Irrigation in Western Kentucky: Initial Results on Soil and Crop Spatial Variation to Improve Water Management.

Spatial and temporal variations of soil properties can be used to improve irrigation management. To determine spatial variations in the soil an analysis was performed in a corn field on a silty loam soil located in Princeton, Kentucky. Soil texture was measured at 96 locations with a distance of 50x50 m at 0-20 and 20-40 cm of depth, and was determined using the pipette method. Electrical Conductivity was measured using a contact sensor Veris 3150 in a wet period (April 2015). Soil water potential and temperature were measured in 48 locations and at three depths (20, 40, 60 cm) using watermark sensors after corn establishment (May 2015). Semivariograms, ordinary kriging and cokriging were performed to analyze spatial variations. Clay content was 19±5% in 0-20 cm and 26±6% in 20-40 cm. A spatial structure was observed in clay content at 0-20 cm of depth; at 20-40 cm the spatial structure was weaker but the sill was similar to the one observed in 0-20 cm. Soil electrical conductivity manifested a strong spatial structure for the deep layer but weak one for the surface. Kriging analysis presented spatial trends in clay content variation at 0-20 cm. Using electrical conductivity as a second variable in cokriging analysis improves the estimation of clay content and also with an increase of sampling locations in electrical conductivity. Measurements after corn establishment presented soil water potential close to field capacity in the three depths (between -27 and -30 kPa) and a temperature of 17-18 ºC, with a weak spatial structure at different depths. These initial results indicated spatial variations in the field that could be considered for a sectored irrigation management. It is expected to observe more variations during the dry part of the season. Using a covariable improves precision to observe soil properties variations in a field.

Key words: Irrigation management, Geostatistics, Soil Physics.