Decrease in soil inorganic nitrogen supply capacity under long‐term areca nut plantations in the tropics

Abstract

Understanding the dynamics and availability of soil nitrogen (N) affected by the conversion of cropping patterns is critical for environmental sustainability, especially in tropical soils with low fertility and high N loss. In this study, the 15 N tracing technology combined with the 15 N tracer model was used to explore the dynamic change of soil N transformation in long-estabished areca nut (Areca catechu) plantations. Areca nut plantations with different ages (2, 5, 10, 14, and 17 years) and paddy fields in the tropical region of China were studied. The results demonstrated that the gross N mineralization rate (M) of areca nut plantation soil was much lower than that of paddy soil. The NH 4 + immobilization (I NH4 ) rate was also significantly reduced in areca nut plantations. Besides, the O NH4 (autotrophic nitrification) in long-term areca nut planted soil decreased significantly with decreasing ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) abundance. Inorganic N supply (INS) capacity of areca nut planted soil was much lower than the paddy soil, indicating declined N supply in long-term areca nut plantations soil. The decline in soil gross N transformations rate and INS capacity of areca nut plantations soil was significantly correlated to reduced levels of TN and soil pH. Thus, agricultural practices that increase the soil pH (e.g., biochar or lime application) and the soil organic matter content (e.g., organic fertilizers) could improve soil INS capacity. K E Y W O R D S 15 N tracing study, gross N transformations, inorganic N supply capacity, long-term areca nut plantations, the 15 N tracer model 1 | INTRODUCTION Driven by economic interests, many agronomic crop farmlands have converted to economic crop farmlands (Lu et al., 2010). The planting area of areca nut, an important economic crop, has increased from 0.56 Â 10 6 ha in 2000 to 1.24 Â 10 6 ha in 2019 worldwide (FAO, 2019). Areca nut yields gradually declined in most regions due to intensive cultivation. Areca nut yield had decreased from 3.23 Â 10 4 kgÁha À1 in 2000 to 2.54 Â 10 4 kg ha À1 in 2019 in China (FAO, 2019). To increase profit, excess fertilizer and water were used in areca nuts plantations, even then, areca nut yield decreased over

Active Soil Organic Carbon Pools Decrease with Increased Time since Land-Use Transition from Rice Paddy Cultivation to Areca Nut Plantations under the Long-Term Application of Inorganic Fertilizer

“…Over the last decades, many croplands in the tropics of China have been converted into areca nut plantations due to their high economic returns [3]. For example, many paddy fields were converted into areca nut plantations in Hainan province, which was accompanied by changes in agricultural practices (e.g., soil moisture and fertilizer inputs) [4]. To increase profit, excess fertilizers and water were used in areca nut plantations than paddy fields; however, nitrogen (N) fertilization may cause soil degradation, nitrogen Agronomy 2024, 14, 946 2 of 11 leaching, and low water and nitrogen use efficiency, especially under high temperature and moisture conditions, ultimately negatively affecting the crop yield [5].…”

“…The fertilizer application rate of paddy fields is generally low, and paddy fields have higher soil C content due to long-term flooding [4]. However, in order to achieve high yield and efficiency, the fertilization inputs of areca nut plantations must be higher than those of paddy fields [4].…”

“…The fertilizer application rate of paddy fields is generally low, and paddy fields have higher soil C content due to long-term flooding [4]. However, in order to achieve high yield and efficiency, the fertilization inputs of areca nut plantations must be higher than those of paddy fields [4]. Differences in management practices (e.g., soil moisture and fertilizer inputs) between paddy and areca nuts resulted in significant differences in soil properties [13].…”