| Pinghe county is the main pomelo production areas,with planting area,output and exports ranking first in China.Long-term excessive fertilization had resulted in soil seriously acidification,nutrients accumulation and imbalance and affected the yield and quality of pomelo.However,there were few studies on copper and boron nutrition of pomelo up till now.In this paper,soil,leaf,fruit samples from 314 pomelo orchards and 48 soil profile samples were analyzed to study the nutrition status of copper and boron as well as their relationship with fruit quality.The main conclusions were as follows:1.Copper nutrition status in Guanxi pomelo orchardsThe content of soil total copper ranged from 3.07mg·kg-1 to 176.93 mg·kg-1,average was 30.15 mg·kg-1.The content of soil available copper ranged from 0.01 mg·kg-1 to 29.62 mg·kg-1,average was 5.20 mg·kg-1.Soil available copper content of 24.13%soil samples was lower than the critical value of 2 mg·kg-1,46.98%soil samples was within the suitable range(2 mg·kg-1-6 mg·kg-1)and 28.89%was enrichment(>6 mg·kg-1).The content of soil available copper decreased with the increase of soil depth in 0-60 cm layer,and the average content of soil available copper in 0-20 cm,20-40 cm and 40-60 cm layers were 19.64 mg·kg-1,9.76 mg·kg-1 and 6.40 mg·kg-1,respectively.Analysis showed that soil available copper content of 0-20 cm layers significantly correlated with 20-40 cm as well as 40-60 cm layers(correlation coefficients was 0.78**,0.54**).Copper accumulation in soil surface may promote copper leaching and lead to the increase of copper in bottom soil.Soil total copper content,CEC,organic matter content and planting years affected the content of soil available copper.Analysis showed that soil available copper content significantly correlated with soil total copper content(y = 0.12 x + 1.55,r = 0.59**).Soil available copper content was increased with the increase of planting years,CEC and organic matter content.Total copper content of 55 commercial organic fertilizers from Pinghe market ranged from 4.33 mg·kg-1 to 291.06 mg·kg-1,average was 63.77 mg·kg-1.Copper content of 21.82%samples from organic fertilizer,biological organic fertilizer and organic-inorganic compound fertilizer was higher than the maximum copper limited level(100 mg·kg-1)of compost in Germany,implying large amounts organic fertilizer application would result in copper enrichment.Copper content of pomelo leaf ranged from 2.82 mg·kg-1 to 180.46 mg·kg-1,average was 44.88 mg·kg-1.The rate of leaf copper content exceeding the upper limit of appropriate range(8.0 mg·kg-1-17 mg·kg-1)was 70.23%,which was obviously higher than 28.89%,the rate of soil samples with available copper enrichment.The results suggested that leaf copper enrichment was caused by extensive use of copper pesticides such as Bordeaux mixture.Leaf copper content increased with the increase of soil available copper content and years of tree.Analysis showed leaf copper content(y)and leaf Ca/Cu ratio(x)had significantly negative correlation(y = 21081.35 x-0 94,r =-0.97**).Copper content of pomelo fruit was within the range of 1.52 mg·kg-1-15.39 mg·kg-1,and average was 5.64 mg·kg-1.It showed that fruit copper content increased with the increase of soil available copper content as well as leaf copper content.Analysis showed fruit copper content(y)and fruit Ca/Cu ratio(x)had significantly negative correlation(y = 138.08 x-0.53,r = 0.72**).Fruit copper accumulation caused the increase of titratable acid and the granulation of pomelo.Fruit granulation decreased with the increase of fruit Ca/Cu ratio.2.Boron nutrition status in Guanxi pomelo orchardsThe range of soil available boron content was within 0.05 mg·kg-1-4.61 mg·kg-1 and average was 0.77 mg·kg-1.Available boron content of 43.57%soil samples was lower than the critical value of 0.5 mg·kg-1,33.54%soil samples was within the suitable range(0.5 mg·kg1-1 mg·kg-1)and 22.89%was enrichment(>1 mg·kg-1).The content of soil available boron was affected by soil depth,planting years and CEC.Soil available boron content in different layers was in the order of 0-20 cm>20-40 cm>40-60 cm.The results showed that soil available boron content increased with the increase of planting years and CEC.The range and average leaf boron content were 9.61 mg·kg-1-252.02 mg·kg-1,72.47 mg·kg-1,respectively.The rate of leaf boron content exceeding the upper limit boron appropriate range(15 mg·kg-1-50 mg·kg-1)was 74.84%,which was obviously higher than 22.89%,the rate of soil samples with available boron enrichment.The results showed that leaf boron enrichment was caused by the extensive use of foliar boron fertilizer.Analysis showed that leaf boron content(y)and soil available boron content(x)had a significantly correlation(y = 11.54 x + 62.94,r =0.24*),while leaf boron content(y)and leaf Ca/B ratio(x)had significantly negative correlation(y = 9033.92 x-0.80,r =-0.88**).The range of fruit boron content was within 1.13 mg·kg-1-57.50 mg·kg-1,and average was 14.07 mg·kg-1.Fruit boron content increased with the increase of soil available boron content as well as leaf boron content.Fruit boron content(y)and fruit Ca/B ratio(x)had significantly negative correlation(y = 304.81 x-0.63,r = 0.77**).The results showed that boron enrichment resulted in pomelo granulation.Fruit granulation decreased with the increase of fruit Ca/B ratio.In summary,there existed high copper and boron content in Guanxi pomelo in Pinghe county.The enrichment of copper and boron lead to pomelo granulation.Efforts should be made to manage copper and boron nutrition for pomelo production.Applying calcium fertilizer could alleviate the harm of excessive copper and boron. |
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