Submitted to: Weed Technology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 2, 1997
Publication Date: N/A
Interpretive Summary: This manuscript describes a simple procedure that provides, to our knowledge for the first time, a direct measurement of the amounts of spray or irrigation water that will be retained by whole corn and cotton plants. This measurement provides fundamental information which should be useful to researchers in (a) irrigation, (b) pesticide efficacy and efficiency (calculations are not possible without this kind of data),(c) chemigation research, (d) water balance calculations, (e) spray adjuvant effects, (f) crop protection chemicals sprayer technology. Previously, researchers in this area have relied on tracer chemicals to calculate spray retention, but the tracer chemicals are likely to mislead because of absorption, preferential deposition or washoff. We believe this direct measurement technique will be adopted and used in a wide range of agricultural research.
Technical Abstract: A spray-table procedure was used to measure the total mass of spray water or mixture intercepted by small whole plants. Corn and cotton plants were grown in 10 cm diameter pots to the four-leaf stage (approximately 50 cm and 25 cm height, respectively). A polyethylene film 'skirt' was sealed around the lower stem of each plant to prevent water entering the pot. Mixtures of water alone, water + 1.1 L/ha crop oil, and water + 1/4% AG-98(R) spreader-activator were applied through cone nozzles operating at 276-345 kPa. Spray volumes of 280 to 28000 L/ha were used to simulate typical agrochemical spray volumes and chemigation volumes. The plant and pot were weighed to the nearest 0.01 g before and after passing under the spray. Leaf areas and shoot fresh and dry weights were measured for each plant. Spray deposition increased linearly with spray volumes up to about 3000 L/ha, after which increasing spray amounts resulted in smaller increases in deposition. In many treatments there was a correlation between plant weight or leaf area and mass of spray deposit. Corn plants were approximately twice as large as cotton in both leaf area and fresh weight, and retained more spray per plant than cotton. Cotton retained more spray per unit of leaf area or fresh weight, however, probably because of the horizontal leaf orientation of cotton. The crop oil had no effect on deposition while AG-98 decreased deposition, apparently because water adhered less to the foliage even though spray droplet spreading was greater. Under field conditions corn and cotton plants of this size would intercept less than 5% and 10%, respectively, of broadcast spray or irrigation water.