The analysis, published in Discover Agriculture by Ibrahim L. Kadigi of Mbeya University of Science and Technology and Lekumok Kironyi of Mwalimu Nyerere University of Agriculture and Technology, draws on the 2019/20 National Sample Census of Agriculture, Tanzania’s most comprehensive agricultural survey. The census, run by the National Bureau of Statistics, covered thousands of villages across the mainland and captured detailed records of household crop production, landholdings, and input use. From an initial pool of 2,830 sorghum-producing households, the researchers assembled an analytical dataset of 2,000 farms with complete harvest information, spanning all seven of the country’s agro-ecological zones.

What the data revealed about fertilizer adoption was stark. Only 91 farms, or 4.6 percent of the sample, reported applying organic fertilizers such as manure to their sorghum, and just 59 farms, about 3 percent, used inorganic mineral fertilizers. The remaining 92 percent of farms grew the crop on whatever nutrients the soil still held. Adoption was heavily concentrated in the Southern Highlands, where 48 of the 59 inorganic fertilizer users were found, a pattern the researchers attribute to better market integration and stronger extension support. In the Central Zone, the heart of Tanzanian sorghum production with more than 255,000 hectares under the crop, not a single sampled farm reported using mineral fertilizer.

To compare productivity across these three farming systems, the team went beyond simple averages. They employed a two-stage Monte Carlo simulation framework, a stochastic technique that converts observed farm-level yields into full probability distributions. In the first stage, yields for each fertilizer category were parameterized as empirical distributions and resampled 500 times using Latin Hypercube Sampling, an efficient method that preserves the statistical properties of the parent data with relatively few iterations. In the second stage, a multivariate empirical procedure introduced correlated randomness across the three systems, ensuring that simulated outcomes respected the real-world covariance structure of the data rather than producing implausible values such as negative yields.

The simulation was validated in two rounds against the observed census data, with goodness-of-fit tests and probability density function overlays confirming that the simulated distributions reproduced the means, spreads, and extremes of actual harvests. The researchers are careful to note what the method cannot do: because fertilizer use was not randomly assigned, the results describe associations between fertilizer categories and yield outcomes, not causal effects. Farms that choose to fertilize may differ in soil quality, management skill, or access to markets in ways the census cannot fully capture. Still, the scale of the differences is striking.

Farms using no fertilizer averaged 1.30 tonnes per hectare, with a minimum observed yield of just 0.49 tonnes. Organic fertilizer users averaged 1.38 tonnes per hectare, a marginal gain accompanied by greater variability, with a coefficient of variation of 56.4 percent compared with 47.2 percent among non-users. The researchers link this inconsistency to the uneven nutrient density and variable quality of manure and compost, which depend on storage, handling, and application rates that few farmers can control precisely. Inorganic fertilizer users, by contrast, averaged 1.94 tonnes per hectare, nearly 50 percent above non-users, with a higher minimum yield of 0.66 tonnes per hectare that suggests mineral nutrients also cushion farmers against the worst outcomes.

The probability analysis sharpened the picture further. Among non-users, 38 percent of farms fell below the national average yield of 1.0 tonne per hectare, and only 10 percent exceeded the 2.0-tonne benchmark widely regarded as the standard for economically viable sorghum production. Organic fertilizer users fared no better in the short term: 41 percent fell below 1.0 tonne, and just 8 percent cleared 2.0 tonnes, a result consistent with evidence from Kenya, Ethiopia, and Burkina Faso showing that organic inputs build soil structure and fertility over multiple seasons but rarely deliver immediate yield gains on their own. Inorganic fertilizer users told a different story. Only 19 percent fell below 1.0 tonne, while 30 percent exceeded 2.0 tonnes, a threefold increase over non-users.

When the bar was raised to the aspirational threshold of 3.0 tonnes per hectare, aligned with global productivity standards and Tanzania’s national goal of doubling cereal output by 2030, the gap widened further. Ninety percent of non-users and 92 percent of organic users remained below 2.0 tonnes, and only 1 percent and 4 percent respectively surpassed 3.0 tonnes. Among inorganic fertilizer users, however, 18 percent, nearly one farm in five, achieved yields above 3.0 tonnes, and a further 12 percent landed between 2.0 and 3.0 tonnes. The authors describe this as a tiered performance gradient: non-users trapped at subsistence levels, organic users marginally and inconsistently better, and mineral fertilizer users shifted decisively toward surplus production with commercial potential.

The findings arrive with important caveats that the authors themselves emphasize. The census does not record fertilizer formulations, nutrient composition, application rates, or timing, so the study cannot say which products or practices drive the gains. It also cannot identify farms applying organic and mineral fertilizers together, leaving integrated soil fertility management, the approach most agronomists consider optimal, empirically untested here. The small number of fertilizer users in the sample limits precision, and simulated iterations, however sophisticated, are not a substitute for additional field observations. Confounding factors such as improved seed varieties, rainfall, and soil type may contribute to the yield differences observed.

Even so, the policy implications are difficult to ignore. Only about one in twelve Tanzanian sorghum farms uses any fertilizer at all, and the yield gap between fertilized and unfertilized fields mirrors patterns documented across Ethiopia, Nigeria, Ghana, and Zimbabwe. The study recommends expanding access to inorganic fertilizers through targeted subsidies and improved distribution, strengthening extension services so that farmers apply nutrients correctly, and integrating mineral inputs with organic amendments to secure both immediate yields and long-term soil health. For a crop that anchors food security in Tanzania’s drought-prone center, where sorghum occupies nearly a quarter of cultivated land in regions like Singida, closing even part of this gap could transform a subsistence staple into a reliable source of food, income, and climate resilience.

Subject of Research: The contribution of organic and inorganic fertilizer use to sorghum productivity in Tanzania's rainfed smallholder farming systems

Article Title: Organic and inorganic fertilizer use and sorghum productivity in Tanzania’s rainfed farming systems using national sample census of agriculture data

Article References: Kadigi, I. L., & Kironyi, L. (2026). Organic and inorganic fertilizer use and sorghum productivity in Tanzania’s rainfed farming systems using national sample census of agriculture data. Discover Agriculture, 4(1), Article 312. https://doi.org/10.1007/s44279-026-00777-z

Image Credits: AI Generated

DOI: 10.1007/s44279-026-00777-z

Keywords: sorghum, Tanzania, fertilizer, inorganic fertilizer, organic fertilizer, crop yield, smallholder farming, rainfed agriculture, Monte Carlo simulation, food security, soil fertility, National Sample Census of Agriculture