Curtis Ransom and Dr. Von Jolley, Plant and Wildlife Science

Food production is fundamental to our existence. A major component of modern agriculture is fertilizer, especially in terms of production to meet heavy demands of domesticated crops. Phosphorus (P) is one of the three major fertilizer components, and is known to be a limited resource.

One proposed method to increase P use efficiency (PUE) is using humic acid in P fertilizers, which acid is derived from humic matter. Humic acids are long chained organic acids which help to keep P soluble in the soil allowing for more available P for plant roots to take up.

My project that was funded by my ORCA grant was to test a humic acid based phosphorus fertilizer and the plant uptake efficiency compared to commonly used P fertilizer, and a new technology using a chemical additive that enhance PUE by creating a water shield around the P fertilizer. To test my hypothesis I completed these experiments in a hydroponic system, as to assure no interference from the soil systems. All procedures were completed according to previous studies done by Dr. Hopkins and Dr. Jolley.

Four experiments were conducted in a complete random block design with Maize (Zea mays). Evaluation was conducted on effects of humic acid with plant roots, as well as root weight and shoot weight.

Maize seed was germinated for seven days until transferred into 14 L of complete nutrient solution (pretreatment) and grown for 14 days prior to placement into 14 L of treatment solution for another 18 days. Pretreatment density was eight plants per 14 L solution. Plant treatment density was four plants per 14 L solution.

In order to maintain the pH of the nutrient solution, pH was at 6.0 or 8.0, dependent on the experiment, with 6 N potassium hydroxide (KOH) for buffering. Nutrient solutions were renewed by additions, totaling four additions per study. Growth chamber temperature was maintained at 25ºC±1º during the 14 h light period and at 19ºC±1º during the 10 h dark period.

Plants were observed in their respective treatments for relative health and appearance, harvested at the end of the treatment periods, separated as shoots and roots; then oven dried at 65ºC for a minimum of 48 hours, weighed, ground (Wiley mill, 1-mm sieve), digested in nitric-perchloric acid and analyzed for nutrient content by inductively coupled plasma (ICP, Thermo Electron Corporation, Franklin, MD, USA) spectroscopy.

Phosphorus concentration differed by experimental variable, concentrations detailed below. Treatments contained equal P concentrations, between fertilizers (Carbond P, Avial, APP), as follows; 72, 400, 3200, 6400, and 9600 micro molar. Treatment additions occurred ten times over the length of the experiment. Four experiments were carried out, each one lasting 6 weeks. Two experiments were done with a pH of 6 and repeated at a pH of 8.

Results were statistically analyzed with SAS (SAS Institute, Cary, NC, USA) using ANOVA with Duncan mean separation tests. Each of the experiments consisted of five P treatments with four plants each with three replications.

Results showed no difference between Avail, a chemical additive to phosphorous fertilizer, and APP, commonly used fertilizer. No significance was seen between Carbond, fertilizer with humic acid additives, and APP. These results are not in concordance with experiments based in the soil which may show a needed soil factor in order to maintain a yield difference. Further studies need to be done at lower and higher pH systems to clarify variables that may be interfering with results in a hydroponic system. Possible reasons why insignificance was seen could have resulted from a poor shelf life of the products, as products as old as a year were used in this experiment.

The results could also prove useful in determining structure and interaction of fertilizer and plants. As possible ester bonds could be modified under a hydroponic system within a few days leaving the product to react as a normal P fertilizer. If this is the proposed method of reaction for Carbond than under soil conditions it would act as a slow releasing fertilizer and prove to be useful as a more efficient P fertilizer.

Further experiments need to be done to determine toxicity levels and interaction with micronutrients with the plants. As high levels of P, toxicity was observed, and at low levels of P plant nutrient deficiencies were also observed.