Effects of nitrogen fertilizer rates on the growth and nutrient utilization of calla lily intercropped with rubber trees

Abstract

Rubber tree (Heveabrasiliensis Müll. Arg.)–calla lily (Alocasiamacrorrhizos L.) intercropping, practiced in Hainan, China, is a new and promising intercropping system suitable for implementation in shaded mature rubber plantations of which the main product is industrial starch. Nutrient competition between rubber trees and calla lilies was significant in this intercropping system, with rubber trees holding a competitive advantage. In addition, nitrogen (N) fertilizer is commonly used in excess in China. Therefore, adequate N supply is the basis of rubber tree–calla lily intercropping systems that reduces inter-species N competition and ensures efficient intercropping. In this study, experiments with monocropping and intercropping systems under five different N application concentrations (0, 100, 200, 300, and 400 kg ha−1) were conducted to assess how the interaction between intercropping and N fertilizer application rates affected the growth, development, distribution of biomass, and nutrient uptake and utilization in calla lilies, using the root barrier method. The results showed that only when the N fertilizer rates were < 200 kg ha−1, intercropping significantly inhibited calla lily growth and development, but significantly increased the number and length of calla lily roots, and allocated more dry matter to the roots. however, intercropping promoted calla lily growth and development at a N fertilizer application rate of 400 kg ha−1. Intercropping increased the phosphorus (P) concentration and decreased the N and potassium (K) concentrations, and lower N fertilizer rates resulted in larger increases in the P concentration. Intercropping decreased N utilization efficiency in calla lilies, whereas adequate N fertilizer increased N utilization efficiency. These results indicated that calla lilies adapted to the intercropping and low N fertilizer rates condition by balancing growth, changing root morphology, and reserving nutrients in roots, and shows that scientific and rational fertilization application rates can eliminate the negative effects caused by intercropping due to nutrient competition. For the long-term success of intercropping calla lily in mature rubber plantations, N fertilizer must be applied to mitigate the adverse effects of interspecific competition. Based on the growth and N utilization efficiency of calla lilies in relation to N input costs, the optimal N fertilizer rate in rubber tree–calla lily intercropping systems is 200 kg ha−1.