Plants need water and nutrients to grow. In this process, plant roots extract water and nutrients from the soil and then in a remarkable ‘balancing act’, replace what has been removed.
Soil water is replaced by rain. If there is not enough soil water, crop irrigation is also necessary.
In forests or grasslands, nutrients taken up by plants are returned to the soil mainly through decaying litter.
As the dead material on the surface decomposes, the nutrients contained in the litter seep back into the soil. So, the plants feed the soil that feeds them.
On cropped land the plant material, with its nutrients, is removed in the form of grain (such as maize) or leaves (such as spinach).
Other plant parts such as roots and tubers (for example, potatoes and pumpkins) may be harvested. Nutrients removed by the plants must be replaced by fertilisation for the production of more crops.
Most commercial farmers use bagged fertilisers for their soils. These can be expensive and have to be transported to rural areas from bigger centres, which adds to input costs. Yet, without fertiliser, crops do not grow well and yields tend to be disappointing.
Manure can be used as an alternative to chemical fertilisers. In fact, before chemical fertilisers were available, this is what all farmers used to restore soil fertility.
They turned to more concentrated chemical fertilisers because these are easier to handle with mechanised planting equipment.
Also, as farms grew bigger, finding enough manure to fertilise the land became more difficult.
But, if you’re cropping a small area, you should be able to find enough manure for your needs.
From the kraal
In rural areas, the most common source of manure is the kraal. Here, the excrement and urine of livestock accumulate to form a layer of manure, which is essentially organic material consisting of plant residues digested by the animals.
How & when to fertilise
Kraal manure is usually applied during winter, which is the fallow period for most crops. The manure is spread evenly over the plot and worked into the soil to a depth of 5cm to 10cm.
Applying manure during winter gives it time to decompose before the crop is planted. In areas where crops are grown in winter, manure can be applied in late spring.
To save labour and transport costs, you can apply double the quantity of manure every second year without loss of yield.
In fact, if you have enough manure, you can apply up to four times the recommended amount every four years.
Source: Using Kraal Manure as Fertiliser, W van Averbeke and S Yoganathan, Agricultural and Rural Development Research Institute, Fort Hare.