Spatiotemporal Soil Moisture Variability in Corn and Cotton Fields with Uniform Irrigation During the Growing Season

Abstract:

In agro-hydrology, a detailed understanding of soil moisture variations in cropland fields is important for developing precision irrigation strategies that can maximize crop production. This study aimed to investigate soil moisture variability, temporal stability, and factors affecting the soil moisture variability in corn and cotton fields under uniform irrigation during the growing season in the Tennessee Valley region of North Alabama, USA. The remotely-controlled sensors were installed for soil moisture collection in three consecutive soil depths, 0-15 cm, 15-30 cm, and 30-60 cm. In both the croplands, 15-30 cm soil depth showed the least spatial variability. It was found that the coefficient of variation decreases with increasing mean soil moisture in the cotton field, and at 30-60 cm depth in the corn field. A convex upward trend was detected between mean soil moisture and standard deviation at 30-60 cm soil depth in the corn field, and at 0-15 cm in the cotton field. However, no trend was detected in the top two soil layers in the corn field. It was found that variability is soil moisture dependent, not soil depth during the growing season. The temporal stability analysis showed one representative sensor location for the entire soil profile in both the fields during the growing season. The significant Spearman’s rank correlation with mean soil moisture varied from -0.33 (poor correlation) for crop evapotranspiration (ET_c) to -0.95 (strong correlation) for accumulated growing degree days in the corn field, and from 0.23 for pressure to -0.67 for ET_c in the cotton field. The elevation was significantly correlated with mean soil moisture in the corn field, and silt percent and electrical conductivity in the cotton field. This study gives insights into soil moisture variability and provides useful information about temporal stability for adopting precision uniform irrigation scheduling. Due to significant correlations with mean soil moisture, it can be advised that the farmers need to consider studied parameters while scheduling irrigation in crop fields during the growing season.