Study On The Water-soluble Organic Nitrogen And Organic Carbon In Intensively Managed Phyllostachys Praecox Stands

Phyllostachys Praecox is a favorite bamboo shoot species that has been widely planted in southern China.High rate of fertilization and heavy winter mulching have been a common practice to gain a good yield and better economic benefit.But along with the practice of new technique for successive years several problems such as bamboo grove deteriorate and soil quantity descent have been raised. The objective of this paper was to get an insight into the effects of intensive management on soil water-soluble 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 Phyllostachys Praecox stands by comparing with natural forest,and effects of the types and rate of fertilizer on WSON and WSOC.There are the following conclusions:1) The content of total organic carbon(TOC),total nitrogen(TN),WSOC,WSON apparently increased with the time of intensive management,the data for WSOC were respective 20.51,32.49,74.96 and 76.17 mg.kg^-1 soil with 0,5,10 and 15 years intensive management.The significantly difference(p＜0.05) in WSOC were observed between short-term(0 and 5 years) and long-term(10 and15 years) intensive management.The WSOC ratios of 15 years to 0 as well 5 years were respective 3.15 and 2.87.The abundance of WSON was in the order:15＞10＞0＞5,and WSON in stands with 15 years intensive management was significantly greater(p＜0.05)than the others,the ratios of 15 years to 0,5 as well 10 years were respective 1.46,3.15 and 2.87.Soil WSON in stands with 10 years intensive management was significantly greater than(p＜0.05) those in 0 and 5 years.It was observed that the proportions of WSOC out of TOC and WSON out of TN at the year 15 stands were significantly lower(p＜0.05) than those in early stages.Information from solid-state ¹³C NMR spectra discovered that alkyl-C and alkoxy-C were dominant,alkyl-C was increased but aromatic-C decreased with the increase time of intensive management,no apparent change in abundance of aromatic C observed was.The content of WSOC was related positively to abundance of bulk soil alkoxy-C(r²=0.9975).2) Dynamics of WOSN and WSOC of soil in intensive management Phyllostachys Praecox 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 WSOC to TOC was not altered by conversation of vegetation from natural forest to Phyllostachys Praecox stands,but improved the ratios WSON to TN by 12.33 and 8.54 times were true.The ratio of WSON to WSN in Phyllostachys Praecox stands was greater than those in natural forest but reached no significant level.The ratio of WSOC to WSON was in the order: broad-leaved forest＞Masson's pine＞Phyllostachys Praecox stands.Soil WSOC and WSON were positively related with TN,hydrolysable N,WSN,ammonium N,nitrate N,available P,available K and TOC at significant or great significant level,respectively,but negatively related to pH.3) It was found that from fertilization experiment in situ mulching with organic material and fertilization with both mineral fertilizer and manure resulted in increase of soil WSOC and WSON by comparing mulching to non-mulching site with same rate of fertilizer,and by comparing fertilization with zero fertilization under base of mulching.Soil WSOC and WSON improved with increase of fertilizer rate, the WSON ratio of higher and lower rate of fertilizer to control with zero fertilizer were respective 3.25 and 4.28,the corresponding data for WSON/TN were 3.22 and 4.08.The WSON ratio of mulching to non-mulching sites was 1.56 and 1.50 for WSON to TN.