Optimizing sowing date to mitigate loss of growing degree days and enhance crop water productivity of groundwater-irrigated spring maize

Abstract

Groundwater irrigation (GWI) decreases soil temperature and increases crop growth duration and water consumption. Optimizing sowing dates offers a cost-effective solution to mitigate these effects. This study evaluated five sowing date treatments for spring maize: GWI on April 20 (GW420), April 25 (GW425), April 30 (GW430), May 5 (GW505), and May 10 (GW510), with surface water irrigation (SWI) on April 20 (SW420) as the control. The evaluated parameters included soil temperature at 5 cm depth (T5), soil-temperature-calculated growing degree days (GDDs), actual crop evapotranspiration (ETc-act), leaf area index (LAI), grain filling, grain yield, and crop water productivity (WPc). GW420 decreased daily maximum T5 by 1.8°C (P<0.05) and daily average GDDs accumulation by 5.9 % and increased the growth duration by 7.8 d and ETc-act by 33.2 mm compared to SW420. GW420 also delayed LAI growth and decreased the weight of maximum grain filling rate (Wmax) and maximum grain filling rate (Gmax), reducing mean LAI (LAIave) by 8.7 %, grain yield by 6.7 %, and WPc by 10.2 % (P<0.05). Late sowing compensated for GDDs loss in the GWI treatments, with the highest daily average GDDs accumulation observed in GW505 and GW510 (21.3°C d–1), followed by SW420 and GW430 (20.2–20.3°C d–1), and the lowest in GW420 and GW425 (19.1–19.4°C d–1). Late sowing also shortened growth duration and decreased ETc-act, with GW510 showing a 13.9 d shorter growth duration and GW425, GW430, GW505, and GW510 exhibiting 30.6, 36.0, 57.6, and 70.2 mm lower ETc-act, respectively, than GW420. Moderately late sowing (GW430) enhanced Gmax and maintained the active grain filling period (Tagp). Late sowing increased WPc by 7.9 %, 16.8 %, 17.4 %, and 17.2 % in GW425, GW430, GW505, and GW510 (P<0.05), respectively, compared to GW420. While the grain yields of GW430 and SW420 did not significantly differ, GW430 had a higher WPc than SW420, indicating that moderately late sowing fully compensated for the decline in grain yield and WPc of groundwater-irrigated maize. Entropy-TOPSIS analysis revealed that GW430 is the optimal sowing date for groundwater-irrigated maize in arid regions of northwest China, offering a cost-effective method to mitigate GWI-induced GDDs loss and enhance WPc.

Keywords

• irrigation water temperature
• growing degree days
• sowing date
• maize