ENVIRONMENT | Soil erosion: The quiet crisis of farming

Once the trees are gone, soil erosion will definitely follow.

The Philippines is an agricultural country. Agriculture is a major sector of the economy, ranking third – after services and industry – among the sectors in 2022. Due to its terrain and tropical climate condition, farming and fisheries are a way of life among most Filipinos. Crop production, particularly sugarcane, rice, coconut, and bananas are among the top export products.

The country has about 30 million hectares, 9.7 million (47%) of which are agricultural land. Unfortunately, about 60% are considered upland areas as they have elevations of more than 100 meters to 500 meters above sea level, according to the Department of Environment and Natural Resources.

Currently, the Philippines is home to more than 117 million people. As a result of the surging population in the lowlands, some uplands are now encroached and have been turned into human settlements. Roughly 24 million are now living in upland areas and a great proportion of them depend on farming as their only source of income.

Agricultural production in most upland areas is generally rainfed; water scarcity is a common and perennial problem. Most of the lowland-turned-upland farmers are converting marginal areas with steep slopes prone to soil erosion.

Topsoil is the primary resource for crop production. “The world grows 95% of its food in the uppermost layer of soil, making topsoil one of the most important components of our food system,” wrote The Guardian’s Susan Cosier.

Topsoil is built up over time. Most soil scientists claim it takes up to 1,000 years to produce two to three centimeters of soil.

“Soil is related to the earth much as the rind is related to an orange,” explains an American geologist. “It is the link between the rock core of the earth and the living things on its surface. It is the foothold for the plants we grow. Therein lies the main reason for our interest in soil.”

On the average, farmlands are losing 2.5 centimeters of topsoil every 16 years, or 17 times faster than it can be replaced. Unfortunately, it seems no one pays attention to this great loss. The government, for one, is more alarmed when there is not enough rice for the people than the loss of topsoil.

Soil erosion is the most common natural landscape forming process. Over thousands of years, erosion wears down mountains and deposits soil elsewhere to form plains, plateaus, valleys, river flats, and deltas. This type of erosion is known as natural erosion.

Erosion occurring at a rate that exceeds the rate of natural erosion is called accelerated erosion. Accelerated erosion can result from certain human land use practices. For soil to erode requires a combination of two factors – loose soil and a physical force that can transport the soil to a new location.

Soil erosion is now one of the biggest threats in crop production.
Soil particles may be detached from a stream bank during high water. Detached soil particles are then transported to a new location by some physical force, including water, wind, ice, or gravity. On forested lands, this force is flowing water.

“No other soil phenomenon is more destructive worldwide than soil erosion,” wrote Nyle C. Brady in his book, The Nature and Properties of Soils. “It involves losing water and plant nutrients at rates far higher than those occurring through leaching.

“More tragically, however, (soil erosion) can result in the loss of the entire soil,” Brady continued. “Furthermore, the soil that is removed finds its way into streams, rivers, and lakes and becomes a pollution problem there.”

The UN Food and Agriculture Organization (FAO) says the world is now losing an equivalent of five to seven million hectares of farmland through erosion each year. This is equivalent to the land area of the Netherlands and Belgium combined.

“If we continue to degrade the soil at the rate we are now, the world could run out of topsoil in about 60 years,” deplored FAO’s Maria-Helena Semedo. “Without topsoil, the earth’s ability to filter water, absorb carbon, and feed people plunges.”

“Soil erosion is an enemy to any nation – far worse than any outside enemy coming into a country conquering it because it is an enemy you cannot see vividly,” declares Harold R. Watson, recipient of the 1985 Ramon Magsaysay Award for peace and international understanding. “It’s a slow creeping enemy that soon possesses the land.”

The problem could be partly solved by planting perennial crops, suggests Craig Jamieson, who once served as consultant for the World Agroforestry Center. Perennial comes from the Latin root word perennis, which means “lasting through the whole year.”

In agriculture, perennialization means converting an annual-based crop system to a perennial (enduring) one. As advocated by the World Agroforestry Center, the method involves “the substitution of annual crops with perennial plants and trees as they provide continuous ground cover and deep root systems for soil protection and stabilization, while increasing carbon stocks and reducing soil nutrients by leaching.”

“The integration of trees into farming practices has the potential to sustain land productivity in addition to providing useful tree products such as firewood and fodder,” explained Jamieson.

Based on existing studies, he said, the system can provide the following benefits to the environment: extend the productive life of soils; develop resilience to extreme rainfall events, droughts, and insect pressures; reduce land run-off that creates coastal dead zones with disastrous effects on fisheries; maintain the quality of surface and groundwater; and build food security.

Compared to annual crops like upland rice, corn, and vegetables, perennials live longer and develop a deeper root system over time. “Their deep root systems make them less prone to wind and rain damage, helping farmers adapt to climate extremes and protecting the soil from erosion,” Jamieson pointed out.

Farmers can also save money as they won’t buy chemicals like pesticides and herbicides anymore. “Aside from the obvious savings on expenses, the planting of perennials likewise reduces the impact of chemicals on local watersheds,” the British expert said.

Jamieson said that perennials can be in the form of grasses, nitrogen-fixing trees and shrubs, beverage crops (coffee and cacao), and fruit trees (durian, pomelo, avocado, and banana).

Perennialization is actually a form of agroforestry, defined as a land use management system in which combinations of trees or shrubs are grown around or among crops. It combines agricultural and forestry technologies to create more diverse, productive, profitable, healthy, and sustainable land-use systems.

Sloping Agricultural Land Technology is one possible solution to the soil erosion problem.

In Davao Region, one of the most popular agroforestry systems developed is the Sloping Agricultural Land Technology (SALT), which was conceptualized by Watson and his Filipino counterparts. The American missionary came to the Philippines in the 1960s.

“When I got here, I had no idea what the problems were up in the hills,” said the agriculturist who opened the Mindanao Baptist Rural Life Center (MBRLC) in Bansalan, Davao del Sur in 1971. “Farming looked pretty good on the surface.”

Soon, Watson – who would be bestowed the prestigious Ramon Magsaysay Award in 1985 for international understanding – discovered that the problem was the surface: It was washing away. Soil erosion, he said, makes farmlands infertile every year. Studies show that loss of a few centimeters of topsoil can reduce the productivity of good soils by 40% and poor soils by 60%.

SALT is basically the planting of field and permanent crops in 4-5 meters bands between double-controlled rows of nitrogen fixing trees and shrubs like ipil-ipil, kakawate, Indigofera, rensonii, and flemingia.

Examples of field crops are legumes (beans, peas, and pulses), cereals (upland rice, corn, and sorghum), root crops (sweet potato, cassava, carrot, and taro), and vegetables (cabbage, ampalaya, tomato, eggplant, etc.). Permanent crops include cacao, coffee, banana, citrus and fruit trees.

With this kind of system, a farmer can harvest every now and then throughout the year. “He has something to look forward to each day,” said Jethro Adang, the current director of MBRLC. “Because the harvested crops are just enough for the market, there is a tendency that the price of his produce is much higher.”

Fertilizer is not a problem. The double hedgerows are pruned frequently (every 5-6 weeks) and the prunings are applied as mulching materials for the crops and also serve as a source of fertilizer (being high in nitrogen). As mulching, the prunings protect the soil from erosion during heavy rainfall.

The double hedgerows and the permanent crops actually help control soil erosion. A seven-year study conducted at the MBRLC 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 20.2 metric tons per hectare per 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. Most soil scientists place acceptable soil loss limits for tropical countries within the range of 10-12 metric tons per hectare per year. The non-SALT farm has an annual soil loss rate of 194.3 metric tons per hectare per year.

“All our food comes from soil,” reminded Paul Stamets, a mycologist and author of Mycelium Running. “When we destroy the biology of the soil, we destroy the food networks that give us life.”

If we have to survive in the next century, we have to halt soil erosion now. “A nation without soil is effectively bankrupt,” FAO surmises. “A nation with appropriate land-use patterns and farming techniques, where erosion has been controlled and contained, is poised on the springboard of development.”

Leave a Reply

Inline Feedbacks
View all comments