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·kg -1 to 844 mg·kg -1 with an average of 68 mg·kg -1 , and 82.7% of topsoil samples were insufficient in RA-K (<100 mg·kg -1 ). Comparatively in 2015 SA-K content ranged from 230 mg·kg -1 to 1340 mg·kg -1 with an average of 595 mg·kg -1 , and 13.7% of soil samples were insufficient in SA-K (<400 mg·kg -1 ); RA-K content ranged from 46 mg·kg -1 to 352 mg·kg -1 with an average of 134 mg·kg -1 , and 25.8% of soil samples were insufficient in RA-K (<100 mg·kg -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.
The potassium content is an important index to evaluate the quality of flue- cured tobacco [
Xuancheng City (29˚57'N - 31˚19'N,117˚58'E - 119˚40'E), located in south Anhui Province, has been the dominant tobacco-planting region of this province since tobacco was initially planted in 2007 due to its well-known “burnt-sweet smelling” style [
The potassium in tobacco leaves mainly comes from soil and applied potassium fertilizer [
The contents of potassium in topsoil were from the following sources in this paper, one is the contents of rapidly available potassium (RA-K) of 7730 topsoil samples (0 - 20 cm) in 2005-2007 obtained from the programme of Soil Testing and Formula Fertilization (STFF), and the other is the contents of slowly available potassium (SA-K) and RA-K of 124 topsoil samples collected in 2015 from the farmlands of model tobacco-farmers.
The spatial distribution of topsoil samples in the two periods are shown in
Region | Xuanzhou (XZ) | Langxi (LX) | Guangde (GD) | Ningguo (NG) | Jingxian (JX) | Jixi (JXX) | Jingde (JD) | Total |
---|---|---|---|---|---|---|---|---|
2005-2007 | 923 | 1083 | 1308 | 930 | 1425 | 1073 | 988 | 7730 |
2015 | 42 | 11 | 13 | 8 | 19 | 10 | 21 | 124 |
spectively [
Data were analyzed with Microsoft Excel 2013 and IBM Statistics SPSS 20.0, the spatial distribution of topsoil samples was mapped on the platform of Esri ArcGIS 10.3.
Index | Sufficient | Medium | Deficient | Severe deficient |
---|---|---|---|---|
SA-K (mg・kg−1) | >500 | 500 - 400 | 400 - 300 | <300 |
RA-K (mg・kg−1) | >150 | 150 - 100 | 100 - 50 | <50 |
Region | XZ | LX | GD | NG | JX | JXX | JD | Total | |
---|---|---|---|---|---|---|---|---|---|
RA-K (mg・kg−1) | Range | 1 - 826 | 9 - 420 | 6 - 310 | 15 - 470 | 2 - 611 | 11 - 844 | 8 - 371 | 1 - 844 |
Average | 57 | 71 | 68 | 94 | 66 | 77 | 47 | 68 |
2005-2007. To the whole Xuancheng City, RA-K content ranged from 1 mg・kg−1 to 844 mg・kg−1 with an average of 68 mg・kg−1, while the average RA-K contents in different administrative regions ranged from 47 mg・kg−1 to 94 mg・kg−1, generally in the deficient grade.
To the whole region, SA-K content ranged from 230 mg・kg−1 to 1340 mg・kg−1 with an average of 595 mg・kg−1, in the sufficient grade; RA-K content ranged from 46 mg・kg−1 to 352 mg・kg−1 with an average of 134 mg・kg−1, in the medium grade.
To various administrative regions, 1) average SA-K content in Jingxian was 485 mg・kg−1, in the medium grade, average SA-K contents ranged from 545 mg・kg−1 to 810 mg・kg−1 in other region, in the sufficient grade. 2) average RA-K contents were 151 mg・kg−1 and 185 mg・kg−1 in Guangde and Ningguo, respectively, in the sufficient grade; average RA-K content ranged from 105 mg・kg−1 to 141 mg・kg−1 in other region, in the medium grade.
Region | Severe deficient | Deficient | Medium | Sufficient | Total | |||||
---|---|---|---|---|---|---|---|---|---|---|
Sample No. | % | Sample No. | % | Sample No. | % | Sample No. | % | Sample No. | % | |
XZ | 450 | 48.7 | 396 | 42.9 | 68 | 7.4 | 9 | 0.9 | 923 | 100 |
LX | 317 | 29.2 | 593 | 54.8 | 129 | 11.9 | 44 | 4 | 1083 | 100 |
GD | 409 | 31.2 | 722 | 55.2 | 134 | 10.2 | 43 | 3.3 | 1308 | 100 |
NG | 98 | 10.5 | 509 | 54.7 | 225 | 24.2 | 98 | 10.6 | 930 | 100 |
JX | 434 | 30.4 | 641 | 45 | 190 | 13.3 | 160 | 11.3 | 1425 | 100 |
JXX | 379 | 35.4 | 508 | 47.3 | 106 | 9.9 | 80 | 7.4 | 1073 | 100 |
JD | 674 | 68.2 | 262 | 26.5 | 36 | 3.6 | 16 | 1.6 | 988 | 100 |
Total | 2761 | 35.7 | 3631 | 47 | 888 | 11.5 | 450 | 5.8 | 7730 | 100 |
Region | Sample Number | S A-K (mg・kg−1) | R A-K (mg・kg−1) | ||
---|---|---|---|---|---|
Range | Average | Range | Average | ||
XZ | 42 | 230 - 1340 | 595 | 46 - 352 | 134 |
LX | 11 | 340 - 730 | 545 | 106 - 200 | 141 |
GD | 13 | 390 - 920 | 618 | 68 - 292 | 151 |
NG | 8 | 390 - 800 | 601 | 106 - 320 | 185 |
JX | 19 | 250 - 690 | 485 | 58 - 224 | 128 |
JXX | 10 | 230 - 950 | 622 | 46 - 352 | 136 |
JD | 21 | 450 - 1340 | 810 | 46 - 158 | 105 |
All | 124 | 230 - 1340 | 595 | 46 - 352 | 134 |
Region | Severe deficient | Deficient | Medium | Sufficient | Total | |||||
---|---|---|---|---|---|---|---|---|---|---|
Sample No. | % | Sample No. | % | Sample No. | % | Sample No. | % | Sample No. | % | |
XZ | 0 | 0 | 7 | 16.7 | 13 | 31.0 | 22 | 52.3 | 42 | 100 |
LX | 0 | 0 | 2 | 18.2 | 3 | 27.3 | 6 | 54.6 | 11 | 100 |
GD | 0 | 0 | 1 | 7.7 | 4 | 30.8 | 8 | 61.6 | 13 | 100 |
NG | 0 | 0 | 1 | 12.5 | 0 | 0 | 7 | 87.5 | 8 | 100 |
JX | 1 | 5.3 | 2 | 10.5 | 7 | 36.8 | 9 | 47.4 | 19 | 100 |
JXX | 3 | 30.0 | 0 | 0 | 0 | 0 | 7 | 70.0 | 10 | 100 |
JD | 0 | 0 | 0 | 0 | 2 | 9.5 | 19 | 90.5 | 21 | 100 |
Total | 4 | 3.2 | 13 | 10.5 | 29 | 23.4 | 78 | 62.9 | 124 | 100 |
the total samples were in the deficient grade while 62.9% (78 samples) of the total samples were in sufficient grade. To various administrative regions, SA-K content in Jingde was in the sufficient grade, while 8% - 30% of the corresponding total samples in other regions were in the deficient grade.
According to the data of RA-K contents in 1987 obtained during the 2nd National Soil Survey in Xuancheng City, 89.4% of topsoils were lack of RA-K (<100 mg・kg−1), however, in 2005-2007 the percentage of RA-K deficient was decreased down to 82.7%, indicating RA-K status of farmlands were slightly improved, which is attributed to potassium fertilization: before 2005-2007, most of the farmlands in Xuancheng were given priority to double rice rotation or rice- wheat rotation. Historical field survey data showed that during this period the annual average crop yield (double rice or rice + wheat) was 1000 kg/667 m2 in total, the grains usually contain 0.4% of K2O, almost all the crop straws were returned to the fields or burnt directly in the fields [
For the surveyed model farmers’ farmlands with tobacco-rice rotation, only 25.8% of the total 124 topsoil samples are insufficient in RA-K content, while the proportion of RA-K content in medium or above grades was 74.2% in total, indicating that obvious improved in RA-K content in topsoil under the tobacco-rice rotation compared with the data under double rice cropping or rice-wheat rotation in 2005-2007, which is resulted from surplus potassium fertilizers applied into the topsoils during the tobacco-planting period. The field survey data surveyed in 2015 showed that during the tobacco-planting period, 55
Region | Severe deficient | Deficient | Medium | Sufficient | Total | |||||
---|---|---|---|---|---|---|---|---|---|---|
Sample No. | % | Sample No. | % | Sample No. | % | Sample No. | % | Sample No. | % | |
XZ | 0 | 0 | 15 | 35.7 | 15 | 35.7 | 12 | 28.6 | 42 | 100 |
LX | 0 | 0 | 0 | 0 | 7 | 63.6 | 4 | 36.4 | 11 | 100 |
GD | 0 | 0 | 2 | 15.4 | 4 | 30.8 | 7 | 53.9 | 13 | 100 |
NG | 0 | 0 | 0 | 0 | 3 | 37.5 | 5 | 62.5 | 8 | 100 |
JX | 0 | 0 | 5 | 26.3 | 9 | 47.4 | 5 | 26.3 | 19 | 100 |
JXX | 1 | 10.0 | 3 | 30.0 | 3 | 30.0 | 3 | 30.0 | 10 | 100 |
JD | 2 | 9.5 | 4 | 19.0 | 14 | 66.7 | 1 | 4.8 | 21 | 100 |
Total | 3 | 2.4 | 29 | 23.4 | 55 | 44.4 | 37 | 29.8 | 124 | 100 |
kg/667 m2 of tobacco specific fertilizer (containing 24% of K2O), 5 kg/667 m2 of potassium sulphate (containing 50% of K2O) and 6.6 kg/667 m2 of potassium nitrate (containing 44% of K2O) were applied into the topsoil, while during the rice-planting period 15 kg/667 m2 of rice specific fertilizer (containing 15% of K2O) was applied to the soil, thus 20.85 kg/667 m2 of K2O in total was input into the topsoil from fertilization. Both the yields of tobacco leaves and stems are about 150 kg/667 m2, which contain 2.2% and 2.0% of K2O, respectively, but the tobacco stems usually were removed out from the tobacco fields to avoid disease spread. The yield of late rice is about 500 kg/667 m2, which containing 0.4% of K2O, also almost all the rice straws were returned to the fields or burnt directly in the fields, thus, about 5.0 kg of K2O was removed out from the soil by the leaves and stems of tobacco and the grains of rice, so the “net” input of K2O into the topsoil is about 15.85 kg/667m2 annually. It is the reason for mean RA-K content (134 mg・kg−1) in the model tobacco-farmers’ farmlands in 2015 is 49.3% higher than that under double rice rotation or rice-wheat rotation in 2005-2007 (68 mg・kg−1), also higher than that of the 20 long-term monitoring farmlands (under double rice rotation or rice-wheat rotation) in Xuancheng City in the same year (ranged from 58 mg・kg−1 to 188 mg・kg−1 with an average of 104 mg・kg−1).
Some tobacco-farmers thought that no potassium fertilizers should be applied into fields during the rice planting period, but the field survey data surveyed in 2015 showed further that for the 87.5% of ‘new tobacco-planting farmlands’ (under tobacco-rice rotation less than 3 years, 23 topsoil samples in total in 2015), the potassium accumulative effect in topsoils is not obvious, RA-K content in topsoil is still in the deficient grade, so the fields need continuous potassium fertilization during the rice planting period.
Generally, the content of rapidly available potassium content has increased gradually in topsoil farmlands in Xuancheng City, which is mainly due to potassium fertilization since 1980s, particularly due to farmlands under tobacco-rice rotation which initially started since 2007. However, more potassium fertilizers should be applied into the farmlands under double rice rotation or wheat-rice rotation, while more potassium fertilizers should be used during the rice planting period to the farmlands under tobacco-rice rotation less than 3 years.
This study was supported by the Program of Anhui Branch of China National Tobacco Co. (20150551009), the External Operation Program of BIC, Chinese Academy of Sciences (151432KYSB2015007), and the Intergovernmental Special Program of National Key R&D Plan (2016YFE0112700) and Sino-EU Cooperation Programme iSQAPER. We also thank the supports and help from the Soil and Fertilization Station of Xuancheng in STFF data supply and field sampling activity.
Lin, K., Li, D.C., Song, X.D., Zu, C.L., Jiang, C.Q., Shen, J., Ma, C.X., Gao, Q., Zhu, Q.F., Ji, X.J., Zhang, G. and Xue, L. (2017) Contents and Changes of Potassium in Plough Layers of Xuancheng, South Anhui Province. Agricultural Sciences, 8, 348-355. https://doi.org/10.4236/as.2017.85026