Nitrate vs Ammonium in Can***is

This Research Highlight is aimed at explaining key advancements in science relative to cultivation. In this article, we’ll evaluate a recent study that investigates the comparative impacts of ammonium (NH4) and nitrate (NO3) nitrogen sources on the physiology and growth of medical Can***is in hydroponic systems. Through a comprehensive exploration of this research, we aspire to provide valuable insights into the optimization of hydroponic techniques and cultivation performance.

SALONER AND BERNSTEIN 2022

Nitrogen Source Matters: High NH4/NO3 Ratio Reduces Cannabinoids, Terpinoids, and Yield in Medical Can***is

Study Overview

Nitrogen is a crucial nutrient for plants, and its form - either as ammonium (NH4+) or nitrate (NO3-) - can greatly affect plant function and metabolic responses. The balance between these two forms can specifically impact the production of certain valuable compounds in some plants. In this excellent study, Avia Saloner and colleagues investigated the effects of five different NH4/ NO3 ratios on plant growth and found that:

• A higher NH4 supply led to adverse responses in secondary metabolite production, yield, plant height, and other factors.

• Moderate levels of NH4 (10-30%) did not have a significant negative impact and were considered suitable for certain types of plant cultivation.

• Ratios above 30% NH4 are not recommended, as they can increase the potential for severe and fatal toxicity damage to the plant.

Background

Competitive market conditions have lead to increasing demand for high-quality, chemically standardized medicinal Cannabis plants due to their potential in modern medicine. The production of various phytochemicals including

Cannabinoids and terpenes in these plants is influenced by environmental and cultivation conditions. Recent research has identified plant sensitivity to mineral nutrition, including nitrogen (N) and phosphorus (P) status, as well as humic acid supplementation. This current study aimed to investigate the effects of different ammonium (NH4+) to nitrate (NO3-) N source ratios on the morpho-development, physiology, and secondary metabolism of a particular medicinal plant.

Nitrogen uptake in plants is primarily through NO3- or NH4+ ions, which are then assimilated into amino acids and other N metabolites. NH4/ NO3 ratios play a critical role in plant energy status, pH adjustment, mineral uptake, and other metabolic and regulatory processes. Many agricultural plants can perform well with up to a certain level of NH4 relative to NO3 supply, at a range of 10-30% NH4/NO3 ratio. However, the optimal NH4/NO3 ratio for the cultivation of this specific medicinal plant is unknown.

Materials And Methods

Growing Conditions

In this study, a specific medical cultivar was used as a model to investigate the effects of different ammonium (NH4+) to nitrate (NO3-) nitrogen source ratios. The plants were propagated from rooted cuttings, replanted to 3L plastic pots, and grown in perlite media under controlled environmental conditions. Uniform plants were selected and divided into five treatment groups with varying N-NH4+ supply: 0, 10, 30, 50, and 100%. The remaining nitrogen was supplied as N-NO3- to maintain a uniform total nitrogen level.

The plants were grown under specific photoperiods: initially, a long photoperiod (18/6 h light/dark) during the vegetative phase, followed by a short photoperiod (12/12 h light/ dark) to induce inflorescence development. Light, temperature, and relative humidity were regulated throughout the experiment. Irrigation was provided via pressure-compensated drippers, and mineral nutrients were supplied in the irrigation solution at each event.

The irrigation solution contained various micronutrients and macronutrients, with concentrations selected based on previous studies to optimize plant development and function. The pH of the irrigation solution was adjusted to 5.6-6.0. The experiment followed a complete randomized design, with five replicated plants per treatment.

Mineral Analysis

Mineral nutrient concentrations in plant organs were analyzed at the end of the experiment, 59 days after the initiation of the NH4/NO3 treatments. Electrical conductivity (EC) and pH of the irrigation and leachate solutions were measured weekly.

Plants were sampled for physiological analyses 45 days after the start of the fertigation treatments, as treatment effects were expected to be prominent by this time and gas exchange activity was still active. Various physiological parameters, including photosynthetic pigments, osmotic potential, membrane leakage, relative water content (RWC), photosynthesis rate, transpiration rate, stomatal conductance, intercellular CO2 concentration, and water use efficiency (WUEi), were determined following established protocols.

Plant Development

Plant architecture and development parameters, including plant height, stem diameter, inflorescence length, and the number of nodes on the main stem, were measured one week before the end of the experiment. Biomass accumulation in plant organs (leaves, stems, inflorescences, inflorescence leaves, and roots) was assessed by destructive sampling 59 days after the initiation of the NH4/NO3 treatments. Dry weights were determined after drying the samples at 64°C for 48 hours (128 hours for inflorescences).

Secondary Metabolite Analysis

Secondary metabolite concentrations were evaluated in primary and secondary inflorescences at the end of the experiment, 59 days after the initiation of treatments. Samples were prepared by wet-trimming, drying, and curing.

For secondary metabolites, concentrations of several compounds were below detection limits. Total weights of relevant metabolites were calculated considering differences in mass between carboxylated and decarboxylated forms. Analysis of aromatic compounds involved extracting volatiles from 100 mg of dried plant material, using MTBE and ethyl myristate as an internal standard. Samples were analyzed with a GC-MSD system, and compounds were identified by comparing retention indices and mass spectra with authentic samples, literature, and GC-MS libraries. Content was not examined in plants from the 100% NH4 treatment group due to severe NH4 toxicity and wilting.

Results

Visual Characteristics

Plants in the 0-30% NH4 treatments appeared visually similar, with adequate structure and color. Plants in the 50% NH4 treatment appeared normal for most of the experiment, but in the last two weeks, leaves became necrotic and wilted, leading to the death of 40% of the plants. The 100% NH4 plants experienced stunted growth, toxicity symptoms, and necrosis from early stages, ultimately resulting in plant death. The visual response of the aerial parts of the plant corresponded with root development, which showed optimal development under 0-50% NH4 and severe damage under 100% NH4.

Development And Biomass

Plant development was significantly influenced by the NH4/NO3 ratio. Plant height and inflorescence length decreased with increased NH4, showing optimal growth with 0-10% NH4 and substantial damage with 100% NH4. Side inflorescences exhibited similar trends but were shorter than top inflorescences. Stem diameter and node count on the main stem were smaller in 100% NH4 plants.

Biomass production decreased with increased NH4 supply. Dry biomass of all organs and whole plants were highest under complete NO3 nutrition (0% NH4) and lowest under 100% NH4. Inflorescence, stem, and whole plant biomass were highest under 0% NH4, significantly lower...

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