Subsurface Drip Irrigation Research-1

Suat Irmak and Richard B. Ferguson

Subsurface Drip Irrigation (SDI) supplies water directly to the crop root-zone via polyethylene drip lines and emitters. To accomplish this, irrigation laterals are buried below the soil surface, typically between 13 to 20 inches, depending on the soil and crop type, climate, and management practices, etc. With the SDI system, irrigated surface soil evaporation and runoff is minimized. An effective irrigation scheduling program provides the opportunity to supply crop water and nutrient needs directly to the crop root-zone; crops can be "spoon-fed" water and nutrients. The "spoon-fed" characteristic of the SDI system has great potential to minimize or eliminate the movement of water and nutrients below the crop root-zone. With SDI, the irrigation water is filtered and fertigation is mixed at the control station before application to the field. When properly managed, irrigation application losses (drift, soil evaporation, deep percolation, and runoff) with the SDI are significantly lower compared to other irrigation systems.

Potential SDI applications in the High Plains:

• Fields with relatively large slopes
  
• Small and/or odd shaped fields where installation of center pivot may not be feasible
  
• Conversion from surface irrigation
  
• Areas with low-capacity wells

Research with Subsurface Drip Irrigation: Field 1

A 33-acre (1,720 ft wide and 845 ft long) SDI system was installed at the UNL South Central Agricultural Laboratory near Clay Center, NE, in 2004 to study following objectives:

1. Use the system as a demonstration site for clientele to gain first-hand experience with system installation, operation and maintenance, and to monitor irrigation and nutrient management practices throughout the season.
2. Learn more about system hydraulics and behavior.
3. Develop corn and soybean specific SDI best management practices that utilize the automation and fertigation advantages of SDI system to improve profitability while reducing water, energy, fertilizer, and labor.
4. Demonstrate that SDI and reactively scheduled nitrogen fertigation will minimize nitrate leaching due to improper irrigation scheduling and substantially decrease precipitation-driven nitrate leaching.
5. Measure crop evapotranspiration and crop coefficients for SDI-irrigated corn and soybeans.
6. Provide clientele information and practical suggestions on system management

The SDI-1 field is one of the largest SDI research fields in the country. There are 11 treatments (including furrow irrigation treatments, F) and each treatment is replicated four times with the exception of reference treatment (R) which is replicated three times (Figure 1). 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.

Procedures

• Three irrigation levels are being evaluated: 100% ETc, 75% ETc, and 50% ETc, where ETc is crop evapotranspiration determined on a daily basis. Irrigations are applied two or three times a week to replenish soil profile. Soil water content is measured at 18 different locations in different treatments every foot up to 6 feet using profile probe and/or neutron probe soil moisture probe. In addition, soil matric potential is being measured every foot up to 6 feet using Watermark granular matrix sensors and Watermark Monitor dataloggers.
  
  
• Three N management strategies are being evaluated within each irrigation level. These are predominately preplant N (75% preplant/25% fertigation), predominately fertigated (25% preplant/75% fertigation), and a reactive strategy (25% preplant, balance reactive). Nitrogen application rates for these treatments will be derived according to current UNL recommendations. Reactive N applications are based on chlorophyll meter readings taken weekly in target plots from V8 to R2 growth stages, and compared to reference strips to which N is applied at a non-limiting rate. If during this period the ratio of chlorophyll meter readings in target plots relative to reference plot falls below 0.95, N is applied twice a week until the ratio increases above 0.95. This strategy has the potential to more effectively account for soil N mineralized during the growing season than N management strategies which result in a fixed application rate.
  
  
• SDI and nitrogen management strategy treatments are compared to a furrow-irrigated, preplant N treatment, which represents a common system with anticipated lower efficiency of water and N.

The experimental design is a split-split plot with main plots arranged in a randomized complete block, replicated four times (Figure 1). The main effect plots are irrigation level; the secondary effect is the fertilizer strategy. The amount of Nitrogen in different treatments is applied in two different ways: some is injected through the system and some is applied pre-plant.

Treatments

All treatments receive 5 gal/acre 10-34-0 as in-furrow starter at planting, providing 5.7 lb/acre N, 19.4 lb/acre P₂O₅.

1. Furrow - 100% N preplant
2. 100% ET - 25% N preplant, 75% fertigation
3. 100% ET - 75% N preplant, 75% fertigation
4. 100% ET - 25% N preplant, balance reactive

5. 75% ET - 25% N preplant, 75% fertigation
6. 75% ET - 75% N preplant, 25% fertigation
7. 75% ET - 25% N preplant, balance reactive

8. 50% ET - 25% N preplant, 75% fertigation
9. 75% ET - 75% N preplant, 25% fertigation
10. 75% ET - 25% N preplant, balance reactive

11. Reference - 100% ET, 100 lb N/acre preplant, 150 lb N/acre fertigation

Crop and soil management:

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

Soil Practices: Cultivation, Tillage

2004: Field was ridge planted on top of existing ridges from year before and only furrow treatments were ridged to allow furrow irrigation.

2005: Field was slot planted with minimal soil movement due to wet conditions and was cultivated on June 17, 2005. A 4.4 lbs/acre of Force 3G granular insecticide was applied at planting.

The first two years of results showed that the SDI can be a viable irrigation system for irrigating corn in Nebraska soil, crop, and climate conditions. The full irrigation (100% ET) treatments resulted in 235 bu/ac corn yield with 10 in. net irrigation. Promisingly, 50% ET treatments resulted in 204 and 190 bu/ac corn yield in 2004 and 2005 with about 5 in. irrigation water.

Figure 2. Irrigation and Yield - 2004

Figure 3. Irrigation and Yield - 2005

Figure 4. Long-term Rainfall

Figure 5. Rainfall in 2004 and 2005

Acknowledgments:

• University of Nebraska-Lincoln Agricultural Research Division
• The staff at the South Central Agricultural Laboratory (special thanks go to Bill Rathje, Dave Althouse, and Perry Ridgeway)
  
• UNL Burlington Northern Endowment
  
• Diversity D Inc., Brownfield, TX (Special thanks to Ross Roberts)
  
• Netafim-USA

You can read more about subsurface drip irrigation by contacting UNL Extension Publications to purchase Extension Circular EC776-2005. Subsurface Drip Irrigation Field 2

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).