Factors impacting yields in rain-fed paddies of the lower Mekong River Basin     

Katsuyuki Shimizu  Takao Masumoto  Thanh Hai Pham 《Paddy and Water Environment》2006,4(3):145-151

The Mekong River Basin (MRB) is the biggest basin in Monsoon Asia. About 80% of the agricultural lands, which occupy about 40% of the basin are rain-fed paddy rice area. Therefore, it is assumed that changes in rain-fed paddy rice production affect the total agricultural production to a great degree in the Mekong River Basin. While there are many factors affecting the productivity of rain-fed paddies, such as climate, water use, rice varieties, applications of manure, fertilizer and agro-chemicals, sowing date and other agronomic practices, this paper focuses on the relation between rainfall and yields of rain-fed paddies. Agricultural statistics and rainfall data were collected and analyzed for all 24 provinces in Cambodia for the years 2001 and 2002. Factors such as soil fertility and other natural conditions were removed by comparing the yield and rainfall in one province for different years. Special attention was given to the relation between yields of paddy in the wet season and rainfall, considering factors such as rice varieties, soil fertility, irrigation ratio and the ratio of area damaged by flood, drought, and insect. Although it is not easy to assess those impact factors on yields because they are organically interactive, the following results were obtained: (1) The ratio of high yielding varieties (HYV), soil fertility, and irrigation ratio among many factors that affect yields individually, especially if they are combined, (2) Total rainfall did not have a significant influence on rice yields even for the rain-fed paddies if it was over 700 mm in wet season, and one of the reasons for this would be that there exist supplementary water uses through small ponds and water ponding in local land depressions in and around paddies.  相似文献   

Interactive effects of ammonium application rates and temperature on nitrous oxide emission from tropical agricultural soil     

Van Ngoc Tuong Hoang 《Soil Science and Plant Nutrition》2013,59(6):767-773

Emissions of nitrous oxide (N₂O), a potent greenhouse gas, from agricultural soil have been recognized to be affected by nitrogen (N) application and temperature. Most of the previous studies were carried out to determine effects of temperature on N₂O emissions at a fixed N application rate or those of N application rates at a specific temperature. Knowledge about the effects of different ammonium (NH₄⁺) application rates and temperatures on N₂O emissions from tropical agricultural soil and their interactions is limited. Five grams of air-dried sandy loam soil, collected in Central Vietnam, were adjusted to 0, 400, 800 and 1200 mg NH₄-N kg^–1 soil (abbreviated as 0 N, 400 N, 800 N and 1200 N, respectively) at 60% water holding capacity were aerobically incubated at 20°C, 25°C, 30°C or 35°C for 28 days. Mineral N contents and N₂O emission rates were determined on days 1, 3, 5, 7, 14, 21 and 28. Cumulative N₂O emissions for 28 days increased with increasing NH₄⁺ application rates from 0 to 800 mg N kg^–1 and then declined to 1200 mg N kg^–1. Cumulative N₂O emissions increased in the order of 35°C, 20°C, 30°C and 25°C. This lowest emission at 35°C occurred because N₂O production was derived only from autotrophic nitrification while other N₂O production processes, e.g., nitrifier denitrification and coupled nitrification-denitrification occurred at lower temperatures. More specifically, cumulative N₂O emissions peaked at 800 N and 25°C, and the lowest emissions occurred at 1200 N and 35°C. In conclusion, N₂O emissions were not exponentially correlated with NH₄⁺ application rates or temperatures. Higher NH₄⁺ application rates at higher temperatures suppressed N₂O emissions.  相似文献   

Simultaneous removal of Cu and PAHs from dredged sediments using flotation     

Dileep Palakkeel Veetil  Guy Mercier  Jean-Francois Blais  Myriam Chartier  Lan Huong Tran 《Journal of Soils and Sediments》2013,13(8):1502-1514

Purpose

This study addresses the feasibility of a flotation technique, using a lab-scale flotation cell, to simultaneously remove both metals and polyaromatic hydrocarbons (PAHs) from fine sediment fractions (<250 μm) that are potentially contaminated with copper (Cu).

Materials and methods

A multiple flotation process with three consecutive flotation stages was performed on three sediments (13S, 14B, and 24A) with different particle size distributions, Cu and PAH concentrations, and organic matter contents.

Results and discussion

Flotations performed under selected conditions allowed for significant removal of both Cu (61–70 %) and PAHs (75–83 %) with acceptable froth recoveries of approximately 23–29 %. Removal rates for arsenic, lead, and zinc were 48–61, 40–48, and 32–36 %, respectively. Flotation selectivity of Cu was greatly influenced by the contents of fine particles and organic matter of the sediments. The maximum flotation selectivity was obtained for the 53–125-μm size fraction. The high flotation selectivity of Cu (2.5–3.2) and PAHs (3.0–3.6) demonstrated the feasibility of flotation to treat soils or sediments containing both organic and inorganic pollutants.

Conclusions

Overall, the flotation results showed a high selectivity for both Cu and PAHs and demonstrated the feasibility of flotation to treat media contaminated with organic and inorganic contaminants.  相似文献   

Nitrogen use efficiency and drought tolerant ability of various sugarcane varieties under drought stress at early growth stage     

Dinh Thai Hoang  Takaragawa Hiroo 《Plant Production Science》2013,16(2):250-261

ABSTRACT