Optimizing intercropping selection for coconut plantations based on PAR and agro-climatic zones

Photosynthetically Active Radiation (PAR) plays a crucial role in agriculture. PAR pertains to the specific range of solar radiation wavelengths (typically between 400 and 700 nm) utilized by plants for photosynthesis. The current investigation aimed to assess the distribution pattern of PAR in the understories of various coconut plantations. The study was conducted at substations affiliated with the Coconut Research Institute of Sri Lanka. For this study, seven age categories of CRIC 60 variety, planted in square spacing, were selected. The coconut square (8 m by 8 m spaced near 4 palms in a square arrangement) was subdivided into equal portions (9 × 9 of 1 m), and 81 data points were sampled within each coconut square. All the collected data were analyzed using R and Minitab statistical software. Simple regression analysis was employed to explore the relationships among PAR, age, and height of the coconut palms. Based on the spatial data, spatial distribution maps were generated for PAR distribution patterns across different age categories using inverse distance interpolation. Besides, PAR distribution patterns of the day and descriptive statistics of PAR were also studied. These analyses provided insights into determining the PAR value variation in the square planting systems in coconut plantations with the age of the palms. Furthermore, K-mean cluster analysis was developed further to understand the patterns and trends in the data. Notably, the 1–10, 10–25, and above 25 years age categories were identified as having distinct clusters. Age 1–10 and above 25 years had the highest, whereas 10–25 recorded the lowest light intensity. A comprehensive list of suitable intercrops was compiled by considering photosynthetically active radiation levels in various age groups of coconut plantations and the unique conditions found in different agro-climatic zones in Sri Lanka.