## 4 Discussion  
The effects of covering crops on grape growth and related indicators are mostly caused by the competition of water and nutrients in the soil. [PERSON] et al. [51] planted rye (_Scale cereale_ L.) and annual bromegrass (_Bromus_ L.) between the vine rows (the soil is calcified and dry) in Madrid's 'Syrah' vineyards in Spain. After 8 years of management, the grape growth vigor and other related indicators were measured. The results showed that compared with the treatment of clean tillage, covering crops increased the water competition with the vines, and reduced the yield and the pruning weight. [PERSON] et al. [52] conducted experiments on covering crops in vineyards in southern Portugal (soil type is silty clay soil) for two consecutive years. The results also showed that covering crops increased the water consumption, and decreased the length of the shoots, the leaf area, the pruning weight, and the berry size compared with the control. [PERSON] [53] conducted an experiment of covering purslane in the vineyards in the Minning area of Ningxia (ordinary  
Figure 10: Effects of covering crop on sensory evaluation of ‘Cabernet Sauvignon’ wines. (**a**) wines in the year of 2018; (**b**) wines in the year 2019. * indicates significant differences between the control and covering purslane (\(p<0.05\), \(t\)-test). gray calcium soil sandy land). The results showed that covering crops increased the content of total phosphorus in the soil and the activities of various enzymes, and increased the photosynthetic rate of leaves, while having little effect on the yield per plant. In this study, covering crops reduced the leaf area and the pruning weight, which should increase exposure in the fruiting zone and lead to an increase in the PAR. But the results showed that covering purslane decreased the PAR, the authors speculated that vigorous purslane reduced the reflected light from the floor, and the effect of reducing ground reflected light on PAR was greater than those of vine vigor on PAR, which further led to a reduction in the PAR. The inter-row plants competed with grapes for water and nutrients, reducing the vine vigor, which was consistent with the results of [PERSON] et al. [51]. [PERSON] et al. [54] showed that water stress appropriately can promote the expression of some metabolic genes, and increase the synthesis of the precursors of norisoprenoids in berries. Covering crops had a certain influence on the physical and chemical indexes of grape berries, such as the soluble solids, the titrated acid, the pH value, and the 100 berries weight. The physical and chemical indexes were important to evaluate the quality of the grapes, and the temperature and the light were important factors to affect these indexes. [PERSON] et al. [55] conducted a 4-year covering crop experiment in France, and the results showed that covering crop treatments increased the content of the total soluble solids in the grapes. [PERSON] et al. [56] also showed that covering crop treatment had effects on most of the physical and chemical indexes in grapes, and increased the content of the total soluble solids, but had no significant effect on the titrated acid and pH value. [PERSON] et al. [57] showed that cover crops increased the soluble solid content of 'Cabernet Sauvignon' fruits, but reduced the content of the titrated acid. They speculated that this result was due to the reduced leaf area, the increased canopy gap, the increased light transmittance, and the improved illumination conditions as the results of the competition of the inter-row plants with grapevines for nutrients. The present study showed that covering purslane treatment decreased the total soluble solids in grapes, and increased the titration acid content. Previously, some researchers speculated that plants on the earth's surface had a certain heat preservation effect after covering crops, reducing the temperature differences between day and night. And in the daytime, the temperature of the fruit zone could be reduced to a certain extent [58].