Acidic Soils

Dealing with Acidic Soils

A Daunting Task waiting Ethiopia

It has been over a decade since the government discovered that a little more than 40Pct of the total arable land of Ethiopia is affected by soil acidity. As a result, the fertility of most Ethiopian soil has already declined posing another challenge to crop production. Soil acidity affects crop growth because acidic soil contains toxic levels of aluminum and manganese and characterized by deficiency of essential plant nutrients such potassium, calcium and magnesium, among others. Had acidic soils been neutralized the country would have increased the production of crops such as cereals four folds. Yet this does not seem like it will be realized soon. EBR’s Ashenafi Endale reports.

Habtamu Alemu, 43, cultivates maize and wheat, among other crops, on six hectares of land he inherited from his father, near Gore town, located south of Metu in the Illu Aba Bora zone of the state of Oromia. He used to be able to grow up to 30 quintals of maize and 38 quintals of wheat per hectare. But his productivity declined by almost 100pct.
Hatamu, who didn’t understand the reason for the decline in productivity, used fertilizer to try and reverse the situation, but to no avail. “Urea and DAP worked only during the first years. Gradually the farms started growing only unusual weeds, rather than the normal crops I used to grow. I’ve now left farming for grazing and a coffee plantation. I buy crops from the market to feed my family. Many farmers in our woreda have complained to the agriculture bureau, but every year they are forced to buy the fertilizer.”

A study conducted a little more than a decade ago in the area where Habtamu lives showed that the decline in productivity is linked with soil acidity. According to studies conducted on the subject, soil acidity affects root development, which leads to reduced nutrient and water uptake. Acidic soils are also deficient in essential plant nutrients such as potassium, calcium and magnesium, among others.

But Hatamu was not the only one affected by soil acidity. In fact, soil acidity is now becoming a serious threat to farmers who cultivate crops in many parts of Ethiopia. Currently, 40.9Pct of the total arable land (around 16 million hectares) in the country is estimated to be affected by soil acidity. Out of the total affected arable land, 13.2Pct has already become infertile.

But this is only based on a study undertaken 11 years ago. “The acidity level is probably higher now, since soil science is dynamic,” said Fasil Kebede (Prof), director general of the Ethiopian Soil Resource Institute, which is currently under establishment.

The level of soil acidity and the extent to which it has affected production have not been studied in recent years. Ethiopia’s first compiled study on soil acidity was published in 1989, and was later revised and published in 2007 by Mesfin Abebe, a renowned soil scientist, under the title “Nature and Management of Acid Soils in Ethiopia”. All institutions, including the Ministry of Agriculture, Livestock and Fishery (MoALF), Agricultural Transformation Agency (ATA), universities and experts use this pioneer research as a reference. Meanwhile, the ATA, which is currently undertaking a study to determine the level of soil acidity as part of the national soil information map, has yet to finalize its work.

Although outdated, the available research indicates that the acidic belt extends from the south-west to the north-west with east-west distribution while the 13.2Pct that has already become infertile is largely distributed in the states of Gambela and SNNP as well as Oromia, areas known as the coffee belt. According to the policy brief presented by ATA three months ago, soil acidity affects up to 6.5 million hectares of Ethiopia’s agricultural land in six regions and two administrative cities, of which 3.7 million hectares is in the state of Oromia.

How did the soil become acidic?
The step of applying fertilizers, mainly urea and DAP, was taken to overcome the problem of decreasing soil fertility in the last four decades. Though the results vary from place to place enormous increase in the yields of several crops achieved, in general.

As Wassie Haile, a researcher at Awassa Agricultural Research Center, indicated in a study conducted on the mitigation of soil acidity, there were numerous occurrences where cereal productivity increased by over 100Pct due to fertilizer mainly because of the availability of nutrients contained in inorganic fertilizer to plants. As a result, fertilizer consumption in Ethiopia increased from 14,000 metric tons in 1974/75 to 802,765 metric tons in 2015.
With increased consumption the soil acidifying nature of fertilizers such as Urea and DAP ultimately caused acidification. Reduced nitrogen fertilizer use efficiency or recovery efficiency by crops is the most important problem associated with the use of chemical fertilizers, according to Wassie.

Stakeholders also stress that inappropriate fertilizer usage is one of the main factors contributing to soil acidity and the decline of soil fertility that continues to plummet, posing another challenge to boost agricultural production and productivity. “Soil acidity highly affects agricultural productivity, which decreased by 50Pct, at least, in all crops in areas impacted by soil acidity. It became difficult to produce crops like legumes, beans, wheat, barley and teff,” explains Tefera Solomon, director of Soil Fertility Improvement Directorate at MoALF. “In addition, inappropriate usage of urea and DAP worsened the acidity problem.”

Not only that, but the blanket use of urea and DAP, according to experts, is another major reason for the acidity of the soil. “If urea is not used at the right moisture and water level, it is wasted in the soil, rather than being taken up by the plant. Then it increases excess nitrogen in the soil, which increases the acidity level,” elaborates Zebene Mikru (PhD), a soil scientist at Horizon Plantation, with over 30 years of experience in the field.

So far, farmers in Ethiopia have only used DAP and urea as fertilizers. However, the ineffectiveness of DAP and urea to improve crop yields until the severity of soil acidity came to light. And starting from this year, the MoALF has replaced DAP with NPS (nitrogen, phosphorous, sulfur) compound fertilizers.

While global reasons for soil acidity range from over fertilization to acid rain, in the case of Ethiopia, over washing of the balancing alkaline elements by rain from the surface of farm land is perhaps the top factor, causing poor nutrient content, and sometimes devastating consequences for crops.

Acidity is concentrated mainly in the rainy and slopey areas of western Ethiopia, including the lowlands, but is limited by the eastern escarpments of the Rift Valley, where the land has other problems like high fluoride levels. In these areas, where the temperature and rainfall are high, with strong intensity of leaching under high soil permeability, the removal of nutrients and minerals from the soil by rainwater increases. “The result is more acidic soil,” says Mesfin.

After the soil becomes deficient in nutrients like sodium, calcium and potassium, the acids and metals left behind, like iron and aluminum, make insoluble compounds, which make it difficult for the root to take in nutrients from the soil. “Ethiopia’s farm lands are exposed to bad weather throughout the year. The nutrients in the upper soil are taken by soil erosion during summer and by wind during the dry season,” elaborates Fasil. Ethiopia, indeed, has the highest rate of topsoil erosion in Africa, with 137 ton per hectare every year, according to information from the ATA.
Such factors, coupled with the different intensities of weathering and leaching, due to low forest coverage, absence of residues and decomposing microorganisms and insects in the soil, raise the acidity level of the soil in most parts of the country.

Neutralizing soil acidity
There are multiple options to revive acidic soil. The first is adding alkaline compounds to neutralize the acidity. Globally lime, or more specifically white powder calcium oxide, commonly known as unslaked lime, burned lime, or quicklime is used to treat acidic soil. Limestone, in general, is capable of reducing acidity, where in Ethiopia, it’s largely found in central and southern parts of the country.

Despite the presence of the mineral, nonetheless, the government has been reluctant to use lime, because coffee and tea plants tolerate acidic soils to some degree. “There was a wrong perception that acidic soil is good for expanding coffee farms, which was tricky,” says Zebene. The government, however, did not maintain the status quo for long. Four years ago, it installed lime crushing plants. A minimum of 20 to 80 quintals of lime is needed per hectare to treat acidic soil depending on the level of acidity.

During the first phase of Growth and Transformation Plan (GTP I), it was planned to rehabilitate acid soils by providing lime to farmers for free. However, as indicated by the policy brief presented by ATA three months ago, only six percent of the target was accomplished. During the GTP II period, an even more ambitious goal of rehabilitating 226,000 hectares of acid soils was set out. Assuming a 50Pct subsidy, achieving the entire GTP II target would cost a total of about ETB430 million. But current projections predict an achievement of only five percent of the target by 2020.

A quintal of lime is sold for up to ETB300, including transport, making it much expensive than the ETB1,200 farmers spend on fertilizers such as urea needed for a hectare of land. Unfortunately, the rehabilitation of acid soils project has not progressed far due to logistical hurdles while distributing to farmers. The lime crushing plants stopped working due to malfunctions, according to Tefera, who says: “The factories currently produce 100,000 quintals of lime combined, despite the huge demand.”

Studies show that using lime is a viable solution for the problem. Soil acidity is reduced by the application of just two to four tons per hectare of agricultural lime, with subsequent yield increases of up to 300Pct reported, according to a recent study by ATA. Taking this for granted, the government is now negotiating with cement industries to manufacture lime on a large scale, according to Kebede. “New factories will be installed. We are also undertaking research, cooperating with Jimma University and other institutions. Lime is available in Ethiopia, but the problem is the distance from farm areas.”

Ethio-Agri CEFT and Horizon plantations, both large scale agricultural producers, are amongst the commercial farmers that have succeeded in reducing acidity using lime produced and supplied by MBI, a sister company. The companies first take samples of soil from the farms. Then they add lime, based on the acidity level. By employing such mechanisms, the coffee productivity at Ethio-Agri CEFT increased to 16 quintals a hectare, far from the national average of seven quintals, according to Zebene.

The success also varies with the crop. Yared Talegeta, farm manager of Pinnaw Business, which exports over 30 million cut flowers annually, says some flowers prefer acidity, up to a point. “However, we continuously monitor the balance. There are a few importers who supply the nutrients for us. However, since they cannot keep stocks up due to the absence of hard currency, they bring it for us from Kenya. Usually we import by ourselves, since they always have shortages.”

However, not all Ethiopian farmers are able to do this. “The ATA discloses only the national soil information map, but not the exact farm location, so it is impossible to know what is recommended for which farm. The information must be included online or be available for purchase. Many soil studies have been done in Ethiopia over the last 30 and more years. However, none of them can be used today, since the samples had no GPS coordinates,” complains Zebene, who says most of the problems in Ethiopia have been identified even though there has been no action.

In spite of being a viable solution for some, neutralizing acidic soil is just the first step to create fertile soil. Adding back the nutrients washed from the soil, in the form of fertilizers is the second available solution. Once the soil is neutral, plants germinate but might not be highly productive, if other micro and macro nutrients are lacking, according to experts.

ATA’s preliminary soil map atlas identified over ten nutrient short falls across soil types. The Agency recommended soil specific fertilizer usage four years ago as a solution. Accordingly, the government replaced DAP with NPS and also installed five fertilizer blending factories, one each in the states of Amhara, Tigrai, and SNNP and two in the state of Oromia. The factories were meant to blend imported basic fertilizers based on nutrients deficits, but they quickly stopped operations, because the inputs were not imported as per the specifications, according to Tefera.

The blending factories, in fact, encountered two problems. First, the factories did not prepare recipes of nutrients needed to be blended, based on the farm and plant nutrient deficits. To the surprise of many, even the imported basic nutrients were the wrong granular sizes and did not fit the granular index the machines were programmed to bend.

The best approach, according to Zebene, is tailoring the blending output with the exact ratio of acidity and nutrient deficit in the soil. “So far their blending ratio is not right. ATA’s soil atlas is based on only soil samples. It is not plant specific,” he says. “The atlases need expert evaluation and interpretation to be used by farmers. Farmers need simplicity, an all in one fertilizer, rather than different fertilizer packages. The blending factories must be able to produce what the soil lacks and what each plant needs.”

Farms under Ethio-Agri CEFT and Horizon plantations currently use imported NPK (nitrogen, phosphorous, potassium),which is good for coffee, and is needed in dry areas in the state of Tigray, rather than the products of the blending factories, according to Zebene. “The lime and blending machines were installed with great ambitions, but remain stuck. I came to Ethio-Agri CEFT three years ago. Here we blend and use NPKSB and NPKSBZ. We are talking with OCP [a Morrocan fertilizer producer] to access a sustainable farm and plant specific fertilizer supply.”

The capacity of the blending machines Ethiopia bought is similar to the machines purchased by Uganda, Kenya and other African countries years ago. They also faced the same granular index problem in the initial years. But they changed it immediately and solved the problem. The Ethiopian government, however, prefers to follow a different path. As of now, OCP is working with the MoALF to fix the problem of the blending factories.

For Ethiopia, it is not only acidity that undermines future agricultural productivity, but also the presence of alkaline soil. This is true especially for the states of Afar and Somali. Alkaline soils, which have poor soil structures and low infiltration capacity, owe their unfavorable chemical properties mainly to the presence of sodium carbonate. Sodium carbonate, also known as washing soda, soda ash and soda crystals, is the water-soluble sodium salt of carbonic acid.

Worryingly, however, alkaline soils are difficult to reclaim unless treated with chemical amendments, according to soil scientists. Mesfin, for his part, suggests irrigation to treat the soil. “If successfully irrigated under sound water management, they could make a difference in the fast-track attainment of food security. If not, they can even go a long way to facilitate market-oriented development,” stresses Mesfin.

7th Year • Oct.16 – Nov. 15 2018 • No. 67

Ashenafi Endale

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