Nutrient Management Research Database

http://ucanr.edu/sites/Nutrient_Management_Solutions/files/212719.pdf

Limited soil nitrogen (N) availability is a common problem in organic vegetable production that often necessitates additional N fertilization. The increasing use of drip irrigation has created a demand for liquid organic fertilizers that can be applied with irrigation. The N availability of three liquid organic fertilizers was evaluated in an incubation study and a greenhouse bioassay. Phytamin 801 contained fishery wastes and seabird guano, while Phytamin 421 and Biolyzer were formulated from plant materials. The fertilizers ranged from 26 to 60 g·kg⁻¹ N, 8% to 21% of which was associated with particulate matter large enough to potentially be removed by drip irrigation system filtration. The fertilizers were incubated aerobically in two organically managed soils at constant moisture at 15 and 25 °C, and sampled for mineral N concentration after 1, 2, and 4 weeks. In the greenhouse study, these fertilizers and an inorganic fertilizer (ammonium sulfate) were applied to pots of the two organically managed soils with established fescue (Festuca arundinacea) turf; the N content of clippings was compared with that from unfertilized pots after 2 and 4 weeks of growth. Across soils and incubation temperatures, the N availability from Phytamin 801 ranged from 79% to 93% of the initial N content after 1 week, and 83% to 99% after 4 weeks. The plant-based fertilizers had significantly lower N availability, but after 4 weeks, had 48% to 92% of initial N in mineral form. Soil and incubation temperature had modest but significant effects on fertilizer N availability. Nitrification was rapid, with >90% of mineral N in nitrate form after 1 week of incubation at 25 °C, or 2 weeks at 15 °C. N recovery in fescue clippings 4 weeks after application averaged 60%, 38%, and 36% of initial N content for Phytamin 801, Phytamin 421, and Biolyzer, respectively, equivalent to or better than the N recovery from ammonium sulfate.

This article presents the results of two experiments, a laboratory study and a greenhouse bioassay, which evaluate the N availability and plant uptake of liquid organic fertilizers that can be used in fertigation systems.  The fertilizers were composed of a variety of materials, including fishery wastes, seabird guano, and plant materials.  Ammonium and nitrate concentrations of each fertilizer were assessed, as well as the potential for loss of N during the irrigation filtration process.  

Soils used in the study were collected from the top 20cm of two organically managed fields. For the incubation experiment, initial soil ammonium and nitrate concentrations were first determined and then soils with liquid fertilizer additions were incubated at 15 and 25 degrees Celsius.  Increase in mineral N was then assessed after 1,2, and 4 weeks of incubation.  

Plant N uptake was evaluated in a greenhouse bioassay using fescue and the same soils as the incubation experiment.  Fescue was grown for 5 weeks before fertilizer application.  Treatments consisting of fescue grown with no fertilizer, with the equivalent rate of minimum fertilizer, and with the liquid organic fertilizers at a rate of 6 g L^-1 N were implemented.  The fescue was clipped and analyzed for total N concentration at 2 and 4 weeks after fertilizer applied, with the N recovery of the fertilizer calculated as the difference between total N in treatments where fertilizer was applied and total N in treatments that did not receive fertilizer.  

The liquid fertilizers Phytamin 801 and Phytamin 421 had greater than 60% of initial N content in mineral form after the first week of incubation, with more than 90% of N found in N03-N form, indicating that nitrification had rapidly occurred.

Phytamin 801 resulted in the highest apparent fertilizer N recovery (ANR), with more than 60% of fertilizer N applied recovered in the fescue after 4 weeks, while the other liquid fertilizers tested resulted in lower ANR that was equivalent to the ammonium sulfate treatments. Higher N recovery with the Phytamin 801 may suggest a decrease in denitrification, as organic fertilizers have an extended mineralization period that could limit mineralizable N in the soil at any one time, limiting the potential for denitrification to occur.