Study On The Water Soluble Organic Nitrogen And Organic Carbon In Intensively Managed Castanea Mollissima Blume Stands

Chestnut (Castaneda mollissima Blume), as a specie of Castanea of Fagaceae, is one of the earliest cultivated fruit trees in China and it has been 2000 to 3000 years of cultivation history. With the development of agriculture more and more fruit forests with good profits, such as chestnut, has been managed intensively. The intensive management was generally undertaken by weeds cleaning and mineral fertilizer application combining with soil plowing. The objective of this paper was to understand the effects of intensive management on soil water-soluble organic nitrogen (WSON) and organic carbon (WSOC). Two investigations and one in situ fertilization experiment have been conducted to reveal the changes of WSN and WSOC with increasing time of intensive management, annually dynamics of WSN and WSOC under chestnut stands by comparing with natural forest and effects of the types and rate of fertilizer on WSN and WSOC. There are following conclusions:1) The content of WSN were respective 22.00, 19.53, 11.80 and 11.28 mg.kg^-1 soil with 0, 5, 10 and 20 years intensive management, the corresponding data for WSOC were 57.32, 50.24, 39.54 and 34.26 mg.kg^-1, indicating that soil WSN was decreasing with intensification time but significant difference (P<0.05) was observed between 5 years and 10 years intensification time. With the intensively managed of Chestnut, the ratios of water-soluble organic N ( WSON ) to WSN, WSOC to soil total organic C (TOC) and WSOC to WSON remain unchanged, while WSON to soil total N (TN) decreased significantly (p<0.05) at 10 years intensive management comparing with 5 years. Soil WSON was negatively (p<0.05) related to TN with correlation coefficient of -0.5745, but positively correlated with the hydrolysable nitrogen and WSN with correlation coefficient of 0.5508 (p<0.05)and 0.9936(p<0.01), respectively, and correlation coefficients between WSON and ammonium N as well nitrate N were respective 0.2159 and -0.0076 indicating no any relationship between them.2) Dynamics of WSN and WSOC of soil in intensive management Chestnut stand, Masson's pine and broad-leaved forest appeared a similar pattern with higher in colder season but lower in warmer ones. The ratios of WSON to TN and WSOC to TOC generally followed similar dynamic pattern of WSON and WSOC. There was no significant difference in the ratios of WSOC to TOC and WSON to WSN between intensive management of chestnut and natural forest. However the average ratio of WSON to TN in chestnut stands was 1.89 and 1.34 time as those in Masson's pine and broad-leaved forest respectively. The decrease ratios were measured for TOC to TN, WSOC to WSON especial the latter one.3) Fertilization experiment in situ composed of 5 treatments was respective: control with zero fertilizer, (1)commonly used fertilizer rate (2250 kg.ha^-1 N:P:K=15:15:15), (2) 2 times of treatment 1,(3) treatment 1 plus rape cake with equivalent N of treatment 1, (4) pure rape cake with 2 times of equivalent N of treatment 1. Higher rate fertilization of mineral fertilizer and mixture of mineral fertilizer and rape cake resulted in increase of soil WSON compared with control and commonly used fertilizer rate, so did the ration of WSON to total N. However fertilization of pure rape cake did not improved soil WSON in Chestnut stands.