Evaluating Nitrogen Fertilizer Utilization Efficiency and Analyzing Its Relationship with Nitrogen Nutrition Index in Lettuce

Document Type : Full Paper

Authors

• Hadisseh Rahimikhoob ¹
• Mojtaba Delshad ²
• romina Habibi ²

¹ Ph.D, Irrigation and Reclamation Engineering Department, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.

² Horticulture Department, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.

Abstract

Keywords

• Critical nitrogen concentration
• Plant nutrition
• Greenhouse
• Nitrogen fertilizer management

Main Subjects

• vegetable plant science

Extended Abstract

Introduction

Nitrogen (N) is an essential element involved in most important physiological plant processes such as photosynthesis, growth and enzymatic functions. In order to achieve crop production at a desired level, application of N fertilizers is an indispensable strategy. Improving crop nitrogen use efficiency (NUE) is a primary goal to reduce N input while maximizing crop yield and production. The commonly stated goal of maximizing NUE will not always result in desired agronomic and environmental outcomes unless both crop N status and biomass are analyzed through a plant-based approach. The term NUE is a product of N uptake efficiency (NU_pE) (the ratio between N uptake and N applied) and N utilization efficiency (NU_tE) (the ratio between dry matter production and N uptake). The objectives of the present study were to calculate lettuce NU_tE, NU_pE and also quantifying the relationships between nitrogen nutrition index (NNI) and NU_tE in lettuce based on the critical nitrogen concentration concept. The NNI is a useful tool to express the N status of a given crop. Values of NNI lower or higher than 1 indicate N deficiency and luxury N consumption, respectively.

Materials and methods

In the present study, two experiments were conducted in the research greenhouse of the College of Agriculture and Natural Resources, University of Tehran, located in Karaj, Iran, with six N fertilizer treatments. The lettuce plants were cultivated as seedlings in pots. Fertilization was carried out at rates of zero (control treatment), 50, 100, 150, 200, and 250 kg ha^-1. Urea fertilizer was applied to the plants in three stages, at one-week intervals, at rates of 30%, 30%, and 40% of the mentioned amounts. In order to prevent water stress, irrigation was performed on a daily basis. Crop sampling was done weekly, one week after the last fertilization. One pot from each treatment and replication was randomly selected, and the plant was cut at soil level. The lettuce plants were placed in bags and dried in an oven at 70˚C for three days. The dry matter of the plant was weighed and then ground. The total nitrogen content in each treatment was also determined using the Kjeldahl method. Then, NU_tE, NU_pE and NNI were calculated for all treatments.

Results and discussion

Results demonstrated that NU_tE, NU_pE and NNI are highly influenced by N application rates and availability. The lettuce NNI varied from 0.70 to 1.22 and 0.60 to 1.23 for the first and second experiments, respectively. The Control N treatment had greater NU_tE (31.75 and 39.36 g g^-1 N for the first and second experiments, respectively) than the highest fertilized treatment (18.79 and 20.95 g g^-1 N for the first and second experiments, respectively). The NU_tE decreased due to the increase in fertilizer application rate. Also, application of nitrogen fertilizer more than the plant uptake capacity led to a decrease in the NU_pE. The relationship between NU_tE and NNI for different dry matter values ​​was investigated. The results showed that at constant NNI values, NU_tE increased non-linearly with increasing dry biomass production. Higher or lower NU_tE can be expected as the result of lettuce grown under N deficiency (NNI <1) or luxury consumption (NNI >1) conditions, respectively. Also, the critical nitrogen utilization efficiency curve (NU_tE_c) discriminated well between different N treatments. Under the optimal nitrogen nutrition conditions (NNI = 1), the critical value of NU_tE for lettuce was equal to 24 (g g^-1 N).

Conclusion

    This study demonstrates that N application rates and availability significantly impact NU_tE, NU_pE, and the NNI in lettuce. Higher NU_tE values were observed in control treatments compared to those with high N application rates, indicating that excessive N application does not enhance efficiency. The NNI values, indicating nitrogen status, showed that NU_tE increased non-linearly with dry biomass at constant NNI, highlighting the need to balance nitrogen supply with crop demand. To enhance lettuce nitrogen use efficiency, it is essential to consider both NNI and biomass production, enabling precise N management to maximize yield while minimizing environmental impact. By monitoring NNI, farmers can adjust nitrogen applications to ensure the crop is neither deficient nor experiencing luxury consumption of nitrogen, thus avoiding inefficiency and potential environmental pollution. Implementing this knowledge, growers can fine-tune fertilization schedules and quantities to match the specific growth stages and nutrient demands of the lettuce crop, leading to more sustainable and efficient agricultural practices. Ultimately, integrating these insights into practical farming can contribute to better resource use, reduced costs, and enhanced environmental conservation, fostering a more sustainable agricultural system.