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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.

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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This work studied the effects, under greenhouse conditions, of six heavy metals (Cd, Co, Cr, Cu, Ni, and Pb) on three leguminous crops representing food, feed, and forage crops commonly grown in Egypt. Metal concentrations ranged from 0 to as high as 4.8 mmol kg -1 soil. Results showed that all three plant parameters measured (dry matter yield, nodulation, and N uptake) decreased significantly with increasing heavy-metal concentrations. Plots of the natural log of each parameter against metal concentration were linear within the ranges studies. From the slopes of these regression lines, the concentration of each heavy metal required to achieve 50% reduction (R 50 ) of each parameter was calculated. In general, the lowest metal concentrations for R 50 were for Cd 2+ and Pb 2+ and the highest were for Cr 3+ and Cu 2+ . Heavy-metal additions to soils should be closely monitored because they can negatively affect nodulation and N nutrition of leguminous crops.

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