Rice Genomics and Genetics 2024, Vol.15, No.4, 203-211 http://cropscipublisher.com/index.php/rgg 206 3.3 Changes in soil physical and chemical properties Rice cultivation has a significant impact on soil pH. Long-term rice cultivation tends to lower soil pH, as observed in a chronosequence study where soil pH dropped from 8.5 to 6.8 over 700 years of cultivation (Wang et al., 2017). The application of organic manures in combination with chemical fertilizers can alleviate soil acidification, thereby maintaining a more balanced pH level (Chen et al., 2017). The content of soil organic matter (OM) is crucial for maintaining soil health and fertility. Long-term application of manures along with chemical fertilizers has been shown to increase soil OM, which in turn supports higher rice yields and improved soil properties (Chen et al., 2017). The integration of organic and inorganic fertilizers enhances soil organic carbon, contributing to better soil structure and nutrient availability (Iqbal et al., 2019). The nitrogen mineralization rate is a key factor in the availability of nitrogen for plant uptake. Long-term rice cultivation improves soil nitrogen mineralization rates, as demonstrated by higher net mineralization rates in paddy soils compared to non-cultivated soils (Wang et al., 2017). The use of organic manures and crop residues further enhances nitrogen mineralization, supporting sustainable rice production (Kaur and Jp, 2018). The long-term effects of rice cultivation on soil organic nitrogen dynamics are multifaceted, involving changes in nitrogen content, soil physical and chemical properties, and nitrogen mineralization rates. The integration of organic and inorganic fertilizers, along with proper nutrient management practices, is essential for sustaining soil fertility and achieving high rice yields over extended periods. 4 Effects of Rice Planting on Soil Organic Nitrogen 4.1 Positive and negative effects of rice cultivation on soil organic nitrogen Long-term rice cultivation has been shown to significantly impact soil organic nitrogen (SON) dynamics. On the positive side, rice cultivation can enhance soil nitrogen (N) accumulation and availability, which is crucial for maintaining soil fertility and supporting sustainable agricultural practices. For instance, a study on paddy soils in China demonstrated that soil total nitrogen (TN) increased significantly with cultivation time, indicating improved soil N fertility (Wang et al., 2017). Additionally, the application of organic fertilizers in rice fields has been found to increase soil urease and catalase activities, which are beneficial for soil health and crop yield (Liu et al., 2021). However, there are also negative effects associated with long-term rice cultivation. Intensive rice cropping can lead to a decline in grain yield due to decreased availability of soil nitrogen, particularly when nitrogen is bonded to aromatic compounds in soil organic matter, making it less available to plants (Schmidt-Rohr et al., 2004). Furthermore, continuous rice cultivation without proper management can result in soil acidification and nutrient imbalances, which can negatively affect soil health and crop productivity (Figure 1) (Liu et al., 2021). Figure 1 Effects of fertilizers on crop yields (Adopted from Liu et al., 2021)
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