Genotypic variation in apparent recovery and productivity of Brassica juncea L. under varying nitrogen levels in poplar (Populus deltoides Bartr.)-based agroforestry system
摘要
Nitrogen management and genotype selection are pivotal determinants of crop productivity and nutrient-use efficiency in agroforestry systems, where tree-crop competition intensifies resource dynamics. This study was conducted to evaluate the growth, productivity, nutrient uptake and nitrogen-use efficiency of Indian mustard genotypes under varying nitrogen levels in a poplar-based agroforestry system. A two-year field experiment was conducted under 4- and 5-year-old poplar plantations using a randomized complete block design. Three Indian mustard (Brassica juncea L.) genotypes—RCH 1, PHR 126 and PBR 357 were evaluated across four nitrogen levels: 0, 100, 125 and 150 kg N ha−1. The poplar canopy exhibited a mean height of 16.7 m, breast-height diameter of 18.1 cm and crown spread area of 18.6 m2, with litterfall contributing 59.44 kg N, 8.28 kg P, 46.08 kg K and 91.50 kg Ca ha−1 during the 5th year of poplar plantation. Genotype PBR 357 consistently outperformed others, recording the highest seed yield (15.21 and 13.02 q ha−1), oil yield, nutrient uptake, agronomic efficiency and apparent recovery across both years. Nitrogen application at 150 kg N ha−1 significantly enhanced yield-attributing traits, increasing siliquae per plant by 33.7–38.6% and seeds per siliqua by 55.0–60.7% over the unfertilized control. Maximum oil yield (6.57 and 5.83 q ha−1) and apparent recovery (79.2 and 73.9%) were also recorded with 150 kg N ha−1. These findings underscore that optimizing genotype-nitrogen interactions; specifically, PBR 357 with 150 kg N ha−1 substantially improves productivity in poplar-based agroforestry, offering a strategic framework for sustainable intensification of intercropping systems.