Effect of Different Concentrations of Humic Acid on Guar (Cyamopsis tetragonoloba L.) Yield and Nutrients Uptake in Different Sowing Densities

To evaluate the effect of different concentrations of humic acid on guar (Cyamopsis tetragonoloba L.) yield and nutrient uptake in different sowing densities, an experiment was carried out by using a split plot design with three replications based on a randomized complete block design, in Agricultural Sciences and Natural Resources University of Khuzestan, Iran at summer 2016. Experimental factors consisted of four levels of humic acid (0, 5, 10 and 15 kg/ha) as the main plots and four plant densities (35, 55, 75 and 95 plants/m2) as sub plots. The density of 35 plants/m2 and 15 kg/ha humic led to increase in nitrogen, phosphorus, zinc and iron content of the plant. Moreover, the highest nitrogen harvest (295 kg/ha) was obtained from density of 95 plants/m2 and 15 kg/ha of humic acid. The lowest plant protein content (8.84%) was obtained from density of 95 plants/m2 and without application of humic acid. The highest grain yield and dry matter (4209 and 17955 kg/ha, respectively) were obtained from density of 95 plant/m2 and application of 15 kg/ha humic acid. Generally, it seems that high levels of plant density (greater than 95 plant/m-2) must be evaluated for cultivation of guar in Khuzestan province. In addition, application of humic acid may lead to significantly increase of guar yield in the region.