A Brief Study on pH, Exchangeable Ca2+ and Mg2+ in Farmlands under Tobacco-Rice Rotation in Xuancheng City of South Anhui

摘要

pH, exchangeable Ca2+ and Mg2+ of soil can influence the yield and quality of flue-cured tobacco. Xuancheng city is the dominant tobacco-planting region in Anhui province since 2008. A general soil survey was conducted in Xuancheng city to understand the current situations of pH, exchangeable Ca2+ and Mg2+ of farmlands under tobacco-rice rotation and to decide whether continuous applying dolomite powders to abate soil acidification. In total 124 topsoil samples (0-20 cm) were collected from the typical farmlands and soil pH, exchangeable Ca2+ and Mg2+ were measured. The results showed that soil pH and Ca2+ and Mg2+ in Xuancheng city were generally in the suitable grades, pH ranged from 4.56 to 8.42 with an average of 5.87, exchangeable Ca2+ ranged from 1.01 cmol(1/2Ca2+) kg style="font-size:10px;white-space:normal;">- style="font-size:10px;white-space:normal;">1 to 100.55 cmol(1/2Ca2+) kg style="font-size:10px;white-space:normal;">- style="font-size:10px;white-space:normal;">1 with an average of 11.07 cmol(1/2Ca2+) kg style="font-size:10px;white-space:normal;">- style="font-size:10px;white-space:normal;">1, and exchangeable Mg2+ ranged from 0.14 cmol(1/2Mg2+) kg style="font-size:10px;white-space:normal;">- style="font-size:10px;white-space:normal;">1 to 2.86 cmol(1/2Mg2+) kg style="font-size:10px;white-space:normal;">- style="font-size:10px;white-space:normal;">1 with an average of 0.81 cmol(1/2Mg2+) kg style="font-size:10px;white-space:normal;">- style="font-size:10px;white-space:normal;">1, all spanned from the low grades to the high grades. To the whole Xuancheng city, 37.10%, 62.10% and 72.58% of the surveyed farmlands were in the low grades of pH, exchangeable Ca2+ and Mg2+, respectively, while 52.42%, 25.00% and 20.97% of the farmlands were in the suitable grades, respectively. pH had an extremely significantly positive Napierian logarithm correlation with exchangeable Ca2+ and an extremely significantly positive power correlation with exchangeable Mg2+. In total about 338.2 kg·hm style="font-size:10px;white-space:normal;">- style="font-size:10px;white-space:normal;">2 of Ca2+ and 202.4 kg·hm-2 of Mg2+ are annually input into the farmlands, while about 110.4 kg·hm style="font-size:10px;white-space:normal;">- style="font-size:10px;white-space:normal;">2 of Ca2+ and 7.4 kg·hm style="font-size:10px;white-space:normal;">- style="font-size:10px;white-space:normal;">2 of Mg2+ are annually moved out from the farmlands, exchangeable Ca2+ and Mg2+ were annually increased by 225.2 kg·hm style="font-size:10px;white-space:normal;">- style="font-size:10px;white-space:normal;">2 and 187.6 kg·hm style="font-size:10px;white-space:normal;">- style="font-size:10px;white-space:normal;">2 in the farmlands, respectively. It is necessary to monitor the farmlands dynamically in order to decide whether continuous applying dolomite powders which should be dependent upon the specific conditions of individual farmlands.