Soybean Yield, Evapotranspiration, Water Productivity, And Soil Water Extraction Response To Subsurface Drip Irrigation And Fertigation

Authors

Suat Irmak, University of Nebraska-LincolnFollow
James E. Specht, University of Nebraska-LincolnFollow
Lameck O. Odhiambo, University of Nebraska-LincolnFollow
J. M. Rees, University of Nebraska-LincolnFollow
K. G. Cassman, University of Nebraska-LincolnFollow

Date of this Version

2014

Citation

Transactions of the ASABE, Vol. 57(3): 729-748

Comments

Copyright 2014 American Society of Agricultural and Biological Engineers

Abstract

Soybean [Glycine max (L.) Merr.] yield, irrigation water use efficiency (IWUE), crop water use efficiency (CWUE), evapotranspiration water use efficiency (ETWUE), and soil water extraction response to eleven treatments of full, limited, or delayed irrigation versus a rainfed control were investigated using a subsurface drip irrigation (SDI) system at a research site in south-central Nebraska. The SDI system laterals were 0.40 m deep in every other row middle of 0.76 m spaced plant rows. Actual evapotranspiration (ET_a) was quantified in all treatments and used to schedule irrigation events on a 100% ET_a replacement basis in all but three of the eleven treatments (i.e., 75% ET_a replacement was used in two, and 60% ET_a replacement was used in one). The irrigation amount (I_a) applied at each event was 100% of the ET_a amount, except for two 100% ET_a treatments in which only 65% or 50% of the water needed to cover the treatment plot area was applied to enable a test of a partial surface area-based irrigation approach. The first irrigation event was delayed until soybean stage R3 (begin pod) in two 100% I_a treatments, but thereafter they were irrigated with either 100% or 75% ET_a replacement. Two 100% ET_a and 100% I_a treatments also were used to evaluate soybean response to nitrogen (N) application methods (i.e., a preplant method versus N injection using the SDI system). Soybean ETa varied from 452 mm for the rainfed treatment to 600 mm (30% greater) for the fully irrigated treatment (100% ET_a and 100% I_a) in 2007, and from 473 to 579 mm (20% greater) for the same treatments, respectively, in 2008. Among the irrigated treatments, 100% ET_a and 65% I_a had the lowest 2007 ET_a value (557 mm), whereas 100% ET_a and 50% I_a had the lowest 2008 ET_a (498 mm). The 100%, 75%, and 60% ET_a treatments with 100% Ia had respective actual ET_a values that declined linearly in 2008 (i.e., 579, 538, and 498 mm), but not in 2007. Seasonal totals for ET_a versus I_a exhibited a linear relationship (R² = 0.68 in 2007 and R2 = 0.67 in 2008). Irrigation enhanced soybean yields from rainfed yield baselines of 4.04 ton ha^-1 in 2007 and 4.82 ton ha^-1 in 2008) to a maximum of 4.94 ton ha^-1 attained in 2007 with the delay to R3 irrigation treatment (its yield was significantly greater, p < 0.05, than that of the seven other treatments) and 4.97 ton ha^-1 attained in 2008 with the 100% ET_a and 100% I_a preplant N treatment. Seed yield had a quadratic relationship with irrigation water applied and a linear relationship with ET_a that was stronger in the drier year of 2007. Each 25.4 mm incremental increase in seasonal irrigation water applied increased soybean yield by 0.323 ton ha^-1 (beyond the intercept) in 2007 and by 0.037 ton ha^-1 in 2008. Each 25.4 mm increase in ET_a generated a yield increase of 0.114 ton ha^-1 (beyond the intercept) in 2007, but only 0.02 ton ha^-1 in the wetter year of 2008. This research demonstrated that delaying the onset of irrigation until the R3 stage and practicing full irrigation thereafter for soybean grown on silt loam soils resulted in yields (and crop water productivity) that were similar to full-season irrigation scheduling strategies, and this result may be applicable in other regions with edaphic and climatic characteristics similar to those in south-central Nebraska.