Farmers often use too much nitrogen fertilizer on tomatoes, which actually makes them produce less and taste worse. Scientists wanted to find out if using less fertilizer combined with planting onions nearby could help. Over two years, they tested tomatoes grown with reduced fertilizer and companion planting. The results were impressive: tomatoes produced 34-35% more fruit, tasted better with more natural sugars, and the soil stayed healthier. The key was that planting onions nearby changed the helpful bacteria in the soil and how tomato roots communicate with those bacteria, making the plants use fertilizer more efficiently.

The Quick Take

  • What they studied: Whether using 30% less nitrogen fertilizer combined with planting onions next to tomatoes could increase tomato production and quality while keeping soil healthy
  • Who participated: Tomato plants grown in pots over two growing seasons under controlled conditions, tested with different amounts of fertilizer and different planting arrangements
  • Key finding: Tomatoes grown with reduced nitrogen and companion planting produced 34-35% more fruit compared to tomatoes grown alone with normal fertilizer amounts. The tomatoes also tasted better and had more beneficial nutrients like lycopene (the red pigment in tomatoes)
  • What it means for you: This suggests that farmers might be able to grow more tomatoes while using less expensive fertilizer and protecting the environment. However, these results are from controlled pot experiments, so real-world farm results may vary. Home gardeners might see similar benefits by planting onions near tomatoes.

The Research Details

Scientists conducted a two-year experiment growing tomatoes in pots under controlled conditions. They tested different amounts of nitrogen fertilizer (including 30% less than normal) and compared tomatoes grown alone versus tomatoes grown next to onions. They analyzed the soil around the tomato roots using advanced DNA sequencing to identify which bacteria were present, and they used special laboratory techniques to identify the chemicals that tomato roots release into the soil. This multi-layered approach helped them understand not just whether the method worked, but how and why it worked.

The researchers measured several important outcomes: how many tomatoes each plant produced, the quality of the tomatoes (sugar content and red pigment), how efficiently the plants used the nitrogen fertilizer, and the health of the soil. They also tracked changes in the bacterial communities in the soil and the specific chemicals released by the tomato roots.

Understanding the biological mechanisms—the actual living processes that make this work—is important because it explains why companion planting with reduced fertilizer is effective. Rather than just showing that it works, this research reveals that planting onions nearby changes the helpful bacteria in the soil and improves how those bacteria help tomatoes absorb nutrients. This knowledge could help farmers and gardeners apply these techniques more effectively and adapt them to different situations.

This study was published in Frontiers in Plant Science, a reputable scientific journal. The researchers used advanced molecular techniques (DNA sequencing and mass spectrometry) to identify bacteria and chemicals, which are reliable methods. The experiment ran for two years, which is good because it shows the effects weren’t just a one-time occurrence. However, the study was conducted in pots under controlled conditions rather than in actual farm fields, so results in real-world farming situations might be somewhat different. The exact number of plant samples tested wasn’t specified in the abstract, which is a limitation for assessing the study’s statistical strength.

What the Results Show

The main finding was dramatic: tomatoes grown with 30% less nitrogen fertilizer combined with companion planting of onions produced 34.26% more fruit in the first year and 35.54% more in the second year compared to tomatoes grown alone with normal fertilizer amounts. This is a huge increase—imagine getting one-third more tomatoes from the same space.

The tomatoes also tasted better. They contained more soluble sugars (which make them sweeter) and more lycopene (the red pigment that gives tomatoes their color and has health benefits). The plants also used the available nitrogen more efficiently, meaning they got more nutrition from less fertilizer—a 9.81% to 11.36% improvement in nitrogen use efficiency.

The soil itself became healthier. Two important enzymes that help break down organic matter and convert nitrogen into forms plants can use increased in activity. This suggests the soil biology was working better to support the tomato plants.

The research revealed that companion planting with onions changed which bacteria lived in the soil around the tomato roots. Specifically, bacteria called Pseudomonas became more abundant. The tomato roots also released different chemicals into the soil when grown with onions, and these chemical signals appeared to help the beneficial bacteria work more effectively.

The study found that certain chemical compounds in the soil—specifically methionine and pipecolic acid—were significantly more abundant when tomatoes were grown with onions compared to tomato monoculture. These compounds appear to play a role in how plants and soil bacteria communicate and work together. The research also identified complex networks of interactions between soil bacteria, with some bacteria like Sphingomonas showing positive relationships with other bacterial species. These interconnected relationships suggest that the soil is functioning as an integrated system rather than isolated organisms, which is important for overall soil health and plant nutrition.

Previous research has shown that excessive nitrogen fertilizer can actually harm tomato production and quality—a counterintuitive finding that this study confirms and explains. The idea of companion planting is not new, but this research provides scientific evidence for how and why it works at the biological level. The finding that companion planting increases specific beneficial bacteria aligns with other research on plant-microbe interactions, but this study goes deeper by identifying the specific bacteria and chemical signals involved. The results suggest that the benefits of reduced nitrogen combined with companion planting are greater than either approach alone.

This experiment was conducted in pots under controlled greenhouse conditions, not in actual farm fields. Real-world farming involves different soil types, weather patterns, pests, and other variables that could affect results. The study doesn’t specify exactly how many tomato plants were tested, making it difficult to assess how confident we should be in the results. The research focused specifically on onions as companion plants; other companion plants might work differently. The study was conducted over two years, which is good, but longer-term studies would help confirm whether these benefits continue over many seasons. Additionally, the study doesn’t provide information about the cost-effectiveness of this approach or how it would work at commercial farm scales.

The Bottom Line

Based on this research, there is moderate-to-strong evidence that growing tomatoes with 30% less nitrogen fertilizer combined with companion planting of onions can increase production and quality. Home gardeners and small-scale farmers might consider trying this approach on a portion of their tomato plants to see if similar results occur in their specific conditions. Commercial farmers should consider pilot testing this method on a small area before implementing it farm-wide. The approach appears most promising for controlled growing environments (greenhouses, high tunnels) similar to where this research was conducted.

Home gardeners growing tomatoes should find this information useful, especially those interested in reducing fertilizer use or improving tomato flavor. Small-scale and commercial farmers could benefit from reduced fertilizer costs and increased yields. Environmental advocates should care because this approach uses less chemical fertilizer, which reduces runoff pollution. Consumers interested in how their food is grown might appreciate knowing that tomatoes can be grown more sustainably. However, people growing tomatoes in very different climates or soil types should be cautious about assuming identical results, and those with very poor soil might need to start with better soil health before reducing fertilizer.

Based on this two-year study, you should expect to see differences in plant growth and bacterial communities within the first growing season. However, the full benefits in terms of yield and fruit quality appear to develop over time, with consistent improvements seen in both year one and year two. If you’re trying this approach, plan to observe results over at least one full growing season, and ideally two seasons to see if benefits continue. Changes in soil health and bacterial communities likely begin within weeks but take months to fully establish.

Want to Apply This Research?

  • Track weekly tomato plant height, number of flowers, and number of mature fruits for plants grown with reduced fertilizer and companion planting versus your control plants. Also note the taste and color of harvested tomatoes using a simple scale (1-10 for sweetness and redness). This creates a personal data set to compare against the research findings.
  • If you grow tomatoes, plant onion sets or seedlings 12-18 inches away from tomato plants at the same time you plant tomatoes. Reduce your nitrogen fertilizer application by 30% compared to your normal amount (or follow package directions for 30% less). Keep a simple log of which plants received which treatment so you can compare results at harvest time.
  • Create a growing season journal documenting: planting date, fertilizer amounts and dates, companion plant placement, weekly observations of plant health and growth, flowering dates, first fruit appearance, and harvest dates with notes on fruit quality (color, firmness, taste). Compare these observations between your reduced-fertilizer-with-companions section and your control section. Photograph plants at similar growth stages for visual comparison. This long-term tracking helps you understand whether the research findings apply to your specific growing conditions.

This research was conducted in controlled pot experiments and may not directly apply to all growing conditions, climates, or soil types. Before significantly reducing fertilizer on a large scale, consider consulting with a local agricultural extension office or agronomist who understands your specific growing conditions. This information is for educational purposes and should not replace professional agricultural advice. Results may vary based on your location, soil quality, water availability, and other environmental factors. If you have concerns about your soil’s nutrient levels, conduct a soil test before reducing fertilizer applications.