Factors Affecting Nitrogen Mineralization in Soils Under Waterlogged Conditions.

Changes in precipitation patterns in recent years resulted in flooding or ponding of many farm lands in the North Central Region of the United States. In this work, field^_moist soils and their air^_dried counterparts were incubated at 20 or 30^oC under waterlogged conditions for times ranging from 3 to 15 days, and the amounts of NH₄^_N released was determined. Results showed that the rates of NH₄-N released were greater in air-dried than in field^_moist soils. The mineralization rates of the field^_moist soils were significantly correlated with organic C (r = 0.59^*), organic N (r = 0.69^*), C_mic (r = 0.62^*), and N_mic (r = 0.63^*). The corresponding r values for the air^_dried soils were 0.76^**, 0.87^**, 0.84^**, and 0.85^***, respectively. Estimation of the amounts of N mineralized per hectare of field^_moist soils in one day ranged from 2.2 to 4.9 kg (avg. = 3.3). Those values for air^_dried soils ranged from 5.2 to 26.2 kg (avg. = 15.5). The rates of hydrolysis of six enzyme substrates studied were significantly correlated with the rates of NH₄^_N released in the field^_moist soils. With the correlation coefficients (r) in parentheses, the relationships were amidase (0.82^**), arginase (0.90^***), asparaginase (0.86^***), glutaminase (0.88^***), β^_glucosidase (0.83^**), and β^_ glucosamindase (0.84^**). Q₁₀ values ranged from 1.2 to 1.4 (avg. = 1.3) for the field^_moist soils and from 1.0 to 1.3 (avg. = 1.1) for air^_dried soils. At 10 mmol kg^-1 soil, Cd²⁺, Co²⁺, Cu²⁺, Ni²⁺, Pb²⁺, and Cr³⁺ inhibited the NH₄^_N release. The relative effectiveness of the selected heavy metals varied with the metal and soil used. This study showed that microbial biomass, heavy metals, air drying, organic C and N, and a number of hydrolases play a major role in hydrolysis of organic N in flooded soils.