Soil acidification, salinization and nutrient characteristics in greenhouse vineyards in Tibet

Abstract:【Objective】Grape is one of the largest fruit trees in facility cultivation, which develops fast in China. The planting area of facility agriculture is increasing in Tibet. However, the relatively closed micro-ecological environment and the concept held by farmers that high yield depends on high input of fertilizer have created many problems in facility cultivation of grape and the problems are becoming more severe with years. Investigation of soil acidification, salinization and nutrients characteristic in grape greenhouses in different areas of Tibet provides guidance for reasonable fertilization and sustainable utilization of soil.【Methods】The p H, electrical conductivity (EC) and nutrients in greenhouse vineyard soils in different regions were studied using the outdoor bare land soil as the controls. Lhasa's soils were sampled from the greenhouses planted with grape for 4 (LS4) and 14 years (LS14) and from bare land (LSB) . Nyingchi's soils were sampled from the greenhouses planted with grape for 9 years (LZ9) and from bare land (LZB) . Shannan's soils were sampled from the greenhouses planted with grape for3 years (SN3) and from bare land (SNB) .【Results】 (1) The 0-60 cm soils of the outdoor bare land in all the areas were neutral to alkaline (p H between 7.0 and 8.0) , while p H values in the 0-60 cm soil in LS14, LS4 and LZ9 were below 7.0. The p H values of the surface (0-20 cm) soils of LS14 and LZ9 were 4.48 and 4.58, respectively, which were 40.44% and 41.21% lower (p < 0.05) than that of LSB and LZB, respectively. In addition, p H values of the 0-40 cm soil in LS14, LS4 and LZ9 ranged from 4.87 to 5.18, which were significantly lower (p < 0.05) than that of the bare soil at 20-40 cm. In general, there were serious soil acidification problems in the grape greenhouse soils in Lhasa and Nyingchi, and the Shannan is facing severe acidification risk. Excessive urea and diammonium phosphate input was the main cause for soils acidification. (2) The EC of the soil (0-60 cm) in the grape greenhouses was significantly higher (p < 0.05) than that of the bare soils and showed a decreasing trend with soil depth.The soil EC in LS14 was 0.75-2.48 m S · cm-1, which was significantly higher than in LSB by 15-31 times (p < 0.05) . The EC in the surface soil of LS4 was 0.48 m S · cm-1, which was significantly higher than that of the LSB (p < 0.05) . The soil EC of LZ9 and SN3 was less than 0.5 m S · cm-1 but still significantly higher than that of LZB and SNB. SN3, LZ9 and LS4 were mildly salinized and LS14 had high salinity. Large amount of potassium fertilizer and sheep manure application might have directly resulted in the salinization in LS14 soil. The combination of large amounts of urea and sheep manure might have exacerbated salinization. (3) The soil organic carbon, total nitrogen and total phosphorus in Lhasa increased with the increase in planting years, and the organic carbon content in LS14 was 50.10 g · kg-1, which was 2.4 times higher than that in LSB (p < 0.05) . Total nitrogen in LS14 was 3.0 times higher than in LSB (p < 0.05) , and total phosphorus was 3.4 times higher (p < 0.05) . Soil organic carbon content and total nitrogen content in LZ9 were not significantly different from those in LZB (p > 0.05) , while total phosphorus and total potassium content were significantly higher than in LZB (p < 0.05) .The organic carbon content in SN3 was 3.1 times higher than that in the control and was as high as67.32 g · kg-1 (p < 0.05) . The contents of soil organic carbon, total nitrogen and total phosphorus in SN3 soil were significantly higher than those in SNB (p < 0.05) , but there was no significant difference in total potassium content between SN3 and SNB. (4) The available soil nutrients in different areas showed different characteristics. The available nitrogen, phosphorus, and potassium contents of the greenhouse soils were significantly higher than those of the bare land (p < 0.05) , with the exception that the available nitrogen content in LS4 was significantly lower than in LSB (p < 0.05) . The available nitrogen, phosphorus and potassium in LS14 reached the highest level among all the treatments and were 1.26, 13.16, and 11.71 times higher than in LSB, respectively.【Conclusion】 (1) The soils in the grape greenhouses in Tibet are threatened by acidification and salinization. The p H in the greenhouse soils ranges from 4.49 to 6.71. Soils in LS14, LZ9 and LS4 are acidic, while that in SN3 is neutral. The main reason is the excessive use of urea and diammonium phosphate. (2) SN3, LZ9 and LS4 have low salinity levels, which may cause slight obstacle to crop growth, while LS14 is highly salinized and ad adverse to crop growth. The excessive use of potassium fertilizer and large amount sheep manure input might be one of the main factors to cause soil salinization in LS14. (3) The nutrient contents of the soils in the grape greenhouses have far exceeded the high level of the quick-acting nutrients. Excessive inputs of fertilizers have undoubtedly reduced the efficiency of nutrient utilization and increased production costs. Therefore, establishing reasonable and efficient fertilization methods based on the current status of the soil is extremely urgent.