Soil Soluble Nitrogen Of In Organic Vs Conventional Vegetable Production Systems

Nowdays, development of organic agriculture has become more and more significant in ecology, economy and people's daily social lives due to its increasing relationship with public health. Among all the indicators of organic agriculture systems, nitrogen is the most decisive one which could represent the quality of soils and may further influence the quality of the agriculture product. In this study, by measuring the content of soluble nitrogen of soils from Chong Ben Tang farm, we evaluated the effect of vegetable production system (organic or conventional), cultivation manners (open field or greenhouse) and sampling time (autumn, winter, spring and summer) on the soluble nitrogen, which may be of great significance for organic production theory.1. Different management practices and their impacts on soil soluble nitrogenThe values of soil total carbon, total nitrogen, pH value, SON, DON, TSN and SON/TSN of organic vegetable production system were significantly higher than conventional vegetable production systems, while the values of TN, EC, FAA and FAA/TN ratio displayed as conventional production system higher than organic production system, and there was a slight change for the ammonium nitrogen of organic production systems. The values of soil SON and TN, TC, C/N, DON and the pH was significantly, negatively correlated and non-correlated with that of NO3--N, NH4+-N and EC.2. The effect of different cultivation manners on soil soluble nitrogenThe values of total carbon, total nitrogen, EC, nitrate, TSN and the FAA showed an order of organic greenhouse> organic open field, while pH value, SON/TSN ratio of organic open field system were higher than those of organic greenhouse. The effect of cultivation manner on SON and ammonium nitrogen content varies due to different seasons, on the SON/TN and organic production systems, FAA/SON had no significant effect. On the other hand, there was no impact of cultivation manners on FAA/SON ratio. As for the nitrate nitrogen, the values of organic open field in autumn and organic greenhouse in winter were significantly higher than that in other seasons, while the values of conventional open field and conventional greenhouse displayed a decreasing sequence of autumn, summer, winter and spring, with an average content of 33.1, 101.0, 225.8 and 396.1 mg·kg-1. There was no significant changes of ammonium according to sampling time, with an average annual concentration of ammonium 9.5, 9.3, 8.1 and 10.5 mg·kg-1. The values of total carbon and total nitrogen of organic open field and greenhouse, conventional open field and greenhouse fluctuated with higher values in winter and summer and lower values in autumn and spring. The average content of total carbon for the systems above were 25.1, 26.5, 19.1 and 18.9 g·kg-1, while the average content of total nitrogen were 3.0, 3.3, 2.7 and 2.7 g·kg-1, respectively.3. Soil organic soluble organic nitrogen in organic production systemThe SON concentration in organic production systems (both open field and greenhouse) displayed an order of summer> spring> winter> autumn, with average annual values of SON 49.8 and 52.4 mg·kg-1, which agreed with the values of FAA. The average content of FAA, FAA / SON ratio and FAA / TN ratio in open field and greenhouse systems were 3.7 and 4.9 mg·kg-1, 6.9% and 9.0%, 0.12% and 0.15%. Compared with ultracentrifugation method, the average content of SON extracted with salt solution (KCl) was 2.3 times of DON content.4. Free amino acid composition and content in soil12-15 amino acids could be detected in all production systems, and the results showed no basic amino acid, while the percentages of neural amino acids and acidic amino acids were >70% and <24.7%, respectively. The sulfur amino acids appeared in some soils and the percentage was lower than 5%. The main types of amino acids in all 18 tested soils were glutamic acid, valine, alanine, leucine, isoleucine, tyrosine and phenylalanine, the content of which occupied 76.3%-80.6% of the whole content of the amino acids. Both the production system and cultivation manner could affect the content of amino acids in the soils based on different FAA types.In short, the soil soluble nitrogen, especially soluble organic nitrogen is of great significance to the nitrogen content in soil, and may be strongly affected by different factors. Organic nitrogen increased due to the inputs of organic manure, straw, etc., which may lead to an improvement of SON and FAA. While the different cultivation manners for vegetables resulted in the elevated soil temperature, enhancement of microorganisms'activities and reducing leaching, this may further lead to increasing of the content of SON and FAA. The seasonally variation of SON and FAA may also demonstrate the crucial role of microorganisms in soil organic nitrogen mineralization and the biodiversity in organic production systems is the main factor of the increasing of SON and FAA.