How Do Organic Fertilizers and Photosynthetic Rate Work Together?

• Most research findings show that organic fertilizers improve the crop’s photosynthetic rate.
• The improvement occurs through increased photosynthetic efficiency, increased leaf number and area, and enhanced leaf chlorophyll content.
• Organic fertilizers enhance the soil’s nutrient status to support better plant growth and health, which increases crop photosynthetic rate.
• In many cases, organic fertilizers were more effective at improving the photosynthetic rate than conventional fertilizers.

Excessive use of chemical fertilizers has increased crop yields, but it has also resulted in groundwater pollution, soil degradation, salinity, and biodiversity loss, ultimately diminishing crop productivity. The judicious use of organic fertilizers can enhance the yield of diverse crops through their numerous benefits to soil and plant growth. Research on the effect of organic fertilizers on photosynthetic parameters started around twenty years ago. In this article, you will find out the various ways through which organic fertilizers can improve the photosynthetic rate to increase yield.

Effect of Organic Fertilizers

Figure 1: “Different types of organic fertilizers used in agriculture,” Liu et al. (2024). (Image credits: https://www.mdpi.com/2073-4395/14/6/1141)

 Organic fertilizers are derived from animal or plant sources, and there are many types, as shown in Figure 1.

• Manure: Organic fertilizers can be derived from manure, which are excellent sources of nutrients, NPK (nitrogen, phosphorus, and potassium), and add organic matter to the soil. The most common source of manure is animals, and is obtained from poultry, pig, and cattle waste. Other sources of manure are plant, human, household, municipal, and agricultural waste.
• Biofertilizers: These contain beneficial microbes, such as bacteria, fungi, and algae, that enhance soil fertility through their activities.

Organic fertilizers enhance soil organic matter, thereby improving soil structure, water retention capacity, and microbial activity. They reverse the harmful effects of chemical fertilizers and contribute to crop productivity.

Increase in Photosynthetic Rate

The gross photosynthetic rate is defined as the rate at which plants capture solar radiation and convert it into chemical energy in the form of carbon compounds. It serves as a metric of plant health and productivity.

Several research studies have demonstrated that organic fertilizers can enhance the photosynthetic rate of various crops, thereby increasing their yield. For example, organic fertilizers such as sheep manure, soybean cake, or biogas increased the photosynthetic rate in pear-jujube trees more than conventional fertilizers or urea. In this case, Ye et al. (2022) found that water use efficiency and stomatal conductance also increased. Still, intercellular carbon dioxide levels (CO2) were lower, indicating that more of the gas was fixed in photosynthesis than in conventional fertilized plants. There is a difference in the performance of the fertilizers, with biogas fertilizers producing the most significant boost in photosynthetic rate, followed by sheep manure, soybean cake, conventional fertilizer, and the control. However, soybean-cake-treated plants yielded the most.

Ferreria et al. (2025) show that biosolids, sanitized sewage, and algae, which add 15 g of biosolids per plant, increase the photosynthetic rate by 60%, with no change in stomatal conductance but a reduction in intercellular carbon dioxide levels.

However, the beneficial effects of organic fertilizer on photosynthesis have a threshold beyond which there is no additional increase in photosynthesis or yield by increasing the dosage.

However, other research suggests that although organic fertilizers increase yield, they have little to no effect on the rate of photosynthesis. For example, organic addition did not enhance the photosynthetic rate or yield, but only the fruit quality of Hongyang kiwifruit.

Plant Parameters Improved by Organic Fertilizers

When organic fertilizers increase the photosynthetic rate, they can do so directly by enhancing photosynthetic efficiency or indirectly by improving plant parameters involved in photosynthesis, such as leaf number, area, canopy, and chlorophyll content.

Improved Photosynthetic Efficiency

Organic fertilizers can improve photosynthetic efficiency by improving light response. Lin et al. (2024) found that pakchoi grown with organic fertilizers had better photosynthetic efficiency, as the plants could utilize light of low intensity and exhibited shade tolerance. Improved soil nutrient availability enables plants to grow even in low-light conditions. However, the benefits of organic fertilizers were seen only for moderate dosage levels.

Increased Chlorophyll Content

In many crops, the application of organic fertilizers, either alone or in combination with conventional fertilizers, increases chlorophyll content. As chlorophyll content increases, light capture and therefore the photosynthetic rate increase. Nitrogen is a major limiting factor, which is replenished by fertilizers. The availability of nitrogen increases chlorophyll content, especially chlorophyll b, which is more involved in photosynthesis than chlorophyll a. The change in the ratio of chlorophyll a and chlorophyll b increases the amount of blue-green light captured and the photosynthetic rate.

For example, Ye et al. (2022) found that organic fertilizers produced significantly more chlorophyll, especially chlorophyll b, in pear-jujube compared to the control. Also, the biogas manure produced more chlorophyll (10.90 mg/dm 2) than conventional fertilizers.

Moreover, nitrogen availability also delays leaf senescence, thereby prolonging the period of photosynthesis.

More Leaves

Organic fertilizers increase the number of leaves per plant, thereby enhancing photosynthesis. Dill cultivars produced progressively more leaves as the application of organic fertilizers increased. However, Ferreria et al. 2025 found that the increase in leaves in sunflowers was not significantly different after a certain threshold of fertilizer dosage; 10 g and 15 g of biosolids per plant did not produce significantly different numbers of leaves.

More Leaf Area and Canopy

An increase in leaf area and leaf area index (LAI) is also reported, along with a boost in leaf numbers per plant. The pear-jujube leaf area increased by 44.46% when plants were given soybean cake. Biogas manure was the most effective in increasing LAI, compared to other organic fertilizers (sheep and soybean cake) or even conventional fertilizers.

Canopy light interception was also significantly better with biogas manure than with conventional or other organic fertilizers.

How do Organic Fertilizers Help?

The plant parameters are positively changed because organic fertilizers improve nutrient availability and stress tolerance.

Figure 2: “Relationship between maximum net photosynthesis rate and organic fertilizer under fresh water (A) and brackish water (B) irrigation. Pnmax, maximum net photosynthesis rate,” Lin et al. 2024. (Image credits: doi: 10.3390/plants13101308)

Improved nutrient availability: The application of organic fertilizers improves soil nutrient content in short-term and long-term experiments. So, the unavailability of nutrients no longer limits plant growth and health. The quantity of nutrients supplied by each type of organic fertilizer varies, explaining the differences in their effects on photosynthesis and yield. For example, manures from aerobic composting and vermicomposting have higher organic nitrogen and nitrates than solid manures. Poultry manure has more nitrogen than pig or cattle manure.

Salinity reduction: Using organic biofertilizers can mitigate the effects of salinity stress, thereby improving photosynthetic rates, even if the degree of increase is less than in optimum conditions in soils without salinity, due to the use of freshwater instead of brackish water.  See Figure 2.

Measuring Photosynthesis in the Field

The contrasting results of the effect of organic fertilizers on photosynthetic rates indicate that further research is necessary to determine the underlying causes of these differences. Such experiments will require frequent and repeated measurements of photosynthesis. Most studies have also concentrated on all gas exchanges to understand plant functioning in organic cultivation.

CID BioScience Inc. offers the CI-340 Handheld Photosynthesis System that can measure photosynthesis, stomatal conductance, and transpiration simultaneously. The portable device provides results in seconds and is suitable for use on farms and in greenhouses. Modules that control factors such as temperature, light, air (CO2), and water vapor make the device more versatile for research on photosynthesis. Such tools will be vital in enhancing photosynthesis and yield through sustainable and environmentally friendly means, thereby feeding growing populations.

Find out more about CID BioScience Inc.’s CI-340 Handheld Photosynthesis System for your research on organic cultivation.

 

Sources

Department of Environment, Science and Innovation, Queensland. (2023, Oct 24). Photosynthesis, WetlandInfo website. Retrieved from https://wetlandinfo.des.qld.gov.au/wetlands/ ecology/processes-systems/photosynthesis/

 

Ferreira, E. T., Caetano, L. E., Candido, J. M., Cechin, I., & Da Silva, G. H. Enhancing Plant Growth and Photosynthesis with Biofertilizers from Sewage Treatment. Agronomy, 15(3), 610. https://doi.org/10.3390/agronomy15030610

 

Lin, S., Wei, K., Wang, Q., Sun, Y., Deng, M., & Tao, W. (2024). Effects of Organic Fertilizer on Photosynthesis, Yield, and Quality of Pakchoi under Different Irrigation Conditions. Plants, 13(10), 1308. https://doi.org/10.3390/plants13101308

 

Liu, Y., Lan, X., Hou, H., Ji, J., Liu, X., & Lv, Z. Multifaceted Ability of Organic Fertilizers to Improve Crop Productivity and Abiotic Stress Tolerance: Review and Perspectives. Agronomy, 14(6), 1141. https://doi.org/10.3390/agronomy14061141

 

Wang, X. J., Jia, Z. K., Liang, L. Y., Ding, R. X., Wang, M., & Li, H. (2012). Effects of organic fertilizer application rate on leaf photosynthetic characteristics and grain yield of dryland maize.

Ying yong sheng tai xue bao = The journal of applied ecology, 23(2), 419–425.

 

Ye, S., Peng, B., & Liu, T. (2022). Effects of organic fertilizers on growth characteristics and fruit quality in Pear-jujube in the Loess Plateau. Scientific Reports, 12(1), 13372.

 

Zhang M.H., Sun D.Y., Niu Z.R., Yan J.X., Zhou X.L., Kang X. (2020). Effects of Combined Organic/Inorganic Fertilizer Application on Growth, Photosynthetic Characteristics, Yield and Fruit Quality of Actinidia Chinesis cv ‘Hongyang’. Glob. Ecol. Conserv.22:e00997. Doi: 10.1016/j.gecco.2020.e00997.