Cumulative Delayed Irrigation Effects on Corn (Zea mays, L.) Biomass and Grain Yield.

A delayed irrigation/tillage study was conducted from 2001 to 2006 at Akron, CO. Water was applied either to fully meet crop evapotranspiration needs for the entire growing season or irrigation was delayed until tasseling and then water was applied at the same rate as full irrigation. Irrigation treatments were conducted under no-till and chisel plow management. Soil water measurements were made twice weekly by neutron attenuation. Plant biomass was determined at the V6, V12, R1 and R6 growth stages. LAI measurements were made weekly. Water contents in the 0- to 30-cm depth were similar between the fully irrigated and delayed irrigation plots. For the first two years, soil water contents in the 30- to 60-cm and 60- to 90-cm depths declined in the delayed irrigation plots compared with the fully irrigated plots and then remained lower during other years. Overwinter precipitation replenished water in the 0- to 30-cm depth but seldom at deeper depths. Delayed irrigation had no effect on crop yield in 2001 and 2002. Delayed irrigation decreased crop yield by 42% to 55% in 2003 and 2006, respectively. All plots were fully irrigated in 2004 but corn yield was reduced by 25% due to dryer soil conditions caused by previous delayed irrigation. Delayed irrigation reduced plant biomass and LAI. Low LAI at the V6 growth stage was poorly correlated (r²=0.1) to final grain yield, but low LAI at the V12 and R1 growth stages was well correlated (r² = 0.6) with reduced final grain yield. There was no interaction between tillage and irrigation management. Beginning deficit irrigation management with a full soil water profile and beginning irrigation shortly after the V6 growth stage may minimize the detrimental effects of deficit irrigation on corn production.