Abstract
Evaluations of gross mineralization (MNorg) and nitrification (ONH4) can be used to evaluate the supply capacity of inorganic N, which is crucial in determining appropriate N fertilizer application. However, the relevant research for banana plantations to date is limited. In this study, natural forest and banana plantations with different cultivation ages (3, 7, 10, and 22 y) were chosen in a subtropical region, and the 15N dilution technique was used to determine the gross MNorg and ONH4 rates. The objective was to evaluate the effect of the conversion of natural forests to banana plantations on inorganic N supply capacity (MNorg + ONH4) and other relevant factors. Compared to other natural forests in tropical and subtropical regions reported on by previous studies, the natural forest in this study was characterized by a relatively low MNorg rate and a high ONH4 rate in the soil, resulting in the presence of inorganic N dominated by nitrate. Compared to the natural forest, 3 y banana cultivation increased the MNorg and ONH4 rates and inorganic N availability in the soil, but these rates were significantly reduced with prolonged banana cultivation. Furthermore, the mean residence times of ammonium and nitrate were shorter in the 3 y than in the 7, 10, and 22 y banana plantations, indicating a reduced turnover of ammonium and nitrate in soil subjected to long-term banana cultivation. In addition, the conversion of natural forest to banana plantation reduced the soil organic carbon (SOC), total N and calcium concentrations, as well as water holding capacity (WHC), cation exchangeable capacity (CEC), and pH, more obviously in soils subjected to long-term banana cultivation. The MNorg and ONH4 rates were significantly and positively related to the SOC and TN concentrations, as well as the WHC and CEC, suggesting that the decline in soil quality after long-term banana cultivation could significantly inhibit MNorg and ONH4 rates, thus reducing inorganic N supply and turnover. Increasing the amount of soil organic matter may be an effective measure for stimulating N cycling for long-term banana cultivation.
Highlights
The soil organic carbon (SOC) and total N (TN) concentrations were significantly positively related to CaO, cation exchangeable capacity (CEC), and water holding capacity (WHC) (p < 0.05), and a significant and positive relationship was found between CaO and pH (p < 0.05)
The present study highlights the fact that short-term (3 y) banana cultivation causes increased mineralization and nitrification rates, as well as increasing the turnover rate for inorganic N in the soil, but these rates are significantly reduced with the prolongation of banana cultivation
These results, combined with those of the previous studies, suggest the rapid reduction in soil inorganic N supply when natural forests are converted to economic crop plantations
Summary
Due to the high economic benefits it offers, the banana (Musa nana) has been widely cultivated as a food source of regional populations in subtropical and tropical regions around the world, occupying an extremely important position in local markets [1,2]. Banana plantation area and production have increased from approximately 4.55 million ha and. In. China, banana plantation area and production amounted to approximately 0.36 million ha and 12.0 million tons in 2019 [3]. To increase banana growth and yield, a suitable nitrogen (N) management strategy is required [4], since N is the main element limiting crop growth [5]. The current recommended rate of N fertilizer application for bananas is between 250 and 600 kg N ha–1 , in the form of split application or basal application [6,7]
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