Rice Genomics and Genetics 2024, Vol.15, No.4, 203-211 http://cropscipublisher.com/index.php/rgg 204 combination with inorganic fertilizers has been shown to significantly increase soil nitrogen fractions and improve nitrogen utilization efficiency. Moreover, the inclusion of legumes in crop rotations can enhance soil nitrogen retention and reduce nitrogen leaching (Singh et al., 2018). 2 Study Area and Methods 2.1 Overview of study site The study site for examining the long-term effects of rice cultivation on soil organic nitrogen (SON) dynamics is located in Cixi, Zhejiang Province, China. This region is characterized by uniform marine deposits, providing a consistent landscape and climate for the study (Wang et al., 2017). Additionally, another significant study was conducted at the Central Farm of Odisha University of Agriculture and Technology (OUAT) in Bhubaneswar, India, under the aegis of ICAR, New Delhi (Mukhi et al., 2022). This site is situated in a subtropical climatic region, which is crucial for understanding the broader implications of rice cultivation on soil properties. The climatic conditions in Cixi, Zhejiang Province, are typical of a subtropical monsoon climate, which includes hot, humid summers and mild, dry winters. This climate is conducive to rice cultivation, which requires substantial water availability during the growing season (Wang et al., 2017). Similarly, the Bhubaneswar site experiences a subtropical climate with distinct wet and dry seasons, which is ideal for studying the effects of continuous rice-rice cropping systems on soil properties (Mukhi et al., 2022). The soil in Cixi, Zhejiang Province, is primarily composed of paddy soils derived from marine deposits. These soils are characterized by their high clay content and poor drainage, which are typical of paddy fields (Wang et al., 2017). The soil pH in this region has been observed to decrease from 8.5 to 6.8 with prolonged rice cultivation, indicating significant changes in soil chemistry over time (Wang et al., 2017). In Bhubaneswar, the soil type is classified as acidic Inceptisol, which is known for its low soil organic carbon (SOC) and cation exchange capacity (CEC). The initial soil pH was recorded at 5.8, with low SOC content (4.3 g/kg) and CEC of 3.75 cmol (p+)/kg (Mukhi et al., 2022). These soil characteristics are essential for understanding the nutrient dynamics and the impact of long-term rice cultivation on soil fertility. The study sites in Cixi, Zhejiang Province, China, and Bhubaneswar, India, provide a comprehensive understanding of the long-term effects of rice cultivation on soil organic nitrogen dynamics. The uniform marine deposits and subtropical monsoon climate in Cixi, along with the acidic Inceptisol and subtropical climate in Bhubaneswar, offer valuable insights into the changes in soil properties and nutrient dynamics under prolonged rice cultivation (Wang et al., 2017; Mukhi et al., 2022). 2.2 Research methods The soil samples for this study were collected from various rice paddy fields with different cultivation histories. Specifically, a chronosequence of rice paddy soils (50, 100, 300, and 700 years) was selected from uniform marine deposits in Cixi, Zhejiang Province, China (Wang et al., 2017). Additionally, samples were taken from a long-term experiment site in the coastal areas of Southeast China, where organic materials such as green manure, pig manure, and rice straw had been applied continuously for 10 years (Yu et al., 2020a). Another set of samples was collected from a 32-year field experiment in Nanchang, Jiangxi Province, China, which involved the application of both inorganic and organic fertilizers (Chen et al., 2017). The experimental design involved comparing soil samples from different cultivation periods and treatments to assess the long-term effects of rice cultivation on soil organic nitrogen (SON) dynamics. The study included control samples from salt marsh soils and tidal flat soils to provide a baseline for comparison (Wang et al., 2017). The effects of various organic materials (milk vetch, rice straw, poultry manure) on soil aggregate and density-based fractions were also evaluated (Yu et al., 2020b). Additionally, the impact of different fertilization treatments (chemical fertilizers, organic manures, and their combinations) on soil properties and microbial communities was examined (Chen et al., 2017; Wang et al., 2021).
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