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Evaluation of Pesticide Scenarios for the Registration Procedure

4. Impact of Application Date on leaching

• 4.1. Conditions for Analysis
• 4.2. Modelled Balances and Leaching Results
  • 4.2.1. Water and Mass Balance
  • 4.2.2. Pesticide Leaching
• 4.3. Summary and Concluding Remarks

Many parameters can be the focus of a sensitivity analysis regarding pesticide leaching (Dubus and Brown, 2002; www.eu-footprint.org). In this chapter we focus on the date of application, since changing this date is a part of the registration procedure, Appendix E. For the five PLAP-scenarios, changes in pesticide A, B, and C leaching due to a change in application date including changes in plant evolution are studied. The purpose of this study is to examine if the choice of application date and plant evolution influence, which type of pesticides that will pass the Danish pesticide approval system.

4.1. Conditions for Analysis

For the five PLAP scenarios Tylstrup, Jyndevad, Silstrup, Estrup, and Faardrup, the dates for spring and fall application are changed to respectively about 2½ weeks later and a month earlier than the dates used in the previous chapter. Both new dates are realistic when looking at the agricultural practice in Denmark and are given in Table 6. For the fall application, the date used in the sensitivity analysis can be regarded as less conservative with respect to pesticide leaching than the date used in the evaluation of scenarios.

Table 6. Crops, dose, and application/emergence dates used annually in the sensitivity analysis and in the evaluation of scenarios (Chapter 4).

To obtain a realistic agreement between application date and plant evolution in the sensitivity analysis, the emergence date of respectively the spring and winter cereals are set to April 15 and October 5 instead of April 1 and November 5 in the evaluation of scenarios, Table 6. The sensitivity analysis is conducted for pesticides A, B, and C defined in Chapter 3.1.3.

4.2. Modelled Balances and Leaching Results

4.2.1. Water and Mass Balance

Generally, the water and mass balance of the whole profile at the PLAP scenarios were not very sensitive to the change in application date and plant evolution.

Changes in the water balance of the whole soil profile were only observed for Tylstrup with spring cereals and Estrup with both spring and winter cereals. By the change in application date and plant evolution:

§  the actual evaporation decreased with 6-10 mm/year for the three scenarios.

§  the percolation increased with 1-6 mm/year for the two scenarios with spring cereals.

§  the drainage at Estrup increased with 8 mm/year for the scenario with spring cereals and decreased with 7 mm/year for the scenario with winter cereals.

Changes in the mass balance of the whole soil profile for:

§  the sand scenarios were less than 2% for the leaching, runoff, degradation, plant uptake and storage + solute infiltration component.

§  the clay scenarios differs with up to 9%. Generally, the changed application date had minor effect on the runoff and plant uptake component, whereas:

o   the scenarios with spring cereals generally gave rise to a decrease in leaching and storage + solute infiltration added with an increasing degradation and drainage,

o   the scenarios with winter cereals generally gave rise to a decrease in leaching and degradation added with an increasing storage + solute infiltration and drainage.

4.2.2. Pesticide Leaching

Changing the application date of pesticides by ~3 weeks had following impact on estimated leaching concentration 1 m b.g.s.:

• At sandy soils only a minor increase in leaching from pesticide A and C was observed. A drastic increase in Pesticide B leaching was however observed at both spring and fall application at Tylstrup and at the fall application at Jyndevad, Figure 11
• At the clay soils only minor effect on leaching was observed. Generally the leaching increased slightly, exception being pesticide B and C applied on Estrup and pesticide A applied on Faardrup, all of which leaching were found to decrease.

Figure 11. The yearly average pesticide leachate 1 m b.g.s. of a 20 years period respectively for Application Date I and II. The pesticide leachate 1 m b.g.s. is presented for sand and clay PLAP-scenarios with spring or winter cereals. Example of simulation ID “KaSC”: Ka represents Karup, S represents spring application, and C represents pesticide C. MAC is the maximum allowed concentration 0.1μg/l.

4.3. Summary and Concluding Remarks

The choice of application date and plant evolution were found to affect some of the estimated leaching output, and may thus influences which type of pesticides will pass the Danish pesticide approval system.

While pesticide A and C were only minor affected by application date, a major impact was observed for pesticide B when applied on the Tylstrup scenario. By  applying the pesticides ~three weeks later in the spring/earlier in the fall the leachate concentration 1 m b.g.s. of pesticide B increases with up to a factor 100 from below to beyond the maximum allow concentration 0.1 mg/l. A new leaching pattern can thus appear by choosing another application date and plant evolution.

Generally, the water and mass balance at the PLAP scenarios were not very sensitive to the change in application date and plant evolution. It should though be noticed that a drastic increase in drainage at the Estrup scenario with spring cereals was observed.

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Version 1.0 August 2007, © Danish Environmental Protection Agency