Study on the effects of coated urea-polyphenol as an environmentally friendly fertilizer on growth, yield and N uptake of maize (Zea maize)

One solution for decreasing the environmental problems of urea in sustainable agriculture is slowing the release of urea via coating with plant metabolites. Plant phenolic compounds are natural urease and nitrification inhibitors, which can directly affect the composition and activity of enzymes and decomposer communities, thus influencing the rates of decomposition and nutrient cycling. Kiran and Patra (2003) and Mohanty et al. (2008) have reported that natural materials such as menta plant materials and neem seed kernel powder containing phenolic compounds, can act as urease and nitrification inhibitors. In addition, polyphenols can alter N availability by forming complexes with proteins (Hättenschwiler and Vitousek, 2000).
For this study, urea was coated with pomegranate fruit powder and its effect on nitrogen uptake, growth and grain yield of maize (single cross var.) was studied in a factorial experiment as a randomized complete block design with three replications. The experiment was conducted in 2013 at the Faculty of New Sciences and Technologies, University of Tehran as a pot and incubation experiment. The treatments were two levels of nitrogen fertilizer (from a urea source) include 100 and 200 mg kg of soil (65 and 130 kg ha-1) and four levels of pomegranate fruit powder including 0, 35, 70 and 100% w/w of urea. Urea was coated with pomegranate fruit powder using common methods and was applied. After maturity, the crops were harvested and traits such as grain yield, stem weight, leaf weight, root weight, biomass and N uptake were measured.
The results showed that the use of coated urea, particularly at the amount of 100% w/w, inhibited nitrification to the level of 15% and 23%, respectively, at 21 and 35 days after incubation and released it at 65 days after incubation. This lead to a significant increase in grain yield and total biomass at the amount of 13.3 and 173 g plant-1, respectively. Total nitrogen uptake also increased 23% with coated urea (in 100% w/w) compared to urea alone.
The results indicated that applying the urea coated with pomegranate fruit powder (PFP) rich in polyphenol, especially at a 100% concentration rate w/w urea, significantly increased the grain yield and biomass of maize. Applying the coated urea with polyphenol also decreased nitrate concentration of the soil during early growth stages and increased its availability during advanced stages of growth.