Optimizing shade and nitrogen for profitable Ficus hirta Vahl. in rubber-based agroforestry

Rubber-based agroforestry is key for diversifying farmers’ incomes and sustaining rubber plantations, particularly considering globally low natural rubber prices. The integration of Ficus hirta Vahl. (FHV), a medicinal plant in China, into rubber plantations has garnered increasing attention, but knowledge on the subject remains limited. This study compared the effects of three shade conditions, namely, deep shade (DS), canopy shade (CS), and proximity shade (PS), and five nitrogen application rates (0, 150, 225, 300, and 375 kg ha −1 ) in two field trials conducted in Hainan, China, from 2020 to 2022. The FHV yields under DS, CS, and PS were 1467.80, 3058.71, and 15,437.50 kg ha −1 , respectively. The PS resulted in a significantly higher yield and did not compromise the medicinal quality, including the contents of psoralen, bergamolide, flavonoids, and polyphenols. The PS also resulted in the highest net profit (60,950 CNY ha −1 ), whereas DS and CS yielded negative economic returns. The superior productivity of FHV under PS was investigated based on its growth dynamics, photosynthetic characteristics, and improved light penetration and soil conditions. Additionally, a nitrogen application rate of 225 kg ha −1 generated the highest returns, and optimal medicinal quality and nitrogen use efficiency were achieved at 150 kg ha −1 . Higher nitrogen rates (300 and 375 kg ha −1 ) did not significantly enhance yield or quality. In conclusion, FHV performs well under PS conditions, and the nitrogen application rate should be capped at 225 kg ha −1 to maximize the output. These results provide insight into the rubber–FHV model, promoting its sustainable development in Hainan, China. • FHV grown in partial shade leads to profitable high yields in rubber plantations. • Nitrogen application enhances yield and profitability of FHV compared to controls. • Excessive nitrogen input reduces fertilizer efficiency and affects FHV yield. • Optimal nitrogen application rate for maximizing yield and profit is 225 kg ha −1 . • The Rubber-FHV agroforestry system is a sustainable choice at early growth stages.