Abstract
The Songnen Plain, whose climatic conditions are perfectly suited to sugar beet growth, is located in northeastern China. Unfortunately, this region has a lot of saline-alkaline land, which is the most important factor limiting sugar beet production. This study was undertaken to determine whether biochar-based organic fertilizer could alleviate the negative effect of saline-alkaline soil on sugar beet yield and whether such an effect correlated with changes in nitrogen assimilation, antioxidant system, root activity, and photosynthesis. Three treatments were established: Chemical fertilizers were applied to neutral soil (CK), chemical fertilizers were applied to saline-alkaline soil (SA), and biochar-based organic fertilizer was applied to saline-alkaline soil (SA + B). Our results showed that saline-alkaline stress significantly inhibited the nitrogen assimilation and antioxidant enzymes activities in root, root activity, and photosynthesis, thus significantly reducing the yield and sugar content of sugar beet. Under saline-alkaline conditions, the application of biochar-based organic fertilizer improved the activities of nitrogen assimilation enzymes in the root; at the same time, the antioxidant enzymes activities of the root were significantly increased for improving root activity in this treatment. Moreover, the application of biochar-based organic fertilizer could improve the synthesis of photosynthetic pigments, PSII (Photosystem II) activity, stomatal opening, and photosynthesis of sugar beet under saline-alkaline conditions. Hence, the growth and yield of sugar beet were improved by applying biochar-based organic fertilizer to saline-alkaline soil. These results proved the significance of biochar-based organic fertilizer in alleviating the negative effect of saline-alkaline stress on sugar beet. The results obtained in the pot experiment may not be viable in field conditions. Therefore, in the future, we will verify whether biochar-based organic fertilizer could alleviate the adverse effects of saline-alkaline stress on sugar beets yield under field conditions.
Highlights
Soil salinization is a major environmental and ecological problem that restricts agricultural production of the world [1]
The biochar-based organic fertilizer treatment under saline-alkaline conditions maintained higher nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and GOGAT activities compared to the SA treatment at the five stages
A possible reason for this positive effect is that the decomposition of organic matter in biochar-based organic fertilizer maintains a relatively high level of soil inorganic nitrogen throughout the growth period [48], which might improve the absorption of inorganic nitrogen by sugar beet roots to avoid the suppressive nitrogen assimilation caused by saline-alkaline stress
Summary
Soil salinization is a major environmental and ecological problem that restricts agricultural production of the world [1]. Agronomy 2020, 10, 1562 root to absorb nutrients and water), and photosynthetic capacity are some of main saline-alkaline injury symptoms in plants. Under saline-alkaline conditions, undernutrition and poor growth of plants is mainly due to the decrease in these enzymes’ activity in the roots [3]. Unconscionable generation of reactive oxygen species (ROS) is one of the main biochemistry changes in plants under salt-alkaline stress [4]. The antioxidant enzyme system, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), can reduce the damage of ROS to roots, which improves root activity [6]. Inhibition of photosynthetic pigments, gas exchange, and PSII activity under saline-alkaline stress limit photosynthesis, leading to a decrease in dry matter accumulation, which limits crop yield [9]. In order to overcome the adverse effects of saline-alkaline stress on plants, various strategies are being implemented, such as deep plowing, drip irrigation, and the application of amendments and organic fertilizers
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