Evaluation of Qualitative Traits of Forage Turnip (Brassica rapa var. rapa) in Intercropping with Basil (Ocimum basilicum) and Influence of Biochar and Vermicompost Application

Intercropping reduces the application of chemical pesticides to control pests and weeds, reducing the environmental risks associated with chemical pesticide application (Himmelstein et al., 2017). Biochar is a soil amendment because of its potential to retain water and nutrients, prevent nitrogen leaching, increase soil fertility, and improve plant growth (Fang et al., 2018; Munoz et al., 2016). Other benefits of vermicompost are increased stability of soil resources, maintenance of production, reduction of environmental pollution, and increased soil biological activity too (Demir, 2019). Therefore, the purpose of this study was to investigate the quality of forage turnip (Brassica rapa var. rapa) leaves in different intercropping ratios of forage turnip and basil (Ocimum basilicum) using biochar as soil amendment and vermicompost.

A biennial study was conducted on the quality performance of forage turnip (Brassica rapa var. Rapa) in the form of split-plot factorial in a randomized complete block design with three replications in the research farm of Islamic Azad University of Karaj in two years (2018-2019). The treatments of this study include: intercropping in four ratio (100% forage turnip (monoculture), 90% forage turnip + 10% basil, 80% forage turnip + 20% basil, 70% forage turnip + 30% basil), in main plots, and vermicompost in two levels (15, 18.5 ton.ha-1) and biochar in two levels (No consumption and 5 ton.ha-1) which was placed in subplots. The forage turnip cultivar was PacFB05. In this study, Photosynthetic pigments were measured by the Arnon  (1967) method, membrane permeability (Ferrat and Loval, 1999), relative moisture content (Bertin et al., 1996), soluble leaf sugars (Sheligl, 1986), catalase (Dazy et al., 2008) and soil respiration (Isermeyer, 1952). Using SAS software (Ver.9) for data analysis of a two-year experiment and analysis of means was done with Duncan’s test in significance at 5% probability level. Excel software was used to plot the graphs.

The results of this study indicated that by increasing the ratio of basil in intercropping, the quality traits of forage turnip leaves increased. Consumption of biochar and application of vermicompost at the level of 18.5 ton.ha-1 increased the quality of forage turnip leaves. The highest chlorophyll a ((17.52 mg.g-1Fw), chlorophyll b (8.76 mg.g-1Fw) total chlorophyll (26.38 mg.g-1Fw), carotenoids (6.91 mg.g-1Fw), relative water content (59.54%), of soluble sugars (69.43%), catalase (0.018 micromole Fresh weight/min) were due to the interaction of (70% forage turnip + 30% basil) × vermicompost 18.5 ton ha-1 × application of biochar. The highest value of membrane stability index was related to 100% forage turnip × vermicompost 15 ton ha-1 (4.85 (mol.ml-1.s-1)). The highest amount of soil respiration is associated with the interaction of vermicompost 18.5 ton.ha-1 × 70% forage turnip + 30% basil with value of 0.28 (micromole.gsoil-1.hour-1)), interaction of biochar ×70% forage turnip + 30% basil (0.32 (micromole.gsoil-1.hour-1)), and interaction of vermicompost of 18.5 ton.ha-1 × biochar 0.31 (micromole. g soil-1.hour-1). Due to the potential of biochar (water and food retention and prevent of nitrogen leaching) it can increase the availability of water and nutrients for the plant, which leads to increased photosynthesis of the plant and thus the quality of forage turnip leaves (Akhtar et al., 2015; Hammer et al., 2015). Vermicompost increases soil organic matter and the uptake of zinc, copper, iron, phosphorus, potassium, and nitrogen in soil. The presence of these elements in the soil and their absorption by the roots increases vegetative growth and leaf production in the plant, which causes the level of light absorption, photosynthetic level, the formation of hydrocarbons in the leaves, and the resulting growth also increases leaf quality (Theunissen et al., 2010).

The results of this study indicated that the application of vermicompost ​​18.5 ton ha-1 and biochar increased forage turnip quality, which is due to the availability of water and nutrients for forage turnip. The best intercropping ratio was related to 70% forage turnip + 30% basil, which can be said to be due to the increase in the percentage of basil and the competition of plants for better use of intercropping components of growth sources such as light, water, and food.