Wednesday, November 15, 2006

Beyond Hydroponics: Improved procedures for studying rhizosphere effects on plant nutrition.

Julie Chard, Utah State University, Utah State University / Crop Physiology Lab, 4820 Old Main Hill, Logan, UT 84322-4820 and Bruce Bugbee, "Plants, Soils & Biomet. Dept.", Utah State University, Utah State University, Logan, UT 84322-4820, United States of America.

Hydroponic culture has been a cornerstone of plant nutrition since the first studies by Hoagland and Arnon in the 1930’s.  Liquid hydroponic culture, however, almost completely eliminates rhizosphere effects, which can have an enormous effect on nutrient availability.  There are a wide variety of porous substrates, watering methods, and nutrient control methods that might be used to study rhizosphere effects.  We refined media and procedures to optimize five root-zone factors:  1) water/oxygen balance, 2) mechanical impedance similar to field soils, 3) buffered pH, 4) precise control of nutrient concentrations, and 5) ease of removal from roots.  We tested several growth media and found that the method used to pack the columns is as important as the growth medium.  An optimal air/water balance is achieved by using coarse media and watering with small volumes, several times per day, using an automated watering system.  Specialized nutrient solutions and pH control can be used to induce specific nutrient deficiencies, and the rhizosphere pH can be manipulated by changing the ratio of NO3 to NH4.

Handout (.pdf format, 148.0 kb)