Subsurface Drip Irrigation Research-2

Suat Irmak

This project addresses several key issues related to irrigation management and water conservation in Nebraska. Our overall objective is to study soil-water-plant-atmosphere dynamics of the Subsurface Drip Irrigaion (SDI) system and to determine whether the SDI system, coupled with reduced tillage practices, can counter the effects of limited water conditions in Nebraska farms. Our specific objectives are to:

1. Measure crop water use efficiency (CWUE), water savings, and crop growth and yield for SDI-irrigated corn coupled with three tillage practices: ridge-till, disk-till, and no-till. Crop yield obtained from non-irrigated treatments will be taken into account when quantifying the CWUE.

2. Develop methods to quantify crop evapotranspiration from canopy temperature.

3. Determine optimum irrigation scheduling parameters for SDI-irrigated corn that will result in the minimum or no deep percolation or runoff.

4. Quantify maximum allowable crop water stress that can be imposed on corn without causing significant yield reduction (see examples in Figures 1 and 2). Develop relationship between seasonal maximum crop water stress index (CWSI) and yield of corn. Develop relationships between plant available soil water and CWSI.

5. Measure and/or model surface soil evaporation in irrigation amount and tillage treatments. This will help quantify water savings due to reduced evaporation with the SDI coupled with reduced tillage management practices.

6. Develop and deliver educational workshops on improved water management practices with SDI and on operation and maintenance to attain high efficiencies and maximize system life.

7. The research facility is also being used in a collaborative project to collect good quality data for calibration and validation of the Hybrid-Maize Crop Growth Model.

Research with Subsurface Drip Irrigation: Field 2

An 11 acre SDI system was installed at the UNL South Central Agricultural Laboratory near Clay Center, NE, in 2005. There are 20 treatments and each treatment was replicated three times. The research project was designed as randomized complete block. The SDI laterals were installed 15 inches deep, every other row, in the center of the row. The drip emitters are pressure compensating with 0.26 gal/hr discharge rate. Each replication (plot) is 400 feet long, 8 rows wide on 30 in. row spacing.

Figure 2. Corn grain yield as a polynomial function of the seasonal mean CWSI. As the CWSI increases, the corn yield decreases (Figure from: Irmak, S., D.Z. Haman, and R. Bastug. 2000. Determination of crop water stress index for irrigation timing and yield estimation of corn. Agronomy Journal 92(6):1221-1227).

• Five irrigation levels evaluated were: 125% ETc, 100% ETc, 75% ET, 50% ETc, and non-irrigated treatment, where ETc is crop evapotranspiration determined on a daily basis using the American Society of Civil Engineers Penman-Monteith (ASCE-PM) standardized combination equation and corn crop coefficients.
  
  
• All aforementioned treatments are being studied with three irrigation frequency levels: high, medium, and low. High-frequency treatments are ones being irrigated every day with the exception of weekends and when rainfall exceeds daily crop water requirement. The medium-frequency treatments are irrigated every other day, and the low-frequency treatments are irrigated twice a week. The irrigation frequency effect on crop water use, crop growth, yield, and starch and protein content of the grain are being quantified.
  
  
• The soil water content is measured at more than 20 locations in different treatments every foot up to 6 feet using a neutron soil moisture probe. In addition, the soil matrix potential is being measured every foot up to 6 feet using Watermark granular matrix sensors and Watermark Monitor dataloggers in selected plots.
  
  
• The nitrogen management is based on the soil samples taken every spring using the UNL nitrogen recommendation algorithm.

Crop and soil management:

Soil: Hastings Silt-Loam (Udic Argiustoll) moderately well drained, fine, montmorillonitic and mesic.

Weed control:

Soil Practices: Cultivation, till, etc.:

The field was dryland corn until 2004. After harvest in 2004, the stalks were shredded and the field was cross-ripped twice to a depth of 18 inches. The field was then disked. Ridges were put in using Hawkins "hiller bottoms" so corn could be planted on top of a ridge this year. Disk till plots were tilled on February 28, 2006. They were tilled the second time just before planting in May 2006.

Benefits or results expected and transferability:

Adaptation and application of new irrigation technology to better manage the use of natural resources cannot be achieved without involvement of growers, the NRCS, NRDs, extension personnel, consultants, and other clientele through extension and education programs. We will work to transfer results and experiences of this project through appropriate means to growers, and decision makers. The public, extension educators, NRCS and NRD personnel, and other interested clientele will be given full exposure to the project through field tours and other forms of educational outreach. Project results will be disseminated through different outlets, including: (i) scientific journals for refereed publications, (ii) extension publications (NebGuides and NebFacts), (iii) presentations will relate project findings to interested parties at local, state, and professional national and international meetings, (iv) field days and demonstrations at the experimental sites, seminars and workshops will be organized to share our knowledge and experiences.

Figure 3. Long-term Rainfall

Figure 4. Rainfall in 2004 and 2005

Acknowledgments:

• Natural Resources Conservation District
  
• University of Nebraska-Lincoln Agricultural Research Division
  
• The staff at the South Central Agricultural Laboratory
  
• UNL Burlington Northern Endowment
  
• Diversity D Inc., Brownfield, TX (Special thanks to Ross Roberts)
  
• Netafim-USA
  
• Upper Big Blue Natural Resources District
  

You can read more about subsurface drip irrigation by contacting UNL Extension Publications to purchase Extension Circular EC776-2005. Subsurface Drip Irrigation 1.

Disclaimer: The mention of trade names or commercial products is solely for the information of the user and does not constitute an endorsement or recommendation for use by the University of Nebraska-Lincoln or the author(s).