Studies On Soil Soluble Organic Nitrogen And Its Seasonal Dynamics Under Adjacent Various Orchards

This study examined the subtropical orchard ecosystems with the same soil parent material and soil type of two different cover types(longan and loquat) in Fujian. Using KCl(2mol/L)extraction-high catalytic oxidation method to carry out the soluble organic nitrogen(SON)concentrations and seasonal variation of different orchard ecosystems,in order to reveal the soil soluble organic nitrogen concentrations, vertical difference, seasonal dynamics and its componentin between the different fruittypes. The main results showed as follows:1.Concentrations of Soil SON in the tested longan and loquat orchard ranged from 11.05-25.83mg/Kg and 6.93-20.72mg/Kg at 0-20cm soil layer and ranged from 7.27-15.73mg/Kg and 2.32-13.56mg/Kg at 20-40cm soil layer. Concentrations of soil SON under different orchards in different seasons at the upper soil layer were respectively higher than that at the lower layer, the differences were both significant or highly significant. The differences in concentrations of soil SON between longan and loquat orchard at 0-20cm and 20-40cm soil layer in different seasons were significant or highly significant .2.Concentrations of soil SON in the tested longan and loquat orchard at 0-20cm soil layer respectively accounted for 63.97-76.26% and 58.81-67.27% of total soluble nitrogen(TSN),the average of SON/TSN was respectively 69.60% and 63.62%; SON concentrations in the corresponding layer respectively accounted for 4.13-4.86% and 4.11-4.31% of total nitrogen(TN),the average of SON/TN was 4.38% and 4.18%.At 20-40cm soil layer,concentrations of soil SON under different orchards accounted for 78.54-92.32%% and 65.12-77.59% of total soluble nitrogen(TSN), the average of SON/TSN was respectively 85.22% and 72.28%; SON concentrations in corresponding layer respectively accounted for 3.92-4.89%% and 3.25-4.31% of total nitrogen(TN),the average of SON/TN was 4.38% and 3.77%.3.Concentrations of total free amino acid(TFAA)in the tested longan and loquat orchard at the upper soil layer were respectively higher 52.35% and 48.55% than that at the lower layer soil,the vertical differences were both highly significant. At 0-20cm soil layer, concentrations of total free amino acid(TFAA) in the tested longan orchard were higher 6.74% than that in the tested loquat orchard, the difference was significant .At 20-40cm soil layer,though the concentrations of total free amino acid (TFAA)in longan orchard were higher than that in loquat orchard, the difference did not reach a significant level. There were 13 kinds of free amino acids at 20-40cm soil layer in the tested longan and loquat orchard: neutral amino acids (threonine,serine, glycine, valine,alanine,isoleucine,leucine and Phenylalanine),amino acids(aspartic acid and glutamic acid),sulfur-containing amino acids(cystine and methionine) and basicamino acid (arginine). At 0-20cm soil layer, concentrations of methionine and arginine amino acid in longan and loquat orchard were in a high proportion of the total free amino acid(TFAA).At 20-40cm soil layer, there were 11 kinds of free amino acids, lack of valine and andisoleucine compare to 0-20cm soil layer;the proportion of methionine and phenylalanine concentrations in longan and loquat orchard was relatively high.4.The average concentrations of total free amino acid (TFAA)in the tested longan and loquat orchard at 0-20cm soil layer respectively accounted for 9.23% and 9.80% of the average concentrations of soluble organic nitrogen(SON),and the average concentrations of the other soluble organic nitrogen(OSON)accounted for 90.77% and 90.20% . At the 20-40cm soil layer,the average concentrations of soil SON in the tested longan and loquat orchard accounted for 32.63% and 37.31% of the average concentrations of soluble organic nitrogen(SON),and the average concentrations of the other soluble organic nitrogen(OSON) accounted for 89.30%,indicating that soil free amino acids in the tested orchards accounted for only a small part of the SON.5.The seasonal variation of soil SON concentrations in different orchards at the same soil layer presented "N" change: soil SON concentrations in summer and winter were higher than that in spring and autumn.In longan orchard, soil SON concentrations at 0-20cm and 20-40cm soil layer in winter were the highest up to 25.83mg/Kg and15.73mg/Kg. In loquat orchard, concentrations soil SON at the different soil layers in summer were the highest of 20.72mg/Kg and 13.56mg/Kg. The differences in concentrations of soil SON at the different soil layers in longan and loquat orchard between winter and spring, winter and autumn, summer and spring, summer and autumn, autumn and spring all reached a highly significant level,while the difference between summer and winter were not significant , which indicated that the maximum concentrations of soil SON in the tested orchards were both in summer and winter.