Nitrogen Sources Vary in Their Ability to Overcome 2,4-D Antagonism from Hard Water.

Nitrogen Sources Vary in Their Ability to Overcome 2,4-D antagonism from Hard Water

Hard water can antagonize weak acid herbicides like 2,4-D, but antagonism can be overcome by the inclusion of water conditioning agents such as ammonium sulfate (AMS) in tank mixtures. The objective of this study was to determine the influence of various nitrogen sources on 2,4-D antagonism from hard water, and to determine their ability to overcome hard water antagonism. Further, the effect of both an adjuvant rate and a higher fertilizer rate of nitrogen sources on hard water antagonism was explored. Nitrogen sources included AMS, ammonium nitrate (AN), urea ammonium nitrate (UAN), potassium nitrate and urea. All nitrogen sources were added to tank mixtures either at an adjuvant rate (2% w/w or 2.5% v/v) or at a fertilizer rate (24.4 kg N ha^-1). In the greenhouse, dandelions (Taraxacum officinale) were treated with 2,4-D at a rate of 1.6 kg ae ha^-1 in distilled or hard water (600 ppm CaCO₃) with one of the nitrogen source and rate treatments. Adjuvants AMS, UAN, and AN were successful at mitigating hard water antagonism when applied at 2% w/w. At the higher fertilizer rate, UAN and AN eliminated hard water antagonism. Unexpectedly, AMS caused herbicide antagonism when applied at the higher fertilizer rate. Urea and potassium nitrate did not reduce hard water antagonism at either rate. This confirms previous research that AMS, AN, and UAN can be used to overcome hard water antagonism, but also identified that rate is an important consideration. Further, this researched confirmed that urea and potassium nitrate are ineffective at reducing hard water antagonism.  

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