The effect of water retaining agents on soil

2.1 Impact on soil physical properties

The soil moisture content in soil physical properties is one of the main indicators that directly affects crop growth. The application of water retaining agents can effectively suppress the decrease in soil moisture content above the application layer, and has a good drought resistance effect, with a duration of 15-20 days. In contrast, the soil moisture content below the application layer of water retaining agent and the soil moisture content without water retaining agent decreased significantly. The larger the amount of water retaining agent applied, the more significant the difference.

There are certain differences in the impact of different application methods of water retaining agents on soil moisture content. Related experiments have shown that the application of ditch, hole or mixed application methods in agricultural fields, with a application rate of 45 kg/hm2 and a controlled application depth of 0-20 cm, can significantly increase the soil moisture content at a depth of 0-40 cm, and maintain an increase range of 7.5% to 12.7%. The effect of ditch application is more significant than that of hole and mixed application. Mainly due to the distribution of mixed water retaining agents in shallow soil, expansion and contraction occur after water absorption, which easily leads to the formation of soil pores connected to the atmosphere, resulting in soil moisture loss. At the same time, it is prone to ground crust, greatly reducing rainwater infiltration [4]. In addition, the water retaining agent applied in the cave is relatively concentrated, with a relatively small contact range with the soil and a small water absorption capacity. At the same time, due to the excessive concentration of the water retaining agent, a large expansion force will be formed, resulting in soil pores connected to the atmosphere, greatly increasing the evaporation of soil moisture. Although similar pores may appear in the ditch application method, due to the soil being covered by the water retaining agent, the pores are usually not easily connected to the atmosphere, resulting in slow soil moisture loss.

The effect of water retaining agents on soil physical properties is related to soil texture to a certain extent. With the continuous increase of water retaining agent dosage, the aggregate of sandy soil shows a significant increase, while medium and heavy loam soils have better self aggregation, and the effect of water retaining agents on them is not significant. The mechanism of the increase of soil aggregates mainly lies in that the water retaining agent presents a gel shape after absorbing water, which can effectively bind loose soil particles into clusters. Therefore, the application effect of water retaining agents in sandy loam and clay loam soil is relatively good, mainly because the higher the content of clay particles and organic matter in soil, the more significant the effect of ion exchange, and the more obvious the water absorption inhibition effect of water retaining agents [5].