Soil water and temperature regimes in drip and sprinkler irrigation, and implications to soybean emergence

Irrigation has long been used in agriculture as a primary means of water management. It is well known that water distributions in the soil differ depending on the methods of irrigation. However, it is less clear how soil thermal regimes would change over time and space when irrigation methods are different. A field study was conducted to investigate the interactive effect of soil water and temperature regimes in drip and sprinkler irrigation. The effect of different methods of irrigation on soil water and thermal environment was then used to interpret differences in soybean emergence and seedling growth under the two irrigation treatments. Time domain reflectometry wave-guides and thermocouples were installed in field plots to provide soil water content and temperature measurements. Soybean seeds were planted to assess the emergence and seedling development. Consistent with infiltration theory, soil water contents were higher directly under the drip tapes in drip irrigation, but were relatively more uniform across the whole soil surface in sprinkler irrigation. Although five times more water was used in the sprinkler than in the drip plot, the soil water content at the seed zone was similar. Soil temperature was significantly higher in the drip than in the sprinkler plot, which led to a higher emergence rate and enhanced seedling growth. Drip irrigation not only conserved water but also maintained the soil profile at a higher temperature more favorable for plant emergence and seedling development.