When chemical fertilisers were introduced in Zimbabwe, soils were still rich in organic matter thus responses to chemical fertilisers for both commercial and communal farmers alike were outstanding.
Besides chemical fertilisers, commercial farmers used to practice green manuring while communal farmers applied cattle manure to their fields.
Wanton burning and none addition of organic matter widespread in Zimbabwe nowadays has changed agriculture.
Consequently, soils are now far less fertile as they lack organic matter or humus necessary in tobacco or other crop production leading to falling productivity despite the application of chemical fertilisers. Climate change has exacerbated the situation resulting in an increase in the frequency of droughts thus continually presenting challenges to our growers.
Topsoil is what we use to produce tobacco and other food crops thus we cannot survive without it.
A great deal of the carbon once stored in the soil is now stored in the atmosphere and this is the largest contributor to climate change. These factors among others are key ingredients of an impending disaster in Zimbabwe’s Agricultural sector hence we need to collectively and promptly act to avert the impending disaster.
We desperately need to return carbon back to the soil as humus.
According to soil physics expert, Professor Rattan Lal of Ohio State University in the US, agriculture has contributed 476 gigatonnes (476 000 billion tonnes) of carbon dioxide to the atmosphere via the loss of humus from soils.
Historically, the earth’s soils averaged 5 percent humus content and now average only 1,5 percent and in Zimbabwe this could even be lower and is likely to be worsened by widespread burning.
A 1,6 percent increase in organic matter in our soil across the globe would drop the current atmospheric carbon dioxide level of 400 parts per million to below 300 parts per million, which effectively reverses climate change. A huge percentage of farmers globally already suffer the ravages of climate change. Zimbabwe tobacco growers are no exception in this as the effects of the current Elnino Effect and other human induced factors are currently being felt by all and sundry.
The most important attributes for farming success in this brave new world are adaptability and flexibility.
This is not a time for apathy, it is a call to action – and it’s about the soil.
The impact of climate change, falling soil fertility, declining yields and reduced agriculture productivity can be averted by returning humus to the soil. Soils with healthy humus content are a determining factor in food security. Humus stabilises top soil, which is essential for growing tobacco and other crops.
Graeme Sait, CEO of Nutri-Tech Solutions in Australia, explained that “Humus is arguably one of the most important contributors to sustainable life on our planet, yet it remains largely unappreciated.”
Humus is the stabilising soil glue that determines whether or not dust, storms and floods will strip thin veil of precious topsoil; the sweet-smelling, chocolate-brown substance, the essence of soil fertility.
Soils hold together based on their organic matter components which are carbon (C), minerals and water and humus is the storage system for the three crucial substances that have an impact on soil, plant, animal, human and planetary health. Zimbabwe like most countries in the world could do with a Soil Restoration Act whose main objective is to ensure that all biodegradable organic matter from the farms is returned to our farmland and not sent to landfills.
Composting should be an integral part of everyone’s lifestyle – from individuals (by using kitchen waste, leaf litter and lawn clippings), to schools, councils and farmers utilising everything that is compostable.
The compost can be added to the soils of home vegetable gardens and croplands, where it will provide a stabilised carbon source for the soil and reintroduce huge numbers of soil microbes that can digest crop residues more effectively.
The humus-building process is thus restored and these soils become healthier, more productive, profitable and retain water efficiently. An increase of just one percent organic matter means that soil can retain 170 000litres water/ha that it could not previously store.
There is no evaporation beneath the surface and there is no carbon footprint in delivering that water to the crop.
Local companies such as Zim Earthworm Farms (PVT) Ltd produce and distribute Nutrich vermicomposts (earthworm based 100 percent organic fertilisers) which farmers are now returning to farm soils. In addition, local initiatives such as the “Greening Zimbabwe” initiative which anchors on composting and returning organic waste to soil, earthworm breeding, tree planting, rearing road runners and production of vegetable such as rugare, if promoted broadly, would significantly contribute to building soil humus.
The wanton burning of crop residue and velds should be banned and made a punishable offense. Not only does burning destroy food for beneficial cellulose-digesting fungi, but every 100kg of burned plant material produces 5kg of mineral-rich ash, which is lost to the atmosphere. Instead, crop residues should be left to decompose to benefit soil life and other plants growing in the soil, and to produce humus.
Inoculating soils with cellulose-digesting fungi will help speed up the decomposition of crop residues into the soil.
Research at the Department of Agriculture in the US suggests that cocktail cover crops between primary crops can be a tremendously productive C-sequestering tool as these crops are vital for feeding the soil while building its humus content.
Researchers have found that planting a cocktail of at least five different cover crops such as cereals, grasses, brassicas, legumes and chenopods results in the plants releasing phenolic compounds into the soil that trigger humus-building.
Every living organism has a carbon to nitrogen (C:N) ratio. Trees have a 500:1 C:N ratio, while soil nematodes, good and bad, have a ratio of 100:1., humans have a 30:1 ratio, while soil bacteria have the highest ratio of 5:1 meaning that their tiny bodies are actually 17percent N.
They crave it, and when we apply fertiliser they embark on a feeding frenzy.
They seek the carbon to balance out their tight ratio and if we apply nitrogen without carbon, the bacteria have no choice but to consume soil humus as their carbon.
Humic acid is the most powerful fungal stimulant known to man and vermicomposts are rich in humates.
This makes it exceptionally important as an aid to replenish the beneficial fungi in our soils that have been so badly affected by modern agriculture. Soluble humate granules can easily be combined with NPK fertilisers. Soluble fulvic acid powder can be dissolved and combined with all foliar inputs to chelate and magnify these inputs, while stimulating leaf and soil life.
It is not just chemical fertilisers that we must apply to our plants, tobacco included, but lots of organic composts to our soils if we are to achieve high yields and a reversal of climate change and as well as its adverse impacts.
Written by Dr E. Whingwiri, a specialist in earthworm technology. For any additional information please contact TIMB on telephone numbers 0772145166/ 9 or 0279-22082 /21982 or 025-3439 or 067-24268 /29246 or 0277-2700 or 064-7280 or 0271-6772 or E-mail: [email protected] or visit our website on www.timb.co.zw