BUFFER COCOPEAT TO LIMIT LOSSES

Hydroponic crop production relies on soilless substrates, like growth media, to support plants and facilitate water and nutrient uptake. Growers prefer organic growth media, such as cocopeat or sawdust, because they are light and have good water retention, which is important in intermittent water flow hydroponic systems.

Growers generally prefer sawdust, which is more affordable and readily available, whereas imported cocopeat is expensive.

However, the price of sawdust has risen dramatically and continues to rise and it cannot be re-used, whereas cocopeat can be used multiple times. Also, it is often reported that cocopeat provides better crop yields compared to other growth medias. Cocopeat that is sold already prepared and buffered is expensive and logistically costly. Affordable cocopeat is purchased in a compressed brick form, which growers must buffer and rinse before use.

A 5kg brick of cocopeat can expand into 6065 litres when prepared and costs up to R105. A prepared 20 litre bag of cocopeat can cost up to R180 – roughly five times more expensive for a 300m2 tunnel fully planted using an open-bag hydroponic system.

Companies that sell the prepared cocopeat may exploit the situation by trying to convince growers that this is the only form of cocopeat suitable for crop production.

Cocopeat is made from coconut coir, which is the outer layer of the coconut fruit. The material contains chemical complexes with large amounts of sodium (Na) and potassium (K) attached. In the presence of calcium (Ca) or magnesium (Mg), these sites will release Na or K cations and replace them with Ca or Mg, through a cation-exchange process. Therefore, when the cation exchange sites bond with Ca or Mg in the place of Na and K, the growth medium is said to be buffered. This is a precautionary measure before planting so that plant nutrient uptake does not become affected. Plants that are grown in unbuffered cocopeat tend to show severe Ca or Mg deficiency. This is because the exchange sites will take Ca or Mg in the nutrient solution and replace them with Na and K, which ultimately affects Ca or Mg availability for plant root uptake.

Buffering the cocopeat before planting prevents nutrient deficiencies and imbalances and ensures the added nutrients are available to the crop at the ratios provided.

Because local farmers have not been trained suffiently in the use of cocopeat, preventable losses are incurred. For this reason, the Agricultural Research Council in collaboration with the Water Research Commission has developed a method for cocopeat buffering to help growers reduce production costs.