|GOEBEL, TIMOTHY - Texas Tech University|
Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2018
Publication Date: 1/17/2019
Citation: Goebel, T.S., Lascano, R.J. 2019. Rainwater use by cotton under subsurface drip and center pivot irrigation.. Agricultural Water Management. 215(C):1-7. https://doi.org/10.1016/j.agwat.2018.12.027.
Interpretive Summary: As water for irrigation from the Ogallala Aquifer decreases, farmers will need to use both rainfall and irrigation-water more efficiently. Further, in selecting an irrigation system the local rainfall distribution and amount needs to be considered. In the Texas High Plains (THP), sub-surface drip irrigation and center pivot sprinkler irrigation are the two most popular irrigation systems used in crop production. For example in cotton both irrigation systems, when properly used, are capable of achieving similar levels of lint yield/acre and the question of interest was, which of these two irrigation systems would make better use of rainfall during the growing season? We scientists from ARS (Lubbock, TX) and Texas Tech University compared the rainwater use by cotton under these two irrigation systems and results showed that when rainfall is infrequent the cotton crop irrigated with a center pivot sprinkler system used more rainwater than the crop irrigated with a sub-surface drip irrigation system. In the THP, this result has implications for the selection of an irrigation system to make better use of rainfall as we transition from irrigation to rainfed cropping systems.
Technical Abstract: To increase the efficiency by which agronomic crops use water from both irrigation and rain during the growing season requires quantifying the proportion of rainfall used by the crop for a rain event. The rainfall pattern in the Texas High Plains (THP) is characterized by isolated thunderstorms of high rates and of short duration, where < 1 % of the storms produce rain events > 50 mm and 80 % of total rain events are < than 13 mm. The primary source of irrigation-water in the THP is pumped from the Ogallala Aquifer (OA), which has a different isotopic (d18O) signature compared to rainfall-captured water. Given this difference, it is feasible to quantify changes in the d18O signature of the plant water as the plant uptakes the rain- and irrigation-water stored in the soil. To this end, cotton (Gossypium hirsutum L.) was grown and irrigated with subsurface drip and center pivot and also under dryland conditions. The irrigation-water was pumped from the OA and rainfall was collected in a rain gauge with mineral oil to prevent evaporation. Additionally, plant and soil samples were collected before and after each rain event. Thereafter, water was extracted from the collected soil and plant samples using cryogenic vacuum distillation and analyzed for '18O (‰) using a Liquid-Water Isotope Analyzer. The difference in isotope concentrations in the extracts showed a change d18O (%) of the cotton petiole water toward that of the rainwater signature of 17% for sub-surface drip, 32% for dryland, and 63% for center pivot irrigation. These results imply that the application of irrigation-water with a center pivot results in increased rainwater use in cotton compared to sub-surface drip.