Micro paddy lysimeter for monitoring solute transport in paddy environment

Abstract

The micro paddy lysimeter (MPL) was developed and evaluated for its performance to simulate solute transport in paddy environment under laboratory conditions. MPLs were constructed using soil collected from Field Museum Honmachi of Tokyo University of Agriculture and Technology, Japan. For the physical characteristics of the hardpan layer, parameters such as thickness, and soil aggregate size, affecting the percolation rate were studied. For the plow layer, two types of plow soils, sieved and un-sieved soils were compared. The sieved soil plow layer was produced by mixing air-dried soils of different aggregate sizes of D [ 9. 50, 9.50 C D [ 4.75, 4.75 C D [ 2.0 mm and D B 2.0 mm at 47.1, 19.5, 20.6, and 12.8%, respectively. The un-sieved plow layer soil was directly used after collecting from the field. Inert tracer was applied to ponding water with controlled boundary conditions to evaluate the reproducibility of the soil hydraulic characteristics. HYDRUS-1D was used to evaluate the movement of bromide tracer in the MPL. The proposed conditions of the MPL were that the hardpan layer can be made from soil aggregates smaller than 0.425 mm with 2 cm thickness and that the plow layer can be prepared with sieved or un-sieved soils. With these conditions, the obtained results proved that MPLs can be a useful tool to simulate solute transport in paddy environment.

Behavior of nursery-box-applied imidacloprid in micro paddy lysimeter

“…7) e MPL preparation protocol for unsieved soil 6) was employed in this study. Brie y, from top to bottom, MPL consisted of four layers: the top layer was pond water (3.0-6.7 cm) followed by a 14.0 cm ploughed soil layer, a 2.0 cm hardpan layer and a 1.0 cm glass bead layer (D. 1.0 mm).…”

“…e hardpan layer, which regulated percolation, was made from nely sieved soil (0.425mm) with a designed porosity of 0.61. e ploughed layer was prepared by mechanically mixing (UT2203-Kaku Han; Makita Corp., Japan) unsieved soil for about 15 sec. 6) Pond water 3 cm deep was added to the MPL about 10 days before transplanting.…”

“…Figure 1 shows that the water balance for the actual paddy plot and in MPL of both BT and AS treatments were identical, indicating the acceptable accuracy and precision of these MPL experiments for simulating the hydrological response of an actual paddy plot. MPL was reported to be capable of simulating homogeneous percolation at the desired rates and theoretical solute transport phenomena through the ploughed layer and the hardpan layer of the paddy eld, 6) and was also reported to be able to simulate di erent water management scenarios. 5) e measured pH at 02:30 p.m. uctuated between 7.7 and 10.7, the average pH was 9.8±0.8 (Table 2), indicating the alkaline condition of paddy water at the monitored time mainly due to CO 2 consumption during photosynthesis processes.…”

“…e micro paddy lysimeter (MPL) has proved to be a useful tool to investigate the fate and transport of solutes in the rice paddy environment. 6) e advantages of using MPL are that it is economical and not labor intensive. MPL can perform multiple experiments per year 6) and was able to simulate the dissipation of two granular herbicides with broadcasting application, yielding good agreement with the data in an actual eld experiment.…”

“…6) e advantages of using MPL are that it is economical and not labor intensive. MPL can perform multiple experiments per year 6) and was able to simulate the dissipation of two granular herbicides with broadcasting application, yielding good agreement with the data in an actual eld experiment. 5) e aim of this study was to utilize MPL to monitor the behavior of nursery-box-applied imidacloprid granules in paddy water and its residue and distribution in the ploughed soil layer (0-15 cm) under the de ned water management scenario of an actual paddy eld.…”