## 4 Discussion  
### Salt Affects Water Movement  
It was reported that the macropores worked as prior water flow channels, which stimulated infiltration to deeper profile, but the empty macroporous structure is difficult to maintain. Based on the above, authors incorporated sandy material into artificial macropores to stabilize the structure [21]. However, the role of sand grains sieved from experimental soil in water transport has not been well analyzed. In addition, the salinity in coastal lands fluctuated periodically due to the incursion of seasonal tidal activity and monsoons [22]. In fact, the domestic coastal saline soils, within west Bohai Gulf, are highly argillaceous with poor permeability. Particularly from May to September, the salt accumulation near surface is severe because of high temperature and strong evapotranspiration, making the soils complicated to restore [23]. Therefore, experimental design in current research differed extremely from the previous ones. Firstly, soil column experiments were conducted to elucidate the roles of sandy particles in enhancing drainage capacity, in which silt and clay were removed from the column center. Secondly, contrasting soils under two salinized levels were selected considering the fluctuation characteristics of salinity. In contrast, in the previous experiments, soils were exposed to slight salinized environments throughout the monitoring stages (i.e., 2.4 g kg\({}^{-1}\) of salt, [PERSON] et al. [21]). Moreover, irrigation for the total plots were carried out simultaneously to ensure the same climate parameters such as temperature, evaporation, and wind, and to thereby simplify measuring process. Finally, a seasonal observation for alfalfa, 2 months approximately, was introduced to investigate its potential significance. In present irrigation events, 25-day observation was conducted. This short-term monitoring came for the following reasons. Primarily, 25 days after irrigation, water movement entered a relatively stable status, and the moisture in each soil layer appeared to be close to the unirrigated farmland area around the study region. Moreover, it was reported that salt accumulating up occurred about 20 days after irrigation under similar soil texture [17]. Although [PERSON] et al. [24] demonstrated that salt accumulation occurred in the 60 th day after irrigation by field crop experiments. This different result could be explained by the 3-time continuous irrigation which made the salt maintain at low values in the initial 40 days of experiments, and the influence of root on salt may also delayed the accumulation process. Higher soil water holding capacity was measured with the increasing of salt content under similar soil texture. This relevant tendency was consistent with the results of [PERSON] and [PERSON] [25]. However, this correlation between salt and improved water environment could not be concluded because the enhanced water holding capacity was relevant to soil  
Figure 6: Aboveground plant biomass of alfalfa under different macropore depth treatments for artificial macropores with sandy fillings (AMSF) method. Control means soils without macropore. Mean values within same initial soil condition followed by different letters are significantly different (\(p=0.05\)). hygroscopic coefficient, which could hardly verify the increase in available water. [PERSON] [26] found that soil hygroscopic coefficient increased to more than 17.9% when salt content was over 7.6 g kg\({}^{-1}\). Meanwhile, with the increasing of soil salt content, wilting coefficient increased [27], and accordingly, the soil available water absorbed by crops was decreased. Therefore, although salt increased the soil water content, the field water environment was not improved because crop water stress was also exacerbated. Subsequent observations for alfalfa verified the above inference, because alfalfa biomass under severe salinized level was less than that of mild salt condition. The salts precipitated at surface would be dissolved and then washed below the rooting zone.