The influence of pruning height on symbiotic nitrogen fixation in a tree-based fodder production system.

Woody species, especially dinitrogen-fixing species, can provide multiple products including food, fuelwood and fodder. In cut-and-carry silvopastoral systems, woody trees are often severely pruned for harvesting nitrogen (N)-rich fodder. However, very few studies have assessed the influence of this management practice on symbiotic N2 fixation. The study was conducted at Fountainhill Estate, Wartburg, South Africa, to assess the influence of pruning height on N₂ fixation of pigeon pea (Cajanus cajan) using the ¹⁵N natural abundance method. Pigeon pea was grown in association with Panicum maximum. The treatments were unpruned, and pruning at 60 or 90 cm height. Results showed that pruning at 60 cm height significantly decreased total N (P ≤ 0.05), percentage of N derived from atmospheric N₂ (P ≤ 0.05) and amount of N₂ fixed (P ≤ 0.05) compared with unpruned plants and those pruned at 90 cm height. It was concluded that harvesting fodder at 90 cm height should be practised for pigeon pea to optimise symbiotic N₂ fixation. [ABSTRACT FROM AUTHOR]