Contents and Changes of Potassium in Plough Layers of Xuancheng, South Anhui Province

Abstract

Xuancheng City is the dominant tobacco-planting area of Anhui province due to the high quality of the tobacco leaves. However, the potassium content in the tobacco leaves shows a gradual decreasing trend in recent years, which may be attributed partly to the possible low potassium content in topsoil of tobacco-planting farmland. Therefore, the content data in the year of 2005-2007 of rapidly available potassium (RA-K) of 7730 topsoil samples mainly under double rice rotation or wheat/rice-rice rotation at that time and the content data of slowly available potassium (SA-K) and RA-K of 124 typical topsoil samples in the year of 2015 under tobacco-rice rotation were used and compared in order to disclose the status of topsoil potassium and to provide a guidance for reasonable potassium fertilization in Xuancheng. The results showed that in 2005-2007 RA-K content ranged from 1 mg&#183kg - 1 to 844 mg&#183kg - 1 with an average of 68 mg&#183kg - 1 , and 82.7% of topsoil samples were insufficient in RA-K (<100 mg&#183kg - 1 ). Comparatively in 2015 SA-K content ranged from 230 mg&#183kg - 1 to 1340 mg&#183kg - 1 with an average of 595 mg&#183kg - 1 , and 13.7% of soil samples were insufficient in SA-K (<400 mg&#183kg - 1 ); RA-K content ranged from 46 mg&#183kg - 1 to 352 mg&#183kg - 1 with an average of 134 mg&#183kg - 1 , and 25.8% of soil samples were insufficient in RA-K (<100 mg&#183kg - 1 ). The above data show that RA-K content has increased gradually in farmland topsoil mainly due to fertilization since 1980s, particularly to farmland under tobacco-rice rotation, but insufficient RA-K in topsoil is still widely and serious for farmland under double rice rotation or wheat/rice-rice rotation. Under tobacco-rice rotation, RA-K insufficiency usually occurred in the farmlands which plant tobacco less than 3 years, indicating more potassium fertilizer should be applied.