Potential Role of Foliar Application of Azotobacter on Growth, Nutritional Value and Quality of Lettuce under Different Nitrogen Levels.

Zahra Razmjooei,Asghar Ramezanian,Javad Alizargar,Faezeh Mirazimi Abarghuei,Saeid Eshghi,Mohammad Etemadi

doi:10.3390/plants11030406

Abstract

Vegetables can be treated with biofertilizers as an alternative to chemical fertilizers because of their low toxicity. We investigated the effects of foliar spraying of Azotobacter under different levels of nitrogen (100, 150 and 200 mg/L in nutrient solution) on the growth, nutritional value, nitrate accumulation and antioxidant enzyme activities of hydroponically grown lettuce. The experiment was laid out in a completely randomized design with four replicates in a factorial combination. Plants treated with Azotobacter and 200 mg/L nitrogen had greater leaf area and photosynthetic pigments than plants treated with 200 mg/L nitrogen without spraying with Azotobacter. Increasing nitrogen levels increased leaf number, fresh and dry weights, leaf area and nitrate accumulation in lettuce plants. Peroxidase (POD) activity increased by 95.4% at a nitrogen level of 200 mg/L compared to a nitrogen level of 100 mg/L. Ascorbate peroxidase (APX) activity and leaf phosphorous (P) and potassium (K) concentrations were the highest in plants treated with a nitrogen source of 100 mg/L without foliar application of Azotobacter. As nitrogen levels increased in all treatments, nitrate reductase (NR) activity decreased and reached a minimum at the 200 mg/L nitrogen level. In general, foliar application of Azotobacter sp. can be used to promote plant growth and reduce nitrate accumulation in lettuce.

Highlights

In agricultural areas, modern technologies such as soilless cultured crops, hydroponics and aquaponics are used for vegetable and herb production [1]
The effects of bacterial application and different nitrogen ratios on leaf number, fresh weight and dry weight of aerial parts of lettuce plants were significant at p < 0.01 (Table 1)
Leaf and canopy areas showed significant differences in lettuce plants sprayed with Azotobacter in combination with different nitrogen concentrations under hydroponic culture (p < 0.001) (Table 2)

Summary

Introduction

Modern technologies such as soilless cultured crops, hydroponics and aquaponics are used for vegetable and herb production [1]. The continued use of nitrogen fertilizers has increased the nitrate content in vegetable leaves without improving output, raising the risk of agricultural pollution and negatively affecting human health [4]. To overcome these problems, there is an alternative method of agricultural management, which is often referred to as a challenge for sustainability in agriculture, and ecologically sound means to reduce the use of inorganic fertilizers by organizing programs to increase agricultural productivity, especially in vegetable production. Clean techniques such as biostimulants are considered an alternative source of nutrition for production [1,5]

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