The Effects of Drip Irrigation on Corn Yield and Soil Salinity in the Arkansas Valley
by Abdel Berrada, Research Scientist, Arkansas Valley Research Center

The sale and transfer of water to municipalities along the Front Range, coupled with recent droughts, have prompted interest in water conservation in the Arkansas Valley of southeastern Colorado (Ark Valley). Furrow irrigation is still the predominant irrigation system in the Ark Valley, but more efficient systems such as drip irrigation are gaining in importance. Drip irrigation is mostly used for the production of vegetable crops such as cantaloupes and onions, which often are rotated with corn. Research in western Kansas has demonstrated the feasibility of subsurface drip irrigation (SDI) for corn production if the system is maintained for 10 years or longer. However, the impact of SDI on salt accumulation in the soil profile and potential crop loss is not well known. Salinity is a serious concern in the Ark Valley and increases from West to East.

A field experiment was initiated at the Arkansas Valley Research Center (AVRC) in 2005 to study the effects of SDI on corn yield and the movement of salts in the root zone. Water was applied through SDI or via furrows as often as possible (full-irrigation regime) or at selected growth stages (deficit irrigation). Other variables were N (0, 60, 120, and 180 lb/acre) and manure rates (0, 10, 20, and 30 T/acre). Drip tapes were placed 8 inches below ground, at 5-foot intervals. Furrows were also 5 feet apart. Corn was planted in late April at approximately 33,000 seeds/acre, in 30-in rows.

There were no significant differences in corn yield between SDI and furrow irrigation (FrI) in 2005 and 2006 (Figure 2), in spite of the fact that 76 and 57 percent more irrigation water was applied with FrI than with SDI in 2005 and 2006 (Figure 1). Full irrigation produced on average 20 bu/acre more corn than deficit irrigation in 2005 (Figure 3). There was no significant difference between the two irrigation regimes in 2006 (Figure 3), probably due to higher rainfall and more targeted deficit irrigation in 2006.
The manure treatments resulted in much higher ECe values than the non-manure treatment of 120 lb N/acre in the top 4 to 12 inches of soil, early in the season (Figure 4). Lower ECe values were observed after corn harvest in 2005 and 2006 (Table 1) due to salt movement and redistribution in the soil profile. In general, there was greater salt concentration (higher ECe) away from the drip tape (located in the middle of the bed) e.g., in the furrow under SDI. Similarly, greater ECe values were measured in the bed center than in the furrow under FrI (Table 1). Another striking difference was the apparent salt accumulation under SDI in the 3 foot to 6 foot depth, compared to FrI, which could be due to the higher leaching potential of FrI. Salt accumulation under SDI is a concern in the Ark Valley, particularly when well water is used (well water is generally more saline than ditch water) and may require periodic flushing.

This study was supported by the Colorado Department of Public Health and Environment (Water Quality Control Division), the Colorado Agriculture Experiment Station, and the Soil Plant Nutrient Research Unit of USDA-ARS in Ft. Collins, Colo.. It will be continued for at least one more year to further assess salt and N movement under SDI and FrI. Concurrently, a new experiment will be started in 2007 to examine in more detail the effects of irrigation scheduling, based on crop ET, on corn DM and grain yield.

Abdel Berrada: Abdel.Berrada@Colostate.edu
CSU Ag. Research Station, Rocky Ford