NITROGEN MINERALIZATION IN A SIMULATED RHIZOSPHERE AS INFLUENCED BY LOW MOLECULAR WEIGHT ORGANIC SUBSTANCES

The influence of three main groups of low molecular weight organic substances (LMWOS) commonly exuded by plant roots into the rhizosphere such as amino acids (AA), carbohydrates (CHYD) and carboxylic acids (CA) on nitrogen mineralization of a loamy soil from Bangladesh were studied under laboratory condition at 25°C for 14 days in a simulated rhizosphere.
For this purpose four different treatments (in three replicates) with addition of artificial LMWOS, namely (1) low molecular weight organic acids (a mixture of malic, tartaric, succinic, citric and lactic acid at a C-ratio of 80:9:5:4:2), (2) carbohydrates (glucose), (3) a mixture of amino acids (a mixture of histidine, valine, glycine and alanine at a C-ratio of 43:35:14:9) along with a (4) control were artificially injected in the simulated rhizosphere under saturated conditions at a rate of 103, 93 and 10 µg C g^-1 soil week^-1 for low molecular weight organic acids, carbohydrates and amino acids, respectively.
N mineralization was assessed by extracting and measuring NO₃^– and NH₄⁺ concentrations at regular time intervals while microbial biomass C (OC_mic) at the end of the experiment.
The OC_mic was significantly higher in all the amended soils compared with control.
The utilization of added OC was highest from AA followed by CHYD and OA. Significant higher N mineralization rate was obtained from AA amended soil whereas OA and CHYD amended soil showed a decrease in N mineralization compared with control soil probably due to N immobilization.
A positive ‘priming effect’ probably developed due to low molecular weight organic substances (LMWOS) amendment.

I International Symposium on Sustainable Vegetable Production in Southeast Asia

S.A. Begum, M.A. Kader, S. Sleutel , S. De Neve

low molecular weight organic substances, nitrogen mineralization, rhizosphere, organic acid, carbohydrates, amino acids

https://doi.org/10.17660/ActaHortic.2012.958.10