Crop Emergence and Near-Surface Soil Temperature for SDI, LEPA, and Spray Irrigation

Abstract

Soybean emergence, grain yield, seasonal water use, water use efficiency (WUE), and irrigation water use efficiency (IWUE) were compared for four irrigation methods and five irrigation rates during the 2005 season. The irrigation methods were mid-elevation spray applicators (MESA), low-elevation spray applicators (LESA), low energy spray applicators (LEPA), and subsurface drip irrigation (SDI). Irrigation rates were 0%, 25%, 50%, 75%, and 100% of the full crop water requirement. Soybean emergence was less with SDI compared with MESA, LESA, and LEPA for all irrigation rates. Grain yield, WUE, and IWUE were greater for SDI at the 25% and 50% irrigation rates, but MESA resulted in greater grain yield, WUE, and IWUE at the 100% irrigation rate. Near-surface soil temperatures were also measured for each irrigation method but at the 50% and 100% irrigation rates only. Soil temperatures were compared in terms of cumulative soil heat units (CSHU). Early season CSHU were significantly greater for SDI at both the 50% and 100% irrigation rates. At the 50% rate, CSHU for MESA and LESA became greater than SDI by V4 to V6 stage, possibly because SDI plants had greater vigor and increased soil shading. At the 100% rate, CSHU for SDI was greater than MESA or LESA throughout the season. LEPA resulted in the least CSHU at the 50% rate, but had the greatest CSHU at the 100% rate. However, the LEPA results may have been affected by run on and run off of irrigation water due to furrow dike erosion.