The effect of soil moisture on mineral nitrogen, soil electrical conductivity, and pH

Inorganic nitrogen in the soil is the source of N for non-legume plants. Rapid methods for monitoring changes in inorganic N concentrations would be helpful for N nutrient management. The effect of varying soil moisture content on soil mineral nitrogen, electrical conductivity (EC), and pH were studied in a laboratory experiment. Soil NO3-N increased as soil water-filled pore space (WFPS) increased from 0 to 80 cm(3) cm(-3). At soil moisture levels greater than 80 cm(3) cm(-3), NO3-N concentration declined rapidly and NH4-N concentration increased, likely due to anaerobic conditions existing at higher WFPS levels. Soil pH did not change as soil moisture increased from 100 g kg(-1) to 400 g kg(-1) and increased from 6.2 to 6.6 at higher levels of soil moisture. Soil EC was correlated with soil mineral N concentration when measured in situ with a portable EC meter (R-2=0.85) or in the laboratory as 1:1 soil water slurries (R-2=0.92). Results suggest that EC can be used to rapidly detect changes in soil inorganic N status in soils where salts and free carbonates are not present in large amounts.