The spatial variability of mineral nitrogen content in topsoil and subsoil

Spatial variability of soil mineral nitrogen Nmin (N-NH4+, N-NO3-) in a soil profile down to 60 cm was determined in a 19-ha experimental field in Prague-Ruzyně for four years. Winter wheat was grown in the years 2000 and 2001, oats in 2002 and mustard in 2003. Root length distribution and depth of the crops were determined at four locations representing different soil conditions within the experimental field. The coefficient of variation as the measure of the variability of nitrate N in topsoil and subsoil (0-30 and 30-60 cm, respectively) in the experimental years ranged between 18-39 and 20-37%, respectively. It was mostly the same or slightly greater in subsoil than in topsoil in respective years. The variability of ammonium N in topsoil and subsoil ranged between 4-58 and 11-27%, respectively. It was similar in topsoil and subsoil, except for autumn 2000. There was a positive relation between nitrate content in top and subsoil on all sampling terms. We did not find a relationship between Nmin contents in experimental years. Spatial dependencies were evaluated on the basis of model variogram parameters. The nugget value expressed as a percentage value of the total variogram's sill was used for the class of spatial dependence determination. When a spatial dependence of the observed factor was found it was within a range of medium-strong dependence. Only in two cases a strong spatial dependence was found. A considerable variability was also found out in the variogram's range, which was between 61 and396 m. All these facts pose a problem for further actions, such as appropriate design of a sampling grid, measured data spatial interpolation and application maps design.