The effects of a surfactants and potassium fertilizer on soybean (DPX cultivar) yield components with water tension

Abstract
Introduction: Potassium fertilizers may increase soybean yield and potassium concentration in leaves. Surfactants are surface-active agents, with simultaneous hydro and lipophilic molecular structures and specific physical and chemical attributes such as surface tension. Surfactants may enhance potassium exchange between soil colloids and the solution through enhanced dispersion of water, which increases available potassium for plant use and yield specially in soils with high specific surface area and limited potassium exchange. The objective in this research was evaluating the effect of a surfactant and potassium fertilizer on soybean yield components with water tension.
Materials and Methods: This study were carried out in Gorgan University of Agricultural Sciences and Natural Resources estate using split plot in completely randomized block design in four replications. Treatments were two levels of potassium fertilizer (108.3 kg ha-1K equivalent to 208 kg ha-1 potassium chloride) and no fertilizer use as main plots and four levels of 2-1 propandiol surfactant (0, 2, 4 and 8 l ha-1) as subplots. Soil water contents at 0-8 and 8-16 cm depths measured at four occasions during growing season (namely 143, 173 and 201 days after planting). Mechanical resistance at 0-5 cm depth was also measured in six occasions (namely 49, 69, 89, 109, 129 and 151 days after planting) using a pocket penetrometer. Yield components obtained at harvest.
Results: Maximum soil water content obtained by four liter per hectare surfactant and soil water content diminished as the rate of application decreased. Higher rates of applications lowered mechanical resistance at all stages of applications, which could be due to higher water content in fine pores. Potassium application increased final soybean yield and yield components significantly but surfactant affected biological yield only (at 5% significance level). Surfactant application without potassium fertilizer was ineffective on yield production, but increased yield in combination with potassium fertilizer. Surfactant reduces surface tension, which allows free dispersion of water and potassium in fine pores, which enter soil solution where roots thrive. More soil water with surfactant reduces soil mechanical resistance and increases root growth and potassium uptake by fertilizer application. In the Study of interactions between the surfactants and potassium fertilizer, the potassium fertilizer in combination with 4 liter per hectare surfactant produced maximum soybean yield, hundred seeds weight, seed number per shell, branch number, harvest index, seed number per unit surface, biological yield and plant number per unit surface. Potassium fertilizer in combination with 8 liter per hectare surfactant produced maximum plant height, node number in main stem and number of shells per branch.
Conclusions: By decreasing surface tension, surfactant improves dispersion of water within soil pores, which results in more surface-soil water retention and content. More soil water content diminishes mechanical resistance against root growth and increases soybean yield. Potassium fertilizer application in combination with 4 liter per hectare surfactant increased soybean yield significantly due possibly to more plant potassium uptake.