A study led by researchers at Pakistan’s National Agricultural Research Centre reported that partially replacing inorganic fertilisers with organic inputs like poultry compost can significantly enhance nitrogen use efficiency and grain yield in rice-based systems, while also reducing nitrogen losses.
In mid-latitude rice systems, mineral nitrogen fertiliser — primarily urea — remains the largest nitrogen input due to limited availability of organic sources. However, this reliance leads to greater nitrogen losses, exacerbated by soil and environmental conditions.
The study investigated the effects of combining urea with organic sources, such as farmyard manure (FYM) and poultry compost. The researchers used a randomized complete block design to assess the impact of these combinations on six elite green super rice (GSR) genotypes over two growing seasons in 2022 and 2023.
News on nitrogen
They found that When organic sources (10 tons per hectare of FYM or poultry compost) supplied 50% of the required nitrogen — with the remainder from urea — soil and plant nitrogen uptake and utilisation improved. This led to better plant photosynthesis and growth, with the highest shoot and root weights recorded in these treatments than in manure-treated plots.
This was followed closely by a mix of manure and synthetic urea. Compost also improved other important soil properties, including the amount of total phosphorus and potassium, which are essential nutrients for plant growth.
Across two years, leaf nitrogen levels and photosynthesis rates increased when treated with both compost and synthetic urea. One rice variety, NUYT-4, had the highest leaf nitrogen levels when grown with compost. These treatments also led to more robust plant growth, with heavier shoots (the parts of the plant above ground) and larger root systems, making it easier for the plants to absorb nutrients.
In fact, over the course of the study, nitrogen content in most treated plots increased by 8.3%, while the untreated control plots saw an 11.3% drop. The best results came from applying 150 kg of nitrogen per hectare, with half coming from organic sources like FYM or poultry compost and the other half from urea. This combination led to the highest nitrogen uptake by the plants and improved overall productivity.
The researchers attributed these improvements to the more consistent nutrient release and enhanced soil structure the organic matter provided, resulting in better root and shoot development.
About the grain
During the grain development phase, the rice plants in compost-treated plots produced the heaviest grains. Compost also sped up the grain-filling process, allowing plants to accumulate nutrients more quickly. This led to heavier grains and better overall grain quality compared to plants treated with only synthetic fertilisers. The grain-filling process in compost and manure-treated plants took less time than in those treated with synthetic urea, contributing to healthier and fuller grains.
At the same time, plants treated with compost or manure showed significant improvements in yield-related traits like plant height, number of shoots, and grain count per panicle. One compost-treated GSR variety, NUYT-6, had the highest biological yield (overall plant growth) and grain yield. Compost also led to longer and fuller rice grains with fewer chalky areas, which improved grain quality.
Furthermore, the use of organic fertilisers like compost resulted in higher-quality grains. Protein and amylose (a component of starch) contents were higher in compost-treated plants. The grains were also longer and wider, thanks to the slow release of nitrogen from organic sources, which supported more uniform growth. Overall, organic fertilisers enhanced grain nutrient levels, leading to higher-quality rice with improved texture and appearance.
Soil and sustainability
Aside from plant growth and grain quality, the researchers addressed the environmental benefits of reducing nitrogen losses. Nitrogen losses in rice farming — primarily through volatilisation — are a major concern in South Asia, where intensive rice production has contributed to elevated greenhouse gas emissions. Reducing reliance on inorganic fertilisers could, therefore, not only sustain productivity but also help minimise environmental pollution.
Looking ahead, the research team recommended further exploration into optimising the ratios and timing of organic-inorganic fertiliser applications in order to maximise its benefits. They stated that future studies should focus on root and shoot morphophysiological responses and examine the biochemical pathways involved in nitrogen adsorption. This would then allow them to refine nitrogen management practices and develop nitrogen-efficient rice varieties.
These findings hold significant positive implications for rice producers and agricultural stakeholders, particularly those looking to improve yields while managing fertiliser costs and environmental impacts. By partially replacing synthetic nitrogen with organic inputs, growers could enhance productivity in a more sustainable and eco-efficient manner in mid-latitude rice systems, offering long-term benefits for both soil health and food security.
Source: BMC Plant Biology
“Partial replacement of inorganic fertilizer with organic inputs for enhanced nitrogen use efficiency, grain yield, and decreased nitrogen losses under rice-based systems of mid-latitudes”
https://www.doi.org/10.1186/s12870-024-05629-w
Authors: Muhammad Shahbaz Farooq, et al.
