Nitrogen fluxes at the root-soil interface show a mismatch of nitrogen fertilizer supply and sugarcane root uptake capacity.
Globally only ≈50% of applied nitrogen (N) fertilizer is captured by crops, and the remainder can cause pollution via runoff and gaseous emissions. Synchronizing soil N supply and crop demand will address this problem, however current soil analysis methods provide little insight into delivery and acquisition of N forms by roots. We used microdialysis, a novel technique for in situ quantification of soil nutrient fluxes, to measure N fluxes in sugarcane cropping soils receiving different fertilizer regimes, and compare these with N uptake capacities of sugarcane roots. We show that in fertilized sugarcane soils, fluxes of inorganic N exceed the uptake capacities of sugarcane roots by several orders of magnitude. Contrary, fluxes of organic N closely matched roots' uptake capacity. These results indicate root uptake capacity constrains plant acquisition of inorganic N. This mismatch between soil N supply and root N uptake capacity is a likely key driver for low N efficiency in the studied crop system. Our results also suggest that (i) the relative contribution of inorganic N for plant nutrition may be overestimated when relying on soil extracts as indicators for root-available N, and (ii) organic N may contribute more to crop N supply than is currently assumed.
School of Agriculture and Food Sciences, The University of Queensland, QLD, 4072, Australia.
Richard
R
Brackin
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.|Department of Forest Genetics and Plant Physiology, Umeå Plant Science Center, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
Torgny
T
Näsholm
School of Agriculture and Food Sciences, The University of Queensland, QLD, 4072, Australia.
Nicole
N
Robinson
School of Agriculture and Food Sciences, The University of Queensland, QLD, 4072, Australia.
Stéphane
S
Guillou
School of Agriculture and Food Sciences, The University of Queensland, QLD, 4072, Australia.
Kerry
K
Vinall
Sugar Research Australia, 50 Meiers Road, Indooroopilly, QLD 4068, Australia.
Prakash
P
Lakshmanan
School of Agriculture and Food Sciences, The University of Queensland, QLD, 4072, Australia.
Susanne
S
Schmidt
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.|University of Vienna, Department of Geography and Regional Research, Vienna, AT-1090, Austria.
Erich
E
Inselsbacher
D000596:Amino Acids / Q000378:metabolism; D064751:Ammonium Compounds / Q000737:chemistry / Q000378:metabolism; D018556:Crops, Agricultural; D007700:Kinetics; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism*; D009587:Nitrogen Isotopes / Q000032:analysis; D018517:Plant Roots / Q000378:metabolism; D031786:Saccharum / Q000254:growth & development / Q000378:metabolism*; D012987:Soil / Q000737:chemistry*
D000596:Amino Acids; D064751:Ammonium Compounds; D009587:Nitrogen Isotopes; D012987:Soil; D009584:Nitrogen