Effects of urea fertilization and urease and nitrification inhibitors on gaseous nitrogen fluxes from a loamy soil as well as the nitrogen content of maize

Publikations-Art

Masterarbeit

Autoren

Adhikari K.P.

Erscheinungsjahr

2014

Herausgeber

Guzman-Bustamante I., Ruser R., Müller T.

Seite (von - bis)

53

Urea is the most used nitrogen (N) fertilizer, which fulfills approximately 50% of the global N demand. Ammonia (NH₃) volatilization and nitrous oxide (N₂O) emission are two major gaseous form of N emitted from soil after surface application of urea. These gaseous N emissions have both environmental and economic impacts. The use of urease inhibitor (UI) and nitrification inhibitor (NI) are some of the tools, which may have impacts in minimizing these gaseous emissions of N. In this study, the N content of above ground maize biomass at V8 developmental stage as influenced by urea fertilization with UI and NI, moisture content of surface soil, and fertilizer application method was investigated in pot experiment. Similarly, the emission of NH₃ and N₂O from loamy soil as influenced by urea fertilization with UI and NI was investigated in an incubation experiment.

Pot experiment was carried out in a greenhouse at Institute of Crop Science of University of Hohenheim in South Germany. It was conducted for 7 weeks - from middle of September to middle of November, 2013 using a mixture of loamy soil and sand (5 mm) in equal proportion (pH 7.3) at the rate of 6 kg dry soil pot^-1. The maximum and minimum temperature during the maize growing period was 28.7 and 9.1ºC respectively. Calcium ammonium nitrate (CAN), urea, ENTEC46 (urea + DMPP: 3, 4-dimethylpyrazole phosphate , 0.5% wt/wt of NH₂-N: amidogen) and UI containing fertilizers UTEC1,UTEC2, Nexen, and BFone were applied at the rate of 250 mg of N kg^-1 dry soil after 3 weeks of seeding. The N-(n-butyl) thiophosphoric triamide (NBPT) concentration on BFone, UTEC1, UTEC2, Nexen were 0.05, 0.09, 0.13, and 0.14% (wt/wt of NH₂-N) respectively. N content of above ground maize biomass was measured at V8 stage. Moisture content of surface soil significantly affected the N content of maize. N content on moist surface was significantly higher than dry surface. Broadcasting did not show significant difference with fertigation with regards to N content. In contrast, UI and NI showed effect on N content - BFone and ENTEC46 resulted in higher N content, whereas UTEC1, UTEC2, and Nexen reduced N content compared to urea alone. However, UI and NI treated treatments did not differ significantly from urea with regards to N content with the exception of UTEC1. These effects of UI could be attributed to NBPT concentration on fertilizers which influences the NH₄⁺ toxicity level and plant available N form (NH₄⁺-N or NO₃^--N). It is possible that higher concentration of NBPT on fertilizers may lead to NH₄⁺ toxicity. The effect of NI can also be influenced by NH₄⁺ toxicity level. It can be argued that higher concentrations of NH₄⁺ lead to phytotoxicity, thereby negatively influencing plant N content, whereas higher concentrations of NO₃^- positively affected the N content of plants. These results suggested that urea fertilization with lower concentration of NBPT (0.05% wt/wt of NH₂-N) and DMPP at the rate of 0.5% wt/wt of NH₂-N may have potential to increase N content of above ground maize biomass under greenhouse conditions.

Incubation experiment was carried out in a climate chamber of the Institute of Crop Science of University of Hohenheim in South Germany for 4 weeks using loamy soil (pH 6.8) at the rate of 300.76 g dry soil vessel^-1. The mean air temperature inside the climate chamber throughout the experiment was found to be 21ºC. The treatments were selected by considering the results of pot experiment with regards to assumed NH₃ volatilized. Urea, UTEC1, UTEC2, and ENTEC46 were applied at the rate of 300 mg of N kg^-1 dry soil. The concentration of NBPT and DMPP in fertilizers was same as in the pot experiment. The quantity of NH₃ volatilization and N₂O emission was measured during the experimental period. UTEC1 reduced NH₃ volatilization by 8.3% over urea alone but was not significantly different than urea whereas UTEC2 reduced NH₃ volatilization by 40.5% over urea alone, showing a highly significant difference with urea. In contrast, both UTEC1 and UTEC2 showed little effect on N₂O emission and reduced emission by 11.9 and 7.4% respectively relative to urea. ENTEC46 reduced N₂O emission by 94.2% in comparison to urea and showed highly significant difference with urea but showed a negative impact on NH₃ volatilization. ENTEC46 increased NH₃ volatilization by 70.2% over urea alone. Therefore, from the result it can be conclude that urea treated with higher concentration of NBPT (0.13% wt/wt of NH₂-N) is effective for reducing NH₃ volatilization whereas urea treated with DMPP at the rate of 0.5% wt/wt of NH₂-N is effective for reducing cumulative N₂O emission from loamy soil.