| With the rapid industrialization and urbanization,the land available for food production has sharply decreased in both its quantity and quality.The desertification,as one of the most serious problems of land degradation,has been widely distributed in more than 30 provincial administrative zones in China.The sandy soil is much variable in size,weak capillarity and loose texture among the particles,which results in bad retention performance and low soil productivity. Although the low productive soil has been developed by force in recent years,the effective control measures are taken deficiently.PAM is one of many water retaining agents,which possesses ultra-intense water absorbing and water retention ability so as to restain the soil water evaporation and increase soil moisture content and enhance the water preserving capability.PAM plays an important role in regulating the water of the sandy soil.Chongqing is in the southwest inland of China,whose terrain is complicated.In recent years, the cultivated land decreased rapidly,so the per capita arable land is in acute shortage.The sandy soil in Chongqing is in a certain percentage,whose exploitation,as the compensation for the occupied farmland,would relieve the pressure from the shortage of farmland in Chongqing somehow.And the growth of crops is threatened by the abnormal climate in Chongqing,such as the hige temprature and the lack of rainfall.Besides the rational use of water resources,water resources conservation are also needed to improve the soil quality and the technical supply for the development of modem agriculture,as well as the recovery of the ecological environment.In this study,the cold sandy yellow clayer soil and alluvial soil were chosen to figure out the effect of different doses and dosage forms of PAM on the water preserving capacity,so as to provide theoretical envidence for the spread and exploitation of PAM on the agricultural irrigation.The conclusions as follows:PAM did restrain the soil water evaporation.Compared with the control,the accumulated evaporation of cold yellow clayer soil was decreased by 2.55%～12.59%,while that of alluvial soil was decreased by 2.37%～12.45%after being treated different doses of PAM.The difference between different doses of PAM was significant and 200mg/kg was the most prominent dose.When PAM with the same molecular weight but different charge density was treated,the accumulated evaporation of cold sandy yellow clayer soil was decreased by 7.76%～20.17%,while that of alluvial soil was decreased by 7.34%～17.81%,compared with the control.And the difference between them was also significant,while 40%was the most prominent dosage of cold sandy yellow clayer soil and 30%was the most prominent one of alluvial soilo When PAM with the same charge density but different molecular weight was treated,the accumulated evaporation of cold sandy yellow clayer soil was decreased by 14.37%～20.74%,while that of alluvial soil was decreased by 12.25%～18.53%,compared with the control.And the difference between them was also sinificant, while 10 million was the most prominent dosage.The difference of anti-evaporation between all the processes of those two kinds of soil was not marked,but the cold sandy yellow clayer soil was slightly better than alluvial soil。PAM did increase the soil water content.Compared with the control,the average water content of cold sandy yellow clayer soil was increased by 1.40%～5.64%,while that of alluvial soil was increased by 1.23%～4.59%after being treated with different doses of PAM.The difference between different doses of PAM was significant and 200mg/kg was the most prominent dose.When PAM with the same molecular weight but different charge density was treated,the average water conten of cold sandy yellow clayer soil was increased by 2.65%～5.96%,while that of alluvial soil was increased by 2.14%～5.38%,compared with the control.And the difference between them was also prominent,while 40%was the most prominent dosage of cold sandy yellow clayer soil and 30%was the most prominent one for alluvial soil.When PAM with the same charge density but different molecular weight was treated,the average water conten of cold sandy yellow clayer soil was increased by 4.85%～6.11%,while that of alluvial soil was increased by 4.49%～5.49%%, compared with the control.And the difference between them was also significant,while 10 million was the most prominent dosage.The difference of average soil water content between all the processes of those two kinds of soil was not marked,but cold sandy yellow clayer soil was slightly better than alluvial soil。Compared with the control,all treatments amended with PAM showed an increase in water holding capacity.The field capacity and capillary capacity were increased by 20.66%～33.67%and 18.42%～29.06%for cold sandy yellow clayer soil,and 8.43%～13.42%and 3.55%～9.83%for alluvial soil.In the same way,the maximum moisture capacity was incerased by 18.60%～29.69% fo cold sandy yellow clayer soil,and 3.91%～10.26%for alluvial soil.The water holding capacity of tested soils was also significantly different with different application doses of PAM,with the dose of 200mg/kg being the most prominent one.
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