Seabird guano has a higher ratio of citric-soluble phosphorus than non-seabird guano, which is higher in non-citric-soluble phosphorus.

However, when looking at seabird guano we need to look beyond the phosphorus percentage and focus a little on the calcium and the silica and how these elements work together.

By weight, calcium and silica in a good quality Guano Gold make up more than 50 per cent of the product.

Adding the calcium percentage to the silica percentage is a good test of how well the Guano Gold you want to buy is going to perform.

Generally, if the silica level is low then the phosphorus available, in terms of citric-soluble verses non-citric-soluble, will be low.

So, what are the benefits of calcium and silica?

Rather than look at each element, let’s look at how they interact.

Jian Feng Ma and Eiichi Takahashi, from Kyoto University in Japan, used soft X-ray irradiation for detection of silica bodies.

They tested shoots and leaves from plants treated with high calcium and low silica, low calcium, high silica and then equal amounts of calcium and silica.

The theory behind the testing was to show that the plant would use silica as a preference in physical structural development instead of calcium.

The results showed that even if calcium levels where applied in field trails at 6.5 times the level of silica, silica was still significantly present in the flag leaves of cereals.

It concluded that increased silica resulted in reduced calcium in the shoots and developing leaves.

It could be drawn from this that the addition of the silica with the calcium leaves more calcium available for metabolic functions in the plant as the silica forms silica bodies in the leaf blades.

The movement of calcium in the plant is relative to transpiration rate — increased transpiration (movement of water) slows calcium movement.

Calcium is required by the plant for fruit and grain set.

If transpiration is affected by excessive evapotranspiration (elevated temperature and water stress) then less calcium is available to increase both yield and fruit or seed quality.

It logically follows that increased available silica reduces the distance calcium needs to move in the plant (long flow) and also silica due to its placement and structure reduces evapotranspiration (drought tolerance).

So to conclude in simple terms, silica and calcium used together, such as is available in seabird Guano Gold, increase the plants' silica structure and increases tolerance to biotic and abiotic stresses but doesn’t effect available calcium, however it enhances the flow and movement of calcium at critical times such as seed or fruit set.

Robert Drewitt

Guano Australia agronomist