Bentonite

The declining fertility of sandy soils in the tropics has become a big problem for food security and sustainability of agricultural systems. Organic matter in these soils because of temperatures and heavy rain is quickly broken down and not easily restored without depleting other resources. Without organic matter it is difficult for these soils to hold positively charged nutrients like calcium, magnesium, potassium and sodium.

80% of agricultural systems are rain fed and it’s of vital importance soil be able to hold as much water as possible when rain is falling. In South East Asia farmers have been adding dredged silt from river bottoms and ant mounds, increasing cation exchange capacity. Adding bentonite to these degraded soils has been proven in a number of studies over the last decade to improve it’s production capacity within a single season. Bentonite holds 10 times it’s weight in water, and increases it’s cation exchange capacity significantly. The addition of bentonite also has the potential to reduce nitrate content of ground water and water ways by retaining more in the soil to be absorbed by plants. Studies done have also proven the addition of bentonite is cost effective by increasing yield and reducing fertilizer use.

Over the second half of this year I'll be conducting some unscientific experiments to see if the back yard food grower in the tropics has anything to gain be adding bentonite to their soil, paying particular attention to seedling and plant growth, resistance to pests and it's effect on worms. - I'll update with the results later.