDI, with higher EDDI values coinciding with reduced corn yields, reflecting heightened drought sensitivity. The study finds that soybeans exhibit better resilience to longer-term moisture indicators, whereas corn yields are more adversely affected by drought conditions. The Palmer Drought Severity Index (PDSI) shows a stronger correlation with soybean yields than with corn yields. The findings indicate that corn is generally more susceptible to drought than soybeans in the study region. These insights can inform decision-making for drought relief efforts, farm management strategies, and grain market planning, enabling stakeholders to address potential drought conditions proactively.