Survey and Study of Soil Nutrients of Sugarcane Field in Southern Guangxi

Yan ZENG ，Jinsheng HUANG，Rulin XIE，Liuqiang ZHOU，Yongxian LIU，Yumo TAN，Hongwei TAN

1.Agricultural Resource and Environment Research Institute，Guangxi Academy of Agricultural Sciences，Nanning530007，China；2.Sugarcane Research Institute，Guangxi Academy of Agricultural Sciences，Nanning 530007，China

1 Introduction

According to statistics，the sugarcane planting area in Guangxi reached 1.0916 million hectare in 2011，accounting for 65%of total planting area in the whole country；the sugarcane yield in crushing season in 2010／2011 was12million，accounting for60%of the whole country.As a pillar industry of Guangxi，the cane sugar industry concerns economic development of Guangxi and plays a decisive role in balance of supply and marketing of the national cane sugar industry（Kong Lingziet al，2014）.Southern Guangxi is situated in southern subtropical zone，both temperature and solar radiation are suitable for sugarcane growth，and annual precipitation can satisfy total water demand of sugarcane growth.At present，the sugarcane industry is a leading industry in southern Guangxi.However，there are distinct differences in soil fertility of different sugarcane areas.Long-term continuous cropping leads to excessive consumption of some nutrients.It is urgent to make overall analysis and understanding of soil nutrients in sugarcane planting areas of Guangxi.Study on soil nutrients will be of great significance for increasing sugarcane yield，improving soil resource utilization，soil protection，and soil fertility.In recent years，many scholars have made extensive studies，analysis and evaluation of soil nutrients in sugarcane planting areas，and revealed changes of soil nutrients in these sugarcane planting areas.Tang Qizhanet al（2003）surveyed soil nutrients of sugarcane planting area in Liucheng，and results show that the fertility of soil nutrients in this area is at medium and low level，the organic matter and nitrogen are insufficient，P and Zn are moderate，K is insufficient，and the trace element B is in great shortage，the soil is slightly acid.Dao Jingmeiet al（2013）analyzed soil nutrients in sugarcane planting area in Cangyuan County and came up with recommendations of combining quick-acting N，Pand K fertilizers with organic fertilizer，which is favorable for increasing yield and sugar content of sugarcane and improving soil ecological environment.Ma Jiabinet al（2014）found that soil in sugarcane planting area of Xinping County contains too much N，but lacks P and K，and the content of exchangeable Ca and Mg is excessive.In the sugarcane production，it is recommended to pay attention to increase of application of organic fertilizer，to foster soil fertility，supplement boron fertilizer，to keep balance of soil nutrients.Xie Rulinet al（2004）analyzed characteristics of major soil nutrients of sugarcane planting area in Xingbin，and suggested that it is required to pay attention to application of N，P，and K fertilizers，properly apply trace element fertilizers，such as B，Sand Mg，and as well as Zn，Cu and Mn.However，there are still no reports about abundance and shortage of soil nutrients in sugarcane planting areas of southern Guangxi.To guide scientific application of fertilizers，effectively increase sugarcane yield and improve sugarcane quality，increase sugarcane farmers' income，and improve soil environment，it is necessary to make in-depth research on soil nutrients of sugarcane planting areas in southern Guangxi and find out factors limiting soil nutrients for sugarcane growth.Through collection and analysis of soil samples，it is expected to compre-hensively grasp soil nutrient situation of sugarcane planting areas in southern Guangxi，make clear major obstacles of sugarcane soil，and provide basic data for scientific and proper fertilization.

2 Materials and methods

2.1 General situation of the study areaThe study area is situated in Chongzuo City（23°14′-23°15′N，108°02′-108°03′E）in southwest of Guangxi Zhuang Autonomous Region.In this area，the quaternary acid lateritic soil is major soil type.Southern Guangxi belongs to subtropical humid monsoon climate zone，so there is plentiful rainfall and the climate is pleasant.The annual mean temperature is20℃，the sunshine hours is1582，the rainfall is1360mm，the frost-free period is331 days.It is the largest sugarcane planting base of China.Now，Xintaitang No.22 is the major sugarcane variety planted in the study area.

2.2 Experimental methodWith the aid of GPS，using50m x 50 m grid distribution point method，taking the sampling point as circle center，in the range of10m radius，we uniformly collected 0-30 cm topsoil using stainless steel spade.We mixed the topsoil fully and uniformly using quartering method，1 kg is a soil sample，and we collected a total of498 soil samples.After being collected，samples were naturally dried，then ground，screened and stored for use.Finally，soil nutrients were measured in the Soil Analysis Laboratory of Agricultural Resources and Environment Science of Guangxi Academy of Agricultural Sciences.

2.3 Measurement items and methodsThe nutrient content of soil samples was measured with reference to Analytical Methods for Soil and Agro-chemistry（Lu Rukun，2000）.The pH value was measured by potentiometric method at the water／soil ratio of 2.5：1.0.The organicmatter was measured using the potassium dichromate heating method.The hydrolyzable nitrogen was measured using alkaline hydrolysis diffusion method.Rapidly available Pwas measured using 0.5 mol／L NaHCO3extraction-phosphomolybdate blue spectrophotometric method.The rapidly available K was measured using 1 mol／L neutral NH4AC extraction flame spectrometry.The available Cu，Zn，Fe and Mn were measured using DTPA extraction and atomic absorption spectrophotometry.The available Ca and Mg were measured using 1mol／L neutral NH4AC extraction atomic absorption spectrophotometry.The available B was measured using hot water extraction spectrophotometic curcumin method.Total N was measured using Semi-micro Kjeldahl method.Total P was measured using NAOH melting molybdatetartaric emetic-ascorbic acid colorimetry.Total K was measured using NAOH melting flame spectrometry.

2.4 Classification standard of soil nutrientsFor the classification standard of soil nutrients，we consulted the Soil Nutrient Classification Standard formulated in the Second National Soil Census（prepared by National Soil Census Office in 1998）and available soil nutrient classification indicators prepared by experts of Guangxi University and Guangxi Academy of Agricultural Sciences.The classification indicators were listed in Table 1.Classification standard for pH of sugarcane soil：pH≤ 4.5：strong acid soil；pH 4.5-5.5：medium acid soil；pH 5.5-6.5：weak acid soil；pH 6.5-7.5：neutral soil；pH 7.5-8.5：alkalescent soil；pH ＞8.5：strong base soil.

Table 1 Classification standard for soil nutrients of Guangxi

2.5 Statistical analysisWe made statistical analysis of measurement results using Excel2003.

3 Results and analyses

3.1 The pH value of soil in sugarcane planting areas of southern GuangxiThe average pH value of soil in sugarcane planting areas of southern Guangxi is 4.94；strong acid soil accounts for 26.5%；acid soil accounts for 57.8%；weak acid soil accounts for 11.2%；neutral soil accounts for3.4%；alkaline soil accounts for 1%.Measurement results indicate that majority soil of sugarcane planting areas in southern Guangxi is acid soil.Especially for strong acid soil，it is required to properly apply lime for sugarcane growth.

3.2 The organic matters of soil in sugarcane p lanting area of southern GuangxiMeasurement result so f organic matters in samples of soil in southern Guangxi sugarcane planting areas are listed in Table3.The average content of organic matters in soil of southern Guangxi sugarcane planting areas is 24.5 g／kg，which remains at the medium level.The organic matter content is 6.03-44.58 g／kg，the standard deviation is7.22，and the coefficient of variation is29.51.6 samples have organic matter content higher than 40 g／kg，accounting for 1.2%of total samples；107 sam-ples have organic matter content of 30-40 g／kg，accounting for 21.5%of total samples，243 samples have organic matter content of20-30 g／kg，accounting for48.4%；107 samples have organic matter content of10-20 g／kg，accounting for27.1%；6 samples have organic matter content lower than 20 g／kg，accounting for 1.4%.

Table 2 Statistics of classification of pH of soil in sugarcane planting areas of southern Guangxi

3.3 Major elementsThe alkali-hydrolyzable N of soil in southern Guangxi sugarcane planting areas is 17.2-394.3 mg／kg，the coefficient of variation is 33.72%；39.76%lacks alkalihydrolyzable N（＜80mg／kg）；45.98%samples are medium level（80-120 mg／kg）；14.30%samples are abundant（＞120 mg／kg），as listed in Table3.The content of available P is1.7-95mg／kg，the coefficient of variation is21.72%，27.51%lacks available P（＜10mg／kg），29.92%is at medium level（10-20 mg／kg），and 42.57%is abundant（＞20mg／kg）.The content of available K is11.0-358.0mg／kg，the coefficient of variation is 85.84%，18.47%lacks available K（＜100 mg／kg），54.22%is at medium level（100-150mg／kg），and 27.31%is abundant（＞150 mg／kg）.The available N，P and K ofmost soil in southern Guangxisugarcane planting areas remain at medium level，and alkali-hydrolyzable N，available P，and rapidly available K is87.85，21.72 and 85.84mg／kg respectively.

Table 3 Statistics of classification of major nutrients of soil in sugarcane planting areas of southern Guangxi

Table 4 Statistics of classification of major nutrients of soil in sugarcane planting areas of southern Guangxi

3.4 Medium and trace elementsFrom Table 4，we can see that average content of available Ca of soil in southern Guangxi sugarcane planting areas is592.68mg／kg；55.02%lacks available Ca（＜500 mg／kg），19.08%is at medium level（500-700 mg／kg），and 26.10%is abundant（＞700mg／kg）.The content of available Mg is21.6-234mg／kg，the coefficient of variation is 54.84%，69.08%lacks available Mg（＜70 mg／kg），27.91%is at medium level（70-150 mg／kg），and 3.01%is abundant（＞30 mg／kg）.The exchangeable Ca and Mg of soil remain at medium and low level.There is variation of available Ca and Mg，the largest coefficient of variation is exchangeable Ca，as high as 82.50%，followed by available Mg（54.84%）.These indicate that there is large difference in available Mg and Ca in different land parcels of southern Guangxi sugarcane planting areas.

In southern Guangxi sugarcane planting areas，the content of available Cu is 0.01-2.28 mg／kg；7.02%lacks available Cu（＜0.2 mg／kg），75.10%remains at medium level（0.2-1.0 mg／kg），and 17.87%is abundant（＞1.0 mg／kg），as listed in Table 4.The available Zn of soil is0.12-3.32mg／kg；19.08%lacks available Zn（＜1.5 mg／kg），42.97%remains at medium level（1.5-3.0mg／kg），and 37.95%is abundant（＞3.0mg／kg）.The available Fe of soil is6.28-197.04mg／kg；0%lacks available Zn（＜1.5 mg／kg），4.02%remains at medium level（1.5-3.0 mg／kg），and 95.98%is abundant（＞3.0 mg／kg）.The available Mn of soil is 0.93-101.98 mg／kg；18.07%lacks available Mn（＜15 mg／kg），31.93%remains at medium level（15-30mg／kg），and 50.00%isa bundant（＞30mg／kg）.The available B of soil is0.08-1.51mg／kg；98.00%lacksavailable B（＜0.5 mg／kg），1.00%remains at medium level（0.5-1.0 mg／kg），and 1.00%is abundant（＞1.0 mg／kg）.There is different degree of variation in available B，Mn，and Zn；the available Mn has the highest coefficient of variation，followed by availa-ble Fe and available Cu，97.85%，89.91%and 63.73%respectively.These indicate that there is large difference in available Cu，Mn and Fe in different land parcels of southern Guangxi sugarcane planting areas.The available B is generally low or extremely low，0.23 mg／kg on average，the available Cu and Zn remain medium and high level，and the available Fe and Mn is generally rich.

4 Discussions

Soil nutrients are material bases of crop growth.Learning situation of soil nutrients is helpful for scientific application and management of fertilizers.Organic matters in soil play an important role in adjusting fertility factors such as water，fertilizer，gasand heat.They are also important for soil structure and cultivation，therefore，the content of soilorganic matters is an essential indicator for evaluating soil fertility.Soil organic matters can improve nutrient preserving capability and improve soil physical properties.Soilorganic matters are essential parts of soil and their content level is closely connected with soil fertility（Lin Dianet al，2007）.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（Wang Feiet al，2012）.Majority soil of southern Guangxi sugarcane planting areas is acid soil，and the content of organic matters，rapidly available N，P and K remain at medium and low level.This is consistent with analysis of Huang Shaofu and Huang Jieji（2006）about soil nutrients of sugarcane planting areas.Our survey of soil fertility in Wuming sugarcane planting area indicates that the soil organic matter is low，the available Pand K is slightly low，and the rapidly available K reserve is low.Studies of Jiang Yong and Huang Zhongxing（2001），Zhang Yuebin and Liu Shaochun（2004）indicate that soil organic matters are generally low，N，P and K are at medium and low level，and some soil seriously lacks K.In view of situation of acid soil，it is recommended to properly apply lime to satisfy growth demand of crops.Low content of rapidly available N，P and K is mainly because soil parent materials in sugarcane planting areas consist of limestone，silicobiolith，and quaternary lateritic soil，as well as weathering and eluviation.Compared with second national soil census，soil nutrients in southern Guangxi sugarcane planting areas have realized great improvement，especially in P and K.There is still a large gap with high yield soil conditions.Therefore，it is required to attach great importance to application of N，P and K fertilizers in sugarcane production.

Soil is an important place for sugarcane root system growing and absorbing water and nutrients，and soil nutrients and scientific fertilization are mineral nutrient bases of sugarcane growth.There are distinct differences in soil conditions of southern Guangxisugarcane planting areas，so it is recommended to manage sugarcane planting areas in accordance with local situations.Applying green manure and organic fertilizers can improve soil structure and improve soil activity.It is recommended to properly apply fertilizers according to situation of soil nutrients，to reach balance of supply and demand of nutrients.Dong Wenbinet al（2009）studied soil nutrients in Wuming district and found that there are great differences in soil nutrients，and argued that low organic matter content and high content of available Fe are major obstacles to growth of cassava.There are rich available Cu，Fe and Mn elements，but available Ca，Mg and B are deficient and may become major obstacles of crop growth.Thus，it is necessary to apply Ca，Mg and B fertilizers in future production.

Our survey results indicate that the pH value of soil in southern Guangxi sugarcane planting areas is generally below 6.5 and the average content of organic matters is24.47 g／kg；the average content of rapidly available N，P and K is87.85，21.72 and 85.84 mg／kg separately，and the percentage of shortage is 39.76%，27.51%and 18.47%respectively；the average content of available Ca and Mg is592.68 and 62.34mg／kg，and the percentage of shortage of available Ca and Mg is55.0%and 69.0%respectively；the average content of available Fe，Mg，Cu，Zn and B is43.35，26.96，0.65，0.93 and 0.24 mg／kg.These reflect that the overall soil fertility of sugarcane planting areas in southern Guangxi is not high，the organic matter is relatively low，the content of rapidly available N，P and K is at medium or low level，the content of Fe and Mn is high，and the available Cu and available Zn of most soil remain at medium level.This paper studies organic matters，pH value and major nutrients of soil in southern Guangxi sugarcane planting areas and discusses soil physical properties，medium and trace elements.In future，it is necessary to make further study on the relationship between soil physical properties，soil nutrients，factors influencing effectiveness of nutrients and crops，to provide theoretical basis for reasonable use and scientific fertilization.

5 Conclusions

It is concluded that the overall soil fertility of sugarcane planting areas in southern Guangxi is not high，the organic matter is relatively low，the content of rapidly available N，P and K is at medium or low level，the content of Fe and Mn is high，and the available Cu and available Zn of most soil remain at medium level.

［1］DONGWB，ZHOU LQ，HUANG JS，et al.Spatial distributions of soil nutrients and nutrient-limited factors on yield of cassava［J］.Guangxi Agricultural Sciences，2009，40（6）：686-690.（in Chinese）.

［2］DAO JM，LIU SC，FAN S，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.

［3］HUANG SF，HUANG JJ.Soil fertility status in sugarcane planting and soil testing and formulated fertilization of sugarcane［J］.Guangxi Sugarcane＆Cane sugar，2006，45（4）：10-12，17.

［4］JIANG Y，HUANG ZX.Analysis on the soil nutrients in the main sugarcane production areas of China［J］.Sugarcane and Canesugar，2001，（5）：5-10.

［5］KONG LZ，LIXH，LAN ZB，etal.Research and construction of management system for economic foundation data of Guangxi sugarcane industry［J］.Acta Agriculturae Jiangxi，2014，26（12）：103-107.

［6］LIN D，ZHENG LY，LIAO ZQ，et al.Soil fertility in banana plantation in Hainan Province［J］.Soil and Fertilizer Sciences in China，2007（2）：26-29.

［7］LU RK.Soil Agrochemistry Analysis Method［M］.Beijing：China Agricultural Science and Technology Press，2000：147-221.

［8］MA JB，YANG MF，TIANWH，et al.Soil nutrient status and fertilization recommendation in Xinping sugarcane planting areas［J］.Sugar Crops of China，2014，2（22）：56-58.

［9］National Soil Survey Office.China Soil［M］.Beijing：China Agriculture Press，1998：860-933.

［10］TANG QZ，TIAN ZX，HOU JK，et al.The soil nutrient condition and its control way on Liucheng sugarcane area［J］.Guangxi Sugarcane＆Canesugar，2003，4（33）：7-9.

［11］WANG F，RAN L，LV HF，etal.Study on classification of soilnutrient status of sweet potato in Chongqing［J］.Southwest China Journal of Agricultural Sciences，2012，25（2）：580-583.

［12］XIERL，TAN HW，ZHOU LQ，et al.Analysis of soil nutrient status in Xingbin sugarcane area of Guangxi［J］.Sugar Crops of China，2004（1）：22-25.

［13］ZHANG YB，LIU SC.Soil and its nutrient status of sugarcane areas in South China［J］.Southwest China Journal of Agricultural Sciences，2004，17（S1）：130-133.