Surfactant Use to Improve Soil Water Distribution and Reduce Nitrate Leaching in Potatoes

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Recent evaluations of soil water use by potato (Solanum tuberosum L.) plants have confirmed that a dry zone develops mid to late in the growing season when potatoes were grown in a ridge and furrow system under sprinkler irrigation on some sandy soils. Although trickle irrigation has been shown to reduce the dry zone in potato hills, a more cost- and labor-effective solution could be the use of a surfactant to change soil water surface tension and thereby promote more uniform water distribution into hills. Water content in surfactant-treated potato hills was compared with no-surfactant―treated hills using data from time domain reflectometry probes collected at 15-minute intervals. In addition, nitrate-nitrogen (NO 3 ― N) concentration in soil water collected 1 m below the crop row with porous cup samplers was evaluated to assess NO 3 ― N leaching below the root zone of potatoes. Data from surfactant applications at 9.35 L ha ―1 at planting with the seed piece in 1998, 1999, and 2003 through 2005 generally resulted in significantly increased movement of water into the dry portion of potato hills and in many cases decreased soil water NO 3 ― concentrations at a depth of 1 m beneath potato hills. Comparison of several surfactants suggested that water movement into the dry zone can be accomplished with a number of different products. Some trends of increased potato yield with surfactant applications as compared with no surfactant were noted in a few cases; but in all cases (P = 0.16―0.24), these were not statistically significant at the 95% level.