Research progress on the application of water retaining agents in agricultural production

Agricultural water retaining agents are a type of chemical water-saving technology and a water-saving measure for farmland that is in line with China's national conditions. Super Absorbent Polymer (SAP), also known as water absorbent or water holding agent, is a water-soluble polymer with strong hydrophilic groups such as carboxyl and hydroxyl groups and a certain degree of crosslinking. It has strong water absorption, wide material sources, and is easy to produce. It is widely used in agricultural development. Adding water retaining agents to soil can reduce soil bulk density, increase total porosity, improve overall soil permeability, and increase water and fertilizer utilization efficiency. However, in practical applications, water retaining agents are influenced by various factors such as their own properties, soil physical and chemical properties, and natural climate. Therefore, researchers need to increase their research efforts on the impact of water retaining agents on soil moisture and physical properties, actively explore the ways in which water retaining agents can exert persistent effects in soil, and provide strong support and guarantee for efficient utilization of water resources and healthy and sustainable development of agriculture.

Characteristics and mechanism of action of water retaining agent

1.1 Characteristics

1) Water retention and release. In practical applications, water retaining agents form a special dispersion system after absorbing water. In this dispersion system, a large amount of water can be adsorbed, and to a certain extent, the degree of water freedom can be limited, promoting water consolidation, effectively improving soil moisture content, alleviating soil water release rate, and reducing soil water infiltration and loss. Reasonable application of water retaining agents in some areas during the dry season can ensure that the local soil environment is always in a moist state, providing sufficient water for local crops or plant roots. After absorbing water, water retaining agents can maximize the free movement of water molecules, but most of them are effective in addressing the absorption of water by roots during crop growth and development. Based on relevant experimental analysis, the amount of water that water retaining agents need to absorb is generally maintained within a soil water potential of 50 kPa, of which 98% is believed to enable plants to better absorb and apply it. The maximum water absorption capacity of water retaining agents is about 14 kg/m3, while the maximum water absorption capacity of plant roots is generally 17 kg/m3. Therefore, water retaining agents will not cause water in plant roots to flow back into the soil.

2) Long service life and good drought resistance. Under normal circumstances, the service life of polyacrylamide type water retaining agents is 4-6 years. In practical applications, they have a repeated water absorption effect of absorbing water, releasing water, drying, and reabsorbing water. However, after the repeated water absorption process, the water absorption rate of the water retaining agent will be reduced by about 50%, and eventually the water retaining agent may even lose its water absorption function. In addition, the persistence of water retaining agents in soil is directly related to their properties, soil texture, and product dosage.