JIA-2019-11

2473 ZHANG He et al. Journal of Integrative Agriculture 2019, 18(11): 2472–2482 “Bohai granary” project (Liu et al . 2018) is a good example of wheat growth in saline soils. Yet, the salt-affected soils have been viewed unsuitable for agricultural production because of contents of soluble salts that produce some chemical compounds like Na 2 CO 3 and NaHCO 3 , resulting in high exchangeable sodium and reducing soil properties (Singh et al . 2016). Moreover, salt and water logging stresses tend to happen simultaneously in saline soils (Haddadi et al . 2016). Therefore, the growth of wheat in saline soils can be affected by improper contents of moisture and salinity (Ghobadi et al . 2017; Wang et al . 2017; Zhang X Q et al . 2017). Futhermore, groundwater depth could affect soil moisture and salinity contents of the root zone (Petheram et al . 2008). Accordingly, it has been tried to lower the groundwater table by constructing drainage canals (Liu et al . 2017). Therefore, investigating the relations among the groundwater depth, soil moisture, salinity contents, and wheat growth and yield are vital for the sustainable production of wheat in saline soils. The wheat root system is long, but the root intensive area is at the soil depths of 0 to 40 cm (Gan et al . 2011). The effects of soil moisture stress on crop growth are by the presence of water logging at the lower groundwater depth (Zhang et al . 2018), and drought stress at the deeper groundwater depth. Besides, salts could always exist in saline soils. Wheat grows normally at the middle groundwater depths from 0.70 to 1.65 m (Nosetto et al . 2009). Xia et al . (2016) discovered that the soil relative moisture content (SRMC) had a negative relationship with the groundwater depth. Contrarily, SRMC showed positive relationship with soil depths (Xia et al . 2016; Zhang H et al . 2017). The salinity displayed inverse relationship with the groundwater depth (Zhang H et al . 2017); nevertheless, salinity increased initially then declined under varying soil depths (Xia et al . 2016). There is little data on how the groundwater depth may affect soil moisture and salinity contents. Zhang H et al . (2017) investigated how the groundwater depth affects soil moisture and salinity in the field of cotton. However, it still needs to be elucidated whether the cotton field results are in consistent with the wheat field results, as the two crops grow in totally different growth seasons. The study by Zhang H et al . (2017) did not indicate a clear correlation between moisture and salinity as it requires further investigation. The influence of soil moisture or salinity contents on wheat growth has been well comprehended. Briefly, wheat would not grow well in water stressed conditions (Meunier et al . 2017; Wang et al . 2017). Water logging stress inhibits wheat growth and development (Ghobadi et al . 2017). Similarly, the growth and development of wheat is adversely influenced under salt stress (Zhang et al . 2016; Zhang X Q et al . 2017). However, the combined effects of soil moisture and salinity contents on plant growth are not fully explored. Saqib et al . (2004) conducted a pot experiment on wheat yield, investigating effective spikes, spikelet per spike, and 1 000-grain weight in saline (mixing different amounts of NaCl into soil) and waterlogged (flooding the pots) compacted soil. They illustrated that the grain yield was more reduced under the combined stresses of water logging and salinity than the single stresses of salinity or water logging. Zhang et al . (2013) also investigated the combined effects of soil drought (keeping SRMC at 50–60%) and salinity (mixing seven types of salts into soil) on the growth of cotton in plastic pots. They found cotton root biomass reduced significantly under drought and salt combined treatment. However, these experiments were carried out using plastic pots (the soil in the pots was not with a part of the field soil) by using water and blending different salt compounds into soil. However, in our experiment, the soil in the black polyvinyl chloride (PVC) tubes was with a part of the field soil. Accordingly, it is necessary to confirm the consistency of the results in the greenhouse and field experiments. Zhang H et al . (2017) carried out a similar experiment on the combined effects of moisture and salinity on cotton, and the soil in the PVC tubes was with a part of the field soil. However, the combined effects of soil moisture and salinity on wheat are uncertain. Furthermore, it must be indicated: 1) what is the most sensitive stage of wheat growth to the groundwater depth (combined moisture and salinity stresses), and 2) whether the optimal groundwater depth for wheat and cotton growth is the same in coastal saline soil. In traditional crop fields, the determination of the ditch depth for reducing salinity and water logging is random and without any scientific logic. With respect to the necessity of determining the combined effects of moisture and salinity, as affected by groundwater depth, on wheat growth and yield, this research was conducted. The main objectives of this study were to indicate: 1) how the groundwater depth affects soil moisture and salinity contents; 2) how the combination of soil moisture and salinity contents affect wheat growth and yield; 3) the optimum soil moisture and salinity contents, for wheat growth, as affected by the optimal groundwater depth. 2. Materials and methods 2.1. Site description The experimental site is located at Seed Stock Station of Dafeng for rice and wheat in a coastal saline soil (33°24´N, 120°34´E), Jiangsu Province, China. The basic characteristics of the plough layer soil for the experimental site in 2013 are shown in Table 1. The daily mean