Date of this Version
Transactions of the ASABE Vol. 55(4): 1223-1238
The effects of full and limited irrigation and rainfed maize production practices on soil water extraction and water use efficiencies were investigated in 2009 and 2010 under center-pivot irrigation near Clay Center, Nebraska. Four irrigation regimes (fully irrigated treatment (FIT), 75% FIT, 60% FIT, and 50% FIT) and a rainfed treatment were implemented. The crop water use efficiency (CWUE, or crop water productivity), irrigation water use efficiency (IWUE), and evapotranspiration water use efficiency (ETWUE) were used to evaluate the water productivity performance of each
treatment. The seasonal rainfall amounts in 2009 and 2010, respectively, were 426 mm (18% below normal) and 563 mm (9% above normal). Irrigation regime impacted soil water extraction pattern, which increased with irrigation amounts. In general, the soil water extraction decreased with soil depth, and the water extraction from the top soil (0-0.30 m) accounted for the largest portion of the seasonal total water extraction as 39%, 42%, 48%, 48%, and 51% of the total extraction under rainfed, 50% FIT, 60% FIT, 75% FIT, and FIT, respectively. The rainfed treatment extracted more water from the 0.60-0.90 m and 0.90-1.2 m layers (19% and 17% of the total, respectively) than all other treatments. In general, the deepest soil layer (1.5-1.8 m) contributed about 5% to 8% to the seasonal total water extraction. The efficiency values for the same treatments varied between the years due to their dependency on the seasonal water supply, water supply impact on water extraction, climatic conditions, and their impact on yield. The CWUE increased with irrigation from 1.89 kg m-3 for the rainfed treatment to 2.58 kg m-3 for the 60% FIT in 2009 and from 2.03 kg m-3 for the rainfed treatment to 2.44 kg m-3 for the FIT in 2010. The CWUE was strongly correlated to actual crop evapotranspiration (ETa) (R2 = 0.99 in both years), irrigation amounts (R2 ≥ 0.97 in both years), and grain yield (R2 = 0.95 in 2009 and R2 = 0.99 in 2010). The IWUE and ETWUE decreased with ETa and the irrigation amounts in 2009, while they showed the opposite trend in 2010.
The IWUE ranged between 3.63 kg m-3 for FIT and 5.9 kg m-3 for 50% FIT in 2009 and between 2.52 kg m-3 for 50% FIT and 3.24 kg m-3 for 75% FIT in 2010. On average, 60% FIT resulted in the largest IWUE of 4.33 kg m-3. The measured ETWUE varied from 4.65 kg m-3 for FIT to 6.09 kg m-3 for 50% FIT in 2009 and from 5.94 kg m-3 for 50% FIT to 6.73 kg m-3 for FIT in 2010. The 60% FIT and 75% FIT had similar or greater CWUE and ETWUE than the FIT in both years. The ETWUE was usually greatest when the ETa was about 580 mm in 2009 and 634 mm in 2010, indicating that in these
experimental, climate, and management conditions, the maximum ETWUE and crop water productivity can be obtained at ETa values smaller than those for the fully irrigated treatment. The 60% and 75% FIT treatments were very comparable to the fully irrigated treatment in terms of productivity performance and are viable supplemental irrigation strategies for increasing crop water productivity of maize while using (withdrawal) 40% or 25% less irrigation water under these experimental, soil and crop management, and climatic conditions.