SCIENCE: Where has all our topsoil gone?

“When soil erodes from fields, it does not simply move to another spot on the farm. Much of it ends up in streams, rivers and lakes.” – James Risser


American missionary Harold Ray Watson came to the Philippines in the late 1960s. His mission was to help Filipino farmers and those from neighboring Asian countries to experience abundant life, as promised in John 10:10.

In 1997, he retired and went back to his birthplace in Brooklyn, Mississippi. But before that happened, he talked about his observation about Asian farmers. “Three out of four farmers in developing countries farm in the hills,” he lamented. “When they hold a fistful of exhausted soil and let it fall to the ground, they feel their livelihood slipping through their fingers.”

Watson received the Ramon Magsaysay Award – Asia’s Nobel Prize – for peace and international understanding in 1985. “Land degradation is a problem that is affecting the standard of living of many nations, but especially on the millions who live on and farm the hillsides,” he said after accepting the coveted award.

In the Philippines, the uplands are considered as the “last frontier” of Filipino farmers. Charles Castro, in a briefing paper, wrote in 1984: “For it is in the uplands where supplementary and additional food sources will be grown. It is in the uplands which will give Filipinos temporary elbow room for the land shortage. It is in the upland where landless rural people will find a new option in fighting rural poverty.”

But despite that observation, even until now, the uplands are still being neglected. Most environmentalists echo the same concern: the uplands have long been subjected to unregulated logging, squatting and slash-and-burn agriculture.

Due to various reasons, including climate change, the country is experiencing droughts and floods every now and then. Degradation of the upland areas is aggravated by rugged terrain and heavy rainfall which brings about rapid soil erosion.

About a billion cubic meters or about 200,000 hectares of one-meter deep topsoil are lost every year due to erosion, according to the Department of Environment and Natural Resources (DENR).

“Soil erosion is an enemy to any nation – far worse than any external enemy coming into a country and conquering it because it’s an enemy you cannot see vividly,” Watson said. “It’s a slow creeping enemy that soon possesses the land.”

Soil erosion is nothing new. Archaeological sites of civilizations, studies showed, were undermined by soil erosion. The fertile wheat-growing lands that made North Africa the granary of the Roman Empire are now largely desert. The lowlands of Guatemala that once nourished a thriving Mayan culture were drained of their fertility by soil erosion.

That human life should depend for its existence on less than a meter of mixed organic and inorganic debris may come as a surprise to modern man. Yet it is so. “If the soil on which all agriculture and all human life depends is wasted away, then the battle to free mankind from want cannot be won,” observed Lord John Boyd Orr.

“Without soil, there would be no food apart from what the rivers and the seas can provide,” said Edouard Saouma, former head of the UN Food and Agriculture Organization (FAO). “The soil is the world’s most precious natural resource. Yet, it is not valued as it should be. Gold, oil, minerals and precious stones command prices which have led us to treat soil as mere dirt.”

In the humid tropics, starting from a sandy base, a soil can be formed in as little as 200 years, experts said. But the process normally takes far longer. Under most conditions, soil is formed at a rate of one centimeter every 100 to 400 years, and it takes 3,000 to 12,000 years to build enough soil to form productive land.

“But what nature takes a very long time to form could be washed away in 20 minutes or less by just one heavy rainfall in areas where the farmers don’t use the land carefully,” Watson deplored.

Once topsoil is lost, it is lost forever. “No other soil phenomenon is more destructive than is soil erosion,” wrote Nyle C. Brady in his book, The Nature and Properties of Soil. “It involves losing water and plant nutrients at rates far higher than those occurring through leaching. More tragically, however, it can result in the loss of the entire soil. Erosion is serious in all climates, since wind as well as water can be the agent of removal.”

Soil is often described as “the bridge between the inanimate and the living.” Without it, a nation will have hard time moving on. “If the soil is not well cared for, a county can never develop a sound agricultural base. And without that, national development plans rarely succeed,” the FAO pointed out.

According to Watson, once the fields are devoid of topsoil, their productivity will always be low – and the farmers won’t earn enough to meet their basic needs.

Lester R. Brown and Edward C. Wolf, authors of Soil Erosion: Quiet Crisis in the World Economy, further explained the consequences of soil erosion in food production: “The loss of topsoil affects the ability to grow food in two ways. It reduces the inherent productivity of land, both through the loss of nutrients and degradation of the physical structure.

“It also increases the costs of food production. When farmers lose topsoil, they may increase land productivity by substituting energy in the form of fertilizer. Hence, farmers losing topsoil may experience either a loss in land productivity or a rise in costs of agricultural inputs. And if the productivity drops too low or agricultural costs rise too high, farmers are forced to abandon their land.”

Watson and his Filipino staff knew it well. That was the reason why they came up with a sustainable farming scheme called Sloping Agricultural Land Technology (SALT). “SALT is a packaged technology of soil conservation and food production that integrates several conservation measures in just one setting,” said Roy C. Alimoane, the current MBRLC director.

“Basically, the SALT method involves planting of field and permanent crops in 3-5 meter bands between double-contoured rows of nitrogen fixing shrubs and trees (examples: ipil-ipil, kakawate and introduced species such as Flemingia macrophylla and Desmodium rensonii) to minimize soil erosion,” Alimoane explains.

Permanent and agricultural crops are planted all over the farm. Permanent crops refer to cacao, coffee, banana, citrus and fruit trees. Among the recommended crops are vegetables, cereals, and legumes.

In SALT, crop rotation is being implemented. For instance, those strips planted with cereals (corn or upland rice) earlier are planted with peanuts or winged beans in the next cropping. “Crop rotation helps to preserve the regenerative properties of the soil and avoid the problems of infertility typical of traditional agricultural practices,” Alimoane says.

Multistory cropping may also be practiced (planting black pepper, corn, and lanzones together in one hedge). In waterlogged areas, gabi, kangkong and other water-loving crops are planted. “We all do these to make use of all the available spaces of the farm,” Alimoane says.

“Some of the crops should be planted to feed the farmer’s family, while other crops are grown for sale, so family income is well spread out over the season,” says Alimoane. “Every week or every month, there’s always something to harvest. The system can, in fact, raise the family income threefold.”

But what makes SALT environment-friendly is that it helps in the establishment of a stable ecosystem. The double hedgerows of leguminous shrubs and trees between the land strips where crops are planted help conserve water and soil. The hedgerows, when cut every 30-45 days and incorporated back into the soil, improve its fertility and serve as mulching materials.

A study conducted at the MBRL C farm showed that a farm tilled in the traditional manner erodes at the rate of 1,163.4 metric tons per hectare per year. In comparison, a SALT farm erodes at the rate of only 20.1 metric tons per hectare pear year.

“The rate of soil loss in a SALT farm is 3.4 metric tons per hectare per year, which is within the tolerable range,” Alimoane claims. “Most soil scientists place acceptable soil loss limits for tropical countries like the Philippines within the range of 10 to 12 metric tons per hectare per year.”

The non-SALT farm, on the other hand, has an annual soil rate of 194.3 metric tons per hectare per year.

“The decline of our soils is a chronic, slow process without the urgency of other environmental crises,” declares Priscilla Grew, former director of the US Department of Conservation for the State of California. “Yet, soil is the basis for our very existence. Where it is lost, civilization goes with it.”