Paddy fields

Development of paddy field rice herbicide Thenylchlor, A-(2,6-dimethyl-phenyl)-A-(3-methoxy-2-thenyl)chloroacetamide 98YGK221. 

A pair of oxen pull a wooden plow through a muddy paddy field in Sri Lanka. (Corbis-Bettmann)... 

Na is a very reactive substance which is never found free in nature. It is not generally used as an incendiary agent as such but, because of its tendency not only to float on w, but also to ignite spontaneously in contact with it, it may be added to napalm for use against river targets or enemy positions in rice paddy fields or in snow (Ref 7, p 103 Ref 4, pp 28-29)... 

The concentration of chlornitrofen in river water released from flooded paddy fields 30-60days after application was detected in the range 0.039-1.25 agL . Eurther, it was reported that the DTso of diphenyl ether herbicides in groundwater, river water and seawater were 17-84, 14-140 and 10-88 days for chlornitrofen, and 18-131,4-206 and 6-23 days forbifenox, respectively. Diphenyl ether herbicides in... 

Sampling sediment and water in rice paddy fields and adjacent water bodies... 

In key rice-producing regions in Asia, rice production is performed mostly in paddy fields where crop production has been highly sustainable owing to ... 

The application of pesticides to paddy fields represents a unique set of issues compared with many other use patterns. Agrochemicals used in rice production are introduced directly or indirectly into paddy water, and there are more opportunities for... 

In this article, sampling methods for sediments of both paddy field and adjacent water bodies, and also for water from paddy surface and drainage sources, streams, and other bodies, are described. Proper sample processing, residue analysis, and mathematical models of dissipation patterns are also overviewed. 

When aimed at a single paddy field, the waterway connected with a paddy field serves as a target for a survey. Since a water intake and a drain are installed in each paddy, a major flow of water prevails from the intake to the drain. Hence, starting and ending points should be considered when water sampling is done. For the sampling of water, at least one point in the upstream of the inflow and more than one point in the downstream of the drain should be set. 

When aimed at a group of paddy fields (an area or a region), sampling points should be set at locations where all the irrigation canals come into the area and all the drainage canals go out from the area. 

For water sampling from drainage or streams, points near a drain port of a paddy field or an industrial factory, etc., should be avoided in order that water monitoring reflects the concentration of agrochemicals in the entire area rather than a point source. 

The physico-chemical characteristics of the sediment sample significantly influence the fate of agrochemicals in a paddy field and a waterway system. Therefore, the factors that influence adsorption, retention, and degradation of agrochemicals are very important. As a minimum the characteristics of the sediment sample listed below should be described ... 

Data on weather conditions, especially temperature and rainfall (temporal distribution and intensity) in the study area are essential for the evaluation of the dissipation data. It is very important to understand the water balance in the paddy field as accurately as possible when calculating the rate of outflow. Records of changes in water temperature and sediment temperature are also helpful for modeling the behavior of a chemical in the rice paddy field. 

Figure 2 Typical work system and water management for rice cultivation in paddy fields...

Recommended sampling points for paddy field area study... 

Figure 3 Recommended sampling points for a single paddy study and a paddy field area study...

Figure 4 Method of taking sediment samples in a paddy field minimizing contamination with surface sediment and water...

Only a few models applicable to paddy field conditions have been developed. RICEWQ by Williams, PADDY by Inao and Kitamura," and PCPF-1 by Watanabe and Takagi are useful for paddy fields. EXAMS2 by the United States Environmental Protection Agency (USEPA), a surface water model, can also be used to simulate paddy fields with an appropriate model scenario and has been used for the prediction of sulfonylurea herbicide behavior in paddy fields. The prediction accuracy of PADDY and PCPF-1 is high, although these models require less parameter... 

RICEWQ was the first model developed for agrochemical runoff from paddy fields, incorporating aircraft application, dissipation by drift, adhesion on leaf surfaces, and dissipation from the leaf surface in addition to the processes affecting degradation and transport in sediment and paddy water. An important parameter, desorption from sediment to paddy water, is not considered, although this is not as important as other parameters in paddy fields such as sedimentation rate, behavior of SS, etc. 

The objective of sediment and water sampling is to obtain reliable information about the behavior of agrochemicals applied to paddy fields. Errors or variability of results can occur randomly or be due to bias. The two major sources of variability are sediment body or water body variability and measurement variability . For the former, a statistical approach is required the latter can be divided into sampling variability, handling, shipping and preparation variability, subsampling variability, laboratory analysis variability, and between-batch variability. ... 

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