THE BIO-INTENSIVE URBAN GARDENING SERIES – EPISODE 17

The ability of Farmers to distinguish between nutrient deficiency and plant disease symptoms helps to prevent wastage of resources and investments. Interestingly, Episode 16 described elaborately the chemistry of soil nutrients. Click here for an insightful read.

Knowing the level of acidity and/or alkalinity of soil is very important as it affects the overall productivity of the growth medium. Episode 17 is designed to shed light on the importance of soil pH.

Soil pH

Soil pH helps you to know the relative acidity or alkalinity of the soil solution (soil water) which greatly affects the availability of nutrients, microbial activity and structure of the planting medium (soil)

Soil pH is measured on a scale from 0 – 14, 0 – 6.9 indicates acidic soil with different ranges. 7 stands for neutral soil while 7.1 – 14 represents alkaline soil at different ranges.

Kindly note that most vegetables and fruits grow best in slightly acidic soil with a pH range of 5.5 – 6.9.

Also, it should be known that the quality of pH is the most important factor to note when testing the soil. The quality of the pH is determined by testing for plant available potassium, magnesium, calcium and sodium in the soil.

Most West African soils are acidic with pH levels often below 5. If the soil pH goes below 5.5, nutrients such as nitrogen, potassium, phosphorus, magnesium and molybdenum can become critically unavailable to the plant even when the nutrients are continuously added to the soil.

In the same vein, when soil pH reads below 5.0, certain nutrients such as manganese, boron, copper, zinc become additionally unavailable at this point. Hence, the need to first increase the pH of the soil before adding any form of nutrients because at this point, no matter the quantity of nutrients added to the soil, no effect will be felt as it relates to plant growth.

To make soils less acidic, lime, calcium carbonate, dolomite, calcium magnesium carbonate, wood ash or compost can be added to the soil. However, over-liming of a garden or farm should be avoided because it can induce phosphorus and micro nutrients deficiency. Also note that all limestones do not have the same mineral composition. Therefore, it is important to ask for the mineral composition of the limestone before purchase if not written on it.

For example, application of dolomite to the soil with high magnesium content instead of caustic lime could destroy the soil balance and adversely affect plant growth.

In conclusion, it must be known that compost can either be acidic or alkaline depending on the material used in making it. It is advised to use enough varieties of plant in compost making for a relatively balanced nutrient compost as discussed in previous episodes.

Thank you