Effect of glucose amendment on microbial biomass,spelling fertilizer 15N-recovery and distribution in a barley-soil-system

Summary One way to conserve fertilizer N in the plant-soil system is to immobilize it at the time of application by adding a readily available C source and to rely on the microorganisms to remineralize it to meet crop N demand during the season. The present study was conducted to determine the effects of microbial activity due to glucose amendment at the time of fertilization and planting on the distribution of fertilizer ¹⁵N at harvest among various N pools. Glucose C (150 g m^-2) was added to soil at Ellerslie (Black Chernozem) in central Alberta at the time of seeding and fertilization with urea-¹⁵N (7.5 g m^-2). Barley shoot mass, root mass, and root N at harvest in the non-glucose treatment were 1.8-fold, 1.9-fold, and 2.2-fold greater, respectively, than in the glucose treatment. The recovery of ¹⁵N in the soil-plant system was greater in the glucose (82%) than the non-glucose treatment (50%). Likewise, the recovery of ¹⁵N in soil was greater in the glucose treatment (72%) than the non-glucose treatment (22%). In both treatments most soil ¹⁵N remaining at the time of harvest was present as non-microbial organic ¹⁵N, but recovery of ¹⁵N in this pool was 3.4-fold greater in glucose-treated than in non-glucose-treated soil. The microbial response to the glucose addition effectively conserved fertilizer N in the active N phase; however, significant remineralization did not occur to meet plant N demands. Microbial transformations in the soil resulted in a constant ratio of non-microbial organic N formed per unit of microbial N formed and this ratio was not affected by the C amendments.