#BTColumn – Better way to use biomass waste

Disclaimer: The views and opinions expressed by this author are their own and do not represent the official position of the Barbados Today.

by Peter Webster

Biomass is plant or animal waste material, including wood or forest residues, crop waste (sugar cane trash or, bagasse), horticulture (yard waste), food processing (corn cobs), animal farming (manure, rich in nitrogen and phosphorus), or human waste from sewage plants.

It is organic matter that can be used to supplement soil fertility.

Soil organic matter is made up of three basic components:

1. The living microbial biomass includes the microorganisms responsible for decomposition (breakdown)
of both plant residues;

2. Active soil organic matter or detritus; and

3. Humus which is the stable fraction of the soil organic matter that is formed from decomposed plant and animal tissue.

The first two types of organic matter contribute to soil fertility because the breakdown of these fractions results in the release of plant nutrients such as nitrogen, phosphorus, potassium, etc.

The humus fraction has less influence on soil fertility because it is the final product of decomposition (hence the term “stable organic matter”) although even that eventually decomposes.

However, it is still important for soil fertility management because it contributes to soil structure, soil tilth, and cation exchange capacity.

There are numerous benefits to having a relatively high stable organic matter level in an agricultural
soil, including:

1. Enhanced aggregate stability, improving water infiltration and soil aeration, reducing runoff;

2. Improved water holding capacity;

3. Reduced stickiness of clay soils making them easier
to till;

4. Reduced surface crusting that facilitates seedbed prepaation.

5. Increase in the soil Cation Exchange Capacity or its ability to hold on to and supply, over time, essential nutrients such as calcium, magnesium and potassium;

6. Improved ability of a soil to resist change, also known
as buffering capacity;

7. Accelerated decomposition of soil minerals over time, which makes the nutrients in the minerals available for
plant uptake.

8. Provision of food for the living organisms in the soil;

9. Enhanced soil microbial biodiversity and activity which can help in the suppression of diseases and pests; and

10. Enhanced pore space through the actions of soil microorganisms which helps to increase infiltration and
reduce runoff.

Research has shown that the active organic matter is decomposed, fully ionized and leached from Barbados soils within four months.

It is the reason why organic matter should be used as mulch on the soil surface, where its decomposition is slower than when integrated or ploughed into the soil.

As a result, the biggest limiting factor to crop growth, productivity and quality of produce in Barbados is the lack
of organic matter in our soils most of which have less than one per cent compared to the three per cent to five per cent
of good soil.

This is the main reason for the reduction in sugar cane productivity from four tons of sugar per acre in 1971 to the current two tons of sugar per acre.

Good agricultural management in Barbados therefore requires the regular replenishment of the soil with organic matter, the main sources of which are:

1. Crop residues;

2. Animal manure;

3. Compost;

4. Cover crops (green manure);

5. Perennial grasses and legumes.

Most of these sources are costly to farmers and in some cases cannot be easily mechanized. Crop residues, for example, cannot be readily stored and must be ploughed into the soil where they are rapidly decomposed.

There is not a great supply of animal manure, and dedicated crops for organic matter are expensive.

It had been hoped that composting of solid waste biomass would have been a possible source, but the Government has not found a way to make that accessible to farmers at cost-effective rates.

Now, we are being informed that this biomass will be incinerated as an alternative source of energy. Would it not have been more readily justified economically to compost this as soil organic matter as it could replace some of the millions of dollars in imported fertilisers and chemicals, not to mention the benefits of improved crop and food production and quality?

When will our economists recognize the true value of our agriculture industry and the role it plays in food security and feeding us?