Effects of cyanobacterial fertilizer, commonly-used organic fertilizers, and plant growth regulators on yield and growth characteristics of carrots (Daucus carota var. sativus), cucumbers (Cucumis sativus), and bell peppers (Capsicum annuum)

Abstract

Nitrogen (N) is arguably the most important agricultural nutrient. More money and resources are spent on N management in agricultural systems than any other nutrient. Producing N fertilizer for agricultural use accounts for more than half of the carbon footprint of crop production. Nitrogen plays a crucial role in plant growth, and adding N fertilizers to agricultural systems can lead to noticeable increases in productivity. Nitrogen fertilizers commonly used in organic production are often energy intensive to produce and expensive to transport. Cyanobacteria fertilizer (cyano-fertilizer) produced on-farm could decrease fertilizer impacts on the environment as well as reduce production costs for organic farmers. In addition, cyanofertilizer may perform similarly to products marketed to increase production via plant growth hormones such as seaweed extract, which is shipped all over the world from coastal regions. The effects of common organic fertilizers as well as organic liquid cyano-fertilizer on carrot (Daucus carota var. sativus) and cucumber (Cucumis sativus) growth and yield characteristics were tested during field experiments at the Horticulture Field Research Center in Fort Collins, CO in 2014 and 2015. Bell peppers (Capsicum annuum) were grown in a greenhouse experiment in 2015 at the Colorado State University Plant Growth Facility. Cyano-fertilizer was produced and evaluated in this study to compare effects of farm-grown cyano-fertilizer and commonly-used organic fertilizers. The purpose of this study was to identify fertilizer and foliar seaweed application effects on yield, stress, and growth characteristics of all three plant species. In all experiments, hydrolyzed and non-hydrolyzed fish fertilizers, and cyano-fertilizer treatments were applied at prescribed N rates throughout the growth period approximately every 10 days. Control treatments received no supplemental N. Each treatment, including the control, was repeated with the addition of two forms of concentrated organic seaweed extract applied foliarly. Neptune’s Harvest and Seacom PGR brand seaweeds were used for their lack of N content. Seaweeds were applied at the manufacturers’ recommended rates. Phytohormones were detected in all N fertilizers and in the PGR seaweed. No phytohormones were detected in the Neptune’s Harvest seaweed. In 2014, carrot length and yield were increased by the addition of cyano-fertilizer compared to the unfertilized control. All fertilizers increased post-season soil N compared to the control. Nitrogen fertilizers increased carrot leaf tissue Mg concentrations compared to the control. Nitrogen fertilizers and foliar seaweed influenced the number of carrots with deformities, and a significant interaction between N fertilizers and seaweed with regard to stress indicated a stress response to the addition of both fish fertilizer and a foliar seaweed application. In 2015, cyano-fertilizer produced a higher carrot yield than hydrolyzed fish fertilizer. Nitrogen fertilizers impacted the total number of cucumbers harvested as well as total cucumber yield, but the results were not consistent across years. The majority of significant differences occurred in the pepper study. Nitrogen fertilizer had an effect on leaf tissue nutrient concentrations as well as phytohormone content. Nitrogen fertilizer also impacted flower death and leaf abscission as well as plant stress. Foliarly applied seaweed treatments had very little significant influence in the carrot or cucumber field studies, but did have an effect on pepper shape and color (crop quality). Pepper yield was impacted by the addition of N fertilizers. Foliar seaweed impacted pepper branching behavior as well as fruit color and shape. Based on these experiments, it can be concluded that cyano-fertilizer can be used as a N source in place of commonly-used organic fertilizers. With regards to plant growth characteristics, it is unclear that any of the products applied consistently impacted plant growth characteristics in a way that improved yield or quality.