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Changes in precipitation patterns in recent years have resulted in flooding or ponding of many farmlands in the North Central region of the United States. In this work, 11 field‐moist surface soils (0–15 cm) and their air‐dried counterparts were incubated at 30°C under waterlogged conditions for times ranging from 3 to 15 d, and the amounts of NH4–N released were determined. Results showed that, presumably because of slaking effects, the rates of NH4–N release 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, P < 0.05), organic N (r = 0.69, P < 0.05), and microbial biomass C (r = 0.62, P < 0.05) and N (r = 0.63, P < 0.05). The corresponding r values for the air‐dried soils were 0.76 (P < 0.01), 0.87 (P < 0.01), 0.84 (P < 0.01), and 0.85 (P < 0.001), respectively. Estimation of the amounts of N mineralized per hectare of field‐moist soils in 1 d ranged from 2.2 to 4.9 kg (average = 3.3). Those values for air‐dried soils ranged from 5.2 to 26.2 kg (average = 15.5). The rates of hydrolysis of six enzyme substrates studied were significantly correlated with the rates of NH4–N release in the field‐moist soils. The relationships were amidase (r = 0.82, P < 0.01), arginase (r = 0.90, P < 0.001), asparaginase (r = 0.86, P < 0.001), glutaminase (r = 0.88, P < 0.001), β‐glucosidase (r = 0.83, P < 0.01), and β‐glucosaminidase (r = 0.84, P < 0.01). Temperature coefficient (Q10) values ranged from 1.2 to 1.4 (average = 1.3) for the field‐moist soils and from 1.0 to 1.3 (average = 1.1) for their air‐dried counterparts. This study showed that microbial biomass, a number of hydrolases, and slaking seem to play a significant role in hydrolysis of N in temporarily flooded soils.

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The aim of this study was to determine temporary impacts of different fertilization systems on some labile soil biochemical and biological properties following potato monocropping under arid conditions. Field and incubation experiments were conducted to determine specifically soil organic carbon (SOC); dissolved organic carbon (DOC); dissolved organic nitrogen (DON); microbial biomass C (C mic), N (N mic), P (P mic); bacterial and fungi counts; soil resistance index (SRI); net N mineralization (N min); and some enzyme activity. Levels of SOC; DOC; N min , C mic , P mic ; bacteria and fungi counts; and soil respiration (SR) were significantly increased under organic and integrated fertilization systems compared with inorganic nano or NPK fertilization system, while levels of microbial biomass N (N mic) and DON were markedly increased under nano or fertilizers compared to organic or integrated (organic + inorganic) fertilizers. By contrast, higher values of metabolic quotient (qCO 2) were recorded in nano or fertilizer treatments suggesting that microbial biomass was less efficient under high maintenance of soil carbon. Enzyme activities of dehydrogenase (DH), β-glucosidase (βG), and acid phosphatase (Ac-P) were in the order of organic > integrated > inorganic fertilization systems, while enzyme activity of urease (UR) was in the vice versa order. Integrated fertilization system recorded greater levels of SOC; DOC; N min , C mic , P mic ; and SR relative to inorganic fertilizers even though applied at lower rates. It is, therefore, important for soils under monocropping system to poise organic and inorganic fertilization system that enhances soil health and soil organic matter build-up.

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Synchronous effects of biochar on heavy metals stress, microbial activity and nodulation process in the soil are rarely addressed. This work studied the effects, under greenhouse conditions, of selected heavy metals Cd2+, Pb2+ and Ni2+ on soybean plants grown in two different soils amended with biochar, and studied their effect on the microbial and enzymatic activity. As a result of the interference between heavy metals and biochar, biochar overcame heavy metal problems and maintained a microbial population of major groups (bacteria–fungi). There was an increase in the degree of resistance (RS) of the major microbial groups to heavy metals when biochar was added to the soil under study. Numbers of bacterial nodules significantly increased, particularly by using the higher rate of biochar compared to the control, either by adding biochar alone or by mixing it with the selected heavy metals. The arginase activity was increased by 25.5% and 37.1% in clay and sandy soil, respectively, compared to the control. For urease (UR), the activity was increased by 105% and 83.8% in clay and sandy soil, respectively, compared to the control. As a result, considerations of using biochar as a soil amendment should be first priority.

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