Optimization of onion planting time and variety under Populus deltoides-based agroforestry system in North-Western India

Abstract

Vegetable-based agroforestry is one of the means to diversify from cereal-based intercrops under agroforestry system. Onion (Allium cepa L.) is one of the most important vegetable crops used for consumption in India and the highest foreign exchange earner among the fruit and vegetables. In this context, the current study was carried out to assess the potential of onion varieties under Populus deltoides Bartr. ex Marsh-based agroforestry system. Six onion varieties (POH-1, PRO-6, PRO-7, PWO-2, PYO-1 and Pb Naroya) were evaluated with three planting times (mid-December, end-December and mid-January), under two cropping systems (sole onion and poplar + onion) for two consecutive years during rabi (winter) seasons 2018–19 and 2019–20. Poplar block plantation was established at 8 × 2.5 m with 8 m width in N–S direction. Age of the trees was 4 and 5 years during the respective period of experiment and attained 17.7 cm mean diameter, 15.8 m height and 17.8 m2 crown spread. Onion variety PRO-7 transplanted in mid-December gave maximum average bulb weight (62.1, 70.3 g), bulb diameter (5.49, 5.79 cm) and bulb yield (27.59, 37.89 tha−1) under both poplar as well as in open field conditions. This is attributed to the short duration nature of PRO-7 which completes its life cycle before whole development of poplar canopy. NPV and annuity value of poplar + onion-based system was 28% higher than the conventionally followed poplar + wheat model. Benefit–cost ratio was also reported highest for the present model (2.94) as compared to poplar + wheat (2.74) and sole onion (1.92). Thus, growing of suitable onion variety at appropriate time can enhance the income of poplar-based agroforestry system.