guest column:Achieford Mhondera
IT has been established that Zimbabwe’s total annual greenhouse gas emissions as of 2015 added up to 22,0 Mt CO2e, which is about 0,045% of the global emissions.
This is coming at a time anthropogenic activities such as power generation, land use practices and other agricultural activities have been scaled up.
An estimated 16,4% increase in deforestation rate has been reported in recent years.
This is a result of rampant deforestation and forest degradation which act as carbon sinks due to over-exploitation for firewood, land clearing for farming and tobacco curing and increased incidents of veldfires, coupled with lack of knowledge on the goods and services provided by trees in agricultural production.
Consequently, carbon and nitrogen cycles are disturbed, soil quality is compromised, water infiltration rate is reduced while loss of essential nutrients is enhanced through erosion as vegetation is lost.
To this effect, promotion of climate smart and conservation agriculture must among other things such as the popular Pfumvudza concept, including education on the advantages of alley cropping.
Alley cropping or hedgerow inter-cropping is a form of conservation agriculture meant to redo the damage caused by the popular gospel of the plough.
In the conventional methods of farming, proper farming is perceived as involving total clearance of the land, addition of manure, basal and top dressing fertilisers.
However, this has proved to be unsustainable particularly in the changing climate coupled with high costs of farming inputs. Alley cropping, therefore, becomes an alternative and one form of climate smart agriculture with mitigatory co-benefits.
Alley cropping is an agroforestry system in which crops are grown in alleys formed by trees or shrubs managed as hedgerows.
Common tree types which can be used include leucaena, pigeon pea, gliricidia sepium as well as acacia angustissima and of late, an experimentation with zumbani recently proved to be yielding favourable results.
The choice of trees although most of them are exotic must be hinged on the fact that they must necessarily provide heavy foliage (leaves), be easy to establish (grow very rapidly), have a deep root system to enable them to extract mineral nutrients and water to tolerate drought and be able to regenerate after pruning.
In addition, they must be able to cope with the changing climatic conditions and have multiple uses such as food, pesticides among other uses.
More significantly, these trees must be easy to eradicate when no longer needed because other tree species cause some weeds which are difficult to eradicate.
All the trees identified above are nitrogen-fixing trees except zumbani, but its leaves provide essential nutrients for other crops as well as acting as a pest repellent.
The trees are cut at planting so that the leaves will provide mulch and manure so that basal fertilisers such as Compound D become unnecessary.
The roots provide nitrogen so that top dressing fertilisers such as ammonium nitrate also become unnecessary.
Alley cropping has advantages which include nitrogen fixing, addition of manure, elimination of basal and top dressing fertilisers as well as cutting the cost on weed removal by over 50%.
The cuttings provide mulch in the field which help to retain moisture as well as suppress the growth of weeds.
This method restores the soils’ organic matter through leaves, which increases the recycling of nutrients and it also controls pests, diseases and noxious weeds.
In addition, it also increases water infiltration and binds the soils through plant cover, thereby preventing erosion that may result from the impacts of raindrops.
Apart from improving soil quality and protecting it from erosion, the trees have other multiple uses. They provide supplementary food, for example, pigeon pea is edible, its seeds and leaves are consumed by human beings.
The flowers of gliricidia sepium can be mixed with beef and they make good stew. The trees also provide protein-rich foods for livestock. These nitrogen fixing trees have carotene which improves the quality of eggs and poultry skin.
When the trees are cut in the dry season, they provide firewood and stacking poles for tomatoes. Also these trees produce a lot of flowers, hence pollen for honey production becomes available.
Trees also provide herbal medicines, pesticides and rodenticides which are more environmentally friendly compared to poisons which are used to fight pests and diseases.
The most common forms of rodenticides and pesticides are harmful to chickens, dogs and even people, but rodenticides from trees such as gliricidia sepium can only eliminate the rats and rodents.
Lastly, these trees are ornamental and are very beautiful, thereby keeping the environment pleasant looking as well as providing carbon sinks and ultimately contributing to low emission development pathways.