Wide variation in nitrification activity in soil associated with different forage plant cultivars and genotypes

There is a growing interest in using plants to manipulate the nitrification rate in soils with the object of reducing losses of nitrogen from the soil-plant system - lower rates of nitrification being associated with reduced leaching of nitrate and reduced emissions of nitrous oxide. Here we screened the potential nitrification rate in soil associated with 126 cultivars from 26 species representing three functional groups used in temperate managed grassland. Plants were grown in pots and the nitrification was measured using two approaches: a) a measure of potential nitrification carried out in the laboratory on soil samples and b) a measure of nitrification in the presence of the growing plants using the ratio of nitrate to ammonium (NO3/NH4) measured on in situ ion exchange membranes after the application of urine. There was about a 2-fold difference among cultivars in nitrification measured using the potential assay and a 10-fold difference using the ratio approach. The ranking of nitrification was different using the two approaches perhaps suggesting that the presence of plants in the ratio approach had an effect on the outcome although further work will be necessary to confirm this. Irrespective of the method used, the results demonstrate substantial differences between cultivars but also within cultivars offering the possibility of selection to enhance plant effects on nitrification.