Univrsity of Tehran Press Iranian Journal of Field Crop Science 2008-4811 56 4 2025 12 22 Growth and Yield Response of Guar (Cyamopsis tetragonoloba L.) to Nitrogen Application Rate Under Sulfur and No-Sulfur Application Growth and Yield Response of Guar (Cyamopsis tetragonoloba L.) to Nitrogen Application Rate Under Sulfur and No-Sulfur Application 133 146 105091 10.22059/ijfcs.2025.396020.655143 FA Sahar Kiani-Motlagh Agronomy Department , Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran. 0009-0002-3456-9206 Seyed Farhad SaberAli Agronomy department, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran. 0000-0002-1868-1313 Majid AghaAlikhani Agronomy Department, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran 0000-0002-8981-5892 Journal Article 2025 05 26 Introduction. Guar (Cyamopsis tetragonoloba L.) is well-suited for cultivation in tropical and subtropical regions with arid and semi-arid climates due to its high tolerance to drought and warm temperatures. Its significant industrial value and rising global demand have increased interest in its cultivation beyond traditional regions like India and Pakistan, including countries such as Iran. Following drought stress, nutrient deficiencies—particularly nitrogen—are major limiting factors for crop production, including guar. Nitrogen is an essential nutrient for plant growth, enhancing photosynthetic efficiency and playing critical roles in processes such as vegetative growth, leaf area expansion, and biomass accumulation. Under drought conditions and in soils with low populations of symbiotic rhizobia, nitrogen deficiency can severely limit guar production. Sulfur is another vital nutrient required for the synthesis of amino acids such as cystine, cysteine, and methionine, and is involved in the function of vitamins (e.g., biotin and thiamine), enzymes, lipids, and other essential plant components. sSulfur deficiency is particularly common in sandy soils with low organic matter. Materials and Methods. This study was conducted in 2024 at the research farm of the Faculty of Agriculture, Tarbiat Modares University, located 17 km west of Tehran (35°44'N, 51°9'E; 1275 m above sea level). During the guar growing season, the average temperature was 28.73°C, and total rainfall was 1.6 mm. The experiment followed a factorial arrangement in a randomized complete block design (RCBD) with three replications. Treatments included two sulfur levels (0 and 100 kgha-1, from a bentonite sulfur source with 90% purity) and four nitrogen levels (0, 50, 100, and 150 kgha-1, applied as urea). Measured traits included biomass, leaf area, number of seeds per plant and pod, thousand-seed weight, harvest index, and seed yield per hectare. Leaf area and biomass were assessed during the vegetative stage through destructive sampling of 50 cm rfow lengths. Final yield components were measured by harvesting 1 m² plots at maturity. Results and Discussion. Analysis of variance revealed that nitrogen application, unlike sulfur, had significant effects on leaf area index, dry matter accumulation, pod and seed numbers per unit area, grain yield, and harvest index. Nitrogen application increased grain yield by 21.2% compared to the control. Yield improvements at 50, 100, and 150 kg N ha-1 were 12.8%, 33.8%, and 16.9%, respectively. Regression analysis indicated a significant quadratic response of grain yield to nitrogen application, explaining approximately 84% of the yield variation. The maximum increase in pod and seed numbers occurred at 100 kg ha-1, while no significant improvement was observed at 150 kg N ha-1, suggesting an optimal nitrogen level. Due to the strong influence of the number of grains formed per plant on grain weight, the increase in grain number in response to nitrogen application resulted in the allocation of dry matter among a larger number of grains, and therefore, changes in grain weight were not significant. Grain yield were attributed to enhanced leaf area index, biomass accumulation, and reproductive organ development. Previous studies support these findings, showing that nitrogen improves light interception, chlorophyll content, enzyme activity, and photosynthetic capacity. At 150 kg N ha-1, despite increased biomass, grain yield declined compared to 100 kg N ha-1, likely due to intra-plant competition and excessive vegetative growth at the expense of reproductive development. This was reflected in a reduced harvest index at the highest nitrogen level. The absence of significant yield or growth response to sulfur application may be attributed to adequate pre-existing soil sulfur levels (18 mg kg-1), suggesting that sulfur was not limiting. Conclusion. Optimizing nitrogen application, considering local soil and climatic conditions, is a viable strategy for enhancing nitrogen use efficiency, improving yield, and reducing the environmental impact of excessive nitrogen fertilization in guar cultivation. Introduction. Guar (Cyamopsis tetragonoloba L.) is well-suited for cultivation in tropical and subtropical regions with arid and semi-arid climates due to its high tolerance to drought and warm temperatures. Its significant industrial value and rising global demand have increased interest in its cultivation beyond traditional regions like India and Pakistan, including countries such as Iran. Following drought stress, nutrient deficiencies—particularly nitrogen—are major limiting factors for crop production, including guar. Nitrogen is an essential nutrient for plant growth, enhancing photosynthetic efficiency and playing critical roles in processes such as vegetative growth, leaf area expansion, and biomass accumulation. Under drought conditions and in soils with low populations of symbiotic rhizobia, nitrogen deficiency can severely limit guar production. Sulfur is another vital nutrient required for the synthesis of amino acids such as cystine, cysteine, and methionine, and is involved in the function of vitamins (e.g., biotin and thiamine), enzymes, lipids, and other essential plant components. sSulfur deficiency is particularly common in sandy soils with low organic matter. Materials and Methods. This study was conducted in 2024 at the research farm of the Faculty of Agriculture, Tarbiat Modares University, located 17 km west of Tehran (35°44'N, 51°9'E; 1275 m above sea level). During the guar growing season, the average temperature was 28.73°C, and total rainfall was 1.6 mm. The experiment followed a factorial arrangement in a randomized complete block design (RCBD) with three replications. Treatments included two sulfur levels (0 and 100 kgha-1, from a bentonite sulfur source with 90% purity) and four nitrogen levels (0, 50, 100, and 150 kgha-1, applied as urea). Measured traits included biomass, leaf area, number of seeds per plant and pod, thousand-seed weight, harvest index, and seed yield per hectare. Leaf area and biomass were assessed during the vegetative stage through destructive sampling of 50 cm rfow lengths. Final yield components were measured by harvesting 1 m² plots at maturity. Results and Discussion. Analysis of variance revealed that nitrogen application, unlike sulfur, had significant effects on leaf area index, dry matter accumulation, pod and seed numbers per unit area, grain yield, and harvest index. Nitrogen application increased grain yield by 21.2% compared to the control. Yield improvements at 50, 100, and 150 kg N ha-1 were 12.8%, 33.8%, and 16.9%, respectively. Regression analysis indicated a significant quadratic response of grain yield to nitrogen application, explaining approximately 84% of the yield variation. The maximum increase in pod and seed numbers occurred at 100 kg ha-1, while no significant improvement was observed at 150 kg N ha-1, suggesting an optimal nitrogen level. Due to the strong influence of the number of grains formed per plant on grain weight, the increase in grain number in response to nitrogen application resulted in the allocation of dry matter among a larger number of grains, and therefore, changes in grain weight were not significant. Grain yield were attributed to enhanced leaf area index, biomass accumulation, and reproductive organ development. Previous studies support these findings, showing that nitrogen improves light interception, chlorophyll content, enzyme activity, and photosynthetic capacity. At 150 kg N ha-1, despite increased biomass, grain yield declined compared to 100 kg N ha-1, likely due to intra-plant competition and excessive vegetative growth at the expense of reproductive development. This was reflected in a reduced harvest index at the highest nitrogen level. The absence of significant yield or growth response to sulfur application may be attributed to adequate pre-existing soil sulfur levels (18 mg kg-1), suggesting that sulfur was not limiting. Conclusion. Optimizing nitrogen application, considering local soil and climatic conditions, is a viable strategy for enhancing nitrogen use efficiency, improving yield, and reducing the environmental impact of excessive nitrogen fertilization in guar cultivation.

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