Conventional fertilization practices can lead to many ecological problems, such as nutrient imbalance, soil acidity, and reduced soil fertility, in natural rubber plantations. To address these challenges, a field investigation was strategically carried out to substitute inorganic fertilizer with organic fertilizer, consisting of six treatments: no fertilization (CK), inorganic fertilizer (NPK), 25% replacement of inorganic through organic (25% manure (M)), 50% replacement of inorganic through organic (50% manure (M)), 75% replacement of inorganic through organic (75% manure (M)), and 100% organic fertilizer (100% manure). The soil physicochemical properties (soil organic carbon (SOC), total nitrogen (TN), mineral nitrogen (N), ammonium nitrogen (NH₄⁺-N), and nitrate nitrogen (NO₃⁻-N)), C:N, pH, and the carbon- and nitrogen-converting enzymes β-1,4-glucosidase (BG), N-acetylglucosaminidase (NAG) and L-leucine aminopeptidase (LAP) were all determined. The partial substitution of inorganic fertilizer with organic fertilizer (i.e., 75% M at surface soil layer) showed higher SOC (14.52 g·kg⁻¹), TN (1.06 g·kg⁻¹), N (20.07 mg·kg⁻¹), C:N (14.63), NH₄⁺-N (10.63 mg·kg⁻¹), and NO₃⁻-N (11.06 mg·kg⁻¹) than NPK and CK. This increase in physicochemical properties after partial replacement of inorganic with organic fertilizer resulted from higher carbon and nitrogen enzyme activities (BG (143.17·nmol·g⁻¹·h⁻¹), NAG (153.96 nmol·g⁻¹·h⁻¹), and LAP (153.48 nmol·g⁻¹·h⁻¹)) compared to NPK and CK. Further, the Pearson correlation and redundancy analysis (RDA) analyses confirmed a significant positive correlation between SOC, N, and soil enzymes. This study presents a new strategy for assessing the impact of partially replacing inorganic fertilizer with organic fertilizer in rubber plantations in tropical regions, mainly by modifying the soil nutrient composition.

Agriculture is increasingly facing major challenges, such as climate change, the scarcity of natural resources, environmental degradation, labor shortages, and changing societal demands. To meet these challenges, there is an urgent need to move towards more sustainable agricultural practices. The aim of this research was to construct the evaluation index system for the sustainable development of tropical agriculture and evaluate the sustainable development level of tropical agriculture in China’s Hainan Province from 1988 to 2020. Eighteen indicators were selected from the four aspects of agricultural resources, the ecological environment, economic conditions, and social conditions to establish an evaluation index system for the sustainable development of tropical agriculture. A combination of the Coefficient of Variation Method (CVM) and the Index Weighted Method (IWM) was applied to evaluate the comprehensive index of the sustainable development of tropical agriculture. The results of our research indicate that there were significant differences in the level of sustainable agricultural development in Hainan in 2020 across counties and cities, with a downward trend from the central mountainous areas to the surrounding coastal areas. The cities and counties of Wuzhishan, Lingshui, and Qiongzhong had a high level of sustainable development, while Sanya, Dongfang, Wenchang, Qionghai, Ding’an, Danzhou, and Haikou had a low level. From 1988 to 2020, the sustainable development level of tropical agriculture in the province gradually improved, with the highest improvement value of the sustainability index (SI) in Wuzhishan, Wanning, Chengmai, Linggao, and Lingshui and the lowest improvement value of the SI in Baisha, Haikou, and Sanya. Indicators such as the use of agricultural mechanization, construction of farmland infrastructure, improvement of crop productivity, investment in science and technology, and investment in agricultural insurance played a positive role in promoting sustainable development. However, the high use of fertilizers, pesticides, and agricultural films per unit area and the increase in agricultural input prices were not conducive to the sustainable development of tropical agriculture. It is suggested to strengthen the construction and protection of farmland quality, improve the farmland ecological environment, promote agricultural scientific and technological innovation, and formulate feasible policies for the sustainable development of tropical agriculture. The results provide a basic theoretical and methodological reference for achieving Hainan’s sustainable development goals and for assessing the sustainable development capacity of tropical agriculture in similar regions.

Conducting suitability assessment for sugarcane cultivation is of great significance for optimizing the sugarcane cultivation structure and industrial layout. In this paper, based on the requirements of sugarcane growth and development on climate, terrain, and other environmental conditions, as well as the influence of natural disasters, a total of 11 specific indicators in terms of climate factor, terrain factor, and disaster factor were selected to construct a sugarcane cultivation suitability assessment system based on the analytic hierarchy process (AHP). Then, using Guangxi Province, China, as an example, a suitability assessment for sugarcane cultivation was conducted using multi-source data on climate, terrain, and hazards over the past 30 years. The results showed that among 11 indicators, including annual average temperature, elevation had the largest contribution rate, followed by precipitation during the period of ≥20 °C, slope, and the autumn drought frequency. From the spatial distribution, 37% of the provincial regions were suitable for sugarcane cultivation, mainly distributed in Chongzuo City, Nanning City, Qinzhou City, and Beihai City. In total, 44% of the provincial regions were moderately suitable for sugarcane cultivation, mainly distributed in Hezhou City, Laibin City, and Liuzhou City. Additionally, only 19% of the provincial regions were unsuitable for sugarcane cultivation, mainly distributed in Baise City, Hechi City, and Guilin City, with the terrain factor being the main influencing factor of sugarcane suitability assessment. In order to make reasonable use of land resources and increase sugarcane yield, it is suggested that sugarcane cultivation areas should be adjusted to the central and southern regions such as Chongzuo City, Nanning City, Beihai City, and Qinzhou City, and other industries should be developed in the northern regions which are not suitable for sugarcane cultivation.

Understanding the water use efficiency (WUE) and adaptation strategies of plants in high-temperature and rainy areas is essential under global climate change. The leaf carbon content (LCC) and intrinsic WUE of 424 plant samples (from 312 plant species) on Hainan Island were measured to examine their relationship with geographical and climatic factors in herbs, trees, vines and ferns. The LCC ranged from 306.30 to 559.20 mg g⁻¹, with an average of 418.85 mg g⁻¹, and decreased with increasing mean annual temperature (MAT). The range of intrinsic WUE was 8.61 to 123.39 μmol mol⁻¹ with an average value of 60.66 μmol mol⁻¹. The intrinsic WUE decreased with increasing altitude and relative humidity (RH) and wind speed (WS), but increased with increasing latitude, MAT and rainy season temperature (RST), indicating that geographical and climatic factors affect the intrinsic WUE. Stepwise regression suggested that in tropical regions with high temperature and humidity, the change in plant intrinsic WUE was mainly driven by WS. In addition, the main factors affecting the intrinsic WUE of different plant functional types of plants are unique, implying that plants of different plant functional types have distinctive adaptive strategies to environmental change. The present study may provide an insight in water management in tropical rainforest.

Leaf stoichiometry effectively indicates the response and adaptation of plants to environmental changes. Although numerous studies on leaf stoichiometry patterns have focused on the mid-latitudes and specific species of plants, these patterns and the effect of the climate change on them across a broad range of plants have remained poorly characterized in hot and humid regions at low latitudes. In the present study, leaf N, P, N:P, C:N, and C:P ratios, were determined from 345 plant leaf samples of 268 species at four forest sites in Hainan Island, China. For all plants, leaf N (3.80 ± 0.20 mg g⁻¹) and P (1.82 ± 0.07 mg g⁻¹) were negatively correlated with latitude and mean annual temperature (MAT) but were positively correlated with longitude. Leaf N was found to be positively correlated with altitude (ALT), and leaf P was positively correlated with mean annual precipitation (MAP). The leaf C:N ratio (278.77 ± 15.86) was significantly correlated with longitude and ALT, leaf C:P ratio (390.69 ± 15.15) was significantly correlated with all factors except ALT, and leaf N:P ratio (2.25 ± 0.10) was significantly correlated with ALT, MAT, and MAP. Comparable results were observed for woody plants. The results suggest that leaf stoichiometry on Hainan Island is affected by changes in geographical and climatic factors. In addition, the low N:P ratio indicates that plant growth may be limited by N availability. Moreover, the significant correlation between leaf N and P implies a possible synergistic relationship between N and P uptake efficiency in the plants of this region. This study helps to reveal the spatial patterns of leaf stoichiometry and their response to global climate change in a variety of plants in tropical regions with hot and humid environments, which may provide an insight in nutrient management in tropical rainforest.