Rice is a staple food for billions around the world, especially in India, where over 50% of the population relies on it as their primary source of nutrients. For decades, farmers have relied heavily on chemical fertilisers, mainly Nitrogen, Phosphorus, and Potassium (or NPK) to boost rice crop yields. While effective in the short term, using only chemical fertilisers year after year can harm the environment as excess nutrients wash into rivers and lakes, and degrade soil health. Long-term use can even lead to the degradation of soil biodiversity, which can eventually lower yields.
Scientists are constantly looking for more sustainable ways to grow our food. One promising approach is using organic fertilisers, like compost. Compost, made from decomposed organic materials like food scraps, manure, or plant waste, acts like a slow-release meal for plants and improves the soil itself, making it better at holding water and nutrients. However, compost often releases nutrients more slowly than plants need for maximum growth. So, what if we combine the best of both worlds - chemical fertilisers and compost?
Researchers from Mizoram University and Manipur University in Northeast India have explored such a combination to see whether mixing different types of locally available composts with chemical fertilisers could grow rice more effectively than using either one alone.
The research team set up a field experiment at the Rice Research Station in Wangbal, Manipur, running it for two consecutive rice-growing seasons (2022 and 2023). They used a local rice variety called RCM-13 and tested three different compost types: Municipal Solid Waste Compost (MSWC) from city garbage carefully selected to avoid harmful contaminants; vermicompost (VC) made with the help of earthworms, using rice straw and cow manure; and Phumdi Compost (PC), a special compost made from Phumdi. Phumdi are unique floating islands of vegetation and soil found in Loktak Lake, a vital wetland in Manipur. Sometimes, these phumdi need to be managed, and composting them is a potential solution.
Using these composts and the regularly used chemical fertilisers, the team concocted eight different fertiliser recipes, using each compost and chemical fertiliser separately and in a 50:50 ratio combination, where one compost was mixed with 50% chemical fertiliser. They also had a control specimen which received no fertilisers at all.
To ensure fair comparisons, the scientists carefully calculated the amounts of compost and fertiliser so that each treatment (except the control) received the same total amount of nitrogen, a key nutrient for plant growth. They laid out the experiment using a randomised block design, which means the different treatments were randomly assigned within different sections of the field. This helps ensure that any differences seen are due to the fertilisers, not just variations in the field soil.
Throughout the growing seasons, the researchers measured the growth of the rice plants, their height, the number of stems or tillers, and, most importantly, the final yield, or how much grain and straw was produced. They also noted the size of the rice heads or panicles and how many grains each panicle contained.
The study's findings were quite striking. While using only compost (MSWC, VC, or PC) resulted in lower yields compared to using only chemical fertiliser (CF), the combination treatments told a different story. The best performer was the 50/50 Phumdi Compost and Chemical Fertilizer (PC+CF) mix. Compared to using 100% chemical fertiliser, this 50/50 blend produced an average of 33.6% more grain yield and 26.21% more straw yield over the two years.
The other mixes also performed well. The Vermicompost and Chemical Fertilizer (VC+CF) mix increased grain yield by about 13.16%, and the Municipal Solid Waste Compost + Chemical Fertilizer (MSWC+CF) mix saw a 5% increase compared to chemical fertiliser alone. Essentially, substituting half of the chemical fertilizer with these composts didn't just maintain yields, it significantly boosted them, especially when using the unique phumdi compost.
The success of the combination comes from the effect of being greater than the sum of its parts. Chemical fertilisers, much like fast food for humans, provide a quick, readily available supply of essential nutrients like nitrogen, giving the rice plants an immediate boost for growth. Compost, on the other hand, is like a balanced meal. It releases nutrients gradually over time, feeding the plants steadily. More than that, it adds valuable organic matter to the soil. This improves the soil's structure, making it less compacted, allowing better root growth, and enhancing its ability to hold onto water and nutrients, reducing runoff. Compost also provides a broader range of micronutrients and supports beneficial soil microorganisms, which are crucial for long-term soil health.
By combining the two, the rice plants get the best of both: an initial nutrient kick from the chemical fertiliser and sustained nourishment plus improved soil conditions from the compost. The results suggest the phumdi compost might have a particularly beneficial nutrient profile or properties that complement the chemical fertiliser exceptionally well for this rice variety and local conditions. The researchers also noted that yields were generally higher in the second year, likely because the compost applied in the first year continued to improve the soil and release nutrients.
Integrating organic and chemical fertilisers can be beneficial. This study quantifies this belief by testing specific, locally available composts in Northeast India and provides a roadmap to integrate the two. It also highlights the potential of phumdi compost, turning a potential environmental management issue of excess humidity in Loktak Lake into a valuable agricultural resource.
The study, however, focused primarily on nitrogen supply and didn't analyse the full range of other factors, like soil microbial life, which plays a huge role in nutrient cycling. More research will be needed to substantiate and confirm the findings. Nevertheless, the conclusion is clear and hopeful that substituting a part of chemical fertiliser with locally sourced composts is a highly effective strategy for boosting rice yields in this region. This approach also offers a pathway towards more sustainable agriculture by reducing reliance on chemical inputs, improving soil health for the long term, and potentially providing innovative solutions to local environmental challenges like managing Loktak Lake's unique phumdi.
This research article was written with the help of generative AI and edited by an editor at Research Matters.