The study of the chemical fertilizer consumption in different countries provides basal data for the decision-making of fertilizer production and for the environmental impact assessment of fertilizer application. Hence, the aim of this research was to study and compare the trend of the chemical fertilizer consumption from 1980 to 2012 in Iran, Turkey, Japan, Germany, France, and the USA. For this purpose, various indices such as application rates (kg ha) of N, P, and K, arable land, and total fertilizer consumption were analysed. Results showed that the application rates of nutrients (N-PO-KO) in Iran, Turkey, Japan, Germany, France, and the USA in 2012 were 100-42-7, 100-42-7, 100-94-60, 100-17-25, 100-13-38, and 100-33-35, respectively. The lowest and highest area under production were observed in Japan with 4.0 million ha (0.033 ha/person) and in the USA with 155.0 million ha (0.51 ha/person) during 2008-2015, respectively. In addition, the highest and lowest application rates of net nutrient consumption were recorded in France and Germany (285 and 285 kg ha) and in Iran (66 kg ha), respectively. Overall, the average net consumption of fertilizers in the studied countries in three recent decades (million tonnes) decreased in the order: the USA (19.282) > France (4.601) > Germany (3.302) > Turkey (1.825) > Japan (1.604) > Iran (1.130). Regarding an estimated 9.2 billion people by 2050, the balanced consumption of nutrients (N-PO-KO) and the principles of optimal consumption of fertilizers are keys for achieving the increased food production, food security, and environmental conservation.

Paddy soils represent the largest anthropogenic wetlands on earth. Soil drying and rewetting that occurs annually inflict significant stress on soil microbial activities in paddy soils. An incubation experiment of 60 years of paddy soil was conducted to simulate the conditions of paddy fields (25 °C and 75% air humidity) during a 16-day incubation time. The effect of drying-rewetting [DRW, with 4 levels: (1) constant soil moisture (CSM), (2) one-stage drought stress (DRW1), (3) twostage drought stress (DRW2), and (4) three-stage drought stress (DRW3)] and how it evolves over 0, 4, 8. 12, and 16 days after incubation on the concentration of available phosphorus (AP), microbial biomass P (MBP) and microbial biomass C (MBC), and respiration rate (RES) was determined using repeated measures analysis (RMA). The results revealed that an increase in the number of drying-rewetting increases MBC and RES. Compared to CSM, frequent drying and rewetting caused an increase in RES, MBC and MBP by 88%, 38%, and 11%, respectively. Drying-rewetting increased microbial biomass C (MBC) and P (MBP) by 24-38% and 11-54%, respectively, during 8-16 days of incubation. Increasing the number of DRW cycles reduced AP concentration (except in DRW1). The decrease in available phosphorus is due to the increase in the intensity of immobilization under these conditions. Positive correlations were also observed between AP and MBP (r = 0.52), and between RES and MBC (r = 0.91). In general, the frequency of moisture in the paddy soil is favorable for increasing microbial activity.