Tuesday, November 14, 2006 - 4:30 PM

Evaluation of Key Soil and Plant Processes Influencing Nitrogen Uptake in DSSAT.

Upendra Singh, IFDC, PO Box 2040, Muscle Shoals, AL 35662

The plant nitrogen (N) uptake component of a crop simulation model is completely dependent on first accurately modeling plant growth, soil and plant water balance, soil carbon and nitrogen dynamics, and coupling of these processes through stress factors that affect daily plant growth. The modeling of plant N uptake and the feedback processes influenced by N are dependent on a multitude of factors.  The challenge for evaluating a nitrogen uptake model therefore requires that: (1) the input data are accurate, (2) the modules for other processes are reliable and validated, and (3) the assumptions of the uptake model are well understood by the user. For instance, in the DSSAT family of crop models, the critical and minimum N tissue concentrations are crop-specific parameters. There is evidence that some new cultivars, particularly genetically modified ones, have different critical and minimum N concentrations. Sensitivity of these parameters will also depend on the supply of N.  The emphasis of this paper is on the plant components that affect the supply of N and the plant demand for N.  However, it is inevitable that environmental and management factors will also influence plant N uptake.  
The role of root quantity and distribution, uptake efficiency of a unit root length, uptake efficiencies of N species, N stress factors, and critical N concentrations as they affect plant N uptake will be explored through sensitivity analyses. The evaluations will be carried out under different weather, climate, and management scenarios. It is envisaged that the results will help direct resources toward research that will fill the existing knowledge gaps and improve N uptake models.