The reaction of vegetative and reproductive growth of Guar (Cyamopsis tetragonoloba L.) to humic acid application with irrigation water in different planting densities

Introduction Guar or cluster bean (Cyamopsis tetragonoloba L.) is a drought-tolerant annual leguminous crop grown mostly in India and Pakistan. Each pod contains 5 to 12 seeds. Seeds vary from dull-white to pink to light gray or black. Like other legumes guar is an excellent soil-building crop with respect to available nitrogen. Guar is one of the unique beans which its large spherical endosperm contains a significant amount of galactomannans that is used in a wide range of food and industrial applications. Organic fertilizers have a positive effect on agricultural sustainability due to the fact that authentic and safe products are important. One of the most important compounds in soil structure is humic acid, which results from organic matter decomposition in the soil. Humic acid is one of the most organic substances that has been used today due to its advantages, such as improving drainage and soil air, causing the development of microorganisms, increasing plant yield and growth, and also reducing the consumption of other fertilizers. In general, humic substances are used as soil modifiers. One of the important factors in plant cultivation is to determine the most suitable planting density. Plant density is an important agronomic factor that manipulates micro environment of the field and affects growth, development and yield formation of crops. The optimum planting density of the plants results in a balance in the competition between the plants and the maximum yield. So, this research focuses on the reaction of vegetative and reproductive growth of guar (cluster bean) to humic acid application with irrigation water in different planting densities in Ahvaz region.   Materials & Methods In order to evaluate the response of vegetative and reproductive growth of guar or Cluster bean (Cyamopsis tetragonoloba L.) to the humic acid application with irrigation water in different planting densities, an experiment carried out in summer of 2016. This experiment was performed by split plot design with three replications based on randomized complete block design in research farm of Agriculture Sciences and Natural Resources University, Khuzestan Ahwaz. The experimental factors were four levels of humic acid, control (H0), 5 Kg.ha-1 (H1), 10 Kg.ha-1 (H2) and 15 Kg.ha-1 (H3) as the main factor in main plots and plants spacing on the planting row with four densities, 35 plant.m-2 (D1), 55 plant.m-2 (D2), 75 plant.m-2 (D3) and 95 plant.m-2 (D4) as sub factor in sub plots. In this experiment, measured traits were plant height, number of branches in the plant, leaf number, grain yield, dry matter, number of pod and number of grain/m2, number of grain in pod and harvest index. Data were analyzed by SAS 9.4 and mean comparison performed by Duncan test in 5% probability level.   Results & Discussion Analysis of variance of data results showed that the main effect of humic acid and plant density were significant at p≤0.01, for all the measured traits (except the number of grains in pod and harvest index). So that as humic acid level increased, the traits increased. Also with increasing in plant density; all studied traits increased significantly except the number of branches of the plant. The interaction effect between humic acid and plant density were significant (p≤0.01) on grain yield, dry matter, plant height and the number of plant.m-2. The results also showed that the effect of humic acid and plant density on leaf number was significant at 1% level. So that, the highest plant height and leaf number per m2 were obtained from density of 95 plants.m-1 and 15 Kg.ha-1 humic acid application. So, with increasing plant density, leaf number increased. Generally, the highest grain yield (4209.7 Kg.ha-1) and dry matter (17955.6 Kg.ha-1) was under 15 Kg.ha-1 application of humic acid and the density of 95 plant.m-2 and the lowest grain yield (1433.2 Kg.ha-1) and dry matter (4812.6 Kg.ha-1) was under zero humic acid level and density of 35 plant.m-2.   Conclusion Generally, the results showed that humic acid solution has a positive effect on the plant, therefore, using humic acid, produced highest grain yield, dry matter and morphological traits. Also, with increasing plant density, traits such as plant height, leaf number, yield and yield components increased but the number of branches decreased. In general, 15 Kg.ha-1 application of humic acid and the density of 95 plants.m-2 produced the highest yield.