保水缓释氮肥水分状态与吸持特征研究

保水肥料的水分有效性不但取决于保水肥料的吸水倍率，还取决于水分在保水肥料中的存在状态及吸持特征。首次用差示扫描量热仪(DSC)和水分特征曲线方法对实验合成的保水缓释氮肥水分状态及吸持特征进行了研究。发现保水缓释氮肥的自由水+束缚水含量随着平衡含水量增大而提高，保水缓释氮肥平衡含水量中94％以上为自由水＋束缚水，其与普通水具有相同或相近的热力学性质，其相当于土壤重力水，毛管水和薄膜水之和，保水缓释氮肥所持水分90％以上是植物有效水。保水缓释氮肥的结合水占5％以下，其相当于土壤吸湿水，是植物难利用水。DSC测定的有效水(94％)和水分特征曲线测定的有效水(91％)十分接近，因此，DSC可作为评价吸水保水缓释肥料有效性快速方法。保水缓释肥料可增加土壤持水量，降低土壤水分蒸发，提高土壤保水和释水量。保水缓释氮肥合成过程中待聚液保温时间是一个重要工艺参数。

State and retention characteristics of water in hydrogel of water-absorbent slow release nitrogen fertilizer

The availability of water retained in water-absorbent fertilizer depends on not only absorbency, but also on state and retention characteristics of water in water-absorbent fertilizer. In the article, Differential Scanning Calorimetry(DSC) and moisture characteristics curve were firstly applied to measure state and retention characteristics of water in Water-Absorbent Slow Release Nitrogen Fertilizer(WASRNF) synthesized in the laboratory. The findings indicate that free and bound water content increased with the increments of equilibrium water content (EWC) of WASRNF, over 94% of EWC in WASRNF is free and bound water which has thermodynamic properties being equal or approximate to that of bulk water, and is equivalent to the sum of gravitation, capillary water and film-like water in soil, 90% of water retained in WASRNF is available for plant use. Less than 5% of the total water retained in WASRNF is non-freezing water which is equivalent to water which is inferior to permanent wilting point of soil, and difficult for plant use. The available water content(94%) in WASRNF measured by DSC is very close to that(91%) of WASRNF measured by water characteristics curve. Thus, DSC is suggested to be a rapid method to estimate the availability of water in WASRNF. Water-holding capacity of soil increased and evaporation reduced and retention and release water increased, the availability of water and nutrients in soil improves while applying WASRNF to soil. The heat preservation time of composite solutions to be polymerized during synthesis of WASRNF is an important process parameter.