Effects of Slow-Release Fertilizer on the Growth and Nutrient Content of Hevea brasiliensis mini-seedling Buddings

This study aimed to investigate the effects of different application methods and release periods of slow-release fertilizer （SRF） on the growth and nutrient content of Hevea brasiliensis mini-seedling buddings, to identify more efficient fertilization strategies for improving mini-seedling buddings quality and propagation efficiency. Using the RY73397 mini-seedling buddings as experimental material, a split-plot design was employed. The main plot was divided into M₁ （topdressing） and M₂ （basal fertilizer） based on the application method of slow-release fertilizer. The sub-plot was set up according to different slow-release periods as F₀ （no fertilizer） and F₁ to F₅ （corresponding to slow-release fertilizers with release periods of 1 to 5 months, with a fertilizer application rate of 1.0 g per plant）. Growth parameters, leaf nutrient content, physiological indicators, and field planting performance of the mini-seedling buddings were monitored. Principal component analysis （PCA） was used to evaluate the comprehensive quality of the mini-seedling buddings. The results showed that M₁ was overall superior to M₂ in terms of plant height, stem diameter, biomass, average leaf spacing, leaf area, leaf SPAD value, seedling survival rate, and leaf N, P, Ca, and starch content. Variance analysis indicated that application method (M), slow-release period (F), and their interaction (M × F) had significant or highly significant effects on most indicators. Correlation analysis shows that the growth indicators of mini-seedling buddings are a complex interaction network with nutrient elements, exhibiting synergistic promotion. Soluble sugar shows a significant negative correlation with growth indicators and P content, reflecting resource allocation competition or metabolic negative feedback regulation. Principal component analysis extracted 5 principal components, with a cumulative contribution rate of 87.79%. The comprehensive scores were calculated using the contribution rate as the weight, and it was evaluated that M₁ was superior to M₂, with M₁F₄ having the highest score (2.86). The plant height (71.53 cm), biomass (100.21 g), leaf area (110.95 cm²), leaf Ca content (0.93%), and seedling survival rate (91.75%) of M₁F₄ were all at their maximum values, followed by M₁F₃ (1.21) and M₁F₁ (0.80). Applying slow-release fertilizer scientifically can improve the seedling quality and planting survival rate of rubber trees, with the best effect achieved by using slow-release fertilizer with a release period of 4 months.