The GROWSAFE^® Calculator: Choosing pesticides that leach less and do not build up in the soil

Valerie Snow^1,3, Steve Green¹, Sarah Gurnsey², Chris Veale¹, Brent Clothier¹, Nigel Ironside⁴ and Peter Ensor⁵

¹HortResearch, PB 11-030, Palmerston North, New Zealand, www.hortresearch.co.nz Email: bclothier@hortresearch.co.nz²HortResearch, PB 1401, Havelock North, New Zealand ³now at AgResearch, PB 11-008, Palmerston North, New Zealand Email: val.snow@agresearch.co.nz⁴Hawke’s Bay Regional Council, Napier, New Zealand (now with Ministry for the Environment, PO Box 10-362, Wellington, New Zealand ⁵New Zealand Agricultural Education Trust, PO Box 10-232, Wellington, New Zealand

Abstract

There is growing concern about the environmental and health risks posed by the use of pesticides in the production and protection of crops in modern agricultural systems. Both for environmental reasons, and market access requirements, tools are being sought to provide growers with advice as to which chemicals, and which practices, provide the best possible results in terms of the environmental performance of pesticide choice and practice.

Here, we describe a decision-support tool, the GROWSAFE^® Calculator that we have recently developed via a multi-stakeholder and multiple end-user project. This provides advice as to which chemicals can be selected for local conditions to minimise the likelihood of leaching, and minimise the risk of soil build-up of pesticide residues. The Calculator covers some 850 combinations of crops, regional climates, and soil types across New Zealand. The Calculator is available free on a CD-ROM.

Introduction

There are genuine and significant concerns amongst consumers and the wider community about the use of pesticides. The potential for leaching of pesticides poses a particular risk to the quality of the groundwater, and the build-up of pesticides in soils can degrade soil quality.

Wise choice of pesticides and sustainable spray practices are needed to protect the environment, and to ensure compliance with non-tariff protocols such as EUREP-GAP, which are increasingly being used for certification of good agricultural practices (GAP).

The key to reducing the negative impacts of pesticides is the provision of information to growers to encourage the purchase of chemicals that leach less, and which do not build-up in the soil. Because the processes that influence the fate of pesticides are crop and site-specific, generic information is of limited use. Something to assist with improving local practices was sought.

To overcome this, a new decision-support tool has been developed, the GROWSAFE^® Calculator, which predicts the fate of pesticides. A critical aspect of this project was the involvement of the broad spectrum of end-users and stakeholders. The success of the project was due in large part to the participatory consensus that was developed between the stakeholder of the NZ Agrichemical Education Trust, the chemical manufacturers represented by Agcarm, the regulatory agencies of the regional governments, the end-user industries, and the science providers. The collective buy-in, and the agreement to work towards an agreed end-product, ensured that this project produced a tool that all the players were happy with. The key requirement was that the tool would have local applicability for an individual grower of a specific crop, in a given region, on a named soil, or a soil that could be inferred from a list of generic soil types. The industries provided agreed spray-diary practices. Yet it was sought that the decision-support tool produced by the science providers, could accommodate local variations from normal practices.

This project was funded by the Sustainable Farming Fund of MAF, and carried out under the auspices of the NZ Agrichemical Education Trust. Financial support came from the Hawke’s Bay Regional Council, Greater Wellington, Environment Waikato, Tasman District Council, and the Marlborough District Council. Additional support was provided by the Gisborne District Council, Auckland Regional Council, Environment Canterbury, Otago Regional Council, Horizons Council, Environment Bay of Plenty, and the Northland Regional Council, that is 12 Local Authorities in total.

The following grower organisations were involved in the project and its management:

Vegfed
NZ Winegrowers
Zespri International
NZ Pipfruit
NZ Fruitgrowers Federation
Arable Food Industry Council
NZ Avocado Growers
Summerfruit NZ
Agcarm.

These are listed here to demonstrate the broad constituency of this project: from regulator through chemical manufacturer, to end-user industries.

The Decision Support Tool

The GROWSAFE^® Calculator uses industry-typical spray diaries for 34 of the major crops grown in New Zealand. These spray diaries were provided by the respective industries on the basis of their recommendations to growers, and the requirements of market entry for our exports. GROWSAFE^® Calculator interrogates the results of simulations done by the SPASMO-Pesticide simulation model using input data supplied by grower bodies, the pesticide manufacturers, and Regional Councils. SPASMO (Soil Plant Atmosphere System Model) is a mechanistic model that predicts the transport of water through the rootzone, and simulates the fate of chemicals (Green et al. 2002). The SPASMO model has been successfully tested against field data on the fate of pesticides (Close et al. 2003; Rosen et al. 2004).

In the GROWSAFE^® Calculator, for each of the crops, and each of the regions, the typical spray-diary practices were modelled for between 7 and 13 of the major soil types in the region. In total more than 850 combinations of crop, climate, and soil were simulated, each for periods of 30 years to determine long-term average pesticide fate. A total of 28,399 SPASMO simulations, each 10,950 days, were carried out.

A critical aspect of the SPASMO modelling was the use of long-term, 30-year weather records. The likelihood of leaching and soil build-up depends on the weather conditions around spraying. By using 30-year daily records, the stochastics of the interaction between the date of spraying and weather events, could be adequately represented in the average case of 50% exceedence, and the worst-case short-term risk scenario of 10% exceedence.

The results of these SPASMO simulations can be interrogated easily using the GROWSAFE^® Calculator, allowing growers to easily see which pesticides leach most, and then they can use this information to make choices between substitutable chemicals. The GROWSAFE^® Calculator is available on CD, or as a Ready-Reckoner in pamphlet form for specific combinations of region and crop. Growers can also examine the impact of different numbers of applications per year of a chemical on the fate of the pesticides.

The SPASMO model outputs are, in the Calculator, quite visual through bar-graph ranking. All the pesticides, namely herbicides, insecticides and fungicides used in normal practice for that crop, are ranked in order of environmental impact; namely leaching and soil build-up. Charts can be selected for ranking in relation to short-term leaching risk, namely the 10% worst-case concentrations of chemical in the soil solution at 3 m deep, over days of the 30-year simulation. Ranking is also provided for the long-term leaching risk that is the average daily concentration at 3 m over the 30-year period simulated by SPASMO (Figure 1).

Figure 1. The screen output of the GROWSAFE^® Calculator for the long-term leaching risk of pesticides under asparagus growing on Red Hill sandy loam in Auckland. The long term risk relates to the average based on the 30-year simulation.

The GROWSAFE^® Calculator can be changed to look at either the short or long-term risk of the build-up of pesticides in the soil (Figure 2). Copper is shown to pose a short-term (and also can be shown to be a long-term) risk in this, and most other scenarios. There is a range of choices for product substitution, especially for copper, to avoid soil build-up (Figure 2), and minimise leaching losses (Figure 1). The environmental impact of heavy metal usage, not only copper, but also zinc and cadmium, are mounting concerns for productive systems.

Figure 2. The short-term risk of soil build-up of pesticides used with asparagus on Red Hill sandy loam in the Auckland region. The short-term risk relates to the 10% of worst daily-cases during the 30-year simulation.

Conclusion

Pesticide purchases are generally made on the basis of price, and some knowledge of efficacy. The GROWSAFE^® Calculator, or its paper companion the GROWSAFE^® Ready-Reckoner, can be used to add a third leg to this decision process – environmental fate. Not only will this help improve the environmental performance of productive land-use practices; but increasingly such tools as the GROWSAFE^® Calculator will be used as proof of compliance with the Good Agricultural Practice (GAP) protocols. In this mode the GROWSAFE^® Calculator can be used to defend sustainable practices to secure premium prices in a differentiated and competitive market place.

References

Close, M.E., Pang, L., Magesan, G.N., Lee, R., and Green S.R. (2003) Field study of pesticide leaching in an allophonic soil in New Zealand. 2: Comparison of simulations from four leaching models. Australian Journal of Soil Research 41, 825-846.

Green, S.R., Clothier, B.E., Caspari, H., and Neal, S. (2002) Root-zone processes, tree water use and the equitable allocation of irrigation water to olives. American Geophysical Union 129, 337-345.

Rosen, MR, Reeves, RR, Green SR, Clothier, BE, Ironside, N. (2004) Prediction of groundwater nitrate contamination after closure of an unlined sheep feed lot in New Zealand, Vadose Zone Journal 3, 990-1006.