Use of ion exchange membrane to assess soil N supply to canola as affected by addition of liquid swine manure and urea

A growth chamber study was conducted using two Saskatchewan soils to evaluate how addition of urea and swine manure affects the supply of plant-available nitrogen (ammonium and nitrate) and its relationship with plant N uptake. Treatments consisted of two different N rates applied as urea and manure (100 and 800 mg N kg−1) and a control. Ion exchange membrane probes were used to measure plant-available N supply rate. Canola was grown under the same environmental conditions to determine plant N uptake. Additions of fertilizer and manure significantly increased the supply of plant-available N measured in the soil. Over an 84-d period the available N supply in the manured soil was about 40% lower than in the urea-fertilized soil at equivalent rates of total N addition due to incomplete mineralization of organic N in the manure. However, plant N uptake was similar between manure and urea-treated soils, which was attributed to other nutrients present in the manure that may have enhanced root growth and plant N uptake. High proportions of ammonium N were measured initially, especially at the high rates of urea and manure. However, inorganic N in the form of ammonium rapidly decreased with time and nitrate N became the main inorganic N form supplied. Overall, there was good correlation (r value 0.79 to 0.96) between plant N uptake and available N supply rate in the soil as measured by ion exchange membrane. Key words: Ion exchange membrane, available N supply rate, urea, swine manure, canola, plant N uptake