The concept of mobile drip irrigation, known as MDI, is to combine the high application efficiency of drip irrigation to a versatile and low maintenance center pivot irrigation system. Instead of sprinkler nozzle packages, a certain length of drip hose corresponding to the design flow rate drags behind the pivot structure.
Although this concept was explored in the early 1980s, several recent design changes have resolved some challenges that have led to an increase in use. The most significant technology that made this concept viable was the availability of pressure compensating emitters with high flow rates. When Kansas State University tested a variant of this technology in 2008, drip hoses did not have pressure compensating emitters. It prevented the system from having a uniform application of water when the hoses ride on top of mature corn plants before going back on the ground. That issue and other design flaws have been addressed with the new designs of MDI. There are currently two vendors offering this technology in the market.
K-State has been conducting research on the latest design of MDI since 2015. Based on field research, we saw about 35% less soil evaporation on MDI compared to low elevation spray application (LESA), with most of that water going into and redistributing across the soil profile. At high well capacities (>600 gpm), there is barely any difference in corn yield between MDI and LESA. When well capacity gets into the lower end, which is between 300 to 150 gpm, then corn yield in MDI is significantly higher than LESA. These results indicate that the concept is working.
However, there are some issues and challenges that MDI users must contend with. To maximize efficiency potential, crops, particularly the tall types like corn and sorghum, must be planted in a circular pattern to avoid the hoses from riding the canopy. Management of MDI is more involved than a typical center pivot system, leaning more toward the management of a drip irrigation system. Since MDI utilizes drip hoses, physical damage and clogging potential are relatively high. The use of a more aggressive filter system is imperative driving the conversion cost higher.
There are, however, some niches that MDI might be able to fill. For fields that have wheel track problems, using MDI might help alleviate the problem. To prevent irrigation water with high salt content or other contaminants from getting into the leaves or plant parts, MDI on a circular-planted field may satisfy that condition. MDI could also work better in some undulating fields with low infiltration rate soils.
Utilizing MDI shows potential in increasing irrigation efficiency and solving some issues with center pivot irrigation systems.
Utilizing MDI shows potential in increasing irrigation efficiency and solving some issues with center pivot irrigation systems. The system still faces some challenges in terms of design, operation and management, including cropping management. It would not be surprising to see more design changes and possibly incorporation of other existing or new technologies in the future.
In the Texas south Plains, water table declines in the Ogallala Aquifer and early season evaporative demand present major challenges to irrigated producers. This has helped motivate the transition of more than 300,000 acres to subsurface drip irrigation from other methods. Researchers at the Texas A&M AgriLife Research Center in Halfway, Texas, are conducting SDI experiments in attempt to answer producer questions and improve overall rainfall and irrigation productivity in this region.
One challenge to wider adoption of SDI is inconsistent cottonseed germination and plant establishment due to traditionally dry overwinter conditions and, in some soils, the difficulty of “pushing” irrigation water upward into the seed germination zone during periods of low rainfall, high temperatures and high wind speeds. During the 2011 Texas drought, after 8 inches of preplant irrigation and well past the optimum cotton planting date, the plan to plant 30-inch spaced crop rows on 60-inch spaced SDI laterals was abandoned. However, single cotton rows were successfully planted directly over SDI laterals in a “skip-row” pattern. Based on this experience and to document methods that might improve crop establishment with SDI, a field experiment having five crop row/SDI lateral configurations, each with two planting dates, was conducted over six consecutive years to determine differences in plant stands, cotton yields, cotton fiber qualities and water productivities (see fig. 1).
Averaged over planting dates and years, the early planted, skip-row and skip-row plus yields at 1,250 and 1,430 lb/acre, respectively, were less than the late planted, traditional treatment at 1,450 lb/acre. Also, irrigation water use efficiencies (known as IWUEs) of skip-row treatments were significantly lower than the traditional treatment. In addition, the every-row configuration with higher initial installation costs increased average cotton yields by 5.1% and IWUE by 6.7% over the traditional crop row/SDI lateral configuration. The 30-50 configuration increased yield by 3.0% over traditional.
Based on these results, use of the traditional or 30-50 planting configurations should be delayed until adequate soil water is obtained through irrigation or rainfall. The skip-row or skip-row plus configurations could possibly be used as a last resort late in the planting window.
Due to its method of water delivery, SDI minimizes irrigation water losses due to evaporation during the preplant and early season periods, resulting in high water storage efficiency particularly important at low irrigation capacity. Experiments were conducted to test this hypothesis using different SDI installation designs and irrigation capacities in adjacent fields on clay loam soils over four- and five-year periods.
Treatments included different levels of preplant and vegetative period irrigations. In both experiments, under seasonal growing conditions ranging from favorable to unfavorable, yields and crop values were only modestly increased by additional preplant irrigations above that required for germination. Among treatments with common preplant amounts, larger irrigation amounts during the vegetative period did not significantly increase yield or crop value in any individual year or any group of years. In growing season groupings, having unfavorable to favorable weather conditions, as seasonal irrigation increased, gross irrigation value decreased. Outcomes were partially attributed to both early season rainfall and weather events that disrupted plant development reducing the value of the “extra” preplant and vegetative irrigation during these years. However, the possibility exists, on heavier soils within the southern High Plains, that SDI productivity can be improved by limiting preplant and early season irrigations under deficit irrigation conditions.
Developments that continue to increase the productivity of SDI systems include improved understanding of the differences in how newer cotton varieties and corn hybrids tolerate water stresses during their growth cycles and the rapid advancement in sensor and communication technologies which can lead to better tools for irrigation management. Research objectives will continue to focus on methods and equipment to elevate both rainfall and irrigation water productivity in water-short environments.