Tree nutrition and productivity changes in mahogany (Swietenia macrophylla King) based agrisilvicultural system in the humid tropics

This study examined the effects of different fertilizer levels on mahogany tree growth and intercrop yield productivity in a six-year-old plantation in Mala, Kerala, India, established in 2009 with a 2.5 × 2.5 m spacing. The trial was laid out in a split plot design in June 2014, with fertilizer levels as main plots and intercrops as subplots in three replications. The trial was repeated for two consecutive years (2014–2016). The various N, P, K fertilizer combinations applied were F₁- 0:0:0; F₂- 50:25:25; F₃- 100:50:50 and F₄- 150:75:75 kg ha⁻¹ yr⁻¹ N, P₂O₅ and K₂O. Tree growth in terms of height, diameter, basal area, and volume, showed a significant increase with rising fertilizer levels. The highest volume production was recorded under the highest fertilizer regimes (F4) (105.28 m³ ha⁻¹) which was approximately 135 per cent higher than the unfertilized control plot (F1: 44.84 m³ ha⁻¹). This clearly indicates that nutrient supplementation at younger ages can markedly increase tree productivity in mahogany. Yet another observation was observed complementarity between mahogany trees and herbaceous intercrops. The positive influence of fertilizer on the tree growth was also reflected in the intercrop yield. The yield reduction in mahogany intercropped plots was compensated by tree fertilization. In summary, this study highlights the rationale for fertilization at younger stages of mahogany growth, which may be desirable for enhancing combined productivity in intercropped scenarios.