Nigerian Rice Research: Biochar and Fertilizer Improve Crop Yield

Nigerian researchers have found that combining agricultural waste-derived biochar with nitrogen fertilizer can improve soil nutrient status and rice performance under the conditions tested in southern Nigeria.

The study, published in Scientific Reports, examined the effects of rice husk biochar and sawdust biochar combined with urea fertilizer in upland and lowland rice systems in Akure, Ondo State, and Abakaliki, Ebonyi State. The researchers found that both combinations improved several soil fertility indicators and rice yield compared with untreated plots, while sawdust biochar combined with urea recorded the highest overall grain yield in the experiment.

The research was led by Adebayo Jonathan Adeyemo and Simon Nwafor Ogboji, with other researchers from the Federal University of Technology, Akure, Federal College of Agriculture, Akure, Olusegun Agagu University of Science and Technology, Federal Polytechnic Ile-Oluji and the University of Arkansas at Little Rock.

What the researchers tested

The researchers wanted to determine whether locally available agricultural residues could be converted into biochar and used alongside conventional nitrogen fertilizer to improve rice production.

Biochar is a carbon-rich material produced by heating organic material under limited oxygen.

In this study, the researchers used two locally available materials: rice husks collected from a rice mill in Ogbese, Akure, and sawdust obtained from a timber-processing source in southern Nigeria.

The materials were converted into biochar through oxygen-limited pyrolysis at about 350°C for 55 minutes.

The researchers then applied the biochars to rice plots together with urea fertilizer.

The experiment compared four treatments:

• No nutrient addition
• Urea alone
• Rice husk biochar plus urea
• Sawdust biochar plus urea

The biochar was applied at 3 tonnes per hectare, while the urea treatment supplied 30 kilograms of nitrogen per hectare.

Researchers tested two different soil environments

One important feature of the research was that it did not rely on a single field condition.

The experiments were conducted at two locations representing different soil types.

The first was at the Federal University of Technology, Akure, in southwestern Nigeria, where the researchers studied an Alfisol.

The second was at Agbalabor Central and North Ameka in Ezza, Abakaliki, southeastern Nigeria, where the study used an Ultisol.

The researchers also examined both upland and lowland rice production environments.

This allowed them to compare how the treatments performed under different soil and production conditions.

Sawdust biochar produced the highest yield

The clearest production result came from the combination of sawdust biochar and urea.

The treatment produced an average grain yield of 4,202.59 kilograms per hectare.

That compared with:

• 2,376.44 kg/ha with urea alone
• 3,940.28 kg/ha with rice husk biochar plus urea
• 1,721.24 kg/ha in the untreated control

The researchers also recorded a straw yield of 4,999.21 kg/ha and a 1,000-grain weight of 30.25 grams under the sawdust-biochar-plus-urea treatment.

The rice husk biochar and urea combination also performed better than the control and urea alone for several yield measures.

However, the researchers noted that the grain and straw yields from the two biochar-plus-urea treatments were statistically comparable.

That means the study does not establish that sawdust biochar is definitively superior to rice husk biochar in every situation.

Soil nutrients also improved

The research examined the condition of the soil after harvesting the rice.

The researchers measured soil pH, organic carbon, total nitrogen, available phosphorus, exchangeable potassium and different forms of inorganic nitrogen.

The strongest responses were generally found in the upper 15 centimetres of soil, where the biochar had been incorporated.

Rice husk biochar combined with urea produced the highest soil organic carbon and total nitrogen in several of the measurements.

In upland topsoil, the rice husk biochar and urea treatment recorded soil organic carbon of 2.04% and total nitrogen of 0.35 grams per kilogram.

The treatment also produced higher nutrient values than the untreated plots for several measured properties.

Sawdust biochar plus urea recorded the highest available phosphorus in the upland topsoil, at 21.01 milligrams per kilogram, compared with 4.11 milligrams per kilogram in the control and 4.05 milligrams per kilogram under urea alone.

Why agricultural waste is important

The study is also relevant because the materials used to produce the biochar are agricultural and industrial residues that are already available in Nigeria.

Rice husks are generated around rice mills, while sawdust is produced by sawmills and timber-processing operations.

Instead of treating these materials solely as waste, researchers are examining whether they can be converted into soil amendments.

The approach could potentially connect waste management with agricultural production.

The researchers note that locally available residues offer opportunities for smallholder-oriented biochar production, although the economics and practical requirements of producing and applying biochar at scale would require further assessment.

The method may improve fertilizer effectiveness

One reason the researchers investigated biochar alongside urea was the difficulty of maintaining nutrients in some tropical soils.

Nitrogen from fertilizer can be lost through several processes, including volatilisation, nitrification, denitrification and leaching.

Biochar has properties that can improve the soil’s ability to retain certain nutrients.

The researchers found higher concentrations of several nutrients in the amended surface soil and concluded that the biochar-urea combinations improved selected soil fertility indicators under the experimental conditions.

However, the study makes an important distinction.

The researchers did not directly measure nitrate leaching.

Because they did not use lysimeters, drainage collection or isotope tracing, they said any suggestion that biochar reduced nitrogen movement into deeper soil should be treated as an inference rather than a direct measurement.

The study was conducted in Nigeria

The Nigerian setting is important because soil conditions can vary considerably across the country.

The study examined an Alfisol in Akure and an Ultisol in Abakaliki.

The researchers found that the Alfisol generally had higher available phosphorus, exchangeable potassium and cation-exchange capacity, while the Ultisol showed stronger acidity and lower fertility in several respects.

These differences affected how the treatments performed.

The findings therefore demonstrate that agricultural amendments cannot necessarily be expected to produce identical results across every Nigerian soil type.

Farmers, researchers and agricultural extension services would need to consider local soil conditions when evaluating the approach.

The research was based on a field experiment

The researchers used a randomized complete block design with three replicates.

The experiment was structured as a factorial study involving two soil types, two rice ecology and variety combinations, and four nutrient treatments.

The researchers recorded plant growth during the season and measured grain yield, straw yield, 1,000-grain weight and harvest index at harvest.

They also collected soil samples from depths of 0 to 15 centimetres and 15 to 30 centimetres after harvest.

The resulting data were analysed using factorial analysis of variance, with Tukey’s honestly significant difference test used where significant effects were detected.

This provides a stronger evidence base than simply reporting observations from individual farmers or demonstration plots.

The researchers identified important limitations

The findings are promising, but the study has limitations that prevent the results from being treated as a nationwide farming recommendation.

First, the experiment covered only one cropping season.

That means the researchers could not determine the long-term effects of repeated biochar application or how the material behaves as it ages in the soil.

Second, the experiment tested only one biochar rate and one urea rate.

The researchers therefore could not establish the best combination of application rates for different farms or soil conditions.

The study also did not directly measure nitrogen leaching or greenhouse-gas emissions.

These issues would need to be investigated in longer and broader studies.

What the findings could mean for Nigerian agriculture

If future research confirms the results across more locations and seasons, biochar made from agricultural residues could become one component of integrated soil-management strategies.

For rice farmers, the potential benefit is not simply higher yields.

Improving soil organic carbon and nutrient availability could also help maintain soil productivity.

For the wider agricultural system, converting rice husks and sawdust into useful soil amendments could provide another way of putting agricultural residues to productive use.

But the economic side of the approach remains important.

Producing biochar requires equipment, labour, energy and transportation, and the cost of collecting and processing feedstocks could determine whether the method is practical for small-scale farmers.

More research is needed before wider recommendations

The researchers themselves call for longer-term and rate-response studies before broad recommendations are made.

Future studies could examine different application rates, additional rice varieties, more soil types and multiple growing seasons.

Researchers could also investigate the economic cost of producing biochar, its effects on greenhouse-gas emissions and whether farmers can adopt the practice without substantial additional production costs.

Those questions will determine whether the technique can move from experimental plots to wider agricultural use.

A research finding, not yet a nationwide farming solution

The study provides evidence that combining locally sourced biochar with urea can improve selected soil properties and rice productivity under the conditions tested in southern Nigeria.

The strongest grain-yield result came from sawdust biochar plus urea, while rice husk biochar plus urea also produced substantial improvements compared with the untreated control.

But the researchers’ limitations are equally important.

The experiment lasted one season, used one biochar rate and did not directly measure some processes that could explain the observed results.

The findings therefore represent a promising research result rather than proof that every Nigerian rice farmer should immediately adopt the method.

The next stage is to determine whether the same benefits can be reproduced across more Nigerian farms, seasons and soil conditions.

If those studies confirm the results, agricultural waste such as rice husks and sawdust could become an increasingly useful part of efforts to improve soil fertility and rice production in Nigeria.