Ammonia and Ammonium Exposure of Basil (Ocimum basilicum L.) Growing in an Organically Fertilized Peat Substrate and Strategies to Mitigate Related Harmful Impacts on Plant Growth

Abstract

Organic pot-based production of basil (Ocimum basilicum L.) often has lower biomass yield than conventional cultivation. Previous investigations indicate that this growth impairment is related to high ammonium (NH 4 + ) concentrations in the growing media released by the mineralization of organic nitrogen (N) fertilizers. However, as a result of this ammonification process substrate pH may also increase. Under neutral to alkaline conditions NH 4 + is converted to ammonia (NH 3 ), which is known to be phytotoxic even at low concentrations. Therefore, we investigated the impact of both ammonical N species on basil grown in a peat substrate. In total, three fertilization pot experiments were conducted in a greenhouse in order to compare the effect of different organic base dressings [250 and 750 mg N (L substrate) -1 mainly supplied by a liquid amino acid fertilizer (AAF)] and two initial substrate pH levels (5.5 and 6.5). In two treatments, 5% (v/v) mature compost was mixed into the peat 1 day and 12-days before the substrate was used for sowing, respectively. The aim of this procedure was to stimulate nitrification in this way to reduce ammonical N concentration. Ammonia concentration in the aerial plant surrounding environment was measured by using NH 3 detector tubes in combination with an open-top chamber method. The results showed that the growth of basil (number of plants, fresh matter yield, plant height) was significantly inhibited in the second and third week of cultivation by rising NH 3 and NH 4 + exposure, as well as by a substrate pH ≥ 7.0.These adverse effects were reduced by lowering the organic base dressing rate and adjusting the initial substrate pH to 5.5. Furthermore, the addition of mature compost to peat in combination with a 12-day storage was proven to be effective for promoting nitrification in the organically fertilized substrate. As a result, plant growth was improved by both lower NH 3 and NH 4 + exposure as well as a faster supply of nitrate (NO 3 -) as an additional N source. Using this approach, it was possible to feed organically fertilized basil Frontiers in Plant Science | www.frontiersin.org

Estimating Nitrogen Release from Organic Fertilizers for Soilless Production by Analysis of C and N Pools

“…Thus, complete stockpiling, as recommended by Heuberger et al [27], is quite risky. Furthermore, in the case of missing nitrification, ammonium-N will accumulate, damaging plants [68]. However, in the current research-except for the OPF-nitrification already started within the first week of incubation.…”

An Analytical Framework on Utilizing Various Integrated Multi-Trophic Scenarios for Basil Production

“…The N-NO 3 reduction rate is lower, in the case of all experimental variants, compared to N-NH 4 and N-NO 2 ( Figure 25 , Figure 26 and Figure 27 ). Thus, previous studies concluded that, in the case of basil, plant growth is improved by lower N-NH 4 exposure, as well as a faster supply of N-NO 3 as an N source [ 70 ]. In aquaponics systems, the crops GM plays a dual role, both as a biofilter, but also as a support media for promoting plant growth.…”

Aquaponic growth of basil (Ocimum basilicum) with African catfish (Clarias gariepinus) in standard substrate combined with a Humicacid Fiber-Substrate (HFS)

“…An increased nitrogen supply resulted in increased shoot-root dry weight and shoot-root length ratios in perennial and annual plant species [32], which was found in the IAU plants with Humicacid Fiber-Substrate compared to the EAU plants (Table 3) and not in the basil in the standard substrate (Table 2). However, the NH 4 -N levels should not be higher than the NO 3 − levels because basil was identi ed as being sensitive to higher levels of NH 4 + [36] especially with contents higher than 250 mg/L of N as amino acids [37], which were not reached by HFS. The change in NO 2 -N was highest in the IAU as an effect of the higher stocking densities compared to the EAU, thus increasing nitri cation processes.…”