Greenhouse Crops and GAP

By Dr. Mike Nichols

HORTICULTURE INVOLVES a wide range of different production systems for different crop plants in a very wide range of environments. As such, there is no doubt that one model will not fit all, particularly when a social component is also incorporated into the equation.

For example, there are huge differences between the small farmer producing snow peas in Kenya for export to Europe, and the large agribusiness glasshouse operation in the Westland of the Netherlands.

Good Agricultural Practises (GAP) involves the integrating of four major pillars, namely

• environmental sustainability,
• social responsibility,
• economic efficiency,
• food safety.

Unfortunately, in many GAP scenarios (e.g., in the USA, Europe, and Japan) food safety has taken the major role and the other pillars have been either disregarded or considered less important. This is not to suggest that food safety is unimportant; in fact, it should be considered an absolute necessity, but not at the expense of the other three pillars.

There has also developed a concept that GAP is from the “field to the fork” (paddock-plate) and, although it must be conceded that food safety considerations must involve the complete continuum from production to consumption, many parts of this supply chain are outside the control of farmers. It is, therefore, suggested that GAP should only involve the production, grading, and packaging of the crop for market, and thereafter the responsibility is taken over by the other players in the supply chain.

The objective of this article is to develop a generic guideline that may then be used as the basis for developing GAP guidelines for any horticultural crop in any specific environment.

The greenhouse is a very specialized environment; in temperate environments many of the problems associated with GAP are less important than in the tropical greenhouse environment. For example, in the tropics crops are still frequently grown in the soil, whereas in a “developed” country hydroponic systems predominate.

Similarly, in a tropical environment diseases and pests are likely to be controlled by the use of pesticides, whereas in a temperate environment diseases tend to be controlled by controlling the humidity of the greenhouse (by heating the air), and pests are controlled by biological or IPM methods.

The key in GAP is to develop a process based on Hazard Analysis Critical Control Points (HACCP) to establish the critical control points (sometimes also called critical failure points) in the production process, where compliance is mandatory. Good examples of this are

• traceability of the produce down to the specific farmer’s field,
• record keeping,
• site history and management,
• crop protection,
• harvesting, etc.

The key to GAP lies in adhering to a range of compliance criteria. In EurepGAP there are 12 such criteria, and in the Assured Produce GAP of the U.K. there are 13 criteria, which essentially follow the same topics.

Currently, GAP is a consumer-driven (supermarket-driven) program, and there is an urgent need for farmers to take title to some of this system, if only to ensure that they are not locked out of important export markets.

FOOD SAFETY

Food safety has been a major factor in the development of GAP, and pesticide residues and microbiological contamination have been the major food safety concern.

SOIL

In greenhouse production, soil-based systems have a greater number of constraints because there are many more risks involved in growing in soil compared to growing in soilless media (hydroponically). For example, the use of animal manure (to improve soil structure) may have some potential microbiological risks, while the requirement to fumigate the soil with chemicals (such as methyl bromide or chloropicrin) pose their own hazards.

Soil pollution from heavy metals or from pesticide residues are further risks in soil-based systems. The use of hydroponic systems such as rockwool or coir, or entirely liquid-based systems such as aeroponics, deep flow or NFT, reduce such risks.

CROP PROTECTION

Crop protection is not currently a major concern in temperate greenhouse operations. Major diseases can be controlled in the aerial environment by reducing the humidity (easily achieved by a combination of judicious heating and ventilation). Soil-borne pathogens are controlled by sound hydroponic practises combined, if necessary, with the use of grafting onto resistant rootstocks. Pests are now controlled by means of either biological control systems (e.g., Encarsia for white fly) or by the use of “soft pesticides.” However, in most developed countries pesticides are avoided because of the common use of bumblebees to provide pollination. In tropical climates pest and disease management depends much more on the use of agrochemicals.

SUSTAINABILITY

At this time, greenhouse production in temperate climates must be considered to be non-sustainable. Large quantities of energy are used not only to keep the crop warm in the winter, but also to control humidity (and, thus, reduce disease levels) and to provide supplementary carbon dioxides to enhance crop growth and productivity.

The energy used to provide heating is not sustainable, and the use of natural gas to provide carbon dioxide to improve crop growth, even when the ventilators are open, is a gross misuse of a non-renewable resource. In fact the only really sustainable component in greenhouse crop production in temperate climates is the efficient use of water and fertilizer. Greenhouses are major users of fertilizer, and there is a very real danger of ground-water contamination when growing in the soil or using hydroponic systems that “water to waste.” Using recirculating systems (such as NFT) means that the level of ground-water contamination can be minimized.

Recirculating hydroponic systems are also five times more efficient (in water and nutrients use) in producing crops than furrow irrigated field-grown crops. For every cubic metre (1.3 cubic yard) of water, tomatoes in the field produce about 18 kg (~40 lb.) of fruit, whereas in an environmentally controlled greenhouse with recirculating nutrient solutions the figure is about 65 kg (~143 lb.) of fruit.

In tropical climates greenhouses are more sustainable, but in the humid tropics the technology still lags behind that of temperate climates, and disease problems frequently require the regular use of pesticides.

SOCIAL RESPONSIBILITY

A key component in GAP is to ensure that the crops are produced in a socially responsible manner. By this it means that there is no exploitation of labour. If children are used to assist in producing the crop, this must not be at the expense of their education.

ECONOMIC EFFICIENCY

It should be axiomatic that any enterprise is profitable. However, this is not always the case, and it is a GAP requirement that the enterprise is profitable, at least in the long term.

HYGIENE

Good worker hygiene is an essential component of GAP, in order to reduce the risk of microbiological contamination of the product. This means the provision of such things as clean toilets and washing facilities, and the training of workers in personal hygiene.

RECORD KEEPING

GAP involves record keeping to allow auditors to evaluate procedures and to allow traceability of any product.

REFERENCES

Anon (2001) Guidelines for on farm food safety for fresh produce. Department of Agriculture Fisheries and Forestry, Australia.

Anon (2004) EUREPGAP. Control Points & Compliance Criteria. Fruit and Vegetables. Version 2.0-Jan04.

Anon (2005) Good Agricultural Practise Standard (Draft 1 March 2005).