Silicon from straw increases soil water holding capacity

Grain straw contains a form of silicon that increases the water holding capacity of the soil. Scientists have found this effect of this silicon form in field experiments on drought-prone sandy soils. They argue in favour of incorporating straw residues after the grain harvest, because otherwise the soil content of this amorphous silica declines and the moisture content of the soil decreases. Water holding capacity is becoming increasingly important, they say, as growing seasons become drier due to climate change.

Cereals and grasses absorb a lot of silicon from the soil. They store this silicon as amorphous silica – a special form of silicon dioxide. Amorphous silica gives crops extra resistance to diseases, pests and other forms of stress. This silica returns in the soil via straw residues and benefits the following crop. Amorphous silica from straw residues increases also the water holding capacity of the soil. Crops have therefore more water at the roots, which makes it easier to bridge dry periods. Scientists have found this property of amorphous silica in experiments on drought-prone sandy soils in eastern Germany. Incorporating straw residues after the grain harvest is a good way to improve the water holding capacity of the soil, according to the researchers in the popular science magazine Plant nutrition courier. They found also that spring wheat evaporates less water on soils enriched with amorphous silica. The digital magazine Plant nutrition courier published the most recent results of this research into the role of amorphous silica in the soil.

Amorphous silica differs from silicon in sand and clay minerals. This silicon cannot be absorbed by plants and it does not or hardly weather. Farmers who remove straw are depleting the amount of amorphous silica in the soil. Regular liming of the soil, however, masks this loss of amorphous silica. Increasing the soil pH accelerates the biodegradation of siliceous crop residues and other organic material. Crops absorb the released silica and at harvest it disappears from the field for good. As a result, the amount of amorphous silica in the soil is declining. In the long run, this will reduce the water holding capacity of the soil, according to the German scientists in the Plant nutrition courier. They consider the water holding capacity of great importance, as growing seasons are becoming drier due to climate change.

The silica research has been carried out by scientists from the Leibnitz Centre for Agricultural Landscape Research and from the universities of Bayreuth and Potsdam. In addition to grain straw, they have also tested industrially produced amorphous silica as a soil amendment. This material has the same effect as amorphous silica from straw, but is many times more expensive. The researchers have not yet found an affordable industrial alternative, and also no clean waste stream with sufficient amorphous silica. Cereal straw is therefore by far the cheapest source of this moisture-retaining silica.

Plant nutrition courier publishes about cutting-edge research into plant nutrition and fertilisers.