天然因素是气候干旱、少雨、多风，土地大量失去水份。降雨量在150毫米以下的地区，沙漠化倾向极为严重。而人为不合理的开垦、放牧、滥砍森林，破坏生态平衡，往往是造成地土地沙漠化的主要原因。因此，防止沙漠化应从两个方面着手，一是制定有关法规、保护天然植被，营造人工林带、人工草场，合理利用森林、草场资源；二是尽量减少天然因素的影响。减少天然因素影响的方法之一是设法减少土壤中水份蒸发、防止土地干燥。
在埃及一个受沙漠严重威胁的地区，从1988年开始，实施一项利用高吸水性树脂的蓄水性能，防止土地沙漠及绿化沙漠计划。
以淀粉及丙烯酸盐构成的树脂，吸水和蓄水量为其本身重量的500～1000倍。把树脂制成大小约1～3毫米的颗粒，然后混合在表层土壤中，由于它有极大的吸水能力，可以吸取天然的降水和露珠，成为具有很大弹性的凝胶状块，形成土壤的极好湿润剂，使细沙土壤不会发生板结现象也不会形成止水层，起到防止土壤沙漠化的作用。
目前，已有多家厂商生产高吸水性树脂并在埃及试用，以准备大面积推广。
The following has evaluated to null or missing:
==> langConfig [in template "public_include/wap/module/version_1/language.html" at line 49, column 14]
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Tip: If the failing expression is known to be legally refer to something that's sometimes null or missing, either specify a default value like myOptionalVar!myDefault, or use <#if myOptionalVar??>when-present<#else>when-missing</#if>. (These only cover the last step of the expression; to cover the whole expression, use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)??
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FTL stack trace ("~" means nesting-related):
- Failed at: #if langConfig.status?string = "false" [in template "public_include/wap/module/version_1/language.html" at line 49, column 9]
- Reached through: #include "/public_include/wap/module/... [in template "tpl/2018/03/17/2613443926933696//wap/com_5.html" at line 5, column 1]
- Reached through: #include "com_5.html" [in template "tpl/2018/03/17/2613443926933696//wap/displaynews.html" at line 69, column 6]
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Java stack trace (for programmers):
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freemarker.core.InvalidReferenceException: [... Exception message was already printed; see it above ...]
at freemarker.core.InvalidReferenceException.getInstance(InvalidReferenceException.java:134)
at freemarker.core.UnexpectedTypeException.newDesciptionBuilder(UnexpectedTypeException.java:80)
at freemarker.core.UnexpectedTypeException.<init>(UnexpectedTypeException.java:43)
at freemarker.core.NonHashException.<init>(NonHashException.java:49)
at freemarker.core.Dot._eval(Dot.java:48)
at freemarker.core.Expression.eval(Expression.java:81)
at freemarker.core.BuiltInsForMultipleTypes$stringBI._eval(BuiltInsForMultipleTypes.java:692)
at freemarker.core.Expression.eval(Expression.java:81)
at freemarker.core.EvalUtil.compare(EvalUtil.java:111)
at freemarker.core.ComparisonExpression.evalToBoolean(ComparisonExpression.java:62)
at freemarker.core.ConditionalBlock.accept(ConditionalBlock.java:48)
at freemarker.core.Environment.visit(Environment.java:327)
at freemarker.core.Environment.visit(Environment.java:333)
at freemarker.core.Environment.include(Environment.java:2509)
at freemarker.core.Include.accept(Include.java:171)
at freemarker.core.Environment.visit(Environment.java:327)
at freemarker.core.Environment.visit(Environment.java:333)
at freemarker.core.Environment.include(Environment.java:2509)
at freemarker.core.Include.accept(Include.java:171)
at freemarker.core.Environment.visit(Environment.java:327)
at freemarker.core.Environment.visit(Environment.java:333)
at freemarker.core.Environment.process(Environment.java:306)
at freemarker.ext.servlet.FreemarkerServlet.processEnvironment(FreemarkerServlet.java:946)
at freemarker.ext.servlet.FreemarkerServlet.process(FreemarkerServlet.java:910)
at freemarker.ext.servlet.FreemarkerServlet.doGet(FreemarkerServlet.java:769)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at com.kenfor.iyong.web.util.filter.NotAllowedToTunFilesFilter.doFilter(NotAllowedToTunFilesFilter.java:154)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at com.kenfor.iyong.web.util.filter.InvalidXSSFilter.doFilter(InvalidXSSFilter.java:40)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:121)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at com.orangefunction.tomcat.redissessions.RedisSessionHandlerValve.invoke(RedisSessionHandlerValve.java:26)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:528)
at org.apache.coyote.ajp.AbstractAjpProcessor.process(AbstractAjpProcessor.java:873)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:687)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1520)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1476)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)