Nutrients of Topsoil for Sugarcane Planting in Xinping County of Yunnan Province

Jiabin MA，W anghai TIAN，Shunfa LONG，Huazhen LI，Long SU，Zhitao YIN，Yuanyuan GAO

Xinping County Soil and FertilizerWorkstation in Yunnan Province，Xinping 653400，China

Since introduction and planting of sugarcane in 1958，Xinping County has become a largest sugarcane planting county in Yunnan Province.In 2009，the sugarcane planting area reached 10 000 hectare and sugarcane planting has become an agricultural leading industry.Sugarcane is high biomass crop and has long growth period.It absorbs a lot of nutrients from soil.If the soil lacks nutrients，it will influence yield and quality of the sugarcane［1］.Physical and chemical property is an indicator for evaluating whether the soil is suitable for planting sugarcane and abundance of soil nutrients is a basis for working out reasonable fertilizer application scheme.The pH value of soil is basic characteristic of soil and has great influence on effect of soil nutrients and it also influences growth of crops，activity of soil microorganism，and physical property of soil［2］.Guo Jiawen et al［3］held that soil suitable for sugarcane growth should have pH value of4.2-8.0，and the soil with pH value of 5.5-8.0 is suitable for growth and development of sugarcane；soil suitable for sugarcane growth should have organic matter content of 1%-3%，and 2%-3%is relatively suitable for growth and development of sugarcane.Liu Shaochun et al［4］believed that there is obvious difference in soil fertility between different sugarcane planting areas and the same sugarcane planting area also has great difference.At present，there are a lot of researches about sugarcane cultivation technologies，but there is no research on fertilizer application based on soil nutrients.To grasp nutrient situation of topsoil in sugarcane planting area of Xinping County and promote sustainable development of sugarcane industry，we came up with recommendations for fertilizer application and soilmanagementaccording to nutrient situation and sugarcane growth rules［5］.

1 Materials and methods

1.1 Collection of soil sam plesIn 2009-2011，we collected soil samples using Sshaped distribution points by soil sample collection methods and requirements［6］in representative fields of sugarcane planting area on the principle of random，equal quantity and multi-point mixing.Each sample contains 15 mixed points；the sampling depth is0-20 cm；the sample weight is1 kg.Samples were marked and brought to laboratory.After air drying，the samples were removed with stone blocks and plant roots and ground and mixed uniformly for measurement.In total，we collected 340 soil samples.

1.2 Analysis of soil nutrientsThe pH value of soilwas measured by 1：2.5 soilwater suspension liquid method；organic matter was measured by potassium chromate-sulfuric acid oil bath titration；alkali-hydrolyzable nitrogen was measured by alkaline hydrolysis diffusion method；available phosphorus was measured by sodium hydrogen carbonate solution-spectrophotometric method；available potassium was measured by ammonium acetate extraction atomic absorption method；available zinc and manganese was measured by DTPA extraction-atomic absorption method；available sulfur was measured by phosphate-acetic acid extraction-spectrophotometric method；exchangeable magnesium was measured by EDTA-ammonium acetate extraction atomic absorption method；available boron was measured by boiling water extraction-Azomethin-h colorimetric method.The specific method could be found in Agricultural Chemical Analysis Methods of Soil［7］.We analyzed pH value，organic matter，alkali-hydrolyzable nitrogen，available phosphorus，and available potassium of340 soil samples，and exchangeable magnesium，available sulfur，available boron，available manganese and available zinc of70 soil samples.

1.3 Classification of abundance of soil nutrientsThe classification of abundance of soil nutrients was determined according to nutrient abundance classification specified in the Second Soil Census［8-10］.The pH classification of soil for sugarcane planting：pH≤4.5 strong acid，pH 4.6-5.5 mediate strong acid，pH 5.6-6.5 weak acid，pH 6.6-7.5 neutral，pH 7.6-8.5 weak alkaline，pH 8.6-9 alkaline，and pH ＞9 strong alkaline.Othersare listed in Table 1.

Table 1 Classification of abundance of soil nutrients

2 Results and analyses

2.1 Soil pH valueResults show that 3 samples（accounting for 0.88%of total samples）are strong acid soil（pH≤4.5）；173 samples（accounting for 50.88%of total samples）are acid soil（pH 4.5-5.5）；121 samples（accounting for 35.59%of total samples）are faintly acid soil（pH 5.6-6.5）；35 samples（accounting for10.29%of total samples）are neutral soil（pH 6.6-7.5）；8 samples（accounting for 2.35%of total samples）are weakly alkaline soil（pH 7.6-8.5）；there is no alkaline and strong alkaline soil，indicating 51.76%soil of sugarcane planting area in Xinping County is faintly acid.

2.2 Soil nutrients

2.2.1 Organic matter.The content of organic matter is an important indicator for evaluating soil fertility.The organic matter plays a great role in adjusting water，fertilizer，air，and heat of soil and has important influence on water-retaining property，fertilizer-retaining property，and buffer property of soil.Thus，the organic matter is an import ant part of soil and the content of organic matter is closely connected with soil fertility［11］.Results indicate that organic matter content in soil of sugarcane planting area in Xinping County is in the range of 0.48-29.2%，the average content is 21.44%，the coefficient of variation is 79.24%，and 1.17%，9.41%，37.94%，45.88%，5.00%，and 0.59%samples have organic matter of 4.0%，3.0%-4.0%，2%-3%，1%-2%，0.6%-1%，and less than 0.6%respectively.173 samples（accounting for 50.88%of total samples）lack organic matter，as listed in Table2.These indicate that most soil of sugarcane planting area in Xinping County lacks organic matter and there is great difference in different fields and soil types.

2.2.2 Available nutrients of major elements.The content of alkali-hydrolyzable nitrogen，available phosphorus and available potassium reflects ability of soil providing nitrogen，phosphorus and potassium，so it has direct guidance significance for application of nitrogen，phosphorus and potassium fertilizer［12］.

Table 2 Nutrient situation of soil for sugarcane planting area in Xinping County

The range of alkali-hydrolyzable nitrogen is 17.2-294.3 mg／kg and the average content is 97.08 mg／kg.1.18%，13.82%，30.88%，16.47%，6.76%samples have alkali-hydrolyzable nitrogen of 30 mg／kg，60-90 mg／kg，90-120 mg／kg，120-150 mg／kg，and higher than 150 mg／kg separately.156 samples（accounting for45.88%of total samples）lack alkali-hydrolyzable nitrogen，as listed in Table 2.This indicate that near a half soil of sugarcane planting area in Xinping County lacksalkalihydrolyzable nitrogen and there is great difference in alkali-hydrolyzable nitrogen content of different fields and soil types.

The range of available phosphorus is0.1-148.4mg／kg and the average content is 27.33 mg／kg.5.88%，5.88%，15.0%，25.29%，20.00%samples have available phosphorus of 3 mg／kg，3-5mg／kg，10-20mg／kg，20-40mg／kg，and higher than 40mg／kg separately.90 samples（accounting for26.47%of total samples）lack available phosphorus（less than 10 mg／kg），as listed in Table 2.This indicates that near 1／3 soil of sugarcane planting area in Xinping County lacks available phosphorus and there is great difference in available phosphorus content of different fields and soil types.

The range of available potassium is 1-628 mg／kg and the average content is 128.33 mg／kg.3.24%，8.53%，38.24%，20.59%，12.65%and 16.76%samples have available potassium of30mg／kg，30-50mg／kg，50-100mg／kg，100-150mg／kg，150-200mg／kg and higher than 200mg／kg separately.171 samples（accounting for 50.29%of total samples）lack available potassium（less than 100 mg／kg），as listed in Table 2.This indicates that near 1／2 soil of sugarcane planting area in Xinping County lacksavailable potassium and there isgreatdifference in available potassium content of different fields and soil types.

The available nitrogen，phosphorus and potassium of soil in sugarcane planting area have variation in varying degrees.The available phosphorus has the largest coefficient of variation（up to 93.56%），followed by available potassium and alkali-hydrolyzable nitrogen（73.76%and 38.16%respectively），indicating that there is great difference in soil fertility between different fields in sugarcane planting areas of Xinping County.

2.2.3 Available nutrients of secondary elements.The range of exchangeable magnesium is 14-747 mg／kg，the average content is 189.72 mg／kg，and the coefficient of variation is 67.32%.5.71%，7.14%，5.71%，22.86%，and 58.57%samples have exchangeable magnesium of 25 mg／kg，25-50 mg／kg，50-100 mg／kg，100-150 mg／kg，higher than 150 mg／kg separately.9 samples（accounting for12.86%of total samples）lack exchangeable magnesium（less than 50mg／kg），as listed in Table 2.This indicates that most soil of sugarcane planting area in Xinping County lacks exchangeable magnesium and there is great difference in exchangeable magnesium of different fields and soil types.

The range of available sulfur is 2-111.8 mg／kg，the average content is29.51mg／kg，and the coefficient of variation is84.31%.14.29%，22.86%，30.00%，17.14%，and 15.71%samples have available sulfur of10mg／kg，10-16mg／kg，16-30mg／kg，30-50 mg／kg，higher than 50 mg／kg separately.26 samples（accounting for 37.14%of total70 samples）lack available sulfur（less than 16mg／kg），as listed in Table 2.This indicates that near 40%soil of sugarcane planting area in Xinping County lacks available sulfur and there is great difference in available sulfur content of different fields and soil types.

2.2.4 Available nutrients of trace elements.The range of available boron is 0.01-0.69 mg／kg，the average content is 0.20 mg／kg，and the coefficient of variation is75.00%.65.71%，28.57%，5.71%，0，and 0 samples of total 70 samples have available boron of 0.25 mg／kg，0.25-0.5 mg／kg，0.5-1 mg／kg，1-2 mg／kg，higher than 2 mg／kg separately.66 samples（accounting for 94.29%of total 70 samples）lack available sulfur（less than 0.5mg／kg），as listed in Table 2.This indicates that all soil of sugarcane planting area in Xinping County lacks available boron and there is great difference in available boron content of different fields and soil types.

The range of available manganese is 7.2-204 mg／kg，the average content is66.93mg／kg，and the coefficient of variation is 70.48%.0，10%，14.28%，22.86%，and 52.86%samples of total 70 samples have available manganese of 7 mg／kg，7-15 mg／kg，15-30 mg／kg，30-50 mg／kg，higher than 50 mg／kg separately.7 samples（accounting for 10%of total 70 samples）lack available manganese（less than 15 mg／kg），as listed in Table 2.This indicates that most soil of sugarcane planting area in Xinping County lacks available manganese and there is great difference in available manganese of different fields and soil types.

The range of available zinc is 0.35-22.5 mg／kg，the average content is 2.70 mg／kg，and the coefficient of variation is 107.04%.15.71%，15.71%，40.00%，22.86%，and 5.71%samples of total70 samples have available zinc of 1 mg／kg，1-1.5mg／kg，1.5-3 mg／kg，3-5 mg／kg，higher than 5 mg／kg separately.22 samples（accounting for 31.43%of total 70 samples）lack available zinc（less than 1.5mg／kg），as listed in Table 2.This indicates that near 1／3 soil of sugarcane planting area in Xinping County lacksavailable zinc and there isgreat difference in available zinc content of different fields and soil types.

3 Conclusions and discussions

（i）About 51.76%soil pH value is in the range of 4.5-5.5，so the soil belongs to acid soil.Researches show that application of lime plays a certain role in increasing sugar and yield of sugarcane［13］.It is recommended to popularize the application of lime and calcium magnesium phosphate fertilizer in sugarcane planting areas of Xinping County.

（ii）50.88%lacks organic matter，45.88%lacks alkali-hydrolyzable nitrogen，26.47%lacksavailable phosphorus，and 50.29%lacks available potassium.This indicates most soil of sugarcane planting area in Xinping County lacks organic matter，alkalihydrolyzable nitrogen and available potassium.Thus，it is recommended to improve the soil fertility through increasing proper fertilizer.First，increasing application of organic fertilizer，especially farm manure；second，energetically developing leguminous plant and green manure crops to increase content of nitrogen and organic matter；third，advocating return of straw to fields；fourth，properly controlling application of fertilizer，especially compound fertilizer，for example，combination of nitrogen，phosphorus and potassium［12］.

（iii）12.86%soil lacks exchangeable magnesium，37.14%lacks available sulfur，94.29%lacks available boron，10.00%lacks available manganese，and 31.43%lacks available zinc.This indicates thatmost soil in sugarcane planting area of Xinping County lacks trace elements such as boron，sulfur and zinc.Therefore，it is recommended to increase application of boron，sulfur，and zinc fertilizer in sugarcane planting，for example，application once every two or three years［14］.

［1］DAO JM，LIUSC，FANX，et al.Study on principal soil nutrients of sugarcane fields in Zhenkang County，Yunnan Province［J］.Southwest China Journal of Agricultural Sciences，2013，26（6）：2391-2396.（in Chinese）.

［2］ZHUANG SD.Analysis on soil fertility in banana garden of Zhangzhou Prefecture［J］.Fujian Journal of Agricultural Sciences，2003，18（3）：168-172.（in Chinese）.

［3］GUO JW，ZHANG YB，LIU SC，et al.The distribution of soilorganicmatter and available nutrient of the sugar balt in Yunnan［J］.Chinese Journal of Soil Science，2010（8）：872-876.（in Chinese）.

［4］LIU SC，ZHANGYB，GUO JW，et al.Soil fertility in Yunnan cane regions and fertilization based on measuring soil and filling the prescription［J］.Sugar Crops of China，2007（2）：39-40.（in Chinese）.

［5］GUOYB，LIUSC，GUO JW.Sugarcane nutrition requirement and balanced fertilization methods［J］.Sugar Crops of China，2008（2）：58-60.（in Chinese）.

［6］GAO XZ，MA CB，DU S.Soil testing and formulated fertilization technology［M］.Beijing：China Agriculture Press，2005：14-18.（in Chinese）.

［7］Soil Science Society of China.Conventional chemistry analysismethods of soil agriculture［M］.Beijing：Science Press，1983.（in Chinese）.

［8］National Soil Survey.Chinese soil［M］.Beijing：China Agricultural Science and Technology Press，1998.（in Chinese）.

［9］SHEN SM.Chinese soil fertility［M］.Beijing：China Agricultural Science and Technology Press，1998.（in Chinese）.

［10］ZHANG YB，WU ZK，LIU SC.High yield and sugar planting techniques of sugarcane in Yunnan［M］.Kunming：Yunnan Science＆Technology Press，2004.（in Chinese）.

［11］LIN D.Fertility in banana plantation in Hainan Province［J］.Soiland Fertilizer Sciences in China，2007（2）：26-29.（in Chinese）.

［12］WANG F，RAN L，LV HF，et al.Study on classification of soil nutrient status of sweet potato in Chongqing［J］.Southwest China Journal of Agricultural Sciences，2012：25（2）：580-583.（in Chinese）.

［13］AO JH，HUANG ZR，JIANG Y，et al.Effects of applying lime on the properties ofacid soiland the growth of sugarcane［J］.Chinese Agricultural Science Bulletin，2010，26（15）：266-299.（in Chinese）.

［14］LISK，LIU YH，LIX，et al.Southwest corn field identification manual［M］.Beijing：China Agriculture Press，2011.（in Chinese）.