Marjorie Stair
AS AGRICULTURAL technology continues to make dramatic advances there can be the tendency to forget the basic principles learnt at the very beginning of the most elementary of farming activity. One such tried and tested principle is the need to 'rest the land' and/or crop rotation.
Dr. Gary Simone, in the report on his visit to sugar cane estates in Jamaica in April 2000 quoted in an earlier article of this series, said that 70 years is too long for a monoculture. He questioned further whether or not Jamaican sugar cane farmers could wait out the disease complex by leaving the land fallow for several years.
'Resting land' means letting it lie fallow. In many small farms in Jamaica and other countries, resting the land from cropping is accompanied by allowing animals to graze the area thereby helping to restore fertility to the land as manure and nutrients are added to the soil by the droppings and urine of the animals.
Crop rotation reduces the build up of soil pests and diseases by introducing crops that 'starve' these pests and disease i.e. they are not hosts to these organisms, thereby preventing the increase in pest and disease populations above economic injury levels. Please note that pests and diseases can and do exist comfortably with plants and animals, creating little or no damage, as long as they are not allowed beyond a particular economic threshold level, peculiar for each crop and/or pest or disease.
Legume crops with nitrogen fixing properties improve soil fertility when introduced into any crop rotation system. Crop rotation also allows more efficient use of fertilisers, as crops that feed in different rooting zones of the soils are able to make use of fertiliser residues from the previous crop. This is also true of mixed cropping whereby crops, planted simultaneously in a mixed farming system, but which have different rooting zones, use fertilisers and other soil nutrients more efficiently.
Land degradation and problems such as 'sick soil' have been the undesirable by-products of commercial agriculture not only in Jamaica but especially so in the developed countries. Monoculture, mechanisation, excessive use of mineral fertilisers, unsafe use of pesticides, and other practices implemented with little regard for some of the tried and tested principles of farming have created land, soil and water degradation in many countries.
The degradation of the land has had devastating effects on not only agricultural yields, as a result of reduced soil fertility and/or conditions such as 'sick soil', but has served to aggravate the effects of natural disasters such as floods and droughts. Agriculture is not isolated from the rest of any economy so, being a part of a complex and intricately linked economic, physical and social system, land degradation has had far-reaching and devastating impact not only at the level of the farm but also in other areas of the particular economy.
What then is land degradation? Under natural vegetation equilibrium is established so exact that one way to estimate the rate of long-term erosion is to estimate the rate of soil formation. This varies with the nature of the parent material and with climate but is usually very slow. Human activities disturb this equilibrium so much so that on an arable field the results of a century of soil formation can be lost in one day.
In undisturbed ecosystems such as tropical rain forests, the processes associated with land degradation, such as erosion and nutrient depletion by leaching exist in most cases. They occur at such a low level, however, that they are balanced by regenerative processes such as weathering, which adds soil material including plant nutrients to the system.
Declines
Degradation means that the land becomes less capable of producing economically useful goods i.e. productivity declines unless steps are taken to restore that productivity.
Land degradation, like Integrated Pest Management mentioned in the previous article, always refers to land use and the value put on the land by people. This makes land degradation a social problem although it has physical symptoms.
Degradation of land, as of anything else including civil society and an economy, is never a one-way street. It is essentially the net result of opposing sets of forces -- those forces that increase the capability of the land to produce economically useful goods; and those which reduce the capability. Degrad-ation is therefore reversible by carrying out improving and restorative measures.
I believe that this is where we are right now in Jamaica. At the point where we must carry out improving and restorative measures, not only to restore our agricultural lands but also our society and our economy. It is now time to let go of the divisive, one-upmanship, dog eat dog, win/lose, lose/win, my way or the highway types of strategies. To drop them to the bottom of the ocean and start striving for real solutions. Agriculture is not isolated from the rest of the economy and the restorative measures must necessarily involve more than the agricultural sector if they are to be effective.
Our agricultural land, as well as other land, is degraded i.e. the output per unit of labour or capital per unit of land is less than it was before. Our situation is compounded by the fact that this degradation has been accompanied by significant increases in both the costs of capital and labour.
Our land is degraded because of high levels of soil erosion, created in some instances, by some of our traditional farming practices e.g. the traditional method of producing yams -- our biggest non-traditional crop now hitting the headlines again. This, despite the preponderance of soil conservation projects, both international and local, in yam growing areas throughout the years. For those who are unsure of what degraded land looks like, take a drive through the hills of Trelawny and see the pinkish red exposed sub-soil in areas where yams used to be grown.
Our land is degraded because of leaching of nutrients with excessive rains or floods. This because of inadequate drainage infrastructure and soil conservation measures.
Our land is degraded because of changes in the soil chemistry. This due to either the over pumping of aquifers resulting in irrigation water contributing to the salinisation of soils in some areas, notably sugarcane areas, or soils becoming too acid because of improper fertiliser use. Land degradation, caused by the clearing of mangroves, has resulted in sea water seeping into the water tables of previously arable lands, making the lands saline and forcing them out of agricultural use.
Our land is degraded because of soil compaction caused by mechanisation on some of our farms. Soil compaction dramatically reduces the rooting of some crops, affects seedling emergence and root elongation and is likely to reduce crop yields dramatically. It also reduces the infiltration capacity of the soil thus causing more soil erosion.
The reduction in crop yields on degraded lands is usually accompanied by the increased presence of hardier weed species. This not only makes weed control so much more difficult but further enhances the increase in the population of pests and diseases either by being hosts of these organisms, or by further weakening of the target crop through competition.
Our land is degraded because of a massive build up of soil pests and diseases over the years; degraded because of our failure to effectively address these problems at an early stage. The 'sick soil' of the sugar cane industry has been highlighted. The fact is that average yam yields have not improved for decades and yam varieties such as yampies have virtually disappeared because of nematode infestation, a problem yet to be effectively addressed although we have known about it for more than three decades.
What are the restorative measures that can be taken to reverse the decline of our agricultural sector? This is the penultimate article of the series, with the next and last article looking at economic and agricultural policies and their contribution not only to the decline but also to the possible solutions. I believe some definitions will help to guide us.
Fertility
Fertility describes the ability of the land to provide the requirements for plant growth and is often used with particular reference to nutrient supply.
Productivity, on the other hand, is the capacity of the land to produce useful products as reflected in yields or potential yields of crops or other products
Land suitability describes the extent to which a piece of land meets the requirement of a specified type of land use. It takes into account not only soil productivity but other aspects of land use such as the cost of production e.g. the need for addition of improvements such as soil conservation, drainage infrastructure and addition of fertilisers.
Jamaica has some outstanding soil scientists and a history of important work in the categorisation of soils and in conducting land capability and suitability studies. Improved technology such as Global Positioning Systems (GPS), yield monitors and computers that generate field maps allow for very precise agricultural information to be made available to the farmer and has increased the demand for agronomists in developed countries. The present Permanent Secretary of the Ministry of Agriculture as well as the Chief Technical Director are highly trained soil scientists with, I suspect, information on the suitability of Jamaican soils at their finger tips.
Knowledge on the suitability of the soil is of little use, however, if there is either no market for a particular enterprise, we do not have competitive advantage and/or our farmers simply cannot afford to farm because of both the high direct and indirect costs of farming in Jamaica. There are a whole lot of issues to be analysed, costs and benefits to be determined, policy issues to be addressed before we can truly speak about reversing the decline in our agricultural sector.
Marjorie A. Stair is an agronomist and horticultural specialist who now lives and works in St. Vincent.
