Organic conversion and its environmental effects

A Costa Rican case study

There is a perceived public perception that large scale agriculture always has an adverse effect on the environment and local biodiversity. Alan Chubb describes an example where it is quite the reverse.

Perhaps as a result of poor planning agribusiness investments large scale agricultural development projects in the tropics have an detrimental effect on the environment. This is often compounded by the lack of any environmental legislation in the country concerned. An exception to this is in Costa Rica where the Government has had a long history in combating enviromentally-damaging agricultural development, and consequently has gained a reputation for its environmentally sensitive land use projects.

The development of the Del Oro citrus estate in north Costa Rica is an example of a large scale agricultural enterprise that places a high priority on an environmental approach in its management. T he citrus estate is owned and managed by the Commonwealth Development Corporation a UK government-owned corporation with worldwide agricultural investments of over £400 million. The estate was developed on disused pastureland and is divided into five farms based on the northern slopes of the Rincon de Ia Vieja. Orosi and Cacao

volcanoes. Two farms border the Santa Rosa National Park. There are 3.150 ha planted to oranges for juice production at the on-site processing factory that has gained the international environmental certification ISO 9002 and ISO 14001. In 1997 it was decided to convert the 550 ha Brasilia citrus farm to certified organic status and to monitor the success of this programme as a model for other areas.

The organic conversion programme has not in fact meant major changes to the existing management programme. The policy on all the farms at Del Gm has always been environmentally sensitive and. for example. the use of insecticides is restricted because of its disruptiv’e nature on natural predators within a perennial crop. Under established Costa Rican legislation it is not permitted to clear forest within 50 m of running water As the groves are situated on volcanic slopes the landscape is such that there arc many streams and mixers running through the Company’s property. Thus, there are 1 00m wide swathes of natural forest bisecting the groves, resulting in many small plots rather than a few large fields of citrus. These fingers of forest are contiguous with the surrounding forest and so permit the free flow of flora and fauna from natural forest to deep within the citrus estates.

Ten years of regularly applied artificial fertilisers and herbicides on the farms has had an effect on soil acidity. which in places have dropped from pH 6 to around ..pH 5. Routine and costly limestone applications throughout the groves have been necessary to counteract the calcium deficiencies induced by the acidifying fertilisers. The use of herbicides has reduced the vegetation under the trees, increasing the potential for erosion and causing a loss of organic matter, which has dropped from 5% to below 2%. These issues have been critically addressed in the organic conversion programme and. in the light of experience. also on the nonorganic groves. When managing perennial crops it is especially important to actively manage the overall soil fertility. Under the conventional management the plants nutrient levels were monitored and fertilisers applied as required. Initially, in the organic conversion programme plant nutrients were supplied in the form of chicken manure. This added slow release nitrogen and potassium. thus reducing the potential nutrient leaching (the annual rainfall ranges from 1 800 mm to 3.000 mm across the estate). It also supplied a range of micro-nutrients, as w ell as humus and the microflora that will regenerate the natural dynamics of nutrient cycling within the soil. However, chicken manure is an expensive form of fertiliser and there are restricted quantities of it available.

Thus, the longer term approach has been _ to utilise the waste citrus peel from the

on-site juicing plant and develop a large scale composting operation. Waste peel is a potential environmental problem as being acidic it will putrefy rapidly’ when left untreated. The standard disposal method of citrus peel in the citrus juicing industry is to convert it to cattle feed which requires large amounts of power and financial investment in an industrial plant. In comparison. composting, even on a large scale, requires little infrastructure and relies on natural products such as plant waste materials, manure and the natural decomposition process.

The advantage of the compost over artificial fertiliser is that the nitrogen is released slowly and is not so susceptible to leaching in the heavy tropical rainstorms. In addition, the organic matter adds structure to the soil thus reducing loss of soil through erosion ‘that is a particular problem on the slopes that characterise the grove landscape.

Soil structure and erosion can also be a problem in the tree lines where the rou has left the soil hare. In some places the bare ground encourages viney-type weeds to develop in the understory thereby minimising the erosion, but these then compete heavily with the trees for the applied fertiliser.

Under the conversion programme the understory development is controlled by regular mowing with offset mowers. This has encouraged the establishment of grasses under the tree line that are not competitive for the soil nutrients. Ideally, the full range of natural grasses would be practice some control over the competitiveness of the grass sward is required. A locallv-occurring pasture grass (Retana) spp) has been successfully encouraged by manually spreading cut grass with seed heads throughout the groves. Certain legumes have been tested for suitability and Arachis pintoi has been successful in establishing itself. However, the attempt to achieve a ground cover that reduces erosion, while not being nutrient demanding has a potential problem. The grove is in danger of developing a monoculture of an easily manageable grass/legume ground cover, and this reduction of plant biodiversity could lead to pest and predator imbalances within the grove The establishment of the Arachis and grass ground cover is thus restricted to four tree interrows out of five, with the fifth row left with the existing plant cover. Insect population dynamics are being studied to assess the effect of the Arachis before a more widespread use is advocated.

When researching the conversion programme for Del Oro it was apparent that there are not many large-scale perennial crop plantations proactively producing certified organic crops. There is also little research published on organic production methods for this sector. I would thus call for the promotion of interchange of research and practical experience on large-scale organic plantations and that this is encouraged through the IFOAM organisation and its membership.

Alan Chubb is a consultant on the organic conversion programme. Tel/Fax: +44-

1225-862334.

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