| By using the pH data of more than 200 thousand soil samples from the "Farmland Productivity Evaluation Project" in recent 10 years and the "Cultivated Land Quality Monitoring Project" of Guangdong Province,this research analyzed the soil pH distribution characteristics and the soil pH trend with different areas,different soil types,and different agricultural development with statistical methods.Besides,typical lands were selected to carry out acid soil improvement field experiments so as to offer references for the large-scale extension of acid soil improvement techniques in the future.The main results were as follows:?1?The acid soils?pH 4.5-5.5?and sub-acid soils?pH 5.5-6.5?were the majority of the cultivated land soils in Guangdong Province which together accounted for 90.57%,neutral soils accounted for 5.13%,alkaline soils only accounted for 0.11%.In terms of land area,there were 47813 hectares of the cultivated soils which behaved neutral,that accounted for1.83%of cultivated area;The cultivated area with sub-acidity was 1088937 hectares,accounting for 41.65%of cultivated area of Guangdong province.The cultivated area with acidity was 1473936 hectares,accounting for 56.38%of the total cultivated area.The cultivated area with strong acidity was 3751 hectares,accounting for 0.14%of the total cultivated area.?2?According to the sample frequency with pH<5.5,among the 10 kinds of soils including latosol,yellow soil,paddy soil,latosolic red soil,fluvo-aquic soil,skeletol soils,red soil,coastal sandy soil,limestone soil and purple soil,the order of the sum of the frequency of both acidic and strongly acidic samples was as follows:latosol>yellow soil>paddy soil>latosolic red soil>fluvo-aquic soil>skeletol soils>red soil>coastal sandy soils>limestone soil>purple soil.?3?Different agricultural use types resulted in differences in topsoil pH values.The pH values of paddy field,dryland and garden land ranged from 3.8 to 7.9.But the most belonged to the lightly acidic and acidic.The pH values of vegetable field were higher,which might be related to the facts that the farmers usually used lime or soil conditioner when they growed vegetables.?4?The cultivated land of Guangdong province showed an obvious acidified trend from the second national soil survey.The sample proportion of paddy field acid soil increased from 42.2%to 58.99%,and that of the dry land was from 31.1%to 56.39%.The distribution frequency of both strong acid soil and acid soil increased obviously,with accounting for 6.3%and 45.1%at the end of the "11th Five-year" ?2006-2010?,being higher 5.2%and 10.9%respectively than those before 1986.The distribution frequency of subacidity soils and sub-alkale soils showed a significant downward trend.The distribution frequency of neutral soils changed little.There is basically no alkaline soil?p H?8.5?in every period.According to the statistics,the paddy soils were mainly acid and sub acid,their sum of distribution frequency in every monitor ing period is over 80%.?5?It was shown with the acid soil improvement experi ments that the pH values of paddy field soils were raised at an average of 0.2 and more,and the rice yields increased by an average of over 470 kg·hm-2 after using soil conditioners made from calcium&magnesium materials. |
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