Increasing salinity poses a problem for many growers. Areas of land clearing can lead to increased water table heights, pushing salt and ions higher into the soil. Dams and lakes with reduced water intake resulting in lower water levels can also lead to increased concentrations of salt within the water (in turn affecting irrigation water) and in the surrounding soil.
Salinity affects plants in two ways; the increase in salt concentration in the soil surrounding a plant inhibits the plant’s ability to take up water, and the build up of sodium ions within plants can be toxic.
Biochar is a charcoal substance created by heating organic materials such as wood and green waste to high temperature in the absence of oxygen. For more information on Biochar and its uses see here. Biochar is known to improve degraded soils and, in the context of salinity, is able to adsorb salt and reduce its uptake in plants.
A recent article in the Journal of Agronomy and Crop Science tested the effects of biochar amendment on potato plants irrigated with increasingly saline water. Over three months the researchers grew potatoes in pots, one set without biochar amendments and one set with amendment, and subjected plants within each group to irrigation water with either no additional salt, 25 mili Molar (mM) of salt or 50mM of salt. They then measured a number of parameters relating to tuber yield, photosynthetic rate and gas exchange amongst other parameters to assess the various affects of the increasing salt concentration between the two groups.
The increase in salinity on potatoes without biochar amendment had the expected effects, reducing the number of tubers per plant and the weight of the tubers, reduced root length and volume, decreased the rate of photosynthesis, reduced the density and aperture of leaf stomata and increased the concentration of salt and potassium ions in the leaves.
For plants grown in amended soil, these negative effects were reduced, many of them in a statistically significant way.
- Tuber yield increased across all treatment groups although only the 25mM treatment group had a statistically significant change.
- The researchers found a significant positive linear relationship between stomatal conductance and photosynthesis rates, suggesting that where stomata are negatively effected by a treatment, a reduction in photosynthesis (and therefore growth and health of the plant) will follow. Biochar amendment was found to improve both these measurements compared to plants grown with the same level of salinity in soil lacking the amendment.
- Salt adsorption was significantly reduced in plants grown with the biochar amendment.
Interestingly, nitrogen and carbon content in plant leaves where reduced under saline conditions with little difference in plants with biochar amendment.
In their discussion the researchers estimated that approximately 97% of the salt was adsorbed from soil treated with the 50mM solution. While this has immediate positive effects on plant growth, over time it is expected that the capacity of the biochar to continue adsorbing the salt will reduce. Similar studies performed by the same researchers using drought stress found similar effects in plants under stress and similar improvements with biochar activation. The researchers also note the limits of their study and urge testing their results under field conditions.
To conclude, biochar addition to saline soils appears to have the ability to improve the viability of potato plants but repeat applications are likely to be required.