Effect of Saline Irrigation Water on Growth and Productivity Growth of Sugar Beet (Beta vulgaris L.) under Nano Irrigation (Case of Moistube) ^†

Abstract

New technologies have been developed to maximize agricultural production with rational use of water resources, especially salt water. We conducted field experiments using either the Nano Irrigation system or the drip irrigation system on sandy loam soil to examine the response of sugar beet to different levels of saline irrigation water. Replicates (n = 4) of elementary plots, 4 m wide × 5 m long with two irrigation water salinity treatments (S1 = 1.6 dS m⁻¹, S2 = 6.3 dS m⁻¹), were established in a factorial design under Nano Irrigation. Soil chemical properties and morphological and physiological parameters of sugar beet were measured over two sampling periods. Irrigation with saline water resulted in proline accumulation in leaves and decreased chlorophyll content, leaf area, and root yield. The results suggest that irrigation water of 6 dS m⁻¹ could be used to obtain an acceptable root biomass yield without significant short-term salinity issues in the cultivated soil.

1. Introduction

Sugar beet has a reputation among high added value crops for tolerating salt stress well. Although previous studies have investigated the effect of salinity on sugar beet [1,2,3], so far, no studies have been performed on the effects occurring under the Nano Irrigation system. Such studies are vital to fully understand how the sugar beet (a large, fleshy taproot that grows to be large) performs under a Nano Irrigation system and how it responds to the salinity of the water under the system. The “nano” system used in this study is a buried, porous tube irrigation system of relatively new technology (Moistube), and is composed of semi-permeable membranes whose pores are of the order of a nanometer [4]. This study follows two previous field experiments [5], that examined the water-saving abilities and performance of two alternative (fibrilroot) crops under Nano Irrigation. Our experience offers an objective vision of biosaline agriculture to better promote the growth of high added value crops by engaging accumulated knowledge and using technologies developed for the recovery of water and salty soils in arid and semi-arid regions.

2. Materials and Methods

Sugar beet (B. vulgaris L.) was cultivated under salt stress from 3 December 2020 to 25 May 2021. A factorial design was established to produce 11 elementary plots of 20 m², each with two salinity treatments (S1 = 1.6 dS m⁻¹, S2 = 6.35 dS m⁻¹) and distributed as follows: (i) Nano Irrigation with salinity S1 (NS1, n = 4), (ii) Nano Irrigation with salinity S2 (NS2, n = 4), drip irrigation with salinity S1 (GS1, n = 1), and (iii) drip irrigation with salinity S2 (GS2, n = 2). The soil and plant samples were collected after 2 months of treatment (flowering stage) and at the end of the growing cycle (harvest stage). Samples were analyzed at the Soil–Water–Plant laboratory at the Regional Center for Agronomic Research in Agadir.

3. Statistical Analyzes of Data

The data collected were analyzed using a general linear analysis of variance (ANOVA) model and SPSS software (IBM Corp. (Armonk, NY, USA), version 22) to estimate the statistical significance of the mean differences between the salinity treatments. The data were transformed to obtain homogeneity of variances, as necessary, and p-values < 0.05 were considered significant.

4. Results and Discussion

4.1. Changes in Soil Parameters

Figure 1 shows the means for soil electrical conductivity (a) and organic matter content (b) as a function of soil depth, the irrigation system used, and salinity treatments provided at the flowering and harvest stages. Similar organic matter content was reported for the different salinity treatments under both irrigation system treatments. The soil salinity increased considerably at the beginning of the experiment and then decreased, particularly at 5 cm soil depth.

Organic matter and pH remained less influenced. The results of the current study are similar to those of other studies [6,7]. The studied soil has a buffering capacity; thus, the monitoring time is short, in part, to reveal differences in these [8]. Conversely, salt concentration is thought to be the result of high evaporation combined with water irrigation that is insufficient to allow the leaching of these salts into the depth of the soil.

4.2. Effect of Salinity on the Physiological Morphological and Productivity Parameters of the Plant

Figure 2 shows changes in proline content (a), photosynthetic pigment (b), leaf area (c), and root yield (d) in sugar beets at different development stages and as a function of salinity and the applied irrigation systems. The results show that irrigation with saline water resulted in the accumulation of proline in the leaves, and a decrease in chlorophyll content, leaf area, and root yield.

Irrigation water salinity showed significant proline accumulation, reflecting the effect of stress compared to control. Our results are consistent with previous studies on the response of plants to salt stress, which reported an increase in proline under salt stress conditions [9,10]. Similar effects would have resulted in a reduction in sugar beet growth in terms of root yield and leaf area. Our results also showed that sugar beets can grow well under the Nano Irrigation system without any significant compression effect on the buried tubes during root enlargement in the growth stages.

5. Conclusions

The results suggest that the Nano Irrigation system would be suitable for the cultivation of sugar beets, provided that the appropriate placement of the laterals—between the crop rows and at an appropriate depth—is chosen. Acceptable yields of root biomass can be obtained using irrigation water of 6 ds m⁻¹ without having a significant impact on cultivated soils in the short term.