『Abstract
The environmental and economic consequences of nitrogen (N) lost
in rice-based systems in Vietnam is important but has not been
extensively studied. The objective of this study was to quantify
the amount of N lost in major cropping systems in the Red River
Delta. An experiment was conducted in the Red River Delta of Vietnam,
on five different crops including rose, daisy, cabbage, chili,
and a rice-rice-maize rotation during 2004 and 2005. Core soil
samples were taken periodically in 20-cm increments to a depth
of 1 m and analyzed for nitrate-nitrogen and ammonium-nitrogen.
The results indicate appreciable leaching losses on N in high-rainfall
and irrigation conditions, especially when fertilizer application
was not well synchronized with crop N demand. Highest annual leaching
losses of N were recorded in flowers with 185-190 mm of percolation
and 173-193 kg N ha-1, followed by vegetable (cabbage
and chili) with 10-122 mm of percolation and 112-115 kg N ha-1,
while it was lowest in rice with about 50 kg N ha-1.
We developed a simple N transport model that combined water and
N movement through the soil profile. In most cases, the model
accurately predicted the seasonal dynamics of N as well as N flow
between soil layers and the amounts of N lost from the soil profile.
The simulated results of N leaching with soil “puddling” conditions
illustrate the advantage of an impermeable or hardpan layer in
increasing water and nutrient use efficiencies in these soils.
These model results also showed that it is possible to accurately
estimate N losses with only a few parameters and helped us identify
the risks of N leaching.
Keywords: Horticulture; Flowers; Vegetables; Rice; Nitrate; Nitrogen
losses; Modeling』
1. Introduction
2. Materials and methods
2.1. Study area
2.2. Experimental setup
2.3. Field sampling, soil, and data analysis
2.4. Nitrogen transport model
2.4.1. Water balance
2.4.2. Nitrogen balance
2.4.3. Model calibration and simulation
3. Results
3.1. Measured nitrogen dynamics
3.1.1. NO3-N dynamics
3.1.2. NH4-N dynamics
3.1.3. Simulated nitrogen dynamics
3.1.4. Nitrogen dynamics in flowers
3.1.5. Nitrogen dynamics in vegetables
3.1.6. Nitrogen dynamics in rice
3.1.7. nitrogen leaching losses
4. Discussion
4.1. Soil mineral nitrogen dynamics
4.2. Modeling nitrogen leaching losses
5. Conclusions
Acknowledgements
References