The Fight Against Soil Acidity in Tanzania: The Bitter Truth and Charting a Sustainable Food Systems Future

*Insights from Dr Joel L. Meliyo, soil scientist

By Anthony Muchoki &  Beda Msimbe 

Soil acidity in Tanzania is an ominous issue impeding agricultural productivity. A stimulating dialogue with Dr. Joel L. Meliyo, the National Project Coordinator of Guiding Acid Soil Management Investment in Africa (GAIA) an International Project Funded by BMGF through CIMMYT Harare. Joel, a local Principal Investigator for GAIA is collaborating with TARI Mlingano, TARI Uyole, TARI Ukiriguru, and SAGCOT Centre Ltd, to highlight this issue extensively.

“We’re grappling with a magnitude of acid soil problem that’s pervasive in all high rainfall areas,” warned Dr. Meliyo. The severity of the issue in Tanzania is stratified into three categories: extremely acidic soils with pH values from 3.6 to 4.4, very strongly acidic soils with pH between 4.4 and 5.0, and strongly acidic soils falling in the 5.1 to 5.5 range. He emphasized, “The soils with pH values greater than 5.5 and less than 8.5 do not pose significant problems for crop growth and are hence, not considered in this discussion.”

Farmers are the frontline observers of this acidity issue, having seen the crippling impacts on their yields. “Over the years, farmers began to notice the acidity problem when acid-sensitive crops failed to establish, or crop production was lower than expected,” Dr. Meliyo cited a 2005 study by Upjohn et al.

Indeed, soil acidity fundamentally impairs nutrient uptake by crops sensitive to low pH levels, impacting their growth and development. “Low soil pH doesn’t necessarily curtail crop yield, as some crops are well adapted to low pH levels. However, nutrient availability reduces with a decrease in pH, and aluminium toxicity arises, impairing root growth and development. This leaves plants unable to rummage for water in the subsoil during dry spells,” Dr. Meliyo explained.

Unfortunately, the country’s primary crops, including maize, wheat, barley, beans, sunflower, tomatoes, and most vegetables, are sensitive to soil acidity. On the other hand, pigeon pea, coffee, and tea showcase more resilience. The acid soils’ ominous signs include stunted or shallow root growth, signs of aluminium and manganese toxicities, and poor or ineffective nodulation in legumes.

Dr. Meliyo reflected on a 2001 study by Hede et al., emphasizing, “The common crop characteristics in acidic soils are truly alarming. Stunted root growth, symptoms of toxicities, and poor nodulation ultimately affect yields and overall productivity.”

The economic repercussions of this issue are significant. “The severity of soil acidity is most evident in our maize production area, which is estimated to be 1.1 million hectares. The monetary loss from the reduction in maize output due to soil acidity stands at a staggering US$400 million annually. Moreover, the inefficient use of fertilizers and other inputs contributes to an additional cost of approximately $70 million annually,” Dr. Meliyo concluded, underlining the urgent need for effective soil acidity management strategies in Tanzania.

According to  Dr. Meliyo’s work highlights, the urgency for solutions is stark – the bitterness of Tanzania’s soil acidity must be addressed for the sweet fruits of agricultural prosperity.

Unearthing the Root Cause: What’s Making Tanzania’s Soils Acidic?

Soil acidity in Tanzania, like in many parts of the world, is a result of both natural processes and human activities. “Acidification of soils is a natural occurrence influenced by numerous factors,” said Dr. Meliyo.

“These factors include climatic conditions like rainfall, temperature, biological influences, and land use. Even the type of parent rock or materials from which soil develops can significantly impact soil acidification,” explained Dr. Meliyo.

In Tanzania, human activities also play a critical role in this process. Practices such as cultivation, which involves crop harvesting and the removal of stover (the leaves and stalks of field crops, such as corn or grain, left in a field after harvesting), can contribute to soil acidification. “Though the usage of fertilizers is limited in Tanzania, in areas where cultivation is a common practice, it can lead to soil acidity,” Dr. Meliyo stated.

Dr. Meliyo pointed out that soil acidity found in National Parks and other woodlands in Tanzania is naturally formed, due to minimal human interference. “Human operations may induce soil acidity in cultivated areas, but in places like National Parks and woodlands, the major cause of soil acidity is natural,” he confirmed.

Certain cropping practices, particularly the overuse of nitrogen, can further accelerate soil acidification. “The repeated applications of nitrogen in amounts exceeding crop uptake lead to net H+ production, increasing the quantity of acidic ions in the soil,” Dr. Meliyo elaborated.

He further explained, “When ammonium fertilizer breaks down due to microbial action, it amplifies the acidity level in the soil, thereby lowering the soil pH. This is a classic case of a beneficial practice backfiring due to overuse.”

These findings illuminate the multidimensional causes of soil acidity as per a huge body of literature available about the subject, shedding light on the complex interplay of natural factors and human interventions. As Dr. Meliyo’s review and research work reveals, understanding these causes is the first step towards managing soil acidity effectively, a necessary endeavor to safeguard Tanzania’s agricultural future.

An Acidic Landscape: The Extent of Soil Acidity in Tanzania

Dr. Meliyo, an expert on soil management in Tanzania, through (TAnSIS/AfSIS works (Markus et al., 2018) brings alarming news about the severity of soil acidity in Tanzania. “Around 32.7 million hectares in Tanzania are covered by acid soils,” he declared, a vast expanse affecting the country’s agricultural potential. Of this figure, 4.7 million hectares are cropland directly impacted by soil acidity; 1.1 million hectares are dedicated to cultivating maize, the staple crop (Markus et al., 2018).

He further pointed out soil acidity starts at pH 5.65, but the level where it becomes problematic, especially in tropical soils like those in Tanzania, is when the pH falls below 5.5.

“Acidity is not evenly spread across the country,” explained Dr. Meliyo. “There are areas more heavily affected than others.” He mentioned several regions in Tanzania where soil acidity is particularly acute. “These areas include the Southern Highland Zone, such as Mbeya, Njombe, Songwe, and Iringa; the Western regions of Kigoma and Tabora; and the Lake Zones of Kagera, Mara, Mwanza, Geita, and Shinyanga. We also see severely affected areas in the northern, eastern, and southern zones.”

The extensive soil acidity across Tanzania is a cause for concern, especially considering the country’s reliance on agriculture. It’s a ticking time bomb, threatening the productivity of the country’s most essential crops.

Liming the Way Forward: A Potential Solution to Tanzania’s Soil Acidity Problem

Striking an optimistic note, Dr. Meliyo, highlighted a promising strategy for managing soil acidity. “Lime application, although not yet extensively adopted in East Africa, including Tanzania, holds significant potential for managing soil acidity,” Dr. said. He cited recent field experiments in Kenya, Rwanda and Tanzania, where liming led to a maize % yield increase of 4% to 14% within the first season (Scoping Study Tanzania, 2018). “Farmers in Iringa recorded an increase in maize production from 3 to 8 tons after adopting lime application in their farms,” he noted.

These early successes hint at even more remarkable yield improvements in the future. “Other studies and field trials have indicated responses to lime of up to 25%, and potentially higher in subsequent years after the full broadcast application is done. Depending on the application rate and method, it is evident that yield increases annually responding to applied lime,” Dr. Meliyo shared.

According to Dr. Meliyo, yield response level depends on the lime application rate and method. Corrective soil levels can be achieved with broadcast application and mixing with the soil or by a band application of placement within a furrow alongside the seed, potentially along with a fertilizer application (Scoping Study Tanzania, 2018). “Microdosing lime via placement of lime at each seed station is feasible for some row crops, such as maize. Broadcast application (with tillage) is the preferred method to increase soil pH levels across the entire soil planting layer. Banding and microdosing require less lime (25%) and are primarily used for maintenance” (Scoping Study Tanzania, 2018).

He went on to explain that the total lime requirement for a broadcast application depends on the soil pH level and soil type (texture). “As a general rule, to reduce acidity by increasing .1 on the pH scale would require 1 metric ton of lime per hectare. Therefore, a soil with a pH of 5.0 would require 6 metric tons of broadcast lime to increase to a pH level of 5.6. Alternatively, annual applications of 1.5 metric tons of lime per hectare over 4 years might be a more affordable and workable method for some farmers. Increasing pH levels to 6.0 would require approximately 10 metric tons per hectare, or 2.5 metric tons per hectare per year” (Scoping Study Tanzania, 2018).

Acidic Lands, Lime in Demand: Estimating Tanzania’s Lime Requirement

Tackling Tanzania’s soil acidity problem requires a strategic and systematic approach, according to Dr. Meliyo. “From our estimates, Tanzania will require between 2.35 and 14.1 million tons of lime per year for just one year of application,” Dr. Meliyo shared, emphasizing the scale of lime required to combat soil acidity across the country’s agricultural lands (Scoping Study Tanzania, 2018).

His estimates provide a detailed insight into the lime requirements for different regions of Tanzania, taking into account their proportion of the total agricultural land, the area of acid soil, and varying lime application rates (Scoping Study Tanzania, 2018).

For the Lake and Western Zones, accounting for 45% of total agricultural land (approximately 2,115,000 hectares), lime requirements range from 1,057,500 tons at a 0.5 tons per hectare rate, to 6,345,000 tons at a 3 tons per hectare rate.

The South Highland and Southern Zones, making up 35% of the agricultural land, equating to 1,645,000 hectares of acid soil, would require lime amounts ranging from 822,500 tons to 4,935,000 tons, depending on the application rate.

Finally, the Central, North, Eastern, and Zanzibar regions, encompassing 20% of the agricultural land (940,000 hectares of acid soil), would require between 470,000 and 2,820,000 tons of lime.

“The lime application isn’t a one-off solution,” Dr. Meliyo cautioned, explaining that its efficacy is determined by the rate and quality of lime used, the type of nitrogen source, and the type of crop. “This is applied for the first year and repetition is determined annually by monitoring changes in soil pH. For instance, ammonium sulphate is more acidifying than diammonium phosphate and urea among the nitrogen sources” (Scoping Study Tanzania, 2018).

These figures underscore the extent of the challenge ahead. However, they also provide a tangible roadmap, allowing Tanzania to tackle soil acidity head-on and invest in the future health of its agricultural sector.

A Silver Lining: Turning Soil Acidity Challenge into a Limestone Industry Boom

While Tanzania grapples with widespread soil acidity, Dr. Meliyo, a noted soil management expert, sees potential for a win-win solution: utilizing the country’s rich limestone deposits to meet the demand for lime in agricultural and other sectors. “Turning to our natural resources is not just practical, but can also be profitable,” he said, revealing an optimistic outlook on the issue.

A report from the Ministry of Minerals indicates that Tanzania is home to 33 limestone deposits. Of these, 21 have been analyzed for quality, such as neutralizing value, extent of impurities, and quantity. “Many of the deposits are conveniently located along the Eastern Coast of Tanzania, from Tanga through Mtwara regions, with one in Dodoma, and smaller deposits in Mbeya and Ruvuma. Several deposits are also found near Lake Victoria and in the Western zone,” Dr. Meliyo explained.

On the basis of the available data, Dr. Meliyo identified the most promising deposits. “These include Dodoma limestone, Kigoma and Kasulu limestones, and Pongwe limestone.” He also recommended additional areas for prioritization, such as Songwe, Matumbi Hills, and Moka, to fulfil the need to locate lime sources close to their areas of use.

Not only does Dr. Meliyo see this as a solution to Tanzania’s soil acidity problem, but he also views it as a lucrative opportunity for investment. “Given the number of limestone deposits in the country, we could build a thriving limestone industry that would not only supply the much-needed lime for our agricultural activities but also extend this service to neighboring countries that face similar problems,” he remarked.

If leveraged properly, this investment can spark a wave of economic development, making Tanzania a regional hub for lime production. Thus, an environmental problem could very well give birth to a booming industry, turning Tanzania’s soil acidity challenge into a catalyst for growth.

Turning the Tide: An All-Inclusive Strategy for Managing Soil Acidity in Tanzania

Given the prevailing soil acidity situation in Tanzania, Dr.  Meliyo, proposes a comprehensive strategy to manage soil acidity, involving government action, private sector engagement, and raising awareness among farmers.

“Low pH soils are a major problem in the country, significantly impairing crop production. The subsidies currently provided by the government aren’t achieving the desired impact on productivity due to the severity of soil acidity,” Dr. Meliyo revealed.

The first step, according to Dr. Meliyo, is an official recognition of the issue at the highest level. “The government should declare soil acidity a problem. We can’t tackle an issue we aren’t acknowledging openly,” he asserted.

After that, the government should rally the private sector and donors to carry out countrywide campaigns for lime supply and application in the regions affected by soil acidity. Simultaneously, the government should promote investment in limestone mining factories in areas with high soil acidity, thus reducing the cost of lime distribution.

“Imagine a joint effort where stakeholders from various sectors come together to manage soil acidity. This collective action could considerably boost our chances of overcoming this issue,” Dr. Meliyo explained.

Yet, it’s not just about lime application. Greater awareness among farmers about the limited benefits of using fertilizers in acid soils is crucial. Dr. Meliyo explained, “Farmers should be made aware that using fertilizers in acid soil yields only about 30% benefit, depending on the severity of the acidity. This information needs to be spread through comprehensive campaigns.”

Lastly, proper soil characterization should be carried out for accurate data that guides the correct lime requirements. While some regions already have data, Dr. Meliyo stresses that this information needs consolidation, refinement, and effective presentation for use.

“Knowledge is power,” Dr. Meliyo said, “With accurate data, we can arm our farmers and policy makers with the right tools to tackle this problem head on.”

This comprehensive strategy paints a hopeful picture for the future of soil management in Tanzania. The integration of governmental support, private sector involvement, awareness campaigns, and data-driven approaches could turn the tide against the formidable challenge of soil acidity.

Celebrating Soil Acidity Solutions: NGO Initiatives Making a Difference in Tanzania

While the soil acidity problem is widespread in Tanzania, several NGOs have risen to the challenge, launching initiatives in the Southern Highland. Organizations such as the Clinton Foundation, Briten, and One Acre Fund have all taken steps to address soil acidity, with varying degrees of success.

Dr. Meliyo, provides a nuanced perspective on the matter. “I wouldn’t say that all these initiatives are successful in the literal sense of the word, but they have been successful in highlighting the problem of soil acidity,” Dr. Meliyo points out.

These NGOs have conducted significant work in limited areas, and the results are promising. They have been able to produce solid facts about lime application and its benefits in agriculture, demonstrating the potential for these interventions to make a meaningful impact on crop yield and farmer livelihoods.

However, the impact of these initiatives is somewhat constrained by their geographical focus. “While these NGOs are doing commendable work, the reality is that soil acidity is a countrywide problem. The majority of these organizations are concentrated in the Southern Highland zone, even though around 45% of the soil acidity issue is situated in the Lake zone and Western zone regions,” Dr. Meliyo notes.

This observation underscores a crucial gap in the efforts to tackle soil acidity in Tanzania. While current NGO initiatives have paved the way by raising awareness and demonstrating practical interventions, there is a pressing need to extend these efforts to other regions of the country, particularly the Lake zone and Western zone regions.

Dr. Meliyo’s call to action is clear: more NGOs should focus their efforts on these underserved regions. With a wider geographical reach and a continued focus on educating farmers about lime application and other soil management practices, Tanzania could make substantial strides in managing soil acidity and improving agricultural outcomes.


Understanding the Devastating Impact of Soil Acidity on Agriculture: A Call for Greater Awareness

Soil acidity is a growing concern in agriculture, particularly in Tanzania. It significantly hinders the availability of natural nutrients and those added as fertilizers, leading to undernourished crops that yield poorly or not at all. This, in turn, contributes to increasing rates of hunger and poverty among farming communities.

The economic impact of soil acidity is immense. Depending on the severity of the acidity, between 20 to 70% of applied fertilizers are lost. At a pH level of 4.5, up to 73% of fertilizers are lost, while at a pH level of 6.0, the loss is around 20%. This loss is detrimental to crop yields and translates into significant financial losses for farmers who invest in fertilizers that the crops cannot fully utilize.

In high rainfall areas, which typically act as the country’s breadbaskets, soil acidity is a leading cause of crop losses. It is essential to treat our soils for sustainable production, especially given that many crops, like wheat, cannot tolerate strong acidity.

However, one of the biggest challenges in addressing soil acidity is the need for more awareness among stakeholders, from farmers to scientists. To many smallholder farmers, soil acidity is a “silent killer” that only manifests itself five to seven years after new land clearing. By that time, crop yields have declined significantly, leading farmers to erroneously conclude that their soils are simply “tired”. Unaware of the actual cause, they may try to improve productivity by applying farmyard manure, which does not address the acidity issue.

Similarly, scientists who are not specialized in soil science often overlook soil testing, missing the opportunity to detect and address soil acidity issues early on. This lack of awareness among those who directly engage with the land is a major hurdle to combating soil acidity.

Dr. Meliyo, argues for a multi-pronged approach to awareness creation. “We need to create awareness about the problem using different pathways. One significant move would be a Ministerial declaration of soil acidity as a problem. This would have a big impact regarding awareness.”

Dr. Meliyo’s assertions  highlight the pressing need for a more comprehensive understanding of soil acidity and its impacts. This will require concerted efforts from various sectors, from government to private sector, NGOs to scientific communities, and, most importantly, the farmers themselves who are at the front line of this agricultural challenge.

Addressing Soil Acidity in Tanzania: Progress Made Under the GAIA Project

The Guiding Acid Soil Management Investment in Africa (GAIA) project is making strides in tackling the widespread problem of soil acidity in Tanzania. The project has launched several work packages designed to understand, manage, and disseminate information about acidic soils, especially within the Geita and Mbozi districts.

Soil Survey:

A key component of the GAIA project is a soil survey, which collected crucial data on the distribution of acidic soils in Tanzania. Detailed surveys were conducted in Geita and Mbozi districts, and the resulting data was used to map the spread of acid soils in these areas. Alongside the surveys, shotgun field trials were conducted to test the effectiveness of different acid soil management practices.

Decision-Support Tool:

A decision-support tool was developed to aid farmers in evaluating the acidity of their soils and selecting appropriate management strategies. This web-based application, now available to farmers in Geita and Mbozi districts, is informed by the results of the shotgun field trials.

Farmer Training:

Direct training was provided to farmers on effective acidic soil management practices. The training covered a wide range of topics, including causes of acidic soils, their impact on crop production, best practices for managing acidic soils, and how to use the newly developed decision-support tool. Results from the shotgun field trials also formed a critical part of the training curriculum.

Information Dissemination:

A robust information dissemination strategy has been implemented to ensure that farmers and stakeholders in Geita and Mbozi districts are well-informed about acid soil management. This strategy includes radio broadcasts to reach a wide audience, workshops for farmers and other stakeholders, and hands-on training through Farmer Field Schools. The results from the shotgun field trials have been widely disseminated through these channels to ensure practical application of the findings.

The GAIA project is expected to benefit over a million farmers across Africa, helping to improve food security and reduce poverty. In particular, the shotgun field trials in Geita and Mbozi have been instrumental in identifying effective acidic soil management practices for these regions. By disseminating these results, the project is helping farmers increase crop yields, providing a sustainable solution to one of the region’s most pressing agricultural challenges.

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