Global Ecological Problems and Issues

The scale of the problem is vast, but many of the solutions are simple and very cheap. Organic farming is one of them. According to a survey on 200 organic farming projects, conducted by Jules Pretty of England's Essex University, organic farming has increased the farmers' yields on average by 73 per cent. The 200 projects evaluated by Pretty had helped about four million farmer families to increase their yields and income in a very significant way.

When Soviet Union collapsed it cut its supplies of cheap grain and agrochemicals to Cuba. This forced Cuba to shift to organic farming in a very short period of time. The consequences of the change, however, have been different than what was expected: mixing maize, beans and cassava in order to replace chemical fertlizers with biological nitrogen fixation has actually doubled the yields.

Many farmers in different parts of the world have stopped ploughing their fields. This reduces their work load and costs. Ploughing does help in reducing the amount of weeds but it also damages soil fertility and increases erosion. If fields are left unploughed they can absorb up to one ton of carbon per year per hectare from the atmosphere, which could help in fighting the global warming. In Argentina fully one third of the farmers have abandoned the use of ploughs, and in other Latin American countries millions of other farmers have done the same.

It is now widely thought that a ground cover of mulch is one of the best and most cost-effective ways of controlling erosion and other forms of declining soil fertility. The mulch laid on the ground protects the soil from the eroding impact of the raindrops: when the rain drops hit the layer of mulch they explode into a fine mist that can no longer do much harm.

Mulch can also have a kind of double-effect in controlling erosion. For instance in oil palm plantations erosion can be reduced in a very dramatic way by placing pruned palm fronds on the ground, optimally with tips downslope to create inward flow towards the stems. When such method is used the mulch also checks the outflow of nutrients in the fine soil by creating countless of tiny micro-catchments that are very efficient in capturing small soil particles.

The organic matter used as mulch also acts as fertilizer, and reduces the need for more expensive, industrially produced fertilizers. One study in Northern Nigeria estimated, that the amount of nutrients in crop residues available in the area, alone, was almost 80 times more than the nutrient content of the mineral fertilizers that were being used. Besides this mulch can reduce soil temperatures and evaporation of water, and increase the amount of rainwater that filters into the soil. In the semi-arid zone of Niger millet grown with no fertilizer only produced about 0.2 tons of grain per hectare. The addition of four tons of mulch per hectare increased the yields four-fold.

The planting of trees is often promoted as an erosion-control measure. The litter produced by the trees can reduce erosion by a major extent (up to 95 per cent) and if the branches and leaves produced by the trees are used as mulch they can be most useful.

If the litter produced by the trees is burned or removed the planting of trees can actually increase erosion by reducing the amount of protective undergrowth (grasses and other herbaceous plants), besides which tall tree canopies can also increase the erosive potential of rain by concentrating the water to larger and heavier drops that can do major damage when they drop down from the high branches. However, the smallest rates of erosion are found from untouched natural forests and from multi-storey home gardens that imitate the structure of the natural forest.

Such multi-storey farming systems mixing tree crops with other kinds of plants deserve special attention because they can, in practically every conceivable ecosystem, produce more food per hectare - in terms of calories, proteins and other nutrients - than conventional farming.

The emergence of tree planting as a widespread custom seems to be a more or less spontaneous and automatic process that is taking place when the population densities reach certain levels and continue to grow beyond them. This can already be seen in many regions of the world. Wherever population densities have reached a certain level they have also led to the development of multi-storey, multi-species agroforestry systems known as tropical home gardens.

In Southeastern Nigeria, where population densities range as high as one thousand people per one square kilometre, the high population densities are usually linked with more trees.

Similar trends can be observed, for example, on densely populated slopes of Kilimanjaro and Meru in Tanzania and Kenya, on the island of Zanzibar, in Rwanda, in China and India and in Java - where tropical home gardens cover 75 per cent of all agricultural land.

In Kenya both the government and dozens of non-governmental organizations have actively encouraged people to plant their own trees. This has made Kenya the first country in Africa that has reversed the decline of living biomass. According to latest studies the biomass - the combined amount of trees and other vegetation - is now growing in 39 out of the 42 districts of Kenya. And in many districts the growth has been rather spectacular.

The reason for these trends is obvious: home gardens involving various tree crops are more productive. For example in the heavily populated areas of Nigeria the production of the multi-storey gardens is, in monetary terms, 5 to 10 times higher than that of conventional field farming.

It has been estimated that fruit trees only occupy 2-3 per cent of the world's agricultural land, but contribute 5-7 per cent of the gross food production and 10-35 per cent of national income from agricultural production.

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