Assessment of nitrogen mineralization of organic materials on sands of Central Vietnam: incubation experiments

Hoang Thi Thai Hoa1, Tran Thi Anh Tuyet1, Do Dinh Thuc1, Surender Mann2, Richard Bell2

1 Hue University- Hue College of Agriculture and Forestry, 102 Phung Hung street, Hue city, Thua Thien Hue province, Vietnam, 530000, http://www.huaf.edu.vn, [email protected]

2 School of Veterinary and Life Sciences, Murdoch University, Murdoch WA 6150 Australia

Abstract

Sandy soils of Central Vietnam represent an important soil order that increasingly contributes to regional economic growth. However these soils have generally low productivity because of chemical and physical constraints associated with low pH values and sand contents exceeding 70%, are common for those soils. Obviously, organic matter management represents a key factor for crop productivity improvement on these soils. However, before considering the possible contributions of various organic amendments, it is important to evaluate the actual contribution of the initial soil organic matter through its N-mineralization, considered as a prime source of N for plants. Therefore, soil samples (0-20 cm) representing peanut growing sandy soils were collected before the spring season to incubate with 4 types of organic materials which added to the same sandy soil amount under anaerobic conditions for 0, 5, 10, 20, 30 and 40 days to determine their N-mineralization capacity. The release of NH4+, NO3- was on average higher in treatments with added organic fertilizers. Significant amounts of NH4+ and NO3- were found with different types of organic materials added to the soil and increased with the time of incubation from 5 to 40 days after incubation. Fitting the results with a first order kinetic equation led to the calculation of potentially mineralizable nitrogen. The N-pool identified in this study can be considered as very labile N which might be available to crops within few weeks. Therefore, the total N-content of soils cannot be considered as a reliable indicator of short term N-availability.