Document Type : Research Paper
Authors
1 Agronomy Department Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran
2 Agronomy Department, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran.
Abstract
Objective: Excessive nitrogen use causes severe economic and environmental problems. Therefore, developing sustainable cropping systems with high nitrogen use efficiency is essential. This study investigated the effects of nitrogen (N) and sulfur (S) fertilization on the photosynthetic characteristics, physiological responses, and nitrogen use efficiency (NUE) of guar (Cyamopsis tetragonoloba). The main goal was to determine the optimal fertilizer rates for sustainable production.
Methods: To evaluate the growth performance and nitrogen productivity of guar (Cyamopsis tetragonoloba), a field experiment was conducted during the 2024 growing season at the Research Farm of Tarbiat Modares University. We used a factorial arrangement based on a randomized complete block design with three replications. The treatments included four nitrogen rates (0,50,100,0, 50, 100,0,50,100, and 150 kg N ha−1 and two sulfur rates (0 and 100 kg S ha−1)
Results: Nitrogen application significantly influenced leaf area index, leaf greenness, photosynthetic rate, cumulative shoot nitrogen, agronomic and physiological nitrogen efficiency, nitrogen recovery, and grain yield. While the leaf area index and greenness of guar increased in response to nitrogen up to 100 kg/ha, higher application rates yielded no further significant changes. Leaf photosynthetic rate, however, continued to increase up to 150 kg/ha of applied nitrogen. Compared to the unfertilized control, nitrogen treatments increased cumulative shoot nitrogen 67.2 percent and the highest agronomic, recovery, and physiological nitrogen efficiencies were all recorded at the 100 kg/ha N rate. Grain yield also responded strongly to nitrogen, showing increases of 12.8%, 33.8%, and 16.9% at 50, 100, and 150 kg/ha, respectively. Regarding sulfur, its application boosted the photosynthetic rate by 25.9 percent during the grain-filling period; however, despite this physiological improvement, it did not significantly affect final grain yield (1203 kg/ha) compared to the untreated control (1235 kg/ha). The lack of significant effect of sulfur application on guar growth traits could be related to the adequacy of sulfur in the soil of the experimental site. Grain yield also strongly correlated with LAI (r=0.75), shoot nitrogen accumulation (r=0.73), leaf greenness (r=0.62), and photosynthetic rate (r=0.50). Overall, applying optimal nitrogen use management can not only increase fertilizer use efficiency while maintaining optimal yield, but also prevent nitrogen losses and environmental consequences resulting from excessive use of nitrogen fertilizers.
Conclusion: Overall, under the soil and climatic conditions of the study area, application of 100 kg N ha⁻¹ optimized seed yield while maximizing nitrogen use efficiency, suggesting that this rate represents a sustainable fertilization strategy that can improve fertilizer use patterns and reduce environmental risks associated with excessive nitrogen application.
Keywords
)