Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 8, 1996
Publication Date: N/A
Interpretive Summary: The question of when to initiate crop irrigation to optimize yield and water use efficiency is not answered by irrigation scheduling methods that are designed to control water application during the growing season. Irrigating early in the season may also lower soil temperature which must be offset by the positive effect on crop growth from minimizing water stress. Two beginning times for early season irrigation of cotton were compared in a field study using high frequency drip irrigation. Irrigating early when cotton seedlings had three main stem nodes was compared with delaying irrigation until square initiation when there were seven main stem nodes. Early irrigation decreased soil temperatures in the top 100 cm of soil depth 2 degrees C and increased plant growth compared with delaying irrigation. However, cotton lint production was highest and the amount of water applied was decreased when irrigation was delayed. Therefore there was no benefit from early irrigation of cotton seedlings when an irrigatio was applied within one month before planting.
Technical Abstract: When to begin irrigation is difficult when negative effects of lowered soil temperature must offset positive effects of eliminating water stress. The effect of different starting times for irrigating cotton prior to 1st bloom was investigated in a two-year field study in 1993 and 1994 using high frequency drip irrigation. Early irrigation (EI) started when cotton seedlings had 3 main stem nodes was compared with delayed irrigation (DI-L at square initiation when the number of mainstem nodes was 7. A 2nd delayed irrigation treatment (DI-H) received an initial large irrigation that equalled the cumulative amount applied to the EI treatment during the early irrigation period. During early irrigation a total of 13 cm in 1993 and 12 cm in 1994 were applied by the EI treatment. This was supplemented with rainfall of 10.9 cm in 1993 and 0.7 cm in 1994. Soil temperatures in the top 100 cm of soil depth during the early irrigation period averaged 25 deg. C in the EI treatment compared with 27 deg. C in the DI treatment. During the late irrigation period, average temps. were 24.5 deg. C in the EI treatment but decreased to 25.5 deg. C in the DI treatment. Plant height by 1st bloom was increased by 3 cm in 1993 and 7 cm in 1994 by the EI irrigation treatment. Lint production was highest in the DI-L treatment in both years (1548 and 1630 kg/ha), compared to the DI-H treatment (1467 and 1460 kg/ha), and the EI treatment (1477 and 1481 kg/ha) in 1993 and 1994, respectively. Water use efficiency based on the total of irrigation and rainfall averaged 33, 24, and 24 kg lint/ha-cm, respectively, for the DI-L, DI-H, and EI irrigation treatments. Initiating automated irrigation scheduling before squaring began in cotton increased seedling height but decreased lint yield and the efficiency of total applied water.