Effects of Residue Burial Depth and Rate on Soil Fertility and Pineapple Yield in Tropical Cultivation Systems

Pineapple is widely cultivated in tropical regions, but intensive management and improper residue disposal can accelerate soil degradation and yield decline. To evaluate under-ridge residue burial (URRB) as a soil improvement practice, parallel field experiments were conducted from 2023 to 2024 at two sites in tropical southern China. A two-factor randomized complete block design was used, with two burial rates (half- and full-rate, i.e., 10 and 20 t ha−1) and three burial depths (10, 20, and 30 cm), plus a residue removal control (CK). Compared with CK, URRB generally increased soil pH and the stocks of soil organic carbon and available nitrogen (N), phosphorus (P), and potassium (K), accompanied by higher leaf area index (LAI), total root surface area (TRSA), photosynthetic pigment contents, fruit vitamin C content, and plant N, P, and K accumulation. Increasing burial rate significantly enhanced plant P and K accumulation and fruit yield, while burial at 30 cm produced greater improvements in soil pH, soil organic carbon (SOC), and available N, P, and K stocks than burial at 10 cm and 20 cm. Compared with other treatments, full-rate residue burial at 30 cm depth under the ridge (FD30) most effectively promoted canopy growth, root development, fruit yield, and chlorophyll a content. On average across the two sites, FD30 increased LAI and TRSA by 20.9% and 34.0%, respectively, compared with CK, with significant increases of 20.1% in fruit yield and 25.3% in fruit vitamin C content. Partial least squares path modeling identified positive indirect associations of soil pH and nutrient availability with yield. Although pineapple yield did not differ significantly between FD30 and FD10, SOC, available N, P, and K stocks were significantly greater under FD30 than under FD10. Thus, FD30 is a more promising strategy for improving both soil fertility and pineapple production under the present experimental conditions. This study also provides new insights into crop residue management in tropical cultivation systems.