| Sandy planting is emerging as a soil-less cultivation mode in recent years.Sand planting with advantages such as huge sandy areas of china,low cost,thorough disinfection,and effectively prevention of harmful soil,etc,has been successfully used in crop cultivation to relieve the lack of cultivated land in China.However,poor water holding and water retention capacity is a big concern of sandy irrigation.To increase water holding and water retention capacity in sandy irrigation,the effects of Super Absorbent Polymers(the abbreviation is SAP)on water movement and the growth of crop in sandy soil were studied by the laboratory experiment of sandy soil drip irrigation simulation and the field experiment of seedling cultivation and drip irrigation sand planting rape,proving reference for the application of SAP in the sand culture.The main conclusions of this article are as follows:(1)Field experiment were conducted to investigate the effects of SAP concentration(0%,0.1%,0.2%,0.6%,1.4%,mass percent)on the seed emergence ratio and growth in the nursery substrate,which making up of perlite,vermiculite,decomposed straw,and peat soil by a certain proportion.Experimental results indicated that the conjunctive use of SAP with a suitable concentration can save water and promote the seed growth,meanwhile,there was a certain degree of inhibition on the seed emergence rate.The results showed also that SAP concentration had significant influences on irrigation frequency when irrigation lower limit was 55%of field capacity and the irrigation upper limit was saturation.With the increase of SAP concentration,irrigation frequency first decreased and then increased.When SAP concentration varied from 0%to 0.6%,irrigation frequency decreased with the increase of the SAP concentration.When SAP concentration increases to 1.4%,irrigation frequency had a tendency of increase as compared with SAP concentration of 0.6%,which because that the increased concentration of SAP makes the substrate harden,water is difficult to enter into the nursery substrate,as a result,irrigation frequency increased.SAP concentration has a significant effect on the seeding growth.Maximum leaf area,fresh weight,and dry weight of rape seedlings increased with the increase of SAP concentration and achieved the best under the1.4%treatment.,all three indicators increase with the increasing of SAP’s concentration,and it performs best when the SAP’s concentration is 1.4%.(2)To investigate water movement of sandy soil under drip irrigation,the effects of SAP concentrations(0%,0.1%,0.2%,0.6%,1.4%,mass percent),discharge rates(1L/h),and irrigation time(4h)on patterns of the wetted sandy soil body and the wetting front dynamics under drip emitters were studied with laboratory experiment.The experimental results showed that the boundary of the wetting front in the sandy soil can be approximately expressed to a semi-ellipse centered on the emitter.The maximum horizontal wetting distance X and the maximum vertical wetting distance Z of the sandy soil wetting front increased with time under different treatment and with irrigation went on,wetting front migration velocity tended to decrease,using the Power Function to fit the wet distance and time has a high correlation.In the case of the same irrigation time and irrigation volume,wetted body volume first increased and then decreased with the increase of SAP concentration.And the maximum value was reached at the SAP concentration of 0.2%.The maximum horizontal wetting distance X increased first and then decreased with the SAP concentration increase.The maximum vertical wetting distance Z decreased with the SAP concentration increase.Sandy soil water content at the same sample location increased with the increasing of SAP concentration,and the farther the distance emitter,the smaller the influence of SAP concentration on soil water content.The results suggested that drip irrigation in sand soil with SAP can decrease vertical water infiltration in sand soil,thereby reducing deep percolation and promoting Sandy soil water retention.(3)Field experiment were conducted to investigate the effects of SAP concentrations(0、15、30、60、90 kg/hm~2)on sandy planting rape growth under drip irrigation.Experimental results indicated that SAP can improve the rape growth.The plant height,leaf number,leaf area and yield of rape under four SAP concentration levels(15、30、60、90 kg/hm~2)was higher as compared with that under control treatment(0 kg/hm~2 SAP concentration).The plant height,leaf number,leaf area and yield of rape under 90 kg/hm~2 SAP concentration treatment enhanced by 1.5cm,1.5leaf,27.99 cm~2 and 71.5%,respectively as compared with that under control treatment(0 kg/hm~2 SAP concentration).SAP has a significant effect on daily average water irrigation volume of rape.Daily average water irrigation volume of per plant decreased with increase SAP concentration,and the water use efficiency as a whole has shown an increasing trend with increasing SAP concentration.The results suggested that the SAP can improve water use efficiency and can play a role in saving water.Soil moisture content had a sharp increase with the increase of soil depth under two treatment(SAP concentration is 0 and 15kg/hm~2),but soil moisture content distribution in soil depth tend to be more uniform under three treatment(SAP concentration is 30,60 and 90kg/hm~2),which showed that the suitable SAP concentration can promote the distribution uniformity of moisture in sand soil. |
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