Balancing the soil bank

On World Soil Day, 5 December, Dr Gamini Keerthisinghe, manager of ACIAR’s Soil Management and Crop Nutrition research program, shares his view on the importance of soil and how ACIAR’s work is helping farmers improve it.

Soils are like a bank account. You can withdraw what you have, but once the nutrients have been depleted, you need to replace them.

Maintaining a healthy soil balance is fundamental for successful and sustainable farming.  Improving soil pays off by giving farmers generous yield gains, which can help boost their incomes dramatically.


ACIAR's is helping farmers in Southern Philippines improve their soils and their incomes

Secrets to success
The most important nutrients for crops are nitrogen, potassium and phosphorus. Plants use these in the largest quantities. The soil’s pH is also important because it affects how available these nutrients are to crops like vegetables, maize and trees.

The principles of good soil nutrient management are simple:

• Measure the levels of the main nutrients in the soil
• Correct any major deficiencies or imbalances by adding the right fertilizers 
• Maintain soil nutrients by regularly replacing the nutrients each crop takes out.

How can soil nutrients be measured and maintained?
Simple test kits can be used to assess the levels of nitrogen, phosphorus and potassium in soils.  Soil test kits are available to farmers.  It is also possible to have soil tested by a laboratory.

Soil test kit

Once the nutrient levels are known, farmers can develop a soil improvement program with help from agricultural extension workers, to return soil nutrients to their optimal levels, and keep them there. In other words, to pay back the soil bank for nutrients they have borrowed for previous crops.

Sometimes farmers simply can’t afford expensive inorganic fertilisers, so part of ACIAR’s work is to trial cheaper alternatives. Options being investigated include readily available farm-waste products such as manures, mulches and compost from earthworms.

In the southern Philippines, many farmers are noticing that their crop yields are gradually declining as a result of soil nutrients depleting. Researchers, funded by ACIAR, have been investigating affordable ways for smallholder vegetable farmers to turn this trend around.

Farmer Samuel uses manure and inorganic fertiliser
in integrated nutrient management

Farmer Samuel Gadrinab, who worked with the ACIAR research team in the Philippines has found he can reduce the amount of commercial fertiliser he uses by using alternative products: “Previously we were buying 10 bags of commercial fertiliser, but now we only need five or six bags because we can also use manure from our chickens and pigs.”

Stopping your soil bank eroding away
Farmers also need to make sure their soil stays where it is, and does not wash away.  Sloping lands are a big problem in places like the Philippines, and some simple changes in farming practices can help a lot.

Farming along contours helps reduce soil washing away downhill

On sloping lands, one thing that should be avoided is ploughing up and down the slope. This can lead to massive soil losses, up to 350 tonnes per hectare year! By changing to ploughing around the hill’s contours, this soil loss can be dramatically reduced (to about 60 tonnes per hectare year).  Planting permanent strips of vegetation on the contours can reduce these soil losses even further, to about 2-6 tonnes per hectare per year.

Growing a cash bonus
In the southern Philippines, farmers who have moved from traditional cultivation practices to contour ploughing and natural vegetative strips are reaping the benefits. A double bonus can be provided by using permanent strips: farmers can plant cash crops in them, making money from them as well as saving their soil.

Planting strips of vegetation along contours
helps prevent erosion and can provide income

Farmer Rebecca Andilao has planted banana, string beans, sweet potato and bitter gourd along the contours of her farmland.  Others have planted pineapple along the hedgerows, all bringing in vital food and cash to the farm households.

At the end of the day, we would like to see the interventions we have introduced with the farmers bringing them extra income from the work they are putting in. Looking after their soil bank balance should bring them better returns in the long run.

See more in the video Dirt Rich: Balancing the soil bank, which shows how these principles are being achieved by Filipino farmers through ACIAR projects.

By Dr Gamini Keerthisinghe, Manager of ACIAR’s Soil Management and Crop Nutrition research program, with input of Dr Gordon Rogers

More information:
Feature ACIAR project: HORT/2007/066 Enhanced profitability of selected vegetable value chains in the southern Philippines and Australia program.
Partners: NSW Dept of Primary Industries, University of Sydney, Applied Horticultural Research, Visayas State University, World Agroforestry Centre (ICRAF) Philippines, Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development (PCAARD), Misamis Oriental State College of Agriculture and Technology, Philippines' Bureau of Soils and Water Management

Another ACIAR project SMCN/2009/031 Watershed evaluation for sustainable use of sloping agricultural land in the southern Philippines is also helping farmers cope with erosion of sloping lands, looking at the suitability of land for farming, and planning land use to meet the communities’ different needs.

Other examples of how ACIAR research is helping to improve soils

• Introducing conservation agriculture – reducing tillage, intercropping with legumes and rotating crops and using crop residue as mulch in countries from the Middle East and Africa, to South Asia and South East Asia (ACIAR Partners magazine Winter 2103) 
• Improving soil management of cash crops – investigating the impact of long-term crops like oil palm on fertility of soils in Papua New Guinea 
• Adapting to waterlogged saline soils in India and Australia
• Improving fertiliser management by smallholder Indian farmers to reduce damage to surrounding environment
• Making and using compost to increase cocoa production in Indonesia
• Reducing soil-borne pathogens in tuberous crops like ginger and increasing soil organic matter in the Pacific (read more in this article in the International Society for Horticultural Science's Chronica Horticulturae)