What is marginal land? Goodbye topsoil, my old friend…

Author: Matt Willis

The food versus fuel debate in the biofuels development world has prompted some policy makers to propose that agrofuel crops should only be planted on land that is considered marginal or degraded, but what exactly does this mean?

Marginal land is defined as arid and generally inhospitable land that usually has little or no potential for profit, and often has poor soil or other undesirable characteristics. This land is often located at the edge of deserts or other desolate or degraded areas.  However, much of the worlds prime agriculture land would be classified as marginal were it not for the advent of cheap, nitrogen based fertilisers and large scale irrigation, to keep it productive.

In fact more and more land is becoming degraded as intensive farming and bad land use practice leaves prime agriculture land vulnerable to severe topsoil erosion. Around the world, including the USA and the UK, soil is being swept and washed away 10 to 40 times faster than it is being replenished, destroying cropland the size of Indiana every year, reports a Cornell University study. The vast majority, 99.7 percent, of human food comes from cropland, which is shrinking by more than 10 million hectares (almost 37,000 square miles) a year due to soil erosion, while more people than ever, more than 3.7 billion, are malnourished. More pessimistic reports state that there may be as little as 70 years left before all the worlds topsoil is eroded.


Photograph by Lynn Betts, NRCS

Heavy rains in northwest Iowa washed away soil, leaving this scarred tableau. This type of erosion, termed sheet-and-rill erosion, occurs when there is insufficient vegetation to hold soil in place. As rain falls, it forms sheets of surface water that transport soil away. As more water accumulates, it forms runoff channels called rills, which further displace soil.

Excessive use of nitrogen based fertilisers also has a price.  Around 60% of nitrate in English waters originate from agricultural land. Elevated levels of these nutrients are of concern because they can cause eutrophication, which harms the water environment. Also, excess nitrate has to be removed before water can be supplied to consumers, raising the cost of supplying fresh water.

Agriculture accounts for 70% of our fresh water use, we pour most of our water straight onto the ground. If soil is not fit for purpose, that water will be wasted, because it washes right through degraded soil and past the root system.

So, although the definition of marginal land may seem obvious, what actually is considered marginal land can change within a relatively short period of time.

Are lands that require huge amounts of irrigation and fertilisers to remain productive, under the current intensive agriculture model, only not marginal due to these inputs and if these inputs become too expensive to maintain the productivity of the land, does it then become marginal?  Citrus greening disease is currently turning once productive, non marginal land, into unproductive acreage that, given time, may lay fallow and be susceptible to soil erosion creating huge swathes of marginal land in States such as Florida.  Options exist to utilise this land now to grow oil seed crops before this acreage becomes truly marginal. Would policy makers prefer the land to become unproductive first before seeing suitable crops such as Pongamia cultivated in these areas?

In the developing world the identification of marginal land is also not so easy.  If you believe what you read, then in continents such as Africa and Latin America, 1000’s upon 1000’s of acres lie unused and waiting to be developed however, it is necessary to draw the distinction between unused, be it commercially or otherwise, and marginal.  Unused acreage is often, in fact, being used by small communities. One example of how estimates for “abandoned cropland” useable for bioenergy are derived is a 2008 study by Christopher Field et al, who suggests that 386 million hectares of such land exist. Any land believed to have been used as cropland at any time since 1700, and which satellite images don’t show as being “cropland” today is classed as “abandoned” unless it is currently forested or part of urban settlements. There has been no critical review to assess whether such satellite-based mapping ignores small-scale mixed farming by communities, but it is clear that other community uses, including the use of land for pasture, are ignored when “abandoned cropland” is defined.

Policy makers need to take into account a far larger range of issues when considering land use for biofuels.  Intelligent use of crops that can actually thrive on truly marginal land are required to develop sustainable agriculture programs that can potentially create a new source of income for struggling farmers, such as in Florida and also help to develop new markets for burgeoning economies in Africa and Latin America.  However, a “one size fits all” approach to these policies simply will not work.

TerViva works responsibly with farmers and landowners to create crops that truly thrive and rehabilitate degraded land, transforming barren landscapes into healthy, profitable environments.Image

Matt Willis is TerViva’s Director of International Markets.

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