By Saul Gwakuba-Ndlovu
ZIMBABWE’s last rain season was largely very poor as only a few areas, if not localities, received adequate rains to result in abundant crop harvests.
That was the case, especially in the Midlands, Masvingo and Matabeleland provinces, regions that usually experience below average rainfall.
When they do receive much rains, however, their harvests are so good that they sustain the communities for two or even three successive years, particularly in areas where drought-resistant cereals such as sorghum (mapfunde, amabele) and millet (mhunga, zembgwe, inyawuthi) are cultivated.
Notwithstanding the current drought, it is important for all those whose source of livelihood is agriculture to prepare their fields for the next rain season which commences usually in November, sometimes in October.
The vast majority of the people of Zimbabwe rely on tilling the soil for their living; so when we talk about promoting Zimbabwe’s national economy, we should address our minds, resources and physical efforts to the agricultural sector.
Mining is, of course, another economic sector of much importance although fewer Zimbabweans depend on it for their very survival than those who depend on agriculture, particularly cropping.
It is generally true that the quantity and quality of crops farmers harvest is as large (quantity) and as good (quality) as the farmer’s pre-planting preparation of their fields, the timing of the planting of the fields, the condition of the planted seed, the timing of the weeding of the fields and the timing and method of harvesting of the fields.
We should mention here that certain unpredictable extraneous variable factors can adversely affect farmers’ harvests, examples of such extraneous variables include pests such as army worms, locusts, grain-consuming birds, and floods, among others.
In this article, we are going to discuss the importance of manuring of fields a couple of months before tilling is done.
A look at kraal manure (also known as barnyard manure) shows that it has three principal elements of plant food which are nitrogen, potash and phosphoric acid.
A tonne of average kraal manure contains about five-to-six kilogrammes of potash, five-to-six kilogrammes of nitrogen and just about three kilogrammes of phosphoric acid.
Components of kraal manure differ in their weight, of course, depending on a number of factors which include how fat the cattle are that produced that manure.
The fatter they are, the richer is the manure; calves and thin cattle produce poor manure.
Fat cattle and fat pigs produce manure rich in nitrogen.
Cattle that feed on wild grass, corn stalks and Timothy grass yield poor quality manure, so do equines (horses, donkeys and mules), but goats and sheep give farms very good manure.
Some manure may not be very good for crops, but it contains roughage that makes the soil hold more moisture for longer periods than unmanured soils.
Chicken manure has much more concentrated plant food than other types of animal-derived manure.
It is slightly less effective than that of guano birds that feed on fish and is found in large numbers in parts of the Peruvian coast in South America.
Some bats in some localities of the Kwekwe rural areas were said some 30 years ago to be producing some manure similar to that of the guano.
Universities may wish to investigate this claim. We now turn to sources of chemical fertilisers; products that are very relevant to Zimbabwe’s agricultural economic sector and thus, to most Zimbabweans.
Nitrogen fertilisers are derived from dried blood obtained from some abattoirs.
Refuse or tankage found in yards of some slaughter houses also supply nitrogen-based fertilisers.
Tankage comprises bones, pieces of intestines and bowel waste that is ground together. In areas where fish abound, discarded fish is ground when dry and is used as fertilisers in gardens as well as in fields if the quantity is large enough.
Red Indians used to throw a dry fish or two into the same holes as maize seeds in their fields before America was settled by white people.
Phosphoric acid fertilisers can be produced by grinding bones, many of which can contain as much as 22 percent phosphoric acid.
Some rocks are rich in phosphoric acid.
That is the case particularly with fossil guano rock.
Such rocks can be ground and applied to fields. This mode of fertiliser production is for large scale commercial farmers and certainly not for small scale crop farmers.
Another source of phosphoric acid fertiliser is by co-operating with steel manufacturers whose process results in a large quantity of phosphoric slag, a by-product of the manufacture of steel.
Phosphoric slag contains between 15-20 percent phosphoric acid.
The well-known super-phosphates or chemical phosphates are produced by treating ground bones and phosphate rock with sulphuric acid.
Super-phosphates are a crop farmer’s first fertiliser choice because plants can use them almost as soon as they are applied to the field.
Potash fertilisers are generally derived from ashes of hard woods such as umtswiri (mbgweti), umbhondo (ntshingizi), the beech tree, a foreign tree whose ashes contain 16 percent potash.
Other foreign trees whose ashes are rich in potash are the elm (24 percent) and the oak (10 percent)
It is important to point out and emphasise that it is advisable for crop farmers to find out the deficiencies of their soils.
That can be done by a pedologist (soil scientist) at some universities or at a local government laboratory that can be identified by any agricultural extension officer.
The last type of manure we should deal with is green manure, comprising green grass and any other plants that can be ploughed into the fields before they have produced seeds.
The optimum benefit of green manure to the soil is while the plants being ploughed into the soil are still green.
After they have flowered and produced seeds, they can increase the weeds in the fields as their seeds may germinate.
However, when they are dry, their main advantage is not so much their nutritional contribution to plant food in the soil, but their moisture retention capability as they turn into roughage that retains soil moisture.
Many times we find that the small scale crop farmer is able to till small parts of his or her field only after harvesting.
That is better than failure to till any part of the field at all immediately after harvesting and should be commended.
It used to be called ‘winter ploughing’.
Turning under a growth of weeds before they produce seeds is one of the easiest ways to fertilise one’s land.
The green plants that are ploughed under increase not only the soil’s fertility, but acids that are caused by the decaying of the plants.
The acids act on the soil and form chemical compounds on which the following season’s crops feed.
Saul Gwakuba-Ndlovu is a retired, Bulawayo-based journalist. He can be contacted on cell 0734 051 705 or through email. firstname.lastname@example.org