Microirrigation continues to grow in various parts of the country as more information about installation, operation, maintenance and irrigation management is developed by scientists cooperating on this project. Expansion of drip-irrigated corn, onion, almonds grapes, apples and poplar trees is related to research efforts.

Micro irrigation has the potential to reduce water use, leaving more water in streams, reservoirs, or groundwater. Surface water contamination of streams by runoff can be less with micro irrigation. Groundwater contamination by nitrate and pesticides can be sharply lower. The environmental benefits of micro irrigation can only be achieved if micro irrigation proves to be economically feasible through reductions in other costs not related to the added costs of the micro irrigation system and improvements in crop yield or quality.

Testing and demonstration of variable irrigation criteria, plant water needs, plant densities and fertilizer requirements provided growers scientific results to optimize their yields of corn, alfalfa, apples, grapes, onions, potatoes, peppers, tomatoes, and other horticultural and seed crops while reducing water inputs.

Plant-based RDI has allowed 40 to 50 percent reductions in irrigation water applied to prune trees, while maintaining or improving economic yields. Water savings in almonds have depended on soil type and depth, with the most substantial water savings on the deepest soils.

Work on grape irrigation for juice has encouraged more grape growers to install drip irrigation systems, especially for newly planted Niagara grapes, a growth component of the industry. Also there has been a significant increase in grower interest in and installations of irrigation systems for apples and wine grapes in the Northeast.

Drip-irrigated onion has demonstrated increases in onion yield and grade on sites that are difficult to irrigate using other systems. The expansion of drip-irrigated onion has been linked to vastly reduced N inputs and no irrigation-induced erosion and associated pollutant runoff. Thirty to 40 percent less water was required using SDI than with surface irrigation systems.

Production function, crop coefficient, and the water use efficiency of corn was established for arid environments under SDI.

The salinity study reveled that corn under subsurface drip irrigation can tolerate higher salinity levels than what is reported in the literature. This is a significant finding in that it will help farmers save water by using poor quality water and lower leaching fraction and achieve a good yield level. Determining the threshold salinity value for corn and the yield reduction per unit of salinity under subsurface drip irrigation will help farmers also develop best management practices necessary when using poor quality water for SDI.

Cooperative work between several states is testing poplar tree clones for productivity using drip irrigation under the constraint of high pH soils. New commercial poplar plantings are being established as a result of this work.

Modeling efforts are underway on soil water movement below and to the side of drip emitters. The effects of soil water movement on soil temperature, salinity, and root distribution are being estimated. Models of crop water use are also being tested.